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NAME

       perlfunc - Perl 內部函數

yz DESCRIPTION
       這一章裏的函數可以作為表達式來使用。 Perl 中的函數主-
       n分為兩類:數組運算符和命名的一元運算符。 不同之處在於他-
       怐瑰u先級關系。(參閱 perlop 中的優先級表 ) 數組運算符需n一-
       茈H上的參數,而一元運算符不能超過一荌捊C 因此,一茬r號將結束一-
       茪@元運算符,  但對於數組運算符,只是起到分隔的作用。
       一元運算符一般只提供一-
       蚍迠q作為參數,而數組運算符可能會提供標量或者數組作為參數。
       如果二者都有,標量參數一般在前情A數組參數跟在後情C (注意,可以只有一-
       蚍桲僆q) 例如, splice() 有三蚍迠q變量,後悼[上一蚍, 相反
       gethostbyname() 有四蚍迠q變量。

       在語法描z中,數組運算符需n一茈咾IST標識的數組作為參數。 這些
       數組可能由標量參數和數組V合組成; 數組N包含在數組中,每-
       茪葛應Q插入數組中, 形成一荍顗齯@維的數組C 數組的元素應該用逗號分開。

       下惘C出的任何函數可以在參數兩邊有括號,也可以沒有。(語法描z中省略括號)
       如果你使用括號,一蚋眾瑼熙W則是 (偶爾會令人吃驚):
       如果是函數,沒有優先級的問題;如果它是一蚍桯B算符或者一元運算符
       那麼就n考慮優先級。並且,函數兩邊的空白和 "(" 是不p算的--因此,
       有時堇愯小心行事。看看下悸煽X茖狺l:

           print 1+2+4;        # Prints 7.
           print(1+2) + 4;     # Prints 3.
           print (1+2)+4;      # Also prints 3!
           print +(1+2)+4;     # Prints 7.
           print ((1+2)+4);    # Prints 7.

       前掩§o似乎有點抽象,那麼你在運行PERL時帶上-w開關你將得到一些
       警告訊息,您可以根據這些信息再體會一下。例如,上悸漕狺l會產生如下信息:

           print (...) interpreted as function at - line 1.
           Useless use of integer addition in void context at - line 1.

       有些函數根本不需n參數,因此工作方式和一元運算符和數組運算符都不同,
       "time" 和 "endpwent" 算是兩茖憳洹a.  如, "time+86_400" 實際上是 "time()
       + 86_400".

       對於可以用在標量或者數組的上下文中的函數,非失敗性的錯誤在標量環境下
       通常暗示返回了未定義的峖b數組環境下返回一茠讀獐捸C

       記住下悸澈n鴢h:
       沒有規則和數組環境下的表達式的行為和他的標量環境的行為有關系,反之亦然。
       這可能產生兩種完全不同的情況。在標量環境下,每-
       蚢B算符和函數決定怎樣以最恰當的次序返回C
       有些運算符在數組環境下返回數組的長度.,有些運算符返回的一-
       茪葛嚏A有些返回數組中的最後一-
       茪葛嚏A有些返回成功執行的操作的語句數。通常,他怐藀^一些你需n的-
       A除非你需n連續性。

       在標量環境下的命名數組在第一眼看上去時和在標量環境下的列表有很大的不同。
       在標量環境下,你不能得到一蚢 "(1,2,3)"
       的列表,因為在編譯時,編譯器是知道當前環境的,它將在那裏產生標量的逗號運算符,
       而不是用於分隔數組元素的逗號. 也就是說,它永遠不會以一蚍梮}始。

       一般說來, PERL中的函數對應相應的系統調用 (如chown(2), fork(2),
       closedir(2), 等等.) 成功調用後返回真A否則返回 "undef" , 下-
       控N會提到。這一點和C的接口不一樣,C中出錯時將返回"-1" .但是也有幾-
       茖狴~,他怓O  "wait", "waitpid", 和 "syscall" 。
       系統調用出錯時出錯信息將通過特殊變量$!返回。其他的函數則不會,除非發生意外。

       Perl Functions by Category

       下惇OPerl中的函數(包括看起來像函數的,如某些關鍵詞,命名運算符)的分類.
       有些函數在多處出現了。

       標量和字符串函數 Functions for SCALARs or strings
           "chomp", "chop", "chr", "crypt", "hex", "index", "lc", "lcfirst",
           "length", "oct", "ord", "pack", "q/STRING/", "qq/STRING/",
           "reverse", "rindex", "sprintf", "substr", "tr///", "uc", "ucfirst",
           "y///"

       正則表達式和模式匹配 Regular expressions and pattern matching
           "m//", "pos", "quotemeta", "s///", "split", "study", "qr//"

       數字運算 Numeric functions
           "abs", "atan2", "cos", "exp", "hex", "int", "log", "oct", "rand",
           "sin", "sqrt", "srand"

       真實數組函數 Functions for real @ARRAYs
           "pop", "push", "shift", "splice", "unshift"

       列表數據函數 Functions for list data
           "grep", "join", "map", "qw/STRING/", "reverse", "sort", "unpack"

       真實哈希函數 Functions for real %HASHes
           "delete", "each", "exists", "keys", "values"

       輸入輸出 Input and output functions
           "binmode", "close", "closedir", "dbmclose", "dbmopen", "die",
           "eof", "fileno", "flock", "format", "getc", "print", "printf",
           "read", "readdir", "rewinddir", "seek", "seekdir", "select",
           "syscall", "sysread", "sysseek", "syswrite", "tell", "telldir",
           "truncate", "warn", "write"

       定長的數據或記錄 Functions for fixed length data or records
           "pack", "read", "syscall", "sysread", "syswrite", "unpack", "vec"

       檔案目錄控制 Functions for filehandles, files, or directories
           "-X", "chdir", "chmod", "chown", "chroot", "fcntl", "glob",
           "ioctl", "link", "lstat", "mkdir", "open", "opendir", "readlink",
           "rename", "rmdir", "stat", "symlink", "sysopen", "umask", "unlink",
           "utime"

       流控制關鍵詞 Keywords related to the control flow of your perl program
           "caller", "continue", "die", "do", "dump", "eval", "exit", "goto",
           "last", "next", "redo", "return", "sub", "wantarray"

       作用域關鍵詞 Keywords related to scoping
           "caller", "import", "local", "my", "our", "package", "use"

       雜項 Miscellaneous functions
           "defined", "dump", "eval", "formline", "local", "my", "our",
           "reset", "scalar", "undef", "wantarray"

       進程和進程組 Functions for processes and process groups
           "alarm", "exec", "fork", "getpgrp", "getppid", "getpriority",
           "kill", "pipe", "qx/STRING/", "setpgrp", "setpriority", "sleep",
           "system", "times", "wait", "waitpid"

       模塊關鍵詞 Keywords related to perl modules
           "do", "import", "no", "package", "require", "use"

       類和惘V對象關鍵詞 Keywords related to classes and object-orientedness
           "bless", "dbmclose", "dbmopen", "package", "ref", "tie", "tied",
           "untie", "use"

       底層 socket 函數 Low-level socket functions
           "accept", "bind", "connect", "getpeername", "getsockname",
           "getsockopt", "listen", "recv", "send", "setsockopt", "shutdown",
           "socket", "socketpair"

       SysV 進程間通訊 System V interprocess communication functions
           "msgctl", "msgget", "msgrcv", "msgsnd", "semctl", "semget",
           "semop", "shmctl", "shmget", "shmread", "shmwrite"

       獲取使用者信息 Fetching user and group info
           "endgrent", "endhostent", "endnetent", "endpwent", "getgrent",
           "getgrgid", "getgrnam", "getlogin", "getpwent", "getpwnam",
           "getpwuid", "setgrent", "setpwent"

       獲取網路信息 Fetching network info
           "endprotoent", "endservent", "gethostbyaddr", "gethostbyname",
           "gethostent", "getnetbyaddr", "getnetbyname", "getnetent",
           "getprotobyname", "getprotobynumber", "getprotoent",
           "getservbyname", "getservbyport", "getservent", "sethostent",
           "setnetent", "setprotoent", "setservent"

       時間函數 Time-related functions
           "gmtime", "localtime", "time", "times"

       PERL5中的新函數 Functions new in perl5
           "abs", "bless", "chomp", "chr", "exists", "formline", "glob",
           "import", "lc", "lcfirst", "map", "my", "no", "our", "prototype",
           "qx", "qw", "readline", "readpipe", "ref", "sub*", "sysopen",
           "tie", "tied", "uc", "ucfirst", "untie", "use"

           * - "sub" was a keyword in perl4, but in perl5 it is an operator,
           which can be used in expressions.

       過時的函數 Functions obsoleted in perl5
           "dbmclose", "dbmopen"

      i Portability

       Perl 誕生於UNIX,因此可以訪問所有的一般系統調用。
       在非UNIX環境中,某些UNIX下有的調用是沒有實現的,或者有輕微的區別。受到影響的有:

       "-X", "binmode", "chmod", "chown", "chroot", "crypt", "dbmclose",
       "dbmopen", "dump", "endgrent", "endhostent", "endnetent",
       "endprotoent", "endpwent", "endservent", "exec", "fcntl", "flock",
       "fork", "getgrent", "getgrgid", "gethostbyname", "gethostent",
       "getlogin", "getnetbyaddr", "getnetbyname", "getnetent", "getppid",
       "getprgp", "getpriority", "getprotobynumber", "getprotoent",
       "getpwent", "getpwnam", "getpwuid", "getservbyport", "getservent",
       "getsockopt", "glob", "ioctl", "kill", "link", "lstat", "msgctl",
       "msgget", "msgrcv", "msgsnd", "open", "pipe", "readlink", "rename",
       "select", "semctl", "semget", "semop", "setgrent", "sethostent",
       "setnetent", "setpgrp", "setpriority", "setprotoent", "setpwent",
       "setservent", "setsockopt", "shmctl", "shmget", "shmread", "shmwrite",
       "socket", "socketpair", "stat", "symlink", "syscall", "sysopen",
       "system", "times", "truncate", "umask", "unlink", "utime", "wait",
       "waitpid"

       參見 perlport 和其他孕x的說明文件以獲得更多關於移植性的資料

      rCPERLAlphabetical Listing of Perl Functions

       -X FILEHANDLE
       -X EXPR
       -X      A file test, where X is one of the letters listed below.  This
               unary operator takes one argument, either a filename or a
               filehandle, and tests the associated file to see if something
               is true about it.  If the argument is omitted, tests $_, except
               for "-t", which tests STDIN.  Unless otherwise documented, it
               returns 1 for true and '' for false, or the undefined value if
               the file doesn't exist.  Despite the funny names, precedence is
               the same as any other named unary operator, and the argument
               may be parenthesized like any other unary operator.  The
               operator may be any of:

                   -r  File is readable by effective uid/gid.
                   -w  File is writable by effective uid/gid.
                   -x  File is executable by effective uid/gid.
                   -o  File is owned by effective uid.

                   -R  File is readable by real uid/gid.
                   -W  File is writable by real uid/gid.
                   -X  File is executable by real uid/gid.
                   -O  File is owned by real uid.

                   -e  File exists.
                   -z  File has zero size (is empty).
                   -s  File has nonzero size (returns size in bytes).

                   -f  File is a plain file.
                   -d  File is a directory.
                   -l  File is a symbolic link.
                   -p  File is a named pipe (FIFO), or Filehandle is a pipe.
                   -S  File is a socket.
                   -b  File is a block special file.
                   -c  File is a character special file.
                   -t  Filehandle is opened to a tty.

                   -u  File has setuid bit set.
                   -g  File has setgid bit set.
                   -k  File has sticky bit set.

                   -T  File is an ASCII text file (heuristic guess).
                   -B  File is a "binary" file (opposite of -T).

                   -M  Script start time minus file modification time, in days.
                   -A  Same for access time.
                   -C  Same for inode change time (Unix, may differ for other platforms)

               Example:

                   while (<>) {
                       chomp;
                       next unless -f $_;      # ignore specials
                       #...
                   }

               The interpretation of the file permission operators "-r", "-R",
               "-w", "-W", "-x", and "-X" is by default based solely on the
               mode of the file and the uids and gids of the user.  There may
               be other reasons you can't actually read, write, or execute the
               file.  Such reasons may be for example network filesystem
               access controls, ACLs (access control lists), read-only
               filesystems, and unrecognized executable formats.

               Also note that, for the superuser on the local filesystems, the
               "-r", "-R", "-w", and "-W" tests always return 1, and "-x" and
               "-X" return 1 if any execute bit is set in the mode.  Scripts
               run by the superuser may thus need to do a stat() to determine
               the actual mode of the file, or temporarily set their effective
               uid to something else.

               If you are using ACLs, there is a pragma called "filetest" that
               may produce more accurate results than the bare stat() mode
               bits.  When under the "use filetest 'access'" the above-
               mentioned filetests will test whether the permission can (not)
               be granted using the access() family of system calls.  Also
               note that the "-x" and "-X" may under this pragma return true
               even if there are no execute permission bits set (nor any extra
               execute permission ACLs).  This strangeness is due to the
               underlying system calls' definitions.  Read the documentation
               for the "filetest" pragma for more information.

               Note that "-s/a/b/" does not do a negated substitution.  Saying
               "-exp($foo)" still works as expected, however--only single
               letters following a minus are interpreted as file tests.

               The "-T" and "-B" switches work as follows.  The first block or
               so of the file is examined for odd characters such as strange
               control codes or characters with the high bit set.  If too many
               strange characters (>30%) are found, it's a "-B" file,
               otherwise it's a "-T" file.  Also, any file containing null in
               the first block is considered a binary file.  If "-T" or "-B"
               is used on a filehandle, the current IO buffer is examined
               rather than the first block.  Both "-T" and "-B" return true on
               a null file, or a file at EOF when testing a filehandle.
               Because you have to read a file to do the "-T" test, on most
               occasions you want to use a "-f" against the file first, as in
               "next unless -f $file && -T $file".

               If any of the file tests (or either the "stat" or "lstat"
               operators) are given the special filehandle consisting of a
               solitary underline, then the stat structure of the previous
               file test (or stat operator) is used, saving a system call.
               (This doesn't work with "-t", and you need to remember that
               lstat() and "-l" will leave values in the stat structure for
               the symbolic link, not the real file.)  (Also, if the stat
               buffer was filled by a "lstat" call, "-T" and "-B" will reset
               it with the results of "stat _").  Example:

                   print "Can do.\n" if -r $a || -w _ || -x _;

                   stat($filename);
                   print "Readable\n" if -r _;
                   print "Writable\n" if -w _;
                   print "Executable\n" if -x _;
                   print "Setuid\n" if -u _;
                   print "Setgid\n" if -g _;
                   print "Sticky\n" if -k _;
                   print "Text\n" if -T _;
                   print "Binary\n" if -B _;

       abs VALUE
       abs     Returns the absolute value of its argument.  If VALUE is
               omitted, uses $_.

       accept NEWSOCKET,GENERICSOCKET
               Accepts an incoming socket connect, just as the accept(2)
               system call does.  Returns the packed address if it succeeded,
               false otherwise.  See the example in "Sockets: Client/Server
               Communication" in perlipc.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptor, as determined
               by the value of $^F.  See "$^F" in perlvar.

       alarm SECONDS
       alarm   Arranges to have a SIGALRM delivered to this process after the
               specified number of wallclock seconds have elapsed.  If SECONDS
               is not specified, the value stored in $_ is used. (On some
               machines, unfortunately, the elapsed time may be up to one
               second less or more than you specified because of how seconds
               are counted, and process scheduling may delay the delivery of
               the signal even further.)

               Only one timer may be counting at once.  Each call disables the
               previous timer, and an argument of 0 may be supplied to cancel
               the previous timer without starting a new one.  The returned
               value is the amount of time remaining on the previous timer.

               For delays of finer granularity than one second, you may use
               Perl's four-argument version of select() leaving the first
               three arguments undefined, or you might be able to use the
               "syscall" interface to access setitimer(2) if your system
               supports it.  The Time::HiRes module (from CPAN, and starting
               from Perl 5.8 part of the standard distribution) may also prove
               useful.

               It is usually a mistake to intermix "alarm" and "sleep" calls.
               ("sleep" may be internally implemented in your system with
               "alarm")

               If you want to use "alarm" to time out a system call you need
               to use an "eval"/"die" pair.  You can't rely on the alarm
               causing the system call to fail with $! set to "EINTR" because
               Perl sets up signal handlers to restart system calls on some
               systems.  Using "eval"/"die" always works, modulo the caveats
               given in "Signals" in perlipc.

                   eval {
                       local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
                       alarm $timeout;
                       $nread = sysread SOCKET, $buffer, $size;
                       alarm 0;
                   };
                   if ($@) {
                       die unless $@ eq "alarm\n";   # propagate unexpected errors
                       # timed out
                   }
                   else {
                       # didn't
                   }

               For more information see perlipc.

       atan2 Y,X
               Returns the arctangent of Y/X in the range -PI to PI.

               For the tangent operation, you may use the "Math::Trig::tan"
               function, or use the familiar relation:

                   sub tan { sin($_[0]) / cos($_[0])  }

       bind SOCKET,NAME
               Binds a network address to a socket, just as the bind system
               call does.  Returns true if it succeeded, false otherwise.
               NAME should be a packed address of the appropriate type for the
               socket.  See the examples in "Sockets: Client/Server
               Communication" in perlipc.

       binmode FILEHANDLE, LAYER
       binmode FILEHANDLE
               Arranges for FILEHANDLE to be read or written in "binary" or
               "text" mode on systems where the run-time libraries distinguish
               between binary and text files.  If FILEHANDLE is an expression,
               the value is taken as the name of the filehandle.  Returns true
               on success, otherwise it returns "undef" and sets $! (errno).

               On some systems (in general, DOS and Windows-based systems)
               binmode() is necessary when you're not working with a text
               file.  For the sake of portability it is a good idea to always
               use it when appropriate, and to never use it when it isn't
               appropriate.  Also, people can set their I/O to be by default
               UTF-8 encoded Unicode, not bytes.

               In other words: regardless of platform, use binmode() on binary
               data, like for example images.

               If LAYER is present it is a single string, but may contain
               multiple directives. The directives alter the behaviour of the
               file handle.  When LAYER is present using binmode on text file
               makes sense.

               If LAYER is omitted or specified as ":raw" the filehandle is
               made suitable for passing binary data. This includes turning
               off possible CRLF translation and marking it as bytes (as
               opposed to Unicode characters).  Note that as despite what may
               be implied in "Programming Perl" (the Camel) or elsewhere
               ":raw" is not the simply inverse of ":crlf" -- other layers
               which would affect binary nature of the stream are also
               disabled. See PerlIO, perlrun and the discussion about the
               PERLIO environment variable.

               The ":bytes", ":crlf", and ":utf8", and any other directives of
               the form ":...", are called I/O layers.  The "open" pragma can
               be used to establish default I/O layers.  See open.

               The LAYER parameter of the binmode() function is described as
               "DISCIPLINE" in "Programming Perl, 3rd Edition".  However,
               since the publishing of this book, by many known as "Camel
               III", the consensus of the naming of this functionality has
               moved from "discipline" to "layer".  All documentation of this
               version of Perl therefore refers to "layers" rather than to
               "disciplines".  Now back to the regularly scheduled
               documentation...

               To mark FILEHANDLE as UTF-8, use ":utf8".

               In general, binmode() should be called after open() but before
               any I/O is done on the filehandle.  Calling binmode() will
               normally flush any pending buffered output data (and perhaps
               pending input data) on the handle.  An exception to this is the
               ":encoding" layer that changes the default character encoding
               of the handle, see open.  The ":encoding" layer sometimes needs
               to be called in mid-stream, and it doesn't flush the stream.
               The ":encoding" also implicitly pushes on top of itself the
               ":utf8" layer because internally Perl will operate on UTF-8
               encoded Unicode characters.

               The operating system, device drivers, C libraries, and Perl
               run-time system all work together to let the programmer treat a
               single character ("\n") as the line terminator, irrespective of
               the external representation.  On many operating systems, the
               native text file representation matches the internal
               representation, but on some platforms the external
               representation of "\n" is made up of more than one character.

               Mac OS, all variants of Unix, and Stream_LF files on VMS use a
               single character to end each line in the external
               representation of text (even though that single character is
               CARRIAGE RETURN on Mac OS and LINE FEED on Unix and most VMS
               files). In other systems like OS/2, DOS and the various flavors
               of MS-Windows your program sees a "\n" as a simple "\cJ", but
               what's stored in text files are the two characters "\cM\cJ".
               That means that, if you don't use binmode() on these systems,
               "\cM\cJ" sequences on disk will be converted to "\n" on input,
               and any "\n" in your program will be converted back to "\cM\cJ"
               on output.  This is what you want for text files, but it can be
               disastrous for binary files.

               Another consequence of using binmode() (on some systems) is
               that special end-of-file markers will be seen as part of the
               data stream.  For systems from the Microsoft family this means
               that if your binary data contains "\cZ", the I/O subsystem will
               regard it as the end of the file, unless you use binmode().

               binmode() is not only important for readline() and print()
               operations, but also when using read(), seek(), sysread(),
               syswrite() and tell() (see perlport for more details).  See the
               $/ and "$\" variables in perlvar for how to manually set your
               input and output line-termination sequences.

       bless REF,CLASSNAME
       bless REF
               This function tells the thingy referenced by REF that it is now
               an object in the CLASSNAME package.  If CLASSNAME is omitted,
               the current package is used.  Because a "bless" is often the
               last thing in a constructor, it returns the reference for
               convenience.  Always use the two-argument version if the
               function doing the blessing might be inherited by a derived
               class.  See perltoot and perlobj for more about the blessing
               (and blessings) of objects.

               Consider always blessing objects in CLASSNAMEs that are mixed
               case.  Namespaces with all lowercase names are considered
               reserved for Perl pragmata.  Builtin types have all uppercase
               names, so to prevent confusion, you may wish to avoid such
               package names as well.  Make sure that CLASSNAME is a true
               value.

               See "Perl Modules" in perlmod.

       caller EXPR
       caller  Returns the context of the current subroutine call.  In scalar
               context, returns the caller's package name if there is a
               caller, that is, if we're in a subroutine or "eval" or
               "require", and the undefined value otherwise.  In list context,
               returns

                   ($package, $filename, $line) = caller;

               With EXPR, it returns some extra information that the debugger
               uses to print a stack trace.  The value of EXPR indicates how
               many call frames to go back before the current one.

                   ($package, $filename, $line, $subroutine, $hasargs,
                   $wantarray, $evaltext, $is_require, $hints, $bitmask) = caller($i);

               Here $subroutine may be "(eval)" if the frame is not a
               subroutine call, but an "eval".  In such a case additional
               elements $evaltext and $is_require are set: $is_require is true
               if the frame is created by a "require" or "use" statement,
               $evaltext contains the text of the "eval EXPR" statement.  In
               particular, for an "eval BLOCK" statement, $filename is
               "(eval)", but $evaltext is undefined.  (Note also that each
               "use" statement creates a "require" frame inside an "eval EXPR"
               frame.)  $subroutine may also be "(unknown)" if this particular
               subroutine happens to have been deleted from the symbol table.
               $hasargs is true if a new instance of @_ was set up for the
               frame.  $hints and $bitmask contain pragmatic hints that the
               caller was compiled with.  The $hints and $bitmask values are
               subject to change between versions of Perl, and are not meant
               for external use.

               Furthermore, when called from within the DB package, caller
               returns more detailed information: it sets the list variable
               @DB::args to be the arguments with which the subroutine was
               invoked.

               Be aware that the optimizer might have optimized call frames
               away before "caller" had a chance to get the information.  That
               means that caller(N) might not return information about the
               call frame you expect it do, for "N > 1".  In particular,
               @DB::args might have information from the previous time
               "caller" was called.

       chdir EXPR
               Changes the working directory to EXPR, if possible. If EXPR is
               omitted, changes to the directory specified by $ENV{HOME}, if
               set; if not, changes to the directory specified by
               $ENV{LOGDIR}. (Under VMS, the variable $ENV{SYS$LOGIN} is also
               checked, and used if it is set.) If neither is set, "chdir"
               does nothing. It returns true upon success, false otherwise.
               See the example under "die".

       chmod LIST
               Changes the permissions of a list of files.  The first element
               of the list must be the numerical mode, which should probably
               be an octal number, and which definitely should not a string of
               octal digits: 0644 is okay, '0644' is not.  Returns the number
               of files successfully changed.  See also "oct", if all you have
               is a string.

                   $cnt = chmod 0755, 'foo', 'bar';
                   chmod 0755, @executables;
                   $mode = '0644'; chmod $mode, 'foo';      # !!! sets mode to
                                                            # --w----r-T
                   $mode = '0644'; chmod oct($mode), 'foo'; # this is better
                   $mode = 0644;   chmod $mode, 'foo';      # this is best

               You can also import the symbolic "S_I*" constants from the
               Fcntl module:

                   use Fcntl ':mode';

                   chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables;
                   # This is identical to the chmod 0755 of the above example.

       chomp VARIABLE
       chomp( LIST )
       chomp   This safer version of "chop" removes any trailing string that
               corresponds to the current value of $/ (also known as
               $INPUT_RECORD_SEPARATOR in the "English" module).  It returns
               the total number of characters removed from all its arguments.
               It's often used to remove the newline from the end of an input
               record when you're worried that the final record may be missing
               its newline.  When in paragraph mode ("$/ = """), it removes
               all trailing newlines from the string.  When in slurp mode ("$/
               = undef") or fixed-length record mode ($/ is a reference to an
               integer or the like, see perlvar) chomp() won't remove
               anything.  If VARIABLE is omitted, it chomps $_.  Example:

                   while (<>) {
                       chomp;  # avoid \n on last field
                       @array = split(/:/);
                       # ...
                   }

               If VARIABLE is a hash, it chomps the hash's values, but not its
               keys.

               You can actually chomp anything that's an lvalue, including an
               assignment:

                   chomp($cwd = `pwd`);
                   chomp($answer = <STDIN>);

               If you chomp a list, each element is chomped, and the total
               number of characters removed is returned.

               Note that parentheses are necessary when you're chomping
               anything that is not a simple variable.  This is because "chomp
               $cwd = `pwd`;" is interpreted as "(chomp $cwd) = `pwd`;",
               rather than as "chomp( $cwd = `pwd` )" which you might expect.
               Similarly, "chomp $a, $b" is interpreted as "chomp($a), $b"
               rather than as "chomp($a, $b)".

       chop VARIABLE
       chop( LIST )
       chop    Chops off the last character of a string and returns the
               character chopped.  It is much more efficient than "s/.$//s"
               because it neither scans nor copies the string.  If VARIABLE is
               omitted, chops $_.  If VARIABLE is a hash, it chops the hash's
               values, but not its keys.

               You can actually chop anything that's an lvalue, including an
               assignment.

               If you chop a list, each element is chopped.  Only the value of
               the last "chop" is returned.

               Note that "chop" returns the last character.  To return all but
               the last character, use "substr($string, 0, -1)".

               See also "chomp".

       chown LIST
               Changes the owner (and group) of a list of files.  The first
               two elements of the list must be the numeric uid and gid, in
               that order.  A value of -1 in either position is interpreted by
               most systems to leave that value unchanged.  Returns the number
               of files successfully changed.

                   $cnt = chown $uid, $gid, 'foo', 'bar';
                   chown $uid, $gid, @filenames;

               Here's an example that looks up nonnumeric uids in the passwd
               file:

                   print "User: ";
                   chomp($user = <STDIN>);
                   print "Files: ";
                   chomp($pattern = <STDIN>);

                   ($login,$pass,$uid,$gid) = getpwnam($user)
                       or die "$user not in passwd file";

                   @ary = glob($pattern);      # expand filenames
                   chown $uid, $gid, @ary;

               On most systems, you are not allowed to change the ownership of
               the file unless you're the superuser, although you should be
               able to change the group to any of your secondary groups.  On
               insecure systems, these restrictions may be relaxed, but this
               is not a portable assumption.  On POSIX systems, you can detect
               this condition this way:

                   use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
                   $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);

       chr NUMBER
       chr     Returns the character represented by that NUMBER in the
               character set.  For example, "chr(65)" is "A" in either ASCII
               or Unicode, and chr(0x263a) is a Unicode smiley face.  Note
               that characters from 128 to 255 (inclusive) are by default not
               encoded in UTF-8 Unicode for backward compatibility reasons
               (but see encoding).

               If NUMBER is omitted, uses $_.

               For the reverse, use "ord".

               Note that under the "bytes" pragma the NUMBER is masked to the
               low eight bits.

               See perlunicode and encoding for more about Unicode.

       chroot FILENAME
       chroot  This function works like the system call by the same name: it
               makes the named directory the new root directory for all
               further pathnames that begin with a "/" by your process and all
               its children.  (It doesn't change your current working
               directory, which is unaffected.)  For security reasons, this
               call is restricted to the superuser.  If FILENAME is omitted,
               does a "chroot" to $_.

       close FILEHANDLE
       close   Closes the file or pipe associated with the file handle,
               returning true only if IO buffers are successfully flushed and
               closes the system file descriptor.  Closes the currently
               selected filehandle if the argument is omitted.

               You don't have to close FILEHANDLE if you are immediately going
               to do another "open" on it, because "open" will close it for
               you.  (See "open".)  However, an explicit "close" on an input
               file resets the line counter ($.), while the implicit close
               done by "open" does not.

               If the file handle came from a piped open "close" will
               additionally return false if one of the other system calls
               involved fails or if the program exits with non-zero status.
               (If the only problem was that the program exited non-zero $!
               will be set to 0.)  Closing a pipe also waits for the process
               executing on the pipe to complete, in case you want to look at
               the output of the pipe afterwards, and implicitly puts the exit
               status value of that command into $?.

               Prematurely closing the read end of a pipe (i.e. before the
               process writing to it at the other end has closed it) will
               result in a SIGPIPE being delivered to the writer.  If the
               other end can't handle that, be sure to read all the data
               before closing the pipe.

               Example:

                   open(OUTPUT, '|sort >foo')  # pipe to sort
                       or die "Can't start sort: $!";
                   #...                        # print stuff to output
                   close OUTPUT                # wait for sort to finish
                       or warn $! ? "Error closing sort pipe: $!"
                                  : "Exit status $? from sort";
                   open(INPUT, 'foo')          # get sort's results
                       or die "Can't open 'foo' for input: $!";

               FILEHANDLE may be an expression whose value can be used as an
               indirect filehandle, usually the real filehandle name.

       closedir DIRHANDLE
               Closes a directory opened by "opendir" and returns the success
               of that system call.

       connect SOCKET,NAME
               Attempts to connect to a remote socket, just as the connect
               system call does.  Returns true if it succeeded, false
               otherwise.  NAME should be a packed address of the appropriate
               type for the socket.  See the examples in "Sockets:
               Client/Server Communication" in perlipc.

       continue BLOCK
               Actually a flow control statement rather than a function.  If
               there is a "continue" BLOCK attached to a BLOCK (typically in a
               "while" or "foreach"), it is always executed just before the
               conditional is about to be evaluated again, just like the third
               part of a "for" loop in C.  Thus it can be used to increment a
               loop variable, even when the loop has been continued via the
               "next" statement (which is similar to the C "continue"
               statement).

               "last", "next", or "redo" may appear within a "continue" block.
               "last" and "redo" will behave as if they had been executed
               within the main block.  So will "next", but since it will
               execute a "continue" block, it may be more entertaining.

                   while (EXPR) {
                       ### redo always comes here
                       do_something;
                   } continue {
                       ### next always comes here
                       do_something_else;
                       # then back the top to re-check EXPR
                   }
                   ### last always comes here

               Omitting the "continue" section is semantically equivalent to
               using an empty one, logically enough.  In that case, "next"
               goes directly back to check the condition at the top of the
               loop.

       cos EXPR
       cos     Returns the cosine of EXPR (expressed in radians).  If EXPR is
               omitted, takes cosine of $_.

               For the inverse cosine operation, you may use the
               "Math::Trig::acos()" function, or use this relation:

                   sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }

       crypt PLAINTEXT,SALT
               Encrypts a string exactly like the crypt(3) function in the C
               library (assuming that you actually have a version there that
               has not been extirpated as a potential munition).  This can
               prove useful for checking the password file for lousy
               passwords, amongst other things.  Only the guys wearing white
               hats should do this.

               Note that crypt is intended to be a one-way function, much like
               breaking eggs to make an omelette.  There is no (known)
               corresponding decrypt function (in other words, the crypt() is
               a one-way hash function).  As a result, this function isn't all
               that useful for cryptography.  (For that, see your nearby CPAN
               mirror.)

               When verifying an existing encrypted string you should use the
               encrypted text as the salt (like "crypt($plain, $crypted) eq
               $crypted").  This allows your code to work with the standard
               crypt and with more exotic implementations.  In other words, do
               not assume anything about the returned string itself, or how
               many bytes in the encrypted string matter.

               Traditionally the result is a string of 13 bytes: two first
               bytes of the salt, followed by 11 bytes from the set
               "[./0-9A-Za-z]", and only the first eight bytes of the
               encrypted string mattered, but alternative hashing schemes
               (like MD5), higher level security schemes (like C2), and
               implementations on non-UNIX platforms may produce different
               strings.

               When choosing a new salt create a random two character string
               whose characters come from the set "[./0-9A-Za-z]" (like "join
               '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]").
               This set of characters is just a recommendation; the characters
               allowed in the salt depend solely on your system's crypt
               library, and Perl can't restrict what salts "crypt()" accepts.

               Here's an example that makes sure that whoever runs this
               program knows their own password:

                   $pwd = (getpwuid($<))[1];

                   system "stty -echo";
                   print "Password: ";
                   chomp($word = <STDIN>);
                   print "\n";
                   system "stty echo";

                   if (crypt($word, $pwd) ne $pwd) {
                       die "Sorry...\n";
                   } else {
                       print "ok\n";
                   }

               Of course, typing in your own password to whoever asks you for
               it is unwise.

               The crypt function is unsuitable for encrypting large
               quantities of data, not least of all because you can't get the
               information back.  Look at the by-module/Crypt and
               by-module/PGP directories on your favorite CPAN mirror for a
               slew of potentially useful modules.

               If using crypt() on a Unicode string (which potentially has
               characters with codepoints above 255), Perl tries to make sense
               of the situation by trying to downgrade (a copy of the string)
               the string back to an eight-bit byte string before calling
               crypt() (on that copy).  If that works, good.  If not, crypt()
               dies with "Wide character in crypt".

       dbmclose HASH
               [This function has been largely superseded by the "untie"
               function.]

               Breaks the binding between a DBM file and a hash.

       dbmopen HASH,DBNAME,MASK
               [This function has been largely superseded by the "tie"
               function.]

               This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB
               file to a hash.  HASH is the name of the hash.  (Unlike normal
               "open", the first argument is not a filehandle, even though it
               looks like one).  DBNAME is the name of the database (without
               the .dir or .pag extension if any).  If the database does not
               exist, it is created with protection specified by MASK (as
               modified by the "umask").  If your system supports only the
               older DBM functions, you may perform only one "dbmopen" in your
               program.  In older versions of Perl, if your system had neither
               DBM nor ndbm, calling "dbmopen" produced a fatal error; it now
               falls back to sdbm(3).

               If you don't have write access to the DBM file, you can only
               read hash variables, not set them.  If you want to test whether
               you can write, either use file tests or try setting a dummy
               hash entry inside an "eval", which will trap the error.

               Note that functions such as "keys" and "values" may return huge
               lists when used on large DBM files.  You may prefer to use the
               "each" function to iterate over large DBM files.  Example:

                   # print out history file offsets
                   dbmopen(%HIST,'/usr/lib/news/history',0666);
                   while (($key,$val) = each %HIST) {
                       print $key, ' = ', unpack('L',$val), "\n";
                   }
                   dbmclose(%HIST);

               See also AnyDBM_File for a more general description of the pros
               and cons of the various dbm approaches, as well as DB_File for
               a particularly rich implementation.

               You can control which DBM library you use by loading that
               library before you call dbmopen():

                   use DB_File;
                   dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
                       or die "Can't open netscape history file: $!";

       defined EXPR
       defined Returns a Boolean value telling whether EXPR has a value other
               than the undefined value "undef".  If EXPR is not present, $_
               will be checked.

               Many operations return "undef" to indicate failure, end of
               file, system error, uninitialized variable, and other
               exceptional conditions.  This function allows you to
               distinguish "undef" from other values.  (A simple Boolean test
               will not distinguish among "undef", zero, the empty string, and
               "0", which are all equally false.)  Note that since "undef" is
               a valid scalar, its presence doesn't necessarily indicate an
               exceptional condition: "pop" returns "undef" when its argument
               is an empty array, or when the element to return happens to be
               "undef".

               You may also use "defined(&func)" to check whether subroutine
               &func has ever been defined.  The return value is unaffected by
               any forward declarations of &func.  Note that a subroutine
               which is not defined may still be callable: its package may
               have an "AUTOLOAD" method that makes it spring into existence
               the first time that it is called -- see perlsub.

               Use of "defined" on aggregates (hashes and arrays) is
               deprecated.  It used to report whether memory for that
               aggregate has ever been allocated.  This behavior may disappear
               in future versions of Perl.  You should instead use a simple
               test for size:

                   if (@an_array) { print "has array elements\n" }
                   if (%a_hash)   { print "has hash members\n"   }

               When used on a hash element, it tells you whether the value is
               defined, not whether the key exists in the hash.  Use "exists"
               for the latter purpose.

               Examples:

                   print if defined $switch{'D'};
                   print "$val\n" while defined($val = pop(@ary));
                   die "Can't readlink $sym: $!"
                       unless defined($value = readlink $sym);
                   sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
                   $debugging = 0 unless defined $debugging;

               Note:  Many folks tend to overuse "defined", and then are
               surprised to discover that the number 0 and "" (the zero-length
               string) are, in fact, defined values.  For example, if you say

                   "ab" =~ /a(.*)b/;

               The pattern match succeeds, and $1 is defined, despite the fact
               that it matched "nothing".  But it didn't really match
               nothing--rather, it matched something that happened to be zero
               characters long.  This is all very above-board and honest.
               When a function returns an undefined value, it's an admission
               that it couldn't give you an honest answer.  So you should use
               "defined" only when you're questioning the integrity of what
               you're trying to do.  At other times, a simple comparison to 0
               or "" is what you want.

               See also "undef", "exists", "ref".

       delete EXPR
               Given an expression that specifies a hash element, array
               element, hash slice, or array slice, deletes the specified
               element(s) from the hash or array.  In the case of an array, if
               the array elements happen to be at the end, the size of the
               array will shrink to the highest element that tests true for
               exists() (or 0 if no such element exists).

               Returns each element so deleted or the undefined value if there
               was no such element.  Deleting from $ENV{} modifies the
               environment.  Deleting from a hash tied to a DBM file deletes
               the entry from the DBM file.  Deleting from a "tie"d hash or
               array may not necessarily return anything.

               Deleting an array element effectively returns that position of
               the array to its initial, uninitialized state.  Subsequently
               testing for the same element with exists() will return false.
               Note that deleting array elements in the middle of an array
               will not shift the index of the ones after them down--use
               splice() for that.  See "exists".

               The following (inefficiently) deletes all the values of %HASH
               and @ARRAY:

                   foreach $key (keys %HASH) {
                       delete $HASH{$key};
                   }

                   foreach $index (0 .. $#ARRAY) {
                       delete $ARRAY[$index];
                   }

               And so do these:

                   delete @HASH{keys %HASH};

                   delete @ARRAY[0 .. $#ARRAY];

               But both of these are slower than just assigning the empty list
               or undefining %HASH or @ARRAY:

                   %HASH = ();         # completely empty %HASH
                   undef %HASH;        # forget %HASH ever existed

                   @ARRAY = ();        # completely empty @ARRAY
                   undef @ARRAY;       # forget @ARRAY ever existed

               Note that the EXPR can be arbitrarily complicated as long as
               the final operation is a hash element, array element,  hash
               slice, or array slice lookup:

                   delete $ref->[$x][$y]{$key};
                   delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};

                   delete $ref->[$x][$y][$index];
                   delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];

       die LIST
               Outside an "eval", prints the value of LIST to "STDERR" and
               exits with the current value of $! (errno).  If $! is 0, exits
               with the value of "($? >> 8)" (backtick `command` status).  If
               "($? >> 8)" is 0, exits with 255.  Inside an "eval()," the
               error message is stuffed into $@ and the "eval" is terminated
               with the undefined value.  This makes "die" the way to raise an
               exception.

               Equivalent examples:

                   die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
                   chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"

               If the last element of LIST does not end in a newline, the
               current script line number and input line number (if any) are
               also printed, and a newline is supplied.  Note that the "input
               line number" (also known as "chunk") is subject to whatever
               notion of "line" happens to be currently in effect, and is also
               available as the special variable $..  See "$/" in perlvar and
               "$." in perlvar.

               Hint: sometimes appending ", stopped" to your message will
               cause it to make better sense when the string "at foo line 123"
               is appended.  Suppose you are running script "canasta".

                   die "/etc/games is no good";
                   die "/etc/games is no good, stopped";

               produce, respectively

                   /etc/games is no good at canasta line 123.
                   /etc/games is no good, stopped at canasta line 123.

               See also exit(), warn(), and the Carp module.

               If LIST is empty and $@ already contains a value (typically
               from a previous eval) that value is reused after appending
               "\t...propagated".  This is useful for propagating exceptions:

                   eval { ... };
                   die unless $@ =~ /Expected exception/;

               If LIST is empty and $@ contains an object reference that has a
               "PROPAGATE" method, that method will be called with additional
               file and line number parameters.  The return value replaces the
               value in $@.  ie. as if "$@ = eval { $@->PROPAGATE(__FILE__,
               __LINE__) };" were called.

               If $@ is empty then the string "Died" is used.

               die() can also be called with a reference argument.  If this
               happens to be trapped within an eval(), $@ contains the
               reference.  This behavior permits a more elaborate exception
               handling implementation using objects that maintain arbitrary
               state about the nature of the exception.  Such a scheme is
               sometimes preferable to matching particular string values of $@
               using regular expressions.  Here's an example:

                   eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
                   if ($@) {
                       if (ref($@) && UNIVERSAL::isa($@,"Some::Module::Exception")) {
                           # handle Some::Module::Exception
                       }
                       else {
                           # handle all other possible exceptions
                       }
                   }

               Because perl will stringify uncaught exception messages before
               displaying them, you may want to overload stringification
               operations on such custom exception objects.  See overload for
               details about that.

               You can arrange for a callback to be run just before the "die"
               does its deed, by setting the $SIG{__DIE__} hook.  The
               associated handler will be called with the error text and can
               change the error message, if it sees fit, by calling "die"
               again.  See "$SIG{expr}" in perlvar for details on setting %SIG
               entries, and "eval BLOCK" for some examples.  Although this
               feature was meant to be run only right before your program was
               to exit, this is not currently the case--the $SIG{__DIE__} hook
               is currently called even inside eval()ed blocks/strings!  If
               one wants the hook to do nothing in such situations, put

                       die @_ if $^S;

               as the first line of the handler (see "$^S" in perlvar).
               Because this promotes strange action at a distance, this
               counterintuitive behavior may be fixed in a future release.

       do BLOCK
               Not really a function.  Returns the value of the last command
               in the sequence of commands indicated by BLOCK.  When modified
               by a loop modifier, executes the BLOCK once before testing the
               loop condition.  (On other statements the loop modifiers test
               the conditional first.)

               "do BLOCK" does not count as a loop, so the loop control
               statements "next", "last", or "redo" cannot be used to leave or
               restart the block.  See perlsyn for alternative strategies.

       do SUBROUTINE(LIST)
               A deprecated form of subroutine call.  See perlsub.

       do EXPR Uses the value of EXPR as a filename and executes the contents
               of the file as a Perl script.  Its primary use is to include
               subroutines from a Perl subroutine library.

                   do 'stat.pl';

               is just like

                   eval `cat stat.pl`;

               except that it's more efficient and concise, keeps track of the
               current filename for error messages, searches the @INC
               libraries, and updates %INC if the file is found.  See
               "Predefined Names" in perlvar for these variables.  It also
               differs in that code evaluated with "do FILENAME" cannot see
               lexicals in the enclosing scope; "eval STRING" does.  It's the
               same, however, in that it does reparse the file every time you
               call it, so you probably don't want to do this inside a loop.

               If "do" cannot read the file, it returns undef and sets $! to
               the error.  If "do" can read the file but cannot compile it, it
               returns undef and sets an error message in $@.   If the file is
               successfully compiled, "do" returns the value of the last
               expression evaluated.

               Note that inclusion of library modules is better done with the
               "use" and "require" operators, which also do automatic error
               checking and raise an exception if there's a problem.

               You might like to use "do" to read in a program configuration
               file.  Manual error checking can be done this way:

                   # read in config files: system first, then user
                   for $file ("/share/prog/defaults.rc",
                              "$ENV{HOME}/.someprogrc")
                  {
                       unless ($return = do $file) {
                           warn "couldn't parse $file: $@" if $@;
                           warn "couldn't do $file: $!"    unless defined $return;
                           warn "couldn't run $file"       unless $return;
                       }
                   }

       dump LABEL
       dump    This function causes an immediate core dump.  See also the -u
               command-line switch in perlrun, which does the same thing.
               Primarily this is so that you can use the undump program (not
               supplied) to turn your core dump into an executable binary
               after having initialized all your variables at the beginning of
               the program.  When the new binary is executed it will begin by
               executing a "goto LABEL" (with all the restrictions that "goto"
               suffers).  Think of it as a goto with an intervening core dump
               and reincarnation.  If "LABEL" is omitted, restarts the program
               from the top.

               WARNING: Any files opened at the time of the dump will not be
               open any more when the program is reincarnated, with possible
               resulting confusion on the part of Perl.

               This function is now largely obsolete, partly because it's very
               hard to convert a core file into an executable, and because the
               real compiler backends for generating portable bytecode and
               compilable C code have superseded it.  That's why you should
               now invoke it as "CORE::dump()", if you don't want to be warned
               against a possible typo.

               If you're looking to use dump to speed up your program,
               consider generating bytecode or native C code as described in
               perlcc.  If you're just trying to accelerate a CGI script,
               consider using the "mod_perl" extension to Apache, or the CPAN
               module, CGI::Fast.  You might also consider autoloading or
               selfloading, which at least make your program appear to run
               faster.

       each HASH
               When called in list context, returns a 2-element list
               consisting of the key and value for the next element of a hash,
               so that you can iterate over it.  When called in scalar
               context, returns only the key for the next element in the hash.

               Entries are returned in an apparently random order.  The actual
               random order is subject to change in future versions of perl,
               but it is guaranteed to be in the same order as either the
               "keys" or "values" function would produce on the same
               (unmodified) hash.  Since Perl 5.8.1 the ordering is different
               even between different runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in perlsec).

               When the hash is entirely read, a null array is returned in
               list context (which when assigned produces a false (0) value),
               and "undef" in scalar context.  The next call to "each" after
               that will start iterating again.  There is a single iterator
               for each hash, shared by all "each", "keys", and "values"
               function calls in the program; it can be reset by reading all
               the elements from the hash, or by evaluating "keys HASH" or
               "values HASH".  If you add or delete elements of a hash while
               you're iterating over it, you may get entries skipped or
               duplicated, so don't.  Exception: It is always safe to delete
               the item most recently returned by "each()", which means that
               the following code will work:

                       while (($key, $value) = each %hash) {
                         print $key, "\n";
                         delete $hash{$key};   # This is safe
                       }

               The following prints out your environment like the printenv(1)
               program, only in a different order:

                   while (($key,$value) = each %ENV) {
                       print "$key=$value\n";
                   }

               See also "keys", "values" and "sort".

       eof FILEHANDLE
       eof ()
       eof     Returns 1 if the next read on FILEHANDLE will return end of
               file, or if FILEHANDLE is not open.  FILEHANDLE may be an
               expression whose value gives the real filehandle.  (Note that
               this function actually reads a character and then "ungetc"s it,
               so isn't very useful in an interactive context.)  Do not read
               from a terminal file (or call "eof(FILEHANDLE)" on it) after
               end-of-file is reached.  File types such as terminals may lose
               the end-of-file condition if you do.

               An "eof" without an argument uses the last file read.  Using
               "eof()" with empty parentheses is very different.  It refers to
               the pseudo file formed from the files listed on the command
               line and accessed via the "<>" operator.  Since "<>" isn't
               explicitly opened, as a normal filehandle is, an "eof()" before
               "<>" has been used will cause @ARGV to be examined to determine
               if input is available.   Similarly, an "eof()" after "<>" has
               returned end-of-file will assume you are processing another
               @ARGV list, and if you haven't set @ARGV, will read input from
               "STDIN"; see "I/O Operators" in perlop.

               In a "while (<>)" loop, "eof" or "eof(ARGV)" can be used to
               detect the end of each file, "eof()" will only detect the end
               of the last file.  Examples:

                   # reset line numbering on each input file
                   while (<>) {
                       next if /^\s*#/;        # skip comments
                       print "$.\t$_";
                   } continue {
                       close ARGV  if eof;     # Not eof()!
                   }

                   # insert dashes just before last line of last file
                   while (<>) {
                       if (eof()) {            # check for end of last file
                           print "--------------\n";
                       }
                       print;
                       last if eof();          # needed if we're reading from a terminal
                   }

               Practical hint: you almost never need to use "eof" in Perl,
               because the input operators typically return "undef" when they
               run out of data, or if there was an error.

       eval EXPR
       eval BLOCK
               In the first form, the return value of EXPR is parsed and
               executed as if it were a little Perl program.  The value of the
               expression (which is itself determined within scalar context)
               is first parsed, and if there weren't any errors, executed in
               the lexical context of the current Perl program, so that any
               variable settings or subroutine and format definitions remain
               afterwards.  Note that the value is parsed every time the eval
               executes.  If EXPR is omitted, evaluates $_.  This form is
               typically used to delay parsing and subsequent execution of the
               text of EXPR until run time.

               In the second form, the code within the BLOCK is parsed only
               once--at the same time the code surrounding the eval itself was
               parsed--and executed within the context of the current Perl
               program.  This form is typically used to trap exceptions more
               efficiently than the first (see below), while also providing
               the benefit of checking the code within BLOCK at compile time.

               The final semicolon, if any, may be omitted from the value of
               EXPR or within the BLOCK.

               In both forms, the value returned is the value of the last
               expression evaluated inside the mini-program; a return
               statement may be also used, just as with subroutines.  The
               expression providing the return value is evaluated in void,
               scalar, or list context, depending on the context of the eval
               itself.  See "wantarray" for more on how the evaluation context
               can be determined.

               If there is a syntax error or runtime error, or a "die"
               statement is executed, an undefined value is returned by
               "eval", and $@ is set to the error message.  If there was no
               error, $@ is guaranteed to be a null string.  Beware that using
               "eval" neither silences perl from printing warnings to STDERR,
               nor does it stuff the text of warning messages into $@.  To do
               either of those, you have to use the $SIG{__WARN__} facility,
               or turn off warnings inside the BLOCK or EXPR using
               "no warnings 'all'".  See "warn", perlvar, warnings and
               perllexwarn.

               Note that, because "eval" traps otherwise-fatal errors, it is
               useful for determining whether a particular feature (such as
               "socket" or "symlink") is implemented.  It is also Perl's
               exception trapping mechanism, where the die operator is used to
               raise exceptions.

               If the code to be executed doesn't vary, you may use the eval-
               BLOCK form to trap run-time errors without incurring the
               penalty of recompiling each time.  The error, if any, is still
               returned in $@.  Examples:

                   # make divide-by-zero nonfatal
                   eval { $answer = $a / $b; }; warn $@ if $@;

                   # same thing, but less efficient
                   eval '$answer = $a / $b'; warn $@ if $@;

                   # a compile-time error
                   eval { $answer = };                 # WRONG

                   # a run-time error
                   eval '$answer =';   # sets $@

               Due to the current arguably broken state of "__DIE__" hooks,
               when using the "eval{}" form as an exception trap in libraries,
               you may wish not to trigger any "__DIE__" hooks that user code
               may have installed.  You can use the "local $SIG{__DIE__}"
               construct for this purpose, as shown in this example:

                   # a very private exception trap for divide-by-zero
                   eval { local $SIG{'__DIE__'}; $answer = $a / $b; };
                   warn $@ if $@;

               This is especially significant, given that "__DIE__" hooks can
               call "die" again, which has the effect of changing their error
               messages:

                   # __DIE__ hooks may modify error messages
                   {
                      local $SIG{'__DIE__'} =
                             sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x };
                      eval { die "foo lives here" };
                      print $@ if $@;                # prints "bar lives here"
                   }

               Because this promotes action at a distance, this
               counterintuitive behavior may be fixed in a future release.

               With an "eval", you should be especially careful to remember
               what's being looked at when:

                   eval $x;            # CASE 1
                   eval "$x";          # CASE 2

                   eval '$x';          # CASE 3
                   eval { $x };        # CASE 4

                   eval "\$$x++";      # CASE 5
                   $$x++;              # CASE 6

               Cases 1 and 2 above behave identically: they run the code
               contained in the variable $x.  (Although case 2 has misleading
               double quotes making the reader wonder what else might be
               happening (nothing is).)  Cases 3 and 4 likewise behave in the
               same way: they run the code '$x', which does nothing but return
               the value of $x.  (Case 4 is preferred for purely visual
               reasons, but it also has the advantage of compiling at compile-
               time instead of at run-time.)  Case 5 is a place where normally
               you would like to use double quotes, except that in this
               particular situation, you can just use symbolic references
               instead, as in case 6.

               "eval BLOCK" does not count as a loop, so the loop control
               statements "next", "last", or "redo" cannot be used to leave or
               restart the block.

               Note that as a very special case, an "eval ''" executed within
               the "DB" package doesn't see the usual surrounding lexical
               scope, but rather the scope of the first non-DB piece of code
               that called it. You don't normally need to worry about this
               unless you are writing a Perl debugger.

       exec LIST
       exec PROGRAM LIST
               The "exec" function executes a system command and never
               returns-- use "system" instead of "exec" if you want it to
               return.  It fails and returns false only if the command does
               not exist and it is executed directly instead of via your
               system's command shell (see below).

               Since it's a common mistake to use "exec" instead of "system",
               Perl warns you if there is a following statement which isn't
               "die", "warn", or "exit" (if "-w" is set  -  but you always do
               that).   If you really want to follow an "exec" with some other
               statement, you can use one of these styles to avoid the
               warning:

                   exec ('foo')   or print STDERR "couldn't exec foo: $!";
                   { exec ('foo') }; print STDERR "couldn't exec foo: $!";

               If there is more than one argument in LIST, or if LIST is an
               array with more than one value, calls execvp(3) with the
               arguments in LIST.  If there is only one scalar argument or an
               array with one element in it, the argument is checked for shell
               metacharacters, and if there are any, the entire argument is
               passed to the system's command shell for parsing (this is
               "/bin/sh -c" on Unix platforms, but varies on other platforms).
               If there are no shell metacharacters in the argument, it is
               split into words and passed directly to "execvp", which is more
               efficient.  Examples:

                   exec '/bin/echo', 'Your arguments are: ', @ARGV;
                   exec "sort $outfile | uniq";

               If you don't really want to execute the first argument, but
               want to lie to the program you are executing about its own
               name, you can specify the program you actually want to run as
               an "indirect object" (without a comma) in front of the LIST.
               (This always forces interpretation of the LIST as a multivalued
               list, even if there is only a single scalar in the list.)
               Example:

                   $shell = '/bin/csh';
                   exec $shell '-sh';          # pretend it's a login shell

               or, more directly,

                   exec {'/bin/csh'} '-sh';    # pretend it's a login shell

               When the arguments get executed via the system shell, results
               will be subject to its quirks and capabilities.  See "`STRING`"
               in perlop for details.

               Using an indirect object with "exec" or "system" is also more
               secure.  This usage (which also works fine with system())
               forces interpretation of the arguments as a multivalued list,
               even if the list had just one argument.  That way you're safe
               from the shell expanding wildcards or splitting up words with
               whitespace in them.

                   @args = ( "echo surprise" );

                   exec @args;               # subject to shell escapes
                                               # if @args == 1
                   exec { $args[0] } @args;  # safe even with one-arg list

               The first version, the one without the indirect object, ran the
               echo program, passing it "surprise" an argument.  The second
               version didn't--it tried to run a program literally called
               "echo surprise", didn't find it, and set $? to a non-zero value
               indicating failure.

               Beginning with v5.6.0, Perl will attempt to flush all files
               opened for output before the exec, but this may not be
               supported on some platforms (see perlport).  To be safe, you
               may need to set $| ($AUTOFLUSH in English) or call the
               "autoflush()" method of "IO::Handle" on any open handles in
               order to avoid lost output.

               Note that "exec" will not call your "END" blocks, nor will it
               call any "DESTROY" methods in your objects.

       exists EXPR
               Given an expression that specifies a hash element or array
               element, returns true if the specified element in the hash or
               array has ever been initialized, even if the corresponding
               value is undefined.  The element is not autovivified if it
               doesn't exist.

                   print "Exists\n"    if exists $hash{$key};
                   print "Defined\n"   if defined $hash{$key};
                   print "True\n"      if $hash{$key};

                   print "Exists\n"    if exists $array[$index];
                   print "Defined\n"   if defined $array[$index];
                   print "True\n"      if $array[$index];

               A hash or array element can be true only if it's defined, and
               defined if it exists, but the reverse doesn't necessarily hold
               true.

               Given an expression that specifies the name of a subroutine,
               returns true if the specified subroutine has ever been
               declared, even if it is undefined.  Mentioning a subroutine
               name for exists or defined does not count as declaring it.
               Note that a subroutine which does not exist may still be
               callable: its package may have an "AUTOLOAD" method that makes
               it spring into existence the first time that it is called --
               see perlsub.

                   print "Exists\n"    if exists &subroutine;
                   print "Defined\n"   if defined &subroutine;

               Note that the EXPR can be arbitrarily complicated as long as
               the final operation is a hash or array key lookup or subroutine
               name:

                   if (exists $ref->{A}->{B}->{$key})  { }
                   if (exists $hash{A}{B}{$key})       { }

                   if (exists $ref->{A}->{B}->[$ix])   { }
                   if (exists $hash{A}{B}[$ix])        { }

                   if (exists &{$ref->{A}{B}{$key}})   { }

               Although the deepest nested array or hash will not spring into
               existence just because its existence was tested, any
               intervening ones will.  Thus "$ref->{"A"}" and
               "$ref->{"A"}->{"B"}" will spring into existence due to the
               existence test for the $key element above.  This happens
               anywhere the arrow operator is used, including even:

                   undef $ref;
                   if (exists $ref->{"Some key"})      { }
                   print $ref;             # prints HASH(0x80d3d5c)

               This surprising autovivification in what does not at first--or
               even second--glance appear to be an lvalue context may be fixed
               in a future release.

               See "Pseudo-hashes: Using an array as a hash" in perlref for
               specifics on how exists() acts when used on a pseudo-hash.

               Use of a subroutine call, rather than a subroutine name, as an
               argument to exists() is an error.

                   exists &sub;        # OK
                   exists &sub();      # Error

       exit EXPR
               Evaluates EXPR and exits immediately with that value.
               Example:

                   $ans = <STDIN>;
                   exit 0 if $ans =~ /^[Xx]/;

               See also "die".  If EXPR is omitted, exits with 0 status.  The
               only universally recognized values for EXPR are 0 for success
               and 1 for error; other values are subject to interpretation
               depending on the environment in which the Perl program is
               running.  For example, exiting 69 (EX_UNAVAILABLE) from a
               sendmail incoming-mail filter will cause the mailer to return
               the item undelivered, but that's not true everywhere.

               Don't use "exit" to abort a subroutine if there's any chance
               that someone might want to trap whatever error happened.  Use
               "die" instead, which can be trapped by an "eval".

               The exit() function does not always exit immediately.  It calls
               any defined "END" routines first, but these "END" routines may
               not themselves abort the exit.  Likewise any object destructors
               that need to be called are called before the real exit.  If
               this is a problem, you can call "POSIX:_exit($status)" to avoid
               END and destructor processing.  See perlmod for details.

       exp EXPR
       exp     Returns e (the natural logarithm base) to the power of EXPR.
               If EXPR is omitted, gives "exp($_)".

       fcntl FILEHANDLE,FUNCTION,SCALAR
               Implements the fcntl(2) function.  You'll probably have to say

                   use Fcntl;

               first to get the correct constant definitions.  Argument
               processing and value return works just like "ioctl" below.  For
               example:

                   use Fcntl;
                   fcntl($filehandle, F_GETFL, $packed_return_buffer)
                       or die "can't fcntl F_GETFL: $!";

               You don't have to check for "defined" on the return from
               "fcntl".  Like "ioctl", it maps a 0 return from the system call
               into "0 but true" in Perl.  This string is true in boolean
               context and 0 in numeric context.  It is also exempt from the
               normal -w warnings on improper numeric conversions.

               Note that "fcntl" will produce a fatal error if used on a
               machine that doesn't implement fcntl(2).  See the Fcntl module
               or your fcntl(2) manpage to learn what functions are available
               on your system.

       fileno FILEHANDLE
               Returns the file descriptor for a filehandle, or undefined if
               the filehandle is not open.  This is mainly useful for
               constructing bitmaps for "select" and low-level POSIX tty-
               handling operations.  If FILEHANDLE is an expression, the value
               is taken as an indirect filehandle, generally its name.

               You can use this to find out whether two handles refer to the
               same underlying descriptor:

                   if (fileno(THIS) == fileno(THAT)) {
                       print "THIS and THAT are dups\n";
                   }

               (Filehandles connected to memory objects via new features of
               "open" may return undefined even though they are open.)

       flock FILEHANDLE,OPERATION
               Calls flock(2), or an emulation of it, on FILEHANDLE.  Returns
               true for success, false on failure.  Produces a fatal error if
               used on a machine that doesn't implement flock(2), fcntl(2)
               locking, or lockf(3).  "flock" is Perl's portable file locking
               interface, although it locks only entire files, not records.

               Two potentially non-obvious but traditional "flock" semantics
               are that it waits indefinitely until the lock is granted, and
               that its locks merely advisory.  Such discretionary locks are
               more flexible, but offer fewer guarantees.  This means that
               files locked with "flock" may be modified by programs that do
               not also use "flock".  See perlport, your port's specific
               documentation, or your system-specific local manpages for
               details.  It's best to assume traditional behavior if you're
               writing portable programs.  (But if you're not, you should as
               always feel perfectly free to write for your own system's
               idiosyncrasies (sometimes called "features").  Slavish
               adherence to portability concerns shouldn't get in the way of
               your getting your job done.)

               OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly
               combined with LOCK_NB.  These constants are traditionally
               valued 1, 2, 8 and 4, but you can use the symbolic names if you
               import them from the Fcntl module, either individually, or as a
               group using the ':flock' tag.  LOCK_SH requests a shared lock,
               LOCK_EX requests an exclusive lock, and LOCK_UN releases a
               previously requested lock.  If LOCK_NB is bitwise-or'ed with
               LOCK_SH or LOCK_EX then "flock" will return immediately rather
               than blocking waiting for the lock (check the return status to
               see if you got it).

               To avoid the possibility of miscoordination, Perl now flushes
               FILEHANDLE before locking or unlocking it.

               Note that the emulation built with lockf(3) doesn't provide
               shared locks, and it requires that FILEHANDLE be open with
               write intent.  These are the semantics that lockf(3)
               implements.  Most if not all systems implement lockf(3) in
               terms of fcntl(2) locking, though, so the differing semantics
               shouldn't bite too many people.

               Note that the fcntl(2) emulation of flock(3) requires that
               FILEHANDLE be open with read intent to use LOCK_SH and requires
               that it be open with write intent to use LOCK_EX.

               Note also that some versions of "flock" cannot lock things over
               the network; you would need to use the more system-specific
               "fcntl" for that.  If you like you can force Perl to ignore
               your system's flock(2) function, and so provide its own
               fcntl(2)-based emulation, by passing the switch "-Ud_flock" to
               the Configure program when you configure perl.

               Here's a mailbox appender for BSD systems.

                   use Fcntl ':flock'; # import LOCK_* constants

                   sub lock {
                       flock(MBOX,LOCK_EX);
                       # and, in case someone appended
                       # while we were waiting...
                       seek(MBOX, 0, 2);
                   }

                   sub unlock {
                       flock(MBOX,LOCK_UN);
                   }

                   open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
                           or die "Can't open mailbox: $!";

                   lock();
                   print MBOX $msg,"\n\n";
                   unlock();

               On systems that support a real flock(), locks are inherited
               across fork() calls, whereas those that must resort to the more
               capricious fcntl() function lose the locks, making it harder to
               write servers.

               See also DB_File for other flock() examples.

       fork    Does a fork(2) system call to create a new process running the
               same program at the same point.  It returns the child pid to
               the parent process, 0 to the child process, or "undef" if the
               fork is unsuccessful.  File descriptors (and sometimes locks on
               those descriptors) are shared, while everything else is copied.
               On most systems supporting fork(), great care has gone into
               making it extremely efficient (for example, using copy-on-write
               technology on data pages), making it the dominant paradigm for
               multitasking over the last few decades.

               Beginning with v5.6.0, Perl will attempt to flush all files
               opened for output before forking the child process, but this
               may not be supported on some platforms (see perlport).  To be
               safe, you may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any open handles in
               order to avoid duplicate output.

               If you "fork" without ever waiting on your children, you will
               accumulate zombies.  On some systems, you can avoid this by
               setting $SIG{CHLD} to "IGNORE".  See also perlipc for more
               examples of forking and reaping moribund children.

               Note that if your forked child inherits system file descriptors
               like STDIN and STDOUT that are actually connected by a pipe or
               socket, even if you exit, then the remote server (such as, say,
               a CGI script or a backgrounded job launched from a remote
               shell) won't think you're done.  You should reopen those to
               /dev/null if it's any issue.

       format  Declare a picture format for use by the "write" function.  For
               example:

                   format Something =
                       Test: @<<<<<<<< @||||| @>>>>>
                             $str,     $%,    '$' . int($num)
                   .

                   $str = "widget";
                   $num = $cost/$quantity;
                   $~ = 'Something';
                   write;

               See perlform for many details and examples.

       formline PICTURE,LIST
               This is an internal function used by "format"s, though you may
               call it, too.  It formats (see perlform) a list of values
               according to the contents of PICTURE, placing the output into
               the format output accumulator, $^A (or $ACCUMULATOR in
               English).  Eventually, when a "write" is done, the contents of
               $^A are written to some filehandle, but you could also read $^A
               yourself and then set $^A back to "".  Note that a format
               typically does one "formline" per line of form, but the
               "formline" function itself doesn't care how many newlines are
               embedded in the PICTURE.  This means that the "~" and "~~"
               tokens will treat the entire PICTURE as a single line.  You may
               therefore need to use multiple formlines to implement a single
               record format, just like the format compiler.

               Be careful if you put double quotes around the picture, because
               an "@" character may be taken to mean the beginning of an array
               name.  "formline" always returns true.  See perlform for other
               examples.

       getc FILEHANDLE
       getc    Returns the next character from the input file attached to
               FILEHANDLE, or the undefined value at end of file, or if there
               was an error (in the latter case $! is set).  If FILEHANDLE is
               omitted, reads from STDIN.  This is not particularly efficient.
               However, it cannot be used by itself to fetch single characters
               without waiting for the user to hit enter.  For that, try
               something more like:

                   if ($BSD_STYLE) {
                       system "stty cbreak </dev/tty >/dev/tty 2>&1";
                   }
                   else {
                       system "stty", '-icanon', 'eol', "\001";
                   }

                   $key = getc(STDIN);

                   if ($BSD_STYLE) {
                       system "stty -cbreak </dev/tty >/dev/tty 2>&1";
                   }
                   else {
                       system "stty", 'icanon', 'eol', '^@'; # ASCII null
                   }
                   print "\n";

               Determination of whether $BSD_STYLE should be set is left as an
               exercise to the reader.

               The "POSIX::getattr" function can do this more portably on
               systems purporting POSIX compliance.  See also the
               "Term::ReadKey" module from your nearest CPAN site; details on
               CPAN can be found on "CPAN" in perlmodlib.

       getlogin
               Implements the C library function of the same name, which on
               most systems returns the current login from /etc/utmp, if any.
               If null, use "getpwuid".

                   $login = getlogin || getpwuid($<) || "Kilroy";

               Do not consider "getlogin" for authentication: it is not as
               secure as "getpwuid".

       getpeername SOCKET
               Returns the packed sockaddr address of other end of the SOCKET
               connection.

                   use Socket;
                   $hersockaddr    = getpeername(SOCK);
                   ($port, $iaddr) = sockaddr_in($hersockaddr);
                   $herhostname    = gethostbyaddr($iaddr, AF_INET);
                   $herstraddr     = inet_ntoa($iaddr);

       getpgrp PID
               Returns the current process group for the specified PID.  Use a
               PID of 0 to get the current process group for the current
               process.  Will raise an exception if used on a machine that
               doesn't implement getpgrp(2).  If PID is omitted, returns
               process group of current process.  Note that the POSIX version
               of "getpgrp" does not accept a PID argument, so only "PID==0"
               is truly portable.

       getppid Returns the process id of the parent process.

               Note for Linux users: on Linux, the C functions "getpid()" and
               "getppid()" return different values from different threads. In
               order to be portable, this behavior is not reflected by the
               perl-level function "getppid()", that returns a consistent
               value across threads. If you want to call the underlying
               "getppid()", you may use the CPAN module "Linux::Pid".

       getpriority WHICH,WHO
               Returns the current priority for a process, a process group, or
               a user.  (See getpriority(2).)  Will raise a fatal exception if
               used on a machine that doesn't implement getpriority(2).

       getpwnam NAME
       getgrnam NAME
       gethostbyname NAME
       getnetbyname NAME
       getprotobyname NAME
       getpwuid UID
       getgrgid GID
       getservbyname NAME,PROTO
       gethostbyaddr ADDR,ADDRTYPE
       getnetbyaddr ADDR,ADDRTYPE
       getprotobynumber NUMBER
       getservbyport PORT,PROTO
       getpwent
       getgrent
       gethostent
       getnetent
       getprotoent
       getservent
       setpwent
       setgrent
       sethostent STAYOPEN
       setnetent STAYOPEN
       setprotoent STAYOPEN
       setservent STAYOPEN
       endpwent
       endgrent
       endhostent
       endnetent
       endprotoent
       endservent
               These routines perform the same functions as their counterparts
               in the system library.  In list context, the return values from
               the various get routines are as follows:

                   ($name,$passwd,$uid,$gid,
                      $quota,$comment,$gcos,$dir,$shell,$expire) = getpw*
                   ($name,$passwd,$gid,$members) = getgr*
                   ($name,$aliases,$addrtype,$length,@addrs) = gethost*
                   ($name,$aliases,$addrtype,$net) = getnet*
                   ($name,$aliases,$proto) = getproto*
                   ($name,$aliases,$port,$proto) = getserv*

               (If the entry doesn't exist you get a null list.)

               The exact meaning of the $gcos field varies but it usually
               contains the real name of the user (as opposed to the login
               name) and other information pertaining to the user.  Beware,
               however, that in many system users are able to change this
               information and therefore it cannot be trusted and therefore
               the $gcos is tainted (see perlsec).  The $passwd and $shell,
               user's encrypted password and login shell, are also tainted,
               because of the same reason.

               In scalar context, you get the name, unless the function was a
               lookup by name, in which case you get the other thing, whatever
               it is.  (If the entry doesn't exist you get the undefined
               value.)  For example:

                   $uid   = getpwnam($name);
                   $name  = getpwuid($num);
                   $name  = getpwent();
                   $gid   = getgrnam($name);
                   $name  = getgrgid($num);
                   $name  = getgrent();
                   #etc.

               In getpw*() the fields $quota, $comment, and $expire are
               special cases in the sense that in many systems they are
               unsupported.  If the $quota is unsupported, it is an empty
               scalar.  If it is supported, it usually encodes the disk quota.
               If the $comment field is unsupported, it is an empty scalar.
               If it is supported it usually encodes some administrative
               comment about the user.  In some systems the $quota field may
               be $change or $age, fields that have to do with password aging.
               In some systems the $comment field may be $class.  The $expire
               field, if present, encodes the expiration period of the account
               or the password.  For the availability and the exact meaning of
               these fields in your system, please consult your getpwnam(3)
               documentation and your pwd.h file.  You can also find out from
               within Perl what your $quota and $comment fields mean and
               whether you have the $expire field by using the "Config" module
               and the values "d_pwquota", "d_pwage", "d_pwchange",
               "d_pwcomment", and "d_pwexpire".  Shadow password files are
               only supported if your vendor has implemented them in the
               intuitive fashion that calling the regular C library routines
               gets the shadow versions if you're running under privilege or
               if there exists the shadow(3) functions as found in System V (
               this includes Solaris and Linux.)  Those systems which
               implement a proprietary shadow password facility are unlikely
               to be supported.

               The $members value returned by getgr*() is a space separated
               list of the login names of the members of the group.

               For the gethost*() functions, if the "h_errno" variable is
               supported in C, it will be returned to you via $? if the
               function call fails.  The @addrs value returned by a successful
               call is a list of the raw addresses returned by the
               corresponding system library call.  In the Internet domain,
               each address is four bytes long and you can unpack it by saying
               something like:

                   ($a,$b,$c,$d) = unpack('C4',$addr[0]);

               The Socket library makes this slightly easier:

                   use Socket;
                   $iaddr = inet_aton("127.1"); # or whatever address
                   $name  = gethostbyaddr($iaddr, AF_INET);

                   # or going the other way
                   $straddr = inet_ntoa($iaddr);

               If you get tired of remembering which element of the return
               list contains which return value, by-name interfaces are
               provided in standard modules: "File::stat", "Net::hostent",
               "Net::netent", "Net::protoent", "Net::servent", "Time::gmtime",
               "Time::localtime", and "User::grent".  These override the
               normal built-ins, supplying versions that return objects with
               the appropriate names for each field.  For example:

                  use File::stat;
                  use User::pwent;
                  $is_his = (stat($filename)->uid == pwent($whoever)->uid);

               Even though it looks like they're the same method calls (uid),
               they aren't, because a "File::stat" object is different from a
               "User::pwent" object.

       getsockname SOCKET
               Returns the packed sockaddr address of this end of the SOCKET
               connection, in case you don't know the address because you have
               several different IPs that the connection might have come in
               on.

                   use Socket;
                   $mysockaddr = getsockname(SOCK);
                   ($port, $myaddr) = sockaddr_in($mysockaddr);
                   printf "Connect to %s [%s]\n",
                      scalar gethostbyaddr($myaddr, AF_INET),
                      inet_ntoa($myaddr);

       getsockopt SOCKET,LEVEL,OPTNAME
               Returns the socket option requested, or undef if there is an
               error.

       glob EXPR
       glob    In list context, returns a (possibly empty) list of filename
               expansions on the value of EXPR such as the standard Unix shell
               /bin/csh would do. In scalar context, glob iterates through
               such filename expansions, returning undef when the list is
               exhausted. This is the internal function implementing the
               "<*.c>" operator, but you can use it directly. If EXPR is
               omitted, $_ is used.  The "<*.c>" operator is discussed in more
               detail in "I/O Operators" in perlop.

               Beginning with v5.6.0, this operator is implemented using the
               standard "File::Glob" extension.  See File::Glob for details.

       gmtime EXPR
               Converts a time as returned by the time function to an
               8-element list with the time localized for the standard
               Greenwich time zone.  Typically used as follows:

                   #  0    1    2     3     4    5     6     7
                   ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) =
                                                           gmtime(time);

               All list elements are numeric, and come straight out of the C
               `struct tm'.  $sec, $min, and $hour are the seconds, minutes,
               and hours of the specified time.  $mday is the day of the
               month, and $mon is the month itself, in the range 0..11 with 0
               indicating January and 11 indicating December.  $year is the
               number of years since 1900.  That is, $year is 123 in year
               2023.  $wday is the day of the week, with 0 indicating Sunday
               and 3 indicating Wednesday.  $yday is the day of the year, in
               the range 0..364 (or 0..365 in leap years.)

               Note that the $year element is not simply the last two digits
               of the year.  If you assume it is, then you create
               non-Y2K-compliant programs--and you wouldn't want to do that,
               would you?

               The proper way to get a complete 4-digit year is simply:

                       $year += 1900;

               And to get the last two digits of the year (e.g., '01' in 2001)
               do:

                       $year = sprintf("%02d", $year % 100);

               If EXPR is omitted, "gmtime()" uses the current time
               ("gmtime(time)").

               In scalar context, "gmtime()" returns the ctime(3) value:

                   $now_string = gmtime;  # e.g., "Thu Oct 13 04:54:34 1994"

               Also see the "timegm" function provided by the "Time::Local"
               module, and the strftime(3) function available via the POSIX
               module.

               This scalar value is not locale dependent (see perllocale), but
               is instead a Perl builtin.  Also see the "Time::Local" module,
               and the strftime(3) and mktime(3) functions available via the
               POSIX module.  To get somewhat similar but locale dependent
               date strings, set up your locale environment variables
               appropriately (please see perllocale) and try for example:

                   use POSIX qw(strftime);
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;

               Note that the %a and %b escapes, which represent the short
               forms of the day of the week and the month of the year, may not
               necessarily be three characters wide in all locales.

       goto LABEL
       goto EXPR
       goto &NAME
               The "goto-LABEL" form finds the statement labeled with LABEL
               and resumes execution there.  It may not be used to go into any
               construct that requires initialization, such as a subroutine or
               a "foreach" loop.  It also can't be used to go into a construct
               that is optimized away, or to get out of a block or subroutine
               given to "sort".  It can be used to go almost anywhere else
               within the dynamic scope, including out of subroutines, but
               it's usually better to use some other construct such as "last"
               or "die".  The author of Perl has never felt the need to use
               this form of "goto" (in Perl, that is--C is another matter).
               (The difference being that C does not offer named loops
               combined with loop control.  Perl does, and this replaces most
               structured uses of "goto" in other languages.)

               The "goto-EXPR" form expects a label name, whose scope will be
               resolved dynamically.  This allows for computed "goto"s per
               FORTRAN, but isn't necessarily recommended if you're optimizing
               for maintainability:

                   goto ("FOO", "BAR", "GLARCH")[$i];

               The "goto-&NAME" form is quite different from the other forms
               of "goto".  In fact, it isn't a goto in the normal sense at
               all, and doesn't have the stigma associated with other gotos.
               Instead, it exits the current subroutine (losing any changes
               set by local()) and immediately calls in its place the named
               subroutine using the current value of @_.  This is used by
               "AUTOLOAD" subroutines that wish to load another subroutine and
               then pretend that the other subroutine had been called in the
               first place (except that any modifications to @_ in the current
               subroutine are propagated to the other subroutine.)  After the
               "goto", not even "caller" will be able to tell that this
               routine was called first.

               NAME needn't be the name of a subroutine; it can be a scalar
               variable containing a code reference, or a block which
               evaluates to a code reference.

       grep BLOCK LIST
       grep EXPR,LIST
               This is similar in spirit to, but not the same as, grep(1) and
               its relatives.  In particular, it is not limited to using
               regular expressions.

               Evaluates the BLOCK or EXPR for each element of LIST (locally
               setting $_ to each element) and returns the list value
               consisting of those elements for which the expression evaluated
               to true.  In scalar context, returns the number of times the
               expression was true.

                   @foo = grep(!/^#/, @bar);    # weed out comments

               or equivalently,

                   @foo = grep {!/^#/} @bar;    # weed out comments

               Note that $_ is an alias to the list value, so it can be used
               to modify the elements of the LIST.  While this is useful and
               supported, it can cause bizarre results if the elements of LIST
               are not variables.  Similarly, grep returns aliases into the
               original list, much as a for loop's index variable aliases the
               list elements.  That is, modifying an element of a list
               returned by grep (for example, in a "foreach", "map" or another
               "grep") actually modifies the element in the original list.
               This is usually something to be avoided when writing clear
               code.

               See also "map" for a list composed of the results of the BLOCK
               or EXPR.

       hex EXPR
       hex     Interprets EXPR as a hex string and returns the corresponding
               value.  (To convert strings that might start with either 0, 0x,
               or 0b, see "oct".)  If EXPR is omitted, uses $_.

                   print hex '0xAf'; # prints '175'
                   print hex 'aF';   # same

               Hex strings may only represent integers.  Strings that would
               cause integer overflow trigger a warning.  Leading whitespace
               is not stripped, unlike oct().

       import  There is no builtin "import" function.  It is just an ordinary
               method (subroutine) defined (or inherited) by modules that wish
               to export names to another module.  The "use" function calls
               the "import" method for the package used.  See also "use",
               perlmod, and Exporter.

       index STR,SUBSTR,POSITION
       index STR,SUBSTR
               The index function searches for one string within another, but
               without the wildcard-like behavior of a full regular-expression
               pattern match.  It returns the position of the first occurrence
               of SUBSTR in STR at or after POSITION.  If POSITION is omitted,
               starts searching from the beginning of the string.  The return
               value is based at 0 (or whatever you've set the $[ variable
               to--but don't do that).  If the substring is not found, returns
               one less than the base, ordinarily "-1".

       int EXPR
       int     Returns the integer portion of EXPR.  If EXPR is omitted, uses
               $_.  You should not use this function for rounding: one because
               it truncates towards 0, and two because machine representations
               of floating point numbers can sometimes produce
               counterintuitive results.  For example, "int(-6.725/0.025)"
               produces -268 rather than the correct -269; that's because it's
               really more like -268.99999999999994315658 instead.  Usually,
               the "sprintf", "printf", or the "POSIX::floor" and
               "POSIX::ceil" functions will serve you better than will int().

       ioctl FILEHANDLE,FUNCTION,SCALAR
               Implements the ioctl(2) function.  You'll probably first have
               to say

                   require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph

               to get the correct function definitions.  If ioctl.ph doesn't
               exist or doesn't have the correct definitions you'll have to
               roll your own, based on your C header files such as
               <sys/ioctl.h>.  (There is a Perl script called h2ph that comes
               with the Perl kit that may help you in this, but it's
               nontrivial.)  SCALAR will be read and/or written depending on
               the FUNCTION--a pointer to the string value of SCALAR will be
               passed as the third argument of the actual "ioctl" call.  (If
               SCALAR has no string value but does have a numeric value, that
               value will be passed rather than a pointer to the string value.
               To guarantee this to be true, add a 0 to the scalar before
               using it.)  The "pack" and "unpack" functions may be needed to
               manipulate the values of structures used by "ioctl".

               The return value of "ioctl" (and "fcntl") is as follows:

                       if OS returns:          then Perl returns:
                           -1                    undefined value
                            0                  string "0 but true"
                       anything else               that number

               Thus Perl returns true on success and false on failure, yet you
               can still easily determine the actual value returned by the
               operating system:

                   $retval = ioctl(...) || -1;
                   printf "System returned %d\n", $retval;

               The special string "0 but true" is exempt from -w complaints
               about improper numeric conversions.

               Here's an example of setting a filehandle named "REMOTE" to be
               non-blocking at the system level.  You'll have to negotiate $|
               on your own, though.

                   use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);

                   $flags = fcntl(REMOTE, F_GETFL, 0)
                               or die "Can't get flags for the socket: $!\n";

                   $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
                               or die "Can't set flags for the socket: $!\n";

       join EXPR,LIST
               Joins the separate strings of LIST into a single string with
               fields separated by the value of EXPR, and returns that new
               string.  Example:

                   $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);

               Beware that unlike "split", "join" doesn't take a pattern as
               its first argument.  Compare "split".

       keys HASH
               Returns a list consisting of all the keys of the named hash.
               (In scalar context, returns the number of keys.)

               The keys are returned in an apparently random order.  The
               actual random order is subject to change in future versions of
               perl, but it is guaranteed to be the same order as either the
               "values" or "each" function produces (given that the hash has
               not been modified).  Since Perl 5.8.1 the ordering is different
               even between different runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in perlsec).

               As a side effect, calling keys() resets the HASH's internal
               iterator, see "each".

               Here is yet another way to print your environment:

                   @keys = keys %ENV;
                   @values = values %ENV;
                   while (@keys) {
                       print pop(@keys), '=', pop(@values), "\n";
                   }

               or how about sorted by key:

                   foreach $key (sort(keys %ENV)) {
                       print $key, '=', $ENV{$key}, "\n";
                   }

               The returned values are copies of the original keys in the
               hash, so modifying them will not affect the original hash.
               Compare "values".

               To sort a hash by value, you'll need to use a "sort" function.
               Here's a descending numeric sort of a hash by its values:

                   foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
                       printf "%4d %s\n", $hash{$key}, $key;
                   }

               As an lvalue "keys" allows you to increase the number of hash
               buckets allocated for the given hash.  This can gain you a
               measure of efficiency if you know the hash is going to get big.
               (This is similar to pre-extending an array by assigning a
               larger number to $#array.)  If you say

                   keys %hash = 200;

               then %hash will have at least 200 buckets allocated for it--256
               of them, in fact, since it rounds up to the next power of two.
               These buckets will be retained even if you do "%hash = ()", use
               "undef %hash" if you want to free the storage while %hash is
               still in scope.  You can't shrink the number of buckets
               allocated for the hash using "keys" in this way (but you
               needn't worry about doing this by accident, as trying has no
               effect).

               See also "each", "values" and "sort".

       kill SIGNAL, LIST
               Sends a signal to a list of processes.  Returns the number of
               processes successfully signaled (which is not necessarily the
               same as the number actually killed).

                   $cnt = kill 1, $child1, $child2;
                   kill 9, @goners;

               If SIGNAL is zero, no signal is sent to the process.  This is a
               useful way to check that a child process is alive and hasn't
               changed its UID.  See perlport for notes on the portability of
               this construct.

               Unlike in the shell, if SIGNAL is negative, it kills process
               groups instead of processes.  (On System V, a negative PROCESS
               number will also kill process groups, but that's not portable.)
               That means you usually want to use positive not negative
               signals.  You may also use a signal name in quotes.

               See "Signals" in perlipc for more details.

       last LABEL
       last    The "last" command is like the "break" statement in C (as used
               in loops); it immediately exits the loop in question.  If the
               LABEL is omitted, the command refers to the innermost enclosing
               loop.  The "continue" block, if any, is not executed:

                   LINE: while (<STDIN>) {
                       last LINE if /^$/;      # exit when done with header
                       #...
                   }

               "last" cannot be used to exit a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "last" can be used to effect an early
               exit out of such a block.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       lc EXPR
       lc      Returns a lowercased version of EXPR.  This is the internal
               function implementing the "\L" escape in double-quoted strings.
               Respects current LC_CTYPE locale if "use locale" in force.  See
               perllocale and perlunicode for more details about locale and
               Unicode support.

               If EXPR is omitted, uses $_.

       lcfirst EXPR
       lcfirst Returns the value of EXPR with the first character lowercased.
               This is the internal function implementing the "\l" escape in
               double-quoted strings.  Respects current LC_CTYPE locale if
               "use locale" in force.  See perllocale and perlunicode for more
               details about locale and Unicode support.

               If EXPR is omitted, uses $_.

       length EXPR
       length  Returns the length in characters of the value of EXPR.  If EXPR
               is omitted, returns length of $_.  Note that this cannot be
               used on an entire array or hash to find out how many elements
               these have.  For that, use "scalar @array" and "scalar keys
               %hash" respectively.

               Note the characters: if the EXPR is in Unicode, you will get
               the number of characters, not the number of bytes.  To get the
               length in bytes, use "do { use bytes; length(EXPR) }", see
               bytes.

       link OLDFILE,NEWFILE
               Creates a new filename linked to the old filename.  Returns
               true for success, false otherwise.

       listen SOCKET,QUEUESIZE
               Does the same thing that the listen system call does.  Returns
               true if it succeeded, false otherwise.  See the example in
               "Sockets: Client/Server Communication" in perlipc.

       local EXPR
               You really probably want to be using "my" instead, because
               "local" isn't what most people think of as "local".  See
               "Private Variables via my()" in perlsub for details.

               A local modifies the listed variables to be local to the
               enclosing block, file, or eval.  If more than one value is
               listed, the list must be placed in parentheses.  See "Temporary
               Values via local()" in perlsub for details, including issues
               with tied arrays and hashes.

       localtime EXPR
               Converts a time as returned by the time function to a 9-element
               list with the time analyzed for the local time zone.  Typically
               used as follows:

                   #  0    1    2     3     4    5     6     7     8
                   ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                                               localtime(time);

               All list elements are numeric, and come straight out of the C
               `struct tm'.  $sec, $min, and $hour are the seconds, minutes,
               and hours of the specified time.  $mday is the day of the
               month, and $mon is the month itself, in the range 0..11 with 0
               indicating January and 11 indicating December.  $year is the
               number of years since 1900.  That is, $year is 123 in year
               2023.  $wday is the day of the week, with 0 indicating Sunday
               and 3 indicating Wednesday.  $yday is the day of the year, in
               the range 0..364 (or 0..365 in leap years.)  $isdst is true if
               the specified time occurs during daylight savings time, false
               otherwise.

               Note that the $year element is not simply the last two digits
               of the year.  If you assume it is, then you create
               non-Y2K-compliant programs--and you wouldn't want to do that,
               would you?

               The proper way to get a complete 4-digit year is simply:

                       $year += 1900;

               And to get the last two digits of the year (e.g., '01' in 2001)
               do:

                       $year = sprintf("%02d", $year % 100);

               If EXPR is omitted, "localtime()" uses the current time
               ("localtime(time)").

               In scalar context, "localtime()" returns the ctime(3) value:

                   $now_string = localtime;  # e.g., "Thu Oct 13 04:54:34 1994"

               This scalar value is not locale dependent, see perllocale, but
               instead a Perl builtin.  Also see the "Time::Local" module (to
               convert the second, minutes, hours, ... back to seconds since
               the stroke of midnight the 1st of January 1970, the value
               returned by time()), and the strftime(3) and mktime(3)
               functions available via the POSIX module.  To get somewhat
               similar but locale dependent date strings, set up your locale
               environment variables appropriately (please see perllocale) and
               try for example:

                   use POSIX qw(strftime);
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;

               Note that the %a and %b, the short forms of the day of the week
               and the month of the year, may not necessarily be three
               characters wide.

       lock THING
               This function places an advisory lock on a shared variable, or
               referenced object contained in THING until the lock goes out of
               scope.

               lock() is a "weak keyword" : this means that if you've defined
               a function by this name (before any calls to it), that function
               will be called instead. (However, if you've said "use threads",
               lock() is always a keyword.) See threads.

       log EXPR
       log     Returns the natural logarithm (base e) of EXPR.  If EXPR is
               omitted, returns log of $_.  To get the log of another base,
               use basic algebra: The base-N log of a number is equal to the
               natural log of that number divided by the natural log of N.
               For example:

                   sub log10 {
                       my $n = shift;
                       return log($n)/log(10);
                   }

               See also "exp" for the inverse operation.

       lstat EXPR
       lstat   Does the same thing as the "stat" function (including setting
               the special "_" filehandle) but stats a symbolic link instead
               of the file the symbolic link points to.  If symbolic links are
               unimplemented on your system, a normal "stat" is done.  For
               much more detailed information, please see the documentation
               for "stat".

               If EXPR is omitted, stats $_.

       m//     The match operator.  See perlop.

       map BLOCK LIST
       map EXPR,LIST
               Evaluates the BLOCK or EXPR for each element of LIST (locally
               setting $_ to each element) and returns the list value composed
               of the results of each such evaluation.  In scalar context,
               returns the total number of elements so generated.  Evaluates
               BLOCK or EXPR in list context, so each element of LIST may
               produce zero, one, or more elements in the returned value.

                   @chars = map(chr, @nums);

               translates a list of numbers to the corresponding characters.
               And

                   %hash = map { getkey($_) => $_ } @array;

               is just a funny way to write

                   %hash = ();
                   foreach $_ (@array) {
                       $hash{getkey($_)} = $_;
                   }

               Note that $_ is an alias to the list value, so it can be used
               to modify the elements of the LIST.  While this is useful and
               supported, it can cause bizarre results if the elements of LIST
               are not variables.  Using a regular "foreach" loop for this
               purpose would be clearer in most cases.  See also "grep" for an
               array composed of those items of the original list for which
               the BLOCK or EXPR evaluates to true.

               "{" starts both hash references and blocks, so "map { ..."
               could be either the start of map BLOCK LIST or map EXPR, LIST.
               Because perl doesn't look ahead for the closing "}" it has to
               take a guess at which its dealing with based what it finds just
               after the "{". Usually it gets it right, but if it doesn't it
               won't realize something is wrong until it gets to the "}" and
               encounters the missing (or unexpected) comma. The syntax error
               will be reported close to the "}" but you'll need to change
               something near the "{" such as using a unary "+" to give perl
               some help:

                   %hash = map {  "\L$_", 1  } @array  # perl guesses EXPR.  wrong
                   %hash = map { +"\L$_", 1  } @array  # perl guesses BLOCK. right
                   %hash = map { ("\L$_", 1) } @array  # this also works
                   %hash = map {  lc($_), 1  } @array  # as does this.
                   %hash = map +( lc($_), 1 ), @array  # this is EXPR and works!

                   %hash = map  ( lc($_), 1 ), @array  # evaluates to (1, @array)

               or to force an anon hash constructor use "+{"

                  @hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end

               and you get list of anonymous hashes each with only 1 entry.

       mkdir FILENAME,MASK
       mkdir FILENAME
               Creates the directory specified by FILENAME, with permissions
               specified by MASK (as modified by "umask").  If it succeeds it
               returns true, otherwise it returns false and sets $! (errno).
               If omitted, MASK defaults to 0777.

               In general, it is better to create directories with permissive
               MASK, and let the user modify that with their "umask", than it
               is to supply a restrictive MASK and give the user no way to be
               more permissive.  The exceptions to this rule are when the file
               or directory should be kept private (mail files, for instance).
               The perlfunc(1) entry on "umask" discusses the choice of MASK
               in more detail.

               Note that according to the POSIX 1003.1-1996 the FILENAME may
               have any number of trailing slashes.  Some operating and
               filesystems do not get this right, so Perl automatically
               removes all trailing slashes to keep everyone happy.

       msgctl ID,CMD,ARG
               Calls the System V IPC function msgctl(2).  You'll probably
               have to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If CMD is
               "IPC_STAT", then ARG must be a variable which will hold the
               returned "msqid_ds" structure.  Returns like "ioctl": the
               undefined value for error, "0 but true" for zero, or the actual
               return value otherwise.  See also "SysV IPC" in perlipc,
               "IPC::SysV", and "IPC::Semaphore" documentation.

       msgget KEY,FLAGS
               Calls the System V IPC function msgget(2).  Returns the message
               queue id, or the undefined value if there is an error.  See
               also "SysV IPC" in perlipc and "IPC::SysV" and "IPC::Msg"
               documentation.

       msgrcv ID,VAR,SIZE,TYPE,FLAGS
               Calls the System V IPC function msgrcv to receive a message
               from message queue ID into variable VAR with a maximum message
               size of SIZE.  Note that when a message is received, the
               message type as a native long integer will be the first thing
               in VAR, followed by the actual message.  This packing may be
               opened with "unpack("l! a*")".  Taints the variable.  Returns
               true if successful, or false if there is an error.  See also
               "SysV IPC" in perlipc, "IPC::SysV", and "IPC::SysV::Msg"
               documentation.

       msgsnd ID,MSG,FLAGS
               Calls the System V IPC function msgsnd to send the message MSG
               to the message queue ID.  MSG must begin with the native long
               integer message type, and be followed by the length of the
               actual message, and finally the message itself.  This kind of
               packing can be achieved with "pack("l! a*", $type, $message)".
               Returns true if successful, or false if there is an error.  See
               also "IPC::SysV" and "IPC::SysV::Msg" documentation.

       my EXPR
       my TYPE EXPR
       my EXPR : ATTRS
       my TYPE EXPR : ATTRS
               A "my" declares the listed variables to be local (lexically) to
               the enclosing block, file, or "eval".  If more than one value
               is listed, the list must be placed in parentheses.

               The exact semantics and interface of TYPE and ATTRS are still
               evolving.  TYPE is currently bound to the use of "fields"
               pragma, and attributes are handled using the "attributes"
               pragma, or starting from Perl 5.8.0 also via the
               "Attribute::Handlers" module.  See "Private Variables via my()"
               in perlsub for details, and fields, attributes, and
               Attribute::Handlers.

       next LABEL
       next    The "next" command is like the "continue" statement in C; it
               starts the next iteration of the loop:

                   LINE: while (<STDIN>) {
                       next LINE if /^#/;      # discard comments
                       #...
                   }

               Note that if there were a "continue" block on the above, it
               would get executed even on discarded lines.  If the LABEL is
               omitted, the command refers to the innermost enclosing loop.

               "next" cannot be used to exit a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "next" will exit such a block early.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       no Module VERSION LIST
       no Module VERSION
       no Module LIST
       no Module
               See the "use" function, which "no" is the opposite of.

       oct EXPR
       oct     Interprets EXPR as an octal string and returns the
               corresponding value.  (If EXPR happens to start off with "0x",
               interprets it as a hex string.  If EXPR starts off with "0b",
               it is interpreted as a binary string.  Leading whitespace is
               ignored in all three cases.)  The following will handle
               decimal, binary, octal, and hex in the standard Perl or C
               notation:

                   $val = oct($val) if $val =~ /^0/;

               If EXPR is omitted, uses $_.   To go the other way (produce a
               number in octal), use sprintf() or printf():

                   $perms = (stat("filename"))[2] & 07777;
                   $oct_perms = sprintf "%lo", $perms;

               The oct() function is commonly used when a string such as 644
               needs to be converted into a file mode, for example. (Although
               perl will automatically convert strings into numbers as needed,
               this automatic conversion assumes base 10.)

       open FILEHANDLE,EXPR
       open FILEHANDLE,MODE,EXPR
       open FILEHANDLE,MODE,EXPR,LIST
       open FILEHANDLE,MODE,REFERENCE
       open FILEHANDLE
               Opens the file whose filename is given by EXPR, and associates
               it with FILEHANDLE.

               (The following is a comprehensive reference to open(): for a
               gentler introduction you may consider perlopentut.)

               If FILEHANDLE is an undefined scalar variable (or array or hash
               element) the variable is assigned a reference to a new
               anonymous filehandle, otherwise if FILEHANDLE is an expression,
               its value is used as the name of the real filehandle wanted.
               (This is considered a symbolic reference, so "use strict
               'refs'" should not be in effect.)

               If EXPR is omitted, the scalar variable of the same name as the
               FILEHANDLE contains the filename.  (Note that lexical
               variables--those declared with "my"--will not work for this
               purpose; so if you're using "my", specify EXPR in your call to
               open.)

               If three or more arguments are specified then the mode of
               opening and the file name are separate. If MODE is '<' or
               nothing, the file is opened for input.  If MODE is '>', the
               file is truncated and opened for output, being created if
               necessary.  If MODE is '>>', the file is opened for appending,
               again being created if necessary.

               You can put a '+' in front of the '>' or '<' to indicate that
               you want both read and write access to the file; thus '+<' is
               almost always preferred for read/write updates--the '+>' mode
               would clobber the file first.  You can't usually use either
               read-write mode for updating textfiles, since they have
               variable length records.  See the -i switch in perlrun for a
               better approach.  The file is created with permissions of 0666
               modified by the process' "umask" value.

               These various prefixes correspond to the fopen(3) modes of 'r',
               'r+', 'w', 'w+', 'a', and 'a+'.

               In the 2-arguments (and 1-argument) form of the call the mode
               and filename should be concatenated (in this order), possibly
               separated by spaces.  It is possible to omit the mode in these
               forms if the mode is '<'.

               If the filename begins with '|', the filename is interpreted as
               a command to which output is to be piped, and if the filename
               ends with a '|', the filename is interpreted as a command which
               pipes output to us.  See "Using open() for IPC" in perlipc for
               more examples of this.  (You are not allowed to "open" to a
               command that pipes both in and out, but see IPC::Open2,
               IPC::Open3, and "Bidirectional Communication with Another
               Process" in perlipc for alternatives.)

               For three or more arguments if MODE is '|-', the filename is
               interpreted as a command to which output is to be piped, and if
               MODE is '-|', the filename is interpreted as a command which
               pipes output to us.  In the 2-arguments (and 1-argument) form
               one should replace dash ('-') with the command.  See "Using
               open() for IPC" in perlipc for more examples of this.  (You are
               not allowed to "open" to a command that pipes both in and out,
               but see IPC::Open2, IPC::Open3, and "Bidirectional
               Communication" in perlipc for alternatives.)

               In the three-or-more argument form of pipe opens, if LIST is
               specified (extra arguments after the command name) then LIST
               becomes arguments to the command invoked if the platform
               supports it.  The meaning of "open" with more than three
               arguments for non-pipe modes is not yet specified. Experimental
               "layers" may give extra LIST arguments meaning.

               In the 2-arguments (and 1-argument) form opening '-' opens
               STDIN and opening '>-' opens STDOUT.

               You may use the three-argument form of open to specify IO
               "layers" (sometimes also referred to as "disciplines") to be
               applied to the handle that affect how the input and output are
               processed (see open and PerlIO for more details). For example

                 open(FH, "<:utf8", "file")

               will open the UTF-8 encoded file containing Unicode characters,
               see perluniintro. (Note that if layers are specified in the
               three-arg form then default layers set by the "open" pragma are
               ignored.)

               Open returns nonzero upon success, the undefined value
               otherwise.  If the "open" involved a pipe, the return value
               happens to be the pid of the subprocess.

               If you're running Perl on a system that distinguishes between
               text files and binary files, then you should check out
               "binmode" for tips for dealing with this.  The key distinction
               between systems that need "binmode" and those that don't is
               their text file formats.  Systems like Unix, Mac OS, and Plan
               9, which delimit lines with a single character, and which
               encode that character in C as "\n", do not need "binmode".  The
               rest need it.

               When opening a file, it's usually a bad idea to continue normal
               execution if the request failed, so "open" is frequently used
               in connection with "die".  Even if "die" won't do what you want
               (say, in a CGI script, where you want to make a nicely
               formatted error message (but there are modules that can help
               with that problem)) you should always check the return value
               from opening a file.  The infrequent exception is when working
               with an unopened filehandle is actually what you want to do.

               As a special case the 3 arg form with a read/write mode and the
               third argument being "undef":

                   open(TMP, "+>", undef) or die ...

               opens a filehandle to an anonymous temporary file.  Also using
               "+<" works for symmetry, but you really should consider writing
               something to the temporary file first.  You will need to seek()
               to do the reading.

               File handles can be opened to "in memory" files held in Perl
               scalars via:

                   open($fh, '>', \$variable) || ..

               Though if you try to re-open "STDOUT" or "STDERR" as an "in
               memory" file, you have to close it first:

                   close STDOUT;
                   open STDOUT, '>', \$variable or die "Can't open STDOUT: $!";

               Examples:

                   $ARTICLE = 100;
                   open ARTICLE or die "Can't find article $ARTICLE: $!\n";
                   while (<ARTICLE>) {...

                   open(LOG, '>>/usr/spool/news/twitlog');     # (log is reserved)
                   # if the open fails, output is discarded

                   open(DBASE, '+<', 'dbase.mine')             # open for update
                       or die "Can't open 'dbase.mine' for update: $!";

                   open(DBASE, '+<dbase.mine')                 # ditto
                       or die "Can't open 'dbase.mine' for update: $!";

                   open(ARTICLE, '-|', "caesar <$article")     # decrypt article
                       or die "Can't start caesar: $!";

                   open(ARTICLE, "caesar <$article |")         # ditto
                       or die "Can't start caesar: $!";

                   open(EXTRACT, "|sort >/tmp/Tmp$$")          # $$ is our process id
                       or die "Can't start sort: $!";

                   # in memory files
                   open(MEMORY,'>', \$var)
                       or die "Can't open memory file: $!";
                   print MEMORY "foo!\n";                      # output will end up in $var

                   # process argument list of files along with any includes

                   foreach $file (@ARGV) {
                       process($file, 'fh00');
                   }

                   sub process {
                       my($filename, $input) = @_;
                       $input++;               # this is a string increment
                       unless (open($input, $filename)) {
                           print STDERR "Can't open $filename: $!\n";
                           return;
                       }

                       local $_;
                       while (<$input>) {              # note use of indirection
                           if (/^#include "(.*)"/) {
                               process($1, $input);
                               next;
                           }
                           #...                # whatever
                       }
                   }

               You may also, in the Bourne shell tradition, specify an EXPR
               beginning with '>&', in which case the rest of the string is
               interpreted as the name of a filehandle (or file descriptor, if
               numeric) to be duped (as dup(2)) and opened.  You may use "&"
               after ">", ">>", "<", "+>", "+>>", and "+<".  The mode you
               specify should match the mode of the original filehandle.
               (Duping a filehandle does not take into account any existing
               contents of IO buffers.) If you use the 3 arg form then you can
               pass either a number, the name of a filehandle or the normal
               "reference to a glob".

               Here is a script that saves, redirects, and restores "STDOUT"
               and "STDERR" using various methods:

                   #!/usr/bin/perl
                   open my $oldout, ">&STDOUT"     or die "Can't dup STDOUT: $!";
                   open OLDERR,     ">&", \*STDERR or die "Can't dup STDERR: $!";

                   open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!";
                   open STDERR, ">&STDOUT"     or die "Can't dup STDOUT: $!";

                   select STDERR; $| = 1;      # make unbuffered
                   select STDOUT; $| = 1;      # make unbuffered

                   print STDOUT "stdout 1\n";  # this works for
                   print STDERR "stderr 1\n";  # subprocesses too

                   close STDOUT;
                   close STDERR;

                   open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!";
                   open STDERR, ">&OLDERR"    or die "Can't dup OLDERR: $!";

                   print STDOUT "stdout 2\n";
                   print STDERR "stderr 2\n";

               If you specify '<&=X', where "X" is a file descriptor number or
               a filehandle, then Perl will do an equivalent of C's "fdopen"
               of that file descriptor (and not call dup(2)); this is more
               parsimonious of file descriptors.  For example:

                   # open for input, reusing the fileno of $fd
                   open(FILEHANDLE, "<&=$fd")

               or

                   open(FILEHANDLE, "<&=", $fd)

               or

                   # open for append, using the fileno of OLDFH
                   open(FH, ">>&=", OLDFH)

               or

                   open(FH, ">>&=OLDFH")

               Being parsimonious on filehandles is also useful (besides being
               parsimonious) for example when something is dependent on file
               descriptors, like for example locking using flock().  If you do
               just "open(A, '>>&B')", the filehandle A will not have the same
               file descriptor as B, and therefore flock(A) will not flock(B),
               and vice versa.  But with "open(A, '>>&=B')" the filehandles
               will share the same file descriptor.

               Note that if you are using Perls older than 5.8.0, Perl will be
               using the standard C libraries' fdopen() to implement the "="
               functionality.  On many UNIX systems fdopen() fails when file
               descriptors exceed a certain value, typically 255.  For Perls
               5.8.0 and later, PerlIO is most often the default.

               You can see whether Perl has been compiled with PerlIO or not
               by running "perl -V" and looking for "useperlio=" line.  If
               "useperlio" is "define", you have PerlIO, otherwise you don't.

               If you open a pipe on the command '-', i.e., either '|-' or
               '-|' with 2-arguments (or 1-argument) form of open(), then
               there is an implicit fork done, and the return value of open is
               the pid of the child within the parent process, and 0 within
               the child process.  (Use "defined($pid)" to determine whether
               the open was successful.)  The filehandle behaves normally for
               the parent, but i/o to that filehandle is piped from/to the
               STDOUT/STDIN of the child process.  In the child process the
               filehandle isn't opened--i/o happens from/to the new STDOUT or
               STDIN.  Typically this is used like the normal piped open when
               you want to exercise more control over just how the pipe
               command gets executed, such as when you are running setuid, and
               don't want to have to scan shell commands for metacharacters.
               The following triples are more or less equivalent:

                   open(FOO, "|tr '[a-z]' '[A-Z]'");
                   open(FOO, '|-', "tr '[a-z]' '[A-Z]'");
                   open(FOO, '|-') || exec 'tr', '[a-z]', '[A-Z]';
                   open(FOO, '|-', "tr", '[a-z]', '[A-Z]');

                   open(FOO, "cat -n '$file'|");
                   open(FOO, '-|', "cat -n '$file'");
                   open(FOO, '-|') || exec 'cat', '-n', $file;
                   open(FOO, '-|', "cat", '-n', $file);

               The last example in each block shows the pipe as "list form",
               which is not yet supported on all platforms.  A good rule of
               thumb is that if your platform has true "fork()" (in other
               words, if your platform is UNIX) you can use the list form.

               See "Safe Pipe Opens" in perlipc for more examples of this.

               Beginning with v5.6.0, Perl will attempt to flush all files
               opened for output before any operation that may do a fork, but
               this may not be supported on some platforms (see perlport).  To
               be safe, you may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any open handles.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptor as determined
               by the value of $^F.  See "$^F" in perlvar.

               Closing any piped filehandle causes the parent process to wait
               for the child to finish, and returns the status value in $?.

               The filename passed to 2-argument (or 1-argument) form of
               open() will have leading and trailing whitespace deleted, and
               the normal redirection characters honored.  This property,
               known as "magic open", can often be used to good effect.  A
               user could specify a filename of "rsh cat file |", or you could
               change certain filenames as needed:

                   $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/;
                   open(FH, $filename) or die "Can't open $filename: $!";

               Use 3-argument form to open a file with arbitrary weird
               characters in it,

                   open(FOO, '<', $file);

               otherwise it's necessary to protect any leading and trailing
               whitespace:

                   $file =~ s#^(\s)#./$1#;
                   open(FOO, "< $file\0");

               (this may not work on some bizarre filesystems).  One should
               conscientiously choose between the magic and 3-arguments form
               of open():

                   open IN, $ARGV[0];

               will allow the user to specify an argument of the form "rsh cat
               file |", but will not work on a filename which happens to have
               a trailing space, while

                   open IN, '<', $ARGV[0];

               will have exactly the opposite restrictions.

               If you want a "real" C "open" (see open(2) on your system),
               then you should use the "sysopen" function, which involves no
               such magic (but may use subtly different filemodes than Perl
               open(), which is mapped to C fopen()).  This is another way to
               protect your filenames from interpretation.  For example:

                   use IO::Handle;
                   sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL)
                       or die "sysopen $path: $!";
                   $oldfh = select(HANDLE); $| = 1; select($oldfh);
                   print HANDLE "stuff $$\n";
                   seek(HANDLE, 0, 0);
                   print "File contains: ", <HANDLE>;

               Using the constructor from the "IO::Handle" package (or one of
               its subclasses, such as "IO::File" or "IO::Socket"), you can
               generate anonymous filehandles that have the scope of whatever
               variables hold references to them, and automatically close
               whenever and however you leave that scope:

                   use IO::File;
                   #...
                   sub read_myfile_munged {
                       my $ALL = shift;
                       my $handle = new IO::File;
                       open($handle, "myfile") or die "myfile: $!";
                       $first = <$handle>
                           or return ();     # Automatically closed here.
                       mung $first or die "mung failed";       # Or here.
                       return $first, <$handle> if $ALL;       # Or here.
                       $first;                                 # Or here.
                   }

               See "seek" for some details about mixing reading and writing.

       opendir DIRHANDLE,EXPR
               Opens a directory named EXPR for processing by "readdir",
               "telldir", "seekdir", "rewinddir", and "closedir".  Returns
               true if successful.  DIRHANDLE may be an expression whose value
               can be used as an indirect dirhandle, usually the real
               dirhandle name.  If DIRHANDLE is an undefined scalar variable
               (or array or hash element), the variable is assigned a
               reference to a new anonymous dirhandle.  DIRHANDLEs have their
               own namespace separate from FILEHANDLEs.

       ord EXPR
       ord     Returns the numeric (the native 8-bit encoding, like ASCII or
               EBCDIC, or Unicode) value of the first character of EXPR.  If
               EXPR is omitted, uses $_.

               For the reverse, see "chr".  See perlunicode and encoding for
               more about Unicode.

       our EXPR
       our EXPR TYPE
       our EXPR : ATTRS
       our TYPE EXPR : ATTRS
               An "our" declares the listed variables to be valid globals
               within the enclosing block, file, or "eval".  That is, it has
               the same scoping rules as a "my" declaration, but does not
               create a local variable.  If more than one value is listed, the
               list must be placed in parentheses.  The "our" declaration has
               no semantic effect unless "use strict vars" is in effect, in
               which case it lets you use the declared global variable without
               qualifying it with a package name.  (But only within the
               lexical scope of the "our" declaration.  In this it differs
               from "use vars", which is package scoped.)

               An "our" declaration declares a global variable that will be
               visible across its entire lexical scope, even across package
               boundaries.  The package in which the variable is entered is
               determined at the point of the declaration, not at the point of
               use.  This means the following behavior holds:

                   package Foo;
                   our $bar;           # declares $Foo::bar for rest of lexical scope
                   $bar = 20;

                   package Bar;
                   print $bar;         # prints 20

               Multiple "our" declarations in the same lexical scope are
               allowed if they are in different packages.  If they happened to
               be in the same package, Perl will emit warnings if you have
               asked for them.

                   use warnings;
                   package Foo;
                   our $bar;           # declares $Foo::bar for rest of lexical scope
                   $bar = 20;

                   package Bar;
                   our $bar = 30;      # declares $Bar::bar for rest of lexical scope
                   print $bar;         # prints 30

                   our $bar;           # emits warning

               An "our" declaration may also have a list of attributes
               associated with it.

               The exact semantics and interface of TYPE and ATTRS are still
               evolving.  TYPE is currently bound to the use of "fields"
               pragma, and attributes are handled using the "attributes"
               pragma, or starting from Perl 5.8.0 also via the
               "Attribute::Handlers" module.  See "Private Variables via my()"
               in perlsub for details, and fields, attributes, and
               Attribute::Handlers.

               The only currently recognized "our()" attribute is "unique"
               which indicates that a single copy of the global is to be used
               by all interpreters should the program happen to be running in
               a multi-interpreter environment. (The default behaviour would
               be for each interpreter to have its own copy of the global.)
               Examples:

                   our @EXPORT : unique = qw(foo);
                   our %EXPORT_TAGS : unique = (bar => [qw(aa bb cc)]);
                   our $VERSION : unique = "1.00";

               Note that this attribute also has the effect of making the
               global readonly when the first new interpreter is cloned (for
               example, when the first new thread is created).

               Multi-interpreter environments can come to being either through
               the fork() emulation on Windows platforms, or by embedding perl
               in a multi-threaded application.  The "unique" attribute does
               nothing in all other environments.

       pack TEMPLATE,LIST
               Takes a LIST of values and converts it into a string using the
               rules given by the TEMPLATE.  The resulting string is the
               concatenation of the converted values.  Typically, each
               converted value looks like its machine-level representation.
               For example, on 32-bit machines a converted integer may be
               represented by a sequence of 4 bytes.

               The TEMPLATE is a sequence of characters that give the order
               and type of values, as follows:

                   a   A string with arbitrary binary data, will be null padded.
                   A   A text (ASCII) string, will be space padded.
                   Z   A null terminated (ASCIZ) string, will be null padded.

                   b   A bit string (ascending bit order inside each byte, like vec()).
                   B   A bit string (descending bit order inside each byte).
                   h   A hex string (low nybble first).
                   H   A hex string (high nybble first).

                   c   A signed char value.
                   C   An unsigned char value.  Only does bytes.  See U for Unicode.

                   s   A signed short value.
                   S   An unsigned short value.
                         (This 'short' is _exactly_ 16 bits, which may differ from
                          what a local C compiler calls 'short'.  If you want
                          native-length shorts, use the '!' suffix.)

                   i   A signed integer value.
                   I   An unsigned integer value.
                         (This 'integer' is _at_least_ 32 bits wide.  Its exact
                          size depends on what a local C compiler calls 'int',
                          and may even be larger than the 'long' described in
                          the next item.)

                   l   A signed long value.
                   L   An unsigned long value.
                         (This 'long' is _exactly_ 32 bits, which may differ from
                          what a local C compiler calls 'long'.  If you want
                          native-length longs, use the '!' suffix.)

                   n   An unsigned short in "network" (big-endian) order.
                   N   An unsigned long in "network" (big-endian) order.
                   v   An unsigned short in "VAX" (little-endian) order.
                   V   An unsigned long in "VAX" (little-endian) order.
                         (These 'shorts' and 'longs' are _exactly_ 16 bits and
                          _exactly_ 32 bits, respectively.)

                   q   A signed quad (64-bit) value.
                   Q   An unsigned quad value.
                         (Quads are available only if your system supports 64-bit
                          integer values _and_ if Perl has been compiled to support those.
                          Causes a fatal error otherwise.)

                   j   A signed integer value (a Perl internal integer, IV).
                   J   An unsigned integer value (a Perl internal unsigned integer, UV).

                   f   A single-precision float in the native format.
                   d   A double-precision float in the native format.

                   F   A floating point value in the native native format
                          (a Perl internal floating point value, NV).
                   D   A long double-precision float in the native format.
                         (Long doubles are available only if your system supports long
                          double values _and_ if Perl has been compiled to support those.
                          Causes a fatal error otherwise.)

                   p   A pointer to a null-terminated string.
                   P   A pointer to a structure (fixed-length string).

                   u   A uuencoded string.
                   U   A Unicode character number.  Encodes to UTF-8 internally
                       (or UTF-EBCDIC in EBCDIC platforms).

                   w   A BER compressed integer.  Its bytes represent an unsigned
                       integer in base 128, most significant digit first, with as
                       few digits as possible.  Bit eight (the high bit) is set
                       on each byte except the last.

                   x   A null byte.
                   X   Back up a byte.
                   @   Null fill to absolute position, counted from the start of
                       the innermost ()-group.
                   (   Start of a ()-group.

               The following rules apply:

               *       Each letter may optionally be followed by a number
                       giving a repeat count.  With all types except "a", "A",
                       "Z", "b", "B", "h", "H", "@", "x", "X" and "P" the pack
                       function will gobble up that many values from the LIST.
                       A "*" for the repeat count means to use however many
                       items are left, except for "@", "x", "X", where it is
                       equivalent to 0, and "u", where it is equivalent to 1
                       (or 45, what is the same).  A numeric repeat count may
                       optionally be enclosed in brackets, as in "pack
                       'C[80]', @arr".

                       One can replace the numeric repeat count by a template
                       enclosed in brackets; then the packed length of this
                       template in bytes is used as a count.  For example,
                       "x[L]" skips a long (it skips the number of bytes in a
                       long); the template "$t X[$t] $t" unpack()s twice what
                       $t unpacks.  If the template in brackets contains
                       alignment commands (such as "x![d]"), its packed length
                       is calculated as if the start of the template has the
                       maximal possible alignment.

                       When used with "Z", "*" results in the addition of a
                       trailing null byte (so the packed result will be one
                       longer than the byte "length" of the item).

                       The repeat count for "u" is interpreted as the maximal
                       number of bytes to encode per line of output, with 0
                       and 1 replaced by 45.

               *       The "a", "A", and "Z" types gobble just one value, but
                       pack it as a string of length count, padding with nulls
                       or spaces as necessary.  When unpacking, "A" strips
                       trailing spaces and nulls, "Z" strips everything after
                       the first null, and "a" returns data verbatim.  When
                       packing, "a", and "Z" are equivalent.

                       If the value-to-pack is too long, it is truncated.  If
                       too long and an explicit count is provided, "Z" packs
                       only "$count-1" bytes, followed by a null byte.  Thus
                       "Z" always packs a trailing null byte under all
                       circumstances.

               *       Likewise, the "b" and "B" fields pack a string that
                       many bits long.  Each byte of the input field of pack()
                       generates 1 bit of the result.  Each result bit is
                       based on the least-significant bit of the corresponding
                       input byte, i.e., on "ord($byte)%2".  In particular,
                       bytes "0" and "1" generate bits 0 and 1, as do bytes
                       "\0" and "\1".

                       Starting from the beginning of the input string of
                       pack(), each 8-tuple of bytes is converted to 1 byte of
                       output.  With format "b" the first byte of the 8-tuple
                       determines the least-significant bit of a byte, and
                       with format "B" it determines the most-significant bit
                       of a byte.

                       If the length of the input string is not exactly
                       divisible by 8, the remainder is packed as if the input
                       string were padded by null bytes at the end.
                       Similarly, during unpack()ing the "extra" bits are
                       ignored.

                       If the input string of pack() is longer than needed,
                       extra bytes are ignored.  A "*" for the repeat count of
                       pack() means to use all the bytes of the input field.
                       On unpack()ing the bits are converted to a string of
                       "0"s and "1"s.

               *       The "h" and "H" fields pack a string that many nybbles
                       (4-bit groups, representable as hexadecimal digits,
                       0-9a-f) long.

                       Each byte of the input field of pack() generates 4 bits
                       of the result.  For non-alphabetical bytes the result
                       is based on the 4 least-significant bits of the input
                       byte, i.e., on "ord($byte)%16".  In particular, bytes
                       "0" and "1" generate nybbles 0 and 1, as do bytes "\0"
                       and "\1".  For bytes "a".."f" and "A".."F" the result
                       is compatible with the usual hexadecimal digits, so
                       that "a" and "A" both generate the nybble "0xa==10".
                       The result for bytes "g".."z" and "G".."Z" is not
                       well-defined.

                       Starting from the beginning of the input string of
                       pack(), each pair of bytes is converted to 1 byte of
                       output.  With format "h" the first byte of the pair
                       determines the least-significant nybble of the output
                       byte, and with format "H" it determines the most-
                       significant nybble.

                       If the length of the input string is not even, it
                       behaves as if padded by a null byte at the end.
                       Similarly, during unpack()ing the "extra" nybbles are
                       ignored.

                       If the input string of pack() is longer than needed,
                       extra bytes are ignored.  A "*" for the repeat count of
                       pack() means to use all the bytes of the input field.
                       On unpack()ing the bits are converted to a string of
                       hexadecimal digits.

               *       The "p" type packs a pointer to a null-terminated
                       string.  You are responsible for ensuring the string is
                       not a temporary value (which can potentially get
                       deallocated before you get around to using the packed
                       result).  The "P" type packs a pointer to a structure
                       of the size indicated by the length.  A NULL pointer is
                       created if the corresponding value for "p" or "P" is
                       "undef", similarly for unpack().

               *       The "/" template character allows packing and unpacking
                       of strings where the packed structure contains a byte
                       count followed by the string itself.  You write length-
                       item"/"string-item.

                       The length-item can be any "pack" template letter, and
                       describes how the length value is packed.  The ones
                       likely to be of most use are integer-packing ones like
                       "n" (for Java strings), "w" (for ASN.1 or SNMP) and "N"
                       (for Sun XDR).

                       For "pack", the string-item must, at present, be "A*",
                       "a*" or "Z*". For "unpack" the length of the string is
                       obtained from the length-item, but if you put in the
                       '*' it will be ignored. For all other codes, "unpack"
                       applies the length value to the next item, which must
                       not have a repeat count.

                           unpack 'C/a', "\04Gurusamy";        gives 'Guru'
                           unpack 'a3/A* A*', '007 Bond  J ';  gives (' Bond','J')
                           pack 'n/a* w/a*','hello,','world';  gives "\000\006hello,\005world"

                       The length-item is not returned explicitly from
                       "unpack".

                       Adding a count to the length-item letter is unlikely to
                       do anything useful, unless that letter is "A", "a" or
                       "Z".  Packing with a length-item of "a" or "Z" may
                       introduce "\000" characters, which Perl does not regard
                       as legal in numeric strings.

               *       The integer types "s", "S", "l", and "L" may be
                       immediately followed by a "!" suffix to signify native
                       shorts or longs--as you can see from above for example
                       a bare "l" does mean exactly 32 bits, the native "long"
                       (as seen by the local C compiler) may be larger.  This
                       is an issue mainly in 64-bit platforms.  You can see
                       whether using "!" makes any difference by

                               print length(pack("s")), " ", length(pack("s!")), "\n";
                               print length(pack("l")), " ", length(pack("l!")), "\n";

                       "i!" and "I!" also work but only because of
                       completeness; they are identical to "i" and "I".

                       The actual sizes (in bytes) of native shorts, ints,
                       longs, and long longs on the platform where Perl was
                       built are also available via Config:

                              use Config;
                              print $Config{shortsize},    "\n";
                              print $Config{intsize},      "\n";
                              print $Config{longsize},     "\n";
                              print $Config{longlongsize}, "\n";

                       (The $Config{longlongsize} will be undefined if your
                       system does not support long longs.)

               *       The integer formats "s", "S", "i", "I", "l", "L", "j",
                       and "J" are inherently non-portable between processors
                       and operating systems because they obey the native
                       byteorder and endianness.  For example a 4-byte integer
                       0x12345678 (305419896 decimal) would be ordered
                       natively (arranged in and handled by the CPU registers)
                       into bytes as

                               0x12 0x34 0x56 0x78     # big-endian
                               0x78 0x56 0x34 0x12     # little-endian

                       Basically, the Intel and VAX CPUs are little-endian,
                       while everybody else, for example Motorola m68k/88k,
                       PPC, Sparc, HP PA, Power, and Cray are big-endian.
                       Alpha and MIPS can be either: Digital/Compaq used/uses
                       them in little-endian mode; SGI/Cray uses them in big-
                       endian mode.

                       The names `big-endian' and `little-endian' are comic
                       references to the classic "Gulliver's Travels" (via the
                       paper "On Holy Wars and a Plea for Peace" by Danny
                       Cohen, USC/ISI IEN 137, April 1, 1980) and the egg-
                       eating habits of the Lilliputians.

                       Some systems may have even weirder byte orders such as

                               0x56 0x78 0x12 0x34
                               0x34 0x12 0x78 0x56

                       You can see your system's preference with

                               print join(" ", map { sprintf "%#02x", $_ }
                                                   unpack("C*",pack("L",0x12345678))), "\n";

                       The byteorder on the platform where Perl was built is
                       also available via Config:

                               use Config;
                               print $Config{byteorder}, "\n";

                       Byteorders '1234' and '12345678' are little-endian,
                       '4321' and '87654321' are big-endian.

                       If you want portable packed integers use the formats
                       "n", "N", "v", and "V", their byte endianness and size
                       are known.  See also perlport.

               *       Real numbers (floats and doubles) are in the native
                       machine format only; due to the multiplicity of
                       floating formats around, and the lack of a standard
                       "network" representation, no facility for interchange
                       has been made.  This means that packed floating point
                       data written on one machine may not be readable on
                       another - even if both use IEEE floating point
                       arithmetic (as the endian-ness of the memory
                       representation is not part of the IEEE spec).  See also
                       perlport.

                       Note that Perl uses doubles internally for all numeric
                       calculation, and converting from double into float and
                       thence back to double again will lose precision (i.e.,
                       "unpack("f", pack("f", $foo)") will not in general
                       equal $foo).

               *       If the pattern begins with a "U", the resulting string
                       will be treated as UTF-8-encoded Unicode. You can force
                       UTF-8 encoding on in a string with an initial "U0", and
                       the bytes that follow will be interpreted as Unicode
                       characters. If you don't want this to happen, you can
                       begin your pattern with "C0" (or anything else) to
                       force Perl not to UTF-8 encode your string, and then
                       follow this with a "U*" somewhere in your pattern.

               *       You must yourself do any alignment or padding by
                       inserting for example enough 'x'es while packing.
                       There is no way to pack() and unpack() could know where
                       the bytes are going to or coming from.  Therefore
                       "pack" (and "unpack") handle their output and input as
                       flat sequences of bytes.

               *       A ()-group is a sub-TEMPLATE enclosed in parentheses.
                       A group may take a repeat count, both as postfix, and
                       for unpack() also via the "/" template character.
                       Within each repetition of a group, positioning with "@"
                       starts again at 0. Therefore, the result of

                           pack( '@1A((@2A)@3A)', 'a', 'b', 'c' )

                       is the string "\0a\0\0bc".

               *       "x" and "X" accept "!" modifier.  In this case they act
                       as alignment commands: they jump forward/back to the
                       closest position aligned at a multiple of "count"
                       bytes.  For example, to pack() or unpack() C's "struct
                       {char c; double d; char cc[2]}" one may need to use the
                       template "C x![d] d C[2]"; this assumes that doubles
                       must be aligned on the double's size.

                       For alignment commands "count" of 0 is equivalent to
                       "count" of 1; both result in no-ops.

               *       A comment in a TEMPLATE starts with "#" and goes to the
                       end of line.  White space may be used to separate pack
                       codes from each other, but a "!" modifier and a repeat
                       count must follow immediately.

               *       If TEMPLATE requires more arguments to pack() than
                       actually given, pack() assumes additional "" arguments.
                       If TEMPLATE requires less arguments to pack() than
                       actually given, extra arguments are ignored.

               Examples:

                   $foo = pack("CCCC",65,66,67,68);
                   # foo eq "ABCD"
                   $foo = pack("C4",65,66,67,68);
                   # same thing
                   $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
                   # same thing with Unicode circled letters

                   $foo = pack("ccxxcc",65,66,67,68);
                   # foo eq "AB\0\0CD"

                   # note: the above examples featuring "C" and "c" are true
                   # only on ASCII and ASCII-derived systems such as ISO Latin 1
                   # and UTF-8.  In EBCDIC the first example would be
                   # $foo = pack("CCCC",193,194,195,196);

                   $foo = pack("s2",1,2);
                   # "\1\0\2\0" on little-endian
                   # "\0\1\0\2" on big-endian

                   $foo = pack("a4","abcd","x","y","z");
                   # "abcd"

                   $foo = pack("aaaa","abcd","x","y","z");
                   # "axyz"

                   $foo = pack("a14","abcdefg");
                   # "abcdefg\0\0\0\0\0\0\0"

                   $foo = pack("i9pl", gmtime);
                   # a real struct tm (on my system anyway)

                   $utmp_template = "Z8 Z8 Z16 L";
                   $utmp = pack($utmp_template, @utmp1);
                   # a struct utmp (BSDish)

                   @utmp2 = unpack($utmp_template, $utmp);
                   # "@utmp1" eq "@utmp2"

                   sub bintodec {
                       unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
                   }

                   $foo = pack('sx2l', 12, 34);
                   # short 12, two zero bytes padding, long 34
                   $bar = pack('s@4l', 12, 34);
                   # short 12, zero fill to position 4, long 34
                   # $foo eq $bar

               The same template may generally also be used in unpack().

       package NAMESPACE
       package Declares the compilation unit as being in the given namespace.
               The scope of the package declaration is from the declaration
               itself through the end of the enclosing block, file, or eval
               (the same as the "my" operator).  All further unqualified
               dynamic identifiers will be in this namespace.  A package
               statement affects only dynamic variables--including those
               you've used "local" on--but not lexical variables, which are
               created with "my".  Typically it would be the first declaration
               in a file to be included by the "require" or "use" operator.
               You can switch into a package in more than one place; it merely
               influences which symbol table is used by the compiler for the
               rest of that block.  You can refer to variables and filehandles
               in other packages by prefixing the identifier with the package
               name and a double colon:  $Package::Variable.  If the package
               name is null, the "main" package as assumed.  That is, $::sail
               is equivalent to $main::sail (as well as to $main'sail, still
               seen in older code).

               If NAMESPACE is omitted, then there is no current package, and
               all identifiers must be fully qualified or lexicals.  However,
               you are strongly advised not to make use of this feature. Its
               use can cause unexpected behaviour, even crashing some versions
               of Perl. It is deprecated, and will be removed from a future
               release.

               See "Packages" in perlmod for more information about packages,
               modules, and classes.  See perlsub for other scoping issues.

       pipe READHANDLE,WRITEHANDLE
               Opens a pair of connected pipes like the corresponding system
               call.  Note that if you set up a loop of piped processes,
               deadlock can occur unless you are very careful.  In addition,
               note that Perl's pipes use IO buffering, so you may need to set
               $| to flush your WRITEHANDLE after each command, depending on
               the application.

               See IPC::Open2, IPC::Open3, and "Bidirectional Communication"
               in perlipc for examples of such things.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptors as determined
               by the value of $^F.  See "$^F" in perlvar.

       pop ARRAY
       pop     Pops and returns the last value of the array, shortening the
               array by one element.  Has an effect similar to

                   $ARRAY[$#ARRAY--]

               If there are no elements in the array, returns the undefined
               value (although this may happen at other times as well).  If
               ARRAY is omitted, pops the @ARGV array in the main program, and
               the @_ array in subroutines, just like "shift".

       pos SCALAR
       pos     Returns the offset of where the last "m//g" search left off for
               the variable in question ($_ is used when the variable is not
               specified).  May be modified to change that offset.  Such
               modification will also influence the "\G" zero-width assertion
               in regular expressions.  See perlre and perlop.

       print FILEHANDLE LIST
       print LIST
       print   Prints a string or a list of strings.  Returns true if
               successful.  FILEHANDLE may be a scalar variable name, in which
               case the variable contains the name of or a reference to the
               filehandle, thus introducing one level of indirection.  (NOTE:
               If FILEHANDLE is a variable and the next token is a term, it
               may be misinterpreted as an operator unless you interpose a "+"
               or put parentheses around the arguments.)  If FILEHANDLE is
               omitted, prints by default to standard output (or to the last
               selected output channel--see "select").  If LIST is also
               omitted, prints $_ to the currently selected output channel.
               To set the default output channel to something other than
               STDOUT use the select operation.  The current value of $, (if
               any) is printed between each LIST item.  The current value of
               "$\" (if any) is printed after the entire LIST has been
               printed.  Because print takes a LIST, anything in the LIST is
               evaluated in list context, and any subroutine that you call
               will have one or more of its expressions evaluated in list
               context.  Also be careful not to follow the print keyword with
               a left parenthesis unless you want the corresponding right
               parenthesis to terminate the arguments to the print--interpose
               a "+" or put parentheses around all the arguments.

               Note that if you're storing FILEHANDLES in an array or other
               expression, you will have to use a block returning its value
               instead:

                   print { $files[$i] } "stuff\n";
                   print { $OK ? STDOUT : STDERR } "stuff\n";

       printf FILEHANDLE FORMAT, LIST
       printf FORMAT, LIST
               Equivalent to "print FILEHANDLE sprintf(FORMAT, LIST)", except
               that "$\" (the output record separator) is not appended.  The
               first argument of the list will be interpreted as the "printf"
               format. See "sprintf" for an explanation of the format
               argument. If "use locale" is in effect, the character used for
               the decimal point in formatted real numbers is affected by the
               LC_NUMERIC locale.  See perllocale.

               Don't fall into the trap of using a "printf" when a simple
               "print" would do.  The "print" is more efficient and less error
               prone.

       prototype FUNCTION
               Returns the prototype of a function as a string (or "undef" if
               the function has no prototype).  FUNCTION is a reference to, or
               the name of, the function whose prototype you want to retrieve.

               If FUNCTION is a string starting with "CORE::", the rest is
               taken as a name for Perl builtin.  If the builtin is not
               overridable (such as "qw//") or its arguments cannot be
               expressed by a prototype (such as "system") returns "undef"
               because the builtin does not really behave like a Perl
               function.  Otherwise, the string describing the equivalent
               prototype is returned.

       push ARRAY,LIST
               Treats ARRAY as a stack, and pushes the values of LIST onto the
               end of ARRAY.  The length of ARRAY increases by the length of
               LIST.  Has the same effect as

                   for $value (LIST) {
                       $ARRAY[++$#ARRAY] = $value;
                   }

               but is more efficient.  Returns the new number of elements in
               the array.

       q/STRING/
       qq/STRING/
       qr/STRING/
       qx/STRING/
       qw/STRING/
               Generalized quotes.  See "Regexp Quote-Like Operators" in
               perlop.

       quotemeta EXPR
       quotemeta
               Returns the value of EXPR with all non-"word" characters
               backslashed.  (That is, all characters not matching
               "/[A-Za-z_0-9]/" will be preceded by a backslash in the
               returned string, regardless of any locale settings.)  This is
               the internal function implementing the "\Q" escape in double-
               quoted strings.

               If EXPR is omitted, uses $_.

       rand EXPR
       rand    Returns a random fractional number greater than or equal to 0
               and less than the value of EXPR.  (EXPR should be positive.)
               If EXPR is omitted, the value 1 is used.  Currently EXPR with
               the value 0 is also special-cased as 1 - this has not been
               documented before perl 5.8.0 and is subject to change in future
               versions of perl.  Automatically calls "srand" unless "srand"
               has already been called.  See also "srand".

               Apply "int()" to the value returned by "rand()" if you want
               random integers instead of random fractional numbers.  For
               example,

                   int(rand(10))

               returns a random integer between 0 and 9, inclusive.

               (Note: If your rand function consistently returns numbers that
               are too large or too small, then your version of Perl was
               probably compiled with the wrong number of RANDBITS.)

       read FILEHANDLE,SCALAR,LENGTH,OFFSET
       read FILEHANDLE,SCALAR,LENGTH
               Attempts to read LENGTH characters of data into variable SCALAR
               from the specified FILEHANDLE.  Returns the number of
               characters actually read, 0 at end of file, or undef if there
               was an error (in the latter case $! is also set).  SCALAR will
               be grown or shrunk so that the last character actually read is
               the last character of the scalar after the read.

               An OFFSET may be specified to place the read data at some place
               in the string other than the beginning.  A negative OFFSET
               specifies placement at that many characters counting backwards
               from the end of the string.  A positive OFFSET greater than the
               length of SCALAR results in the string being padded to the
               required size with "\0" bytes before the result of the read is
               appended.

               The call is actually implemented in terms of either Perl's or
               system's fread() call.  To get a true read(2) system call, see
               "sysread".

               Note the characters: depending on the status of the filehandle,
               either (8-bit) bytes or characters are read.  By default all
               filehandles operate on bytes, but for example if the filehandle
               has been opened with the ":utf8" I/O layer (see "open", and the
               "open" pragma, open), the I/O will operate on UTF-8 encoded
               Unicode characters, not bytes.  Similarly for the ":encoding"
               pragma: in that case pretty much any characters can be read.

       readdir DIRHANDLE
               Returns the next directory entry for a directory opened by
               "opendir".  If used in list context, returns all the rest of
               the entries in the directory.  If there are no more entries,
               returns an undefined value in scalar context or a null list in
               list context.

               If you're planning to filetest the return values out of a
               "readdir", you'd better prepend the directory in question.
               Otherwise, because we didn't "chdir" there, it would have been
               testing the wrong file.

                   opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
                   @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
                   closedir DIR;

       readline EXPR
               Reads from the filehandle whose typeglob is contained in EXPR.
               In scalar context, each call reads and returns the next line,
               until end-of-file is reached, whereupon the subsequent call
               returns undef.  In list context, reads until end-of-file is
               reached and returns a list of lines.  Note that the notion of
               "line" used here is however you may have defined it with $/ or
               $INPUT_RECORD_SEPARATOR).  See "$/" in perlvar.

               When $/ is set to "undef", when readline() is in scalar context
               (i.e. file slurp mode), and when an empty file is read, it
               returns '' the first time, followed by "undef" subsequently.

               This is the internal function implementing the "<EXPR>"
               operator, but you can use it directly.  The "<EXPR>" operator
               is discussed in more detail in "I/O Operators" in perlop.

                   $line = <STDIN>;
                   $line = readline(*STDIN);           # same thing

               If readline encounters an operating system error, $! will be
               set with the corresponding error message.  It can be helpful to
               check $! when you are reading from filehandles you don't trust,
               such as a tty or a socket.  The following example uses the
               operator form of "readline", and takes the necessary steps to
               ensure that "readline" was successful.

                   for (;;) {
                       undef $!;
                       unless (defined( $line = <> )) {
                           die $! if $!;
                           last; # reached EOF
                       }
                       # ...
                   }

       readlink EXPR
       readlink
               Returns the value of a symbolic link, if symbolic links are
               implemented.  If not, gives a fatal error.  If there is some
               system error, returns the undefined value and sets $! (errno).
               If EXPR is omitted, uses $_.

       readpipe EXPR
               EXPR is executed as a system command.  The collected standard
               output of the command is returned.  In scalar context, it comes
               back as a single (potentially multi-line) string.  In list
               context, returns a list of lines (however you've defined lines
               with $/ or $INPUT_RECORD_SEPARATOR).  This is the internal
               function implementing the "qx/EXPR/" operator, but you can use
               it directly.  The "qx/EXPR/" operator is discussed in more
               detail in "I/O Operators" in perlop.

       recv SOCKET,SCALAR,LENGTH,FLAGS
               Receives a message on a socket.  Attempts to receive LENGTH
               characters of data into variable SCALAR from the specified
               SOCKET filehandle.  SCALAR will be grown or shrunk to the
               length actually read.  Takes the same flags as the system call
               of the same name.  Returns the address of the sender if
               SOCKET's protocol supports this; returns an empty string
               otherwise.  If there's an error, returns the undefined value.
               This call is actually implemented in terms of recvfrom(2)
               system call.  See "UDP: Message Passing" in perlipc for
               examples.

               Note the characters: depending on the status of the socket,
               either (8-bit) bytes or characters are received.  By default
               all sockets operate on bytes, but for example if the socket has
               been changed using binmode() to operate with the ":utf8" I/O
               layer (see the "open" pragma, open), the I/O will operate on
               UTF-8 encoded Unicode characters, not bytes.  Similarly for the
               ":encoding" pragma: in that case pretty much any characters can
               be read.

       redo LABEL
       redo    The "redo" command restarts the loop block without evaluating
               the conditional again.  The "continue" block, if any, is not
               executed.  If the LABEL is omitted, the command refers to the
               innermost enclosing loop.  This command is normally used by
               programs that want to lie to themselves about what was just
               input:

                   # a simpleminded Pascal comment stripper
                   # (warning: assumes no { or } in strings)
                   LINE: while (<STDIN>) {
                       while (s|({.*}.*){.*}|$1 |) {}
                       s|{.*}| |;
                       if (s|{.*| |) {
                           $front = $_;
                           while (<STDIN>) {
                               if (/}/) {      # end of comment?
                                   s|^|$front\{|;
                                   redo LINE;
                               }
                           }
                       }
                       print;
                   }

               "redo" cannot be used to retry a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "redo" inside such a block will
               effectively turn it into a looping construct.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       ref EXPR
       ref     Returns a true value if EXPR is a reference, false otherwise.
               If EXPR is not specified, $_ will be used.  The value returned
               depends on the type of thing the reference is a reference to.
               Builtin types include:

                   SCALAR
                   ARRAY
                   HASH
                   CODE
                   REF
                   GLOB
                   LVALUE

               If the referenced object has been blessed into a package, then
               that package name is returned instead.  You can think of "ref"
               as a "typeof" operator.

                   if (ref($r) eq "HASH") {
                       print "r is a reference to a hash.\n";
                   }
                   unless (ref($r)) {
                       print "r is not a reference at all.\n";
                   }
                   if (UNIVERSAL::isa($r, "HASH")) {  # for subclassing
                       print "r is a reference to something that isa hash.\n";
                   }

               See also perlref.

       rename OLDNAME,NEWNAME
               Changes the name of a file; an existing file NEWNAME will be
               clobbered.  Returns true for success, false otherwise.

               Behavior of this function varies wildly depending on your
               system implementation.  For example, it will usually not work
               across file system boundaries, even though the system mv
               command sometimes compensates for this.  Other restrictions
               include whether it works on directories, open files, or pre-
               existing files.  Check perlport and either the rename(2)
               manpage or equivalent system documentation for details.

       require VERSION
       require EXPR
       require Demands a version of Perl specified by VERSION, or demands some
               semantics specified by EXPR or by $_ if EXPR is not supplied.

               VERSION may be either a numeric argument such as 5.006, which
               will be compared to $], or a literal of the form v5.6.1, which
               will be compared to $^V (aka $PERL_VERSION).  A fatal error is
               produced at run time if VERSION is greater than the version of
               the current Perl interpreter.  Compare with "use", which can do
               a similar check at compile time.

               Specifying VERSION as a literal of the form v5.6.1 should
               generally be avoided, because it leads to misleading error
               messages under earlier versions of Perl which do not support
               this syntax.  The equivalent numeric version should be used
               instead.

                   require v5.6.1;     # run time version check
                   require 5.6.1;      # ditto
                   require 5.006_001;  # ditto; preferred for backwards compatibility

               Otherwise, demands that a library file be included if it hasn't
               already been included.  The file is included via the do-FILE
               mechanism, which is essentially just a variety of "eval".  Has
               semantics similar to the following subroutine:

                   sub require {
                       my($filename) = @_;
                       return 1 if $INC{$filename};
                       my($realfilename,$result);
                       ITER: {
                           foreach $prefix (@INC) {
                               $realfilename = "$prefix/$filename";
                               if (-f $realfilename) {
                                   $INC{$filename} = $realfilename;
                                   $result = do $realfilename;
                                   last ITER;
                               }
                           }
                           die "Can't find $filename in \@INC";
                       }
                       delete $INC{$filename} if $@ || !$result;
                       die $@ if $@;
                       die "$filename did not return true value" unless $result;
                       return $result;
                   }

               Note that the file will not be included twice under the same
               specified name.  The file must return true as the last
               statement to indicate successful execution of any
               initialization code, so it's customary to end such a file with
               "1;" unless you're sure it'll return true otherwise.  But it's
               better just to put the "1;", in case you add more statements.

               If EXPR is a bareword, the require assumes a ".pm" extension
               and replaces "::" with "/" in the filename for you, to make it
               easy to load standard modules.  This form of loading of modules
               does not risk altering your namespace.

               In other words, if you try this:

                       require Foo::Bar;    # a splendid bareword

               The require function will actually look for the "Foo/Bar.pm"
               file in the directories specified in the @INC array.

               But if you try this:

                       $class = 'Foo::Bar';
                       require $class;      # $class is not a bareword
                   #or
                       require "Foo::Bar";  # not a bareword because of the ""

               The require function will look for the "Foo::Bar" file in the
               @INC array and will complain about not finding "Foo::Bar"
               there.  In this case you can do:

                       eval "require $class";

               Now that you understand how "require" looks for files in the
               case of a bareword argument, there is a little extra
               functionality going on behind the scenes.  Before "require"
               looks for a ".pm" extension, it will first look for a filename
               with a ".pmc" extension.  A file with this extension is assumed
               to be Perl bytecode generated by B::Bytecode.  If this file is
               found, and it's modification time is newer than a coinciding
               ".pm" non-compiled file, it will be loaded in place of that
               non-compiled file ending in a ".pm" extension.

               You can also insert hooks into the import facility, by putting
               directly Perl code into the @INC array.  There are three forms
               of hooks: subroutine references, array references and blessed
               objects.

               Subroutine references are the simplest case.  When the
               inclusion system walks through @INC and encounters a
               subroutine, this subroutine gets called with two parameters,
               the first being a reference to itself, and the second the name
               of the file to be included (e.g. "Foo/Bar.pm").  The subroutine
               should return "undef" or a filehandle, from which the file to
               include will be read.  If "undef" is returned, "require" will
               look at the remaining elements of @INC.

               If the hook is an array reference, its first element must be a
               subroutine reference.  This subroutine is called as above, but
               the first parameter is the array reference.  This enables to
               pass indirectly some arguments to the subroutine.

               In other words, you can write:

                   push @INC, \&my_sub;
                   sub my_sub {
                       my ($coderef, $filename) = @_;  # $coderef is \&my_sub
                       ...
                   }

               or:

                   push @INC, [ \&my_sub, $x, $y, ... ];
                   sub my_sub {
                       my ($arrayref, $filename) = @_;
                       # Retrieve $x, $y, ...
                       my @parameters = @$arrayref[1..$#$arrayref];
                       ...
                   }

               If the hook is an object, it must provide an INC method, that
               will be called as above, the first parameter being the object
               itself.  (Note that you must fully qualify the sub's name, as
               it is always forced into package "main".)  Here is a typical
               code layout:

                   # In Foo.pm
                   package Foo;
                   sub new { ... }
                   sub Foo::INC {
                       my ($self, $filename) = @_;
                       ...
                   }

                   # In the main program
                   push @INC, new Foo(...);

               Note that these hooks are also permitted to set the %INC entry
               corresponding to the files they have loaded. See "%INC" in
               perlvar.

               For a yet-more-powerful import facility, see "use" and perlmod.

       reset EXPR
       reset   Generally used in a "continue" block at the end of a loop to
               clear variables and reset "??" searches so that they work
               again.  The expression is interpreted as a list of single
               characters (hyphens allowed for ranges).  All variables and
               arrays beginning with one of those letters are reset to their
               pristine state.  If the expression is omitted, one-match
               searches ("?pattern?") are reset to match again.  Resets only
               variables or searches in the current package.  Always returns
               1.  Examples:

                   reset 'X';          # reset all X variables
                   reset 'a-z';        # reset lower case variables
                   reset;              # just reset ?one-time? searches

               Resetting "A-Z" is not recommended because you'll wipe out your
               @ARGV and @INC arrays and your %ENV hash.  Resets only package
               variables--lexical variables are unaffected, but they clean
               themselves up on scope exit anyway, so you'll probably want to
               use them instead.  See "my".

       return EXPR
       return  Returns from a subroutine, "eval", or "do FILE" with the value
               given in EXPR.  Evaluation of EXPR may be in list, scalar, or
               void context, depending on how the return value will be used,
               and the context may vary from one execution to the next (see
               "wantarray").  If no EXPR is given, returns an empty list in
               list context, the undefined value in scalar context, and (of
               course) nothing at all in a void context.

               (Note that in the absence of an explicit "return", a
               subroutine, eval, or do FILE will automatically return the
               value of the last expression evaluated.)

       reverse LIST
               In list context, returns a list value consisting of the
               elements of LIST in the opposite order.  In scalar context,
               concatenates the elements of LIST and returns a string value
               with all characters in the opposite order.

                   print reverse <>;           # line tac, last line first

                   undef $/;                   # for efficiency of <>
                   print scalar reverse <>;    # character tac, last line tsrif

               This operator is also handy for inverting a hash, although
               there are some caveats.  If a value is duplicated in the
               original hash, only one of those can be represented as a key in
               the inverted hash.  Also, this has to unwind one hash and build
               a whole new one, which may take some time on a large hash, such
               as from a DBM file.

                   %by_name = reverse %by_address;     # Invert the hash

       rewinddir DIRHANDLE
               Sets the current position to the beginning of the directory for
               the "readdir" routine on DIRHANDLE.

       rindex STR,SUBSTR,POSITION
       rindex STR,SUBSTR
               Works just like index() except that it returns the position of
               the LAST occurrence of SUBSTR in STR.  If POSITION is
               specified, returns the last occurrence at or before that
               position.

       rmdir FILENAME
       rmdir   Deletes the directory specified by FILENAME if that directory
               is empty.  If it succeeds it returns true, otherwise it returns
               false and sets $! (errno).  If FILENAME is omitted, uses $_.

       s///    The substitution operator.  See perlop.

       scalar EXPR
               Forces EXPR to be interpreted in scalar context and returns the
               value of EXPR.

                   @counts = ( scalar @a, scalar @b, scalar @c );

               There is no equivalent operator to force an expression to be
               interpolated in list context because in practice, this is never
               needed.  If you really wanted to do so, however, you could use
               the construction "@{[ (some expression) ]}", but usually a
               simple "(some expression)" suffices.

               Because "scalar" is unary operator, if you accidentally use for
               EXPR a parenthesized list, this behaves as a scalar comma
               expression, evaluating all but the last element in void context
               and returning the final element evaluated in scalar context.
               This is seldom what you want.

               The following single statement:

                       print uc(scalar(&foo,$bar)),$baz;

               is the moral equivalent of these two:

                       &foo;
                       print(uc($bar),$baz);

               See perlop for more details on unary operators and the comma
               operator.

       seek FILEHANDLE,POSITION,WHENCE
               Sets FILEHANDLE's position, just like the "fseek" call of
               "stdio".  FILEHANDLE may be an expression whose value gives the
               name of the filehandle.  The values for WHENCE are 0 to set the
               new position in bytes to POSITION, 1 to set it to the current
               position plus POSITION, and 2 to set it to EOF plus POSITION
               (typically negative).  For WHENCE you may use the constants
               "SEEK_SET", "SEEK_CUR", and "SEEK_END" (start of the file,
               current position, end of the file) from the Fcntl module.
               Returns 1 upon success, 0 otherwise.

               Note the in bytes: even if the filehandle has been set to
               operate on characters (for example by using the ":utf8" open
               layer), tell() will return byte offsets, not character offsets
               (because implementing that would render seek() and tell()
               rather slow).

               If you want to position file for "sysread" or "syswrite", don't
               use "seek"--buffering makes its effect on the file's system
               position unpredictable and non-portable.  Use "sysseek"
               instead.

               Due to the rules and rigors of ANSI C, on some systems you have
               to do a seek whenever you switch between reading and writing.
               Amongst other things, this may have the effect of calling
               stdio's clearerr(3).  A WHENCE of 1 ("SEEK_CUR") is useful for
               not moving the file position:

                   seek(TEST,0,1);

               This is also useful for applications emulating "tail -f".  Once
               you hit EOF on your read, and then sleep for a while, you might
               have to stick in a seek() to reset things.  The "seek" doesn't
               change the current position, but it does clear the end-of-file
               condition on the handle, so that the next "<FILE>" makes Perl
               try again to read something.  We hope.

               If that doesn't work (some IO implementations are particularly
               cantankerous), then you may need something more like this:

                   for (;;) {
                       for ($curpos = tell(FILE); $_ = <FILE>;
                            $curpos = tell(FILE)) {
                           # search for some stuff and put it into files
                       }
                       sleep($for_a_while);
                       seek(FILE, $curpos, 0);
                   }

       seekdir DIRHANDLE,POS
               Sets the current position for the "readdir" routine on
               DIRHANDLE.  POS must be a value returned by "telldir".  Has the
               same caveats about possible directory compaction as the
               corresponding system library routine.

       select FILEHANDLE
       select  Returns the currently selected filehandle.  Sets the current
               default filehandle for output, if FILEHANDLE is supplied.  This
               has two effects: first, a "write" or a "print" without a
               filehandle will default to this FILEHANDLE.  Second, references
               to variables related to output will refer to this output
               channel.  For example, if you have to set the top of form
               format for more than one output channel, you might do the
               following:

                   select(REPORT1);
                   $^ = 'report1_top';
                   select(REPORT2);
                   $^ = 'report2_top';

               FILEHANDLE may be an expression whose value gives the name of
               the actual filehandle.  Thus:

                   $oldfh = select(STDERR); $| = 1; select($oldfh);

               Some programmers may prefer to think of filehandles as objects
               with methods, preferring to write the last example as:

                   use IO::Handle;
                   STDERR->autoflush(1);

       select RBITS,WBITS,EBITS,TIMEOUT
               This calls the select(2) system call with the bit masks
               specified, which can be constructed using "fileno" and "vec",
               along these lines:

                   $rin = $win = $ein = '';
                   vec($rin,fileno(STDIN),1) = 1;
                   vec($win,fileno(STDOUT),1) = 1;
                   $ein = $rin | $win;

               If you want to select on many filehandles you might wish to
               write a subroutine:

                   sub fhbits {
                       my(@fhlist) = split(' ',$_[0]);
                       my($bits);
                       for (@fhlist) {
                           vec($bits,fileno($_),1) = 1;
                       }
                       $bits;
                   }
                   $rin = fhbits('STDIN TTY SOCK');

               The usual idiom is:

                   ($nfound,$timeleft) =
                     select($rout=$rin, $wout=$win, $eout=$ein, $timeout);

               or to block until something becomes ready just do this

                   $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);

               Most systems do not bother to return anything useful in
               $timeleft, so calling select() in scalar context just returns
               $nfound.

               Any of the bit masks can also be undef.  The timeout, if
               specified, is in seconds, which may be fractional.  Note: not
               all implementations are capable of returning the $timeleft.  If
               not, they always return $timeleft equal to the supplied
               $timeout.

               You can effect a sleep of 250 milliseconds this way:

                   select(undef, undef, undef, 0.25);

               Note that whether "select" gets restarted after signals (say,
               SIGALRM) is implementation-dependent.

               WARNING: One should not attempt to mix buffered I/O (like
               "read" or <FH>) with "select", except as permitted by POSIX,
               and even then only on POSIX systems.  You have to use "sysread"
               instead.

       semctl ID,SEMNUM,CMD,ARG
               Calls the System V IPC function "semctl".  You'll probably have
               to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If CMD is
               IPC_STAT or GETALL, then ARG must be a variable which will hold
               the returned semid_ds structure or semaphore value array.
               Returns like "ioctl": the undefined value for error, ""0 but
               true"" for zero, or the actual return value otherwise.  The ARG
               must consist of a vector of native short integers, which may be
               created with "pack("s!",(0)x$nsem)".  See also "SysV IPC" in
               perlipc, "IPC::SysV", "IPC::Semaphore" documentation.

       semget KEY,NSEMS,FLAGS
               Calls the System V IPC function semget.  Returns the semaphore
               id, or the undefined value if there is an error.  See also
               "SysV IPC" in perlipc, "IPC::SysV", "IPC::SysV::Semaphore"
               documentation.

       semop KEY,OPSTRING
               Calls the System V IPC function semop to perform semaphore
               operations such as signalling and waiting.  OPSTRING must be a
               packed array of semop structures.  Each semop structure can be
               generated with "pack("s!3", $semnum, $semop, $semflag)".  The
               number of semaphore operations is implied by the length of
               OPSTRING.  Returns true if successful, or false if there is an
               error.  As an example, the following code waits on semaphore
               $semnum of semaphore id $semid:

                   $semop = pack("s!3", $semnum, -1, 0);
                   die "Semaphore trouble: $!\n" unless semop($semid, $semop);

               To signal the semaphore, replace "-1" with 1.  See also "SysV
               IPC" in perlipc, "IPC::SysV", and "IPC::SysV::Semaphore"
               documentation.

       send SOCKET,MSG,FLAGS,TO
       send SOCKET,MSG,FLAGS
               Sends a message on a socket.  Attempts to send the scalar MSG
               to the SOCKET filehandle.  Takes the same flags as the system
               call of the same name.  On unconnected sockets you must specify
               a destination to send TO, in which case it does a C "sendto".
               Returns the number of characters sent, or the undefined value
               if there is an error.  The C system call sendmsg(2) is
               currently unimplemented.  See "UDP: Message Passing" in perlipc
               for examples.

               Note the characters: depending on the status of the socket,
               either (8-bit) bytes or characters are sent.  By default all
               sockets operate on bytes, but for example if the socket has
               been changed using binmode() to operate with the ":utf8" I/O
               layer (see "open", or the "open" pragma, open), the I/O will
               operate on UTF-8 encoded Unicode characters, not bytes.
               Similarly for the ":encoding" pragma: in that case pretty much
               any characters can be sent.

       setpgrp PID,PGRP
               Sets the current process group for the specified PID, 0 for the
               current process.  Will produce a fatal error if used on a
               machine that doesn't implement POSIX setpgid(2) or BSD
               setpgrp(2).  If the arguments are omitted, it defaults to
               "0,0".  Note that the BSD 4.2 version of "setpgrp" does not
               accept any arguments, so only "setpgrp(0,0)" is portable.  See
               also "POSIX::setsid()".

       setpriority WHICH,WHO,PRIORITY
               Sets the current priority for a process, a process group, or a
               user.  (See setpriority(2).)  Will produce a fatal error if
               used on a machine that doesn't implement setpriority(2).

       setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
               Sets the socket option requested.  Returns undefined if there
               is an error.  OPTVAL may be specified as "undef" if you don't
               want to pass an argument.

       shift ARRAY
       shift   Shifts the first value of the array off and returns it,
               shortening the array by 1 and moving everything down.  If there
               are no elements in the array, returns the undefined value.  If
               ARRAY is omitted, shifts the @_ array within the lexical scope
               of subroutines and formats, and the @ARGV array at file scopes
               or within the lexical scopes established by the "eval ''",
               "BEGIN {}", "INIT {}", "CHECK {}", and "END {}" constructs.

               See also "unshift", "push", and "pop".  "shift" and "unshift"
               do the same thing to the left end of an array that "pop" and
               "push" do to the right end.

       shmctl ID,CMD,ARG
               Calls the System V IPC function shmctl.  You'll probably have
               to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If CMD is
               "IPC_STAT", then ARG must be a variable which will hold the
               returned "shmid_ds" structure.  Returns like ioctl: the
               undefined value for error, "0 but true" for zero, or the actual
               return value otherwise.  See also "SysV IPC" in perlipc and
               "IPC::SysV" documentation.

       shmget KEY,SIZE,FLAGS
               Calls the System V IPC function shmget.  Returns the shared
               memory segment id, or the undefined value if there is an error.
               See also "SysV IPC" in perlipc and "IPC::SysV" documentation.

       shmread ID,VAR,POS,SIZE
       shmwrite ID,STRING,POS,SIZE
               Reads or writes the System V shared memory segment ID starting
               at position POS for size SIZE by attaching to it, copying
               in/out, and detaching from it.  When reading, VAR must be a
               variable that will hold the data read.  When writing, if STRING
               is too long, only SIZE bytes are used; if STRING is too short,
               nulls are written to fill out SIZE bytes.  Return true if
               successful, or false if there is an error.  shmread() taints
               the variable. See also "SysV IPC" in perlipc, "IPC::SysV"
               documentation, and the "IPC::Shareable" module from CPAN.

       shutdown SOCKET,HOW
               Shuts down a socket connection in the manner indicated by HOW,
               which has the same interpretation as in the system call of the
               same name.

                   shutdown(SOCKET, 0);    # I/we have stopped reading data
                   shutdown(SOCKET, 1);    # I/we have stopped writing data
                   shutdown(SOCKET, 2);    # I/we have stopped using this socket

               This is useful with sockets when you want to tell the other
               side you're done writing but not done reading, or vice versa.
               It's also a more insistent form of close because it also
               disables the file descriptor in any forked copies in other
               processes.

       sin EXPR
       sin     Returns the sine of EXPR (expressed in radians).  If EXPR is
               omitted, returns sine of $_.

               For the inverse sine operation, you may use the
               "Math::Trig::asin" function, or use this relation:

                   sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }

       sleep EXPR
       sleep   Causes the script to sleep for EXPR seconds, or forever if no
               EXPR.  May be interrupted if the process receives a signal such
               as "SIGALRM".  Returns the number of seconds actually slept.
               You probably cannot mix "alarm" and "sleep" calls, because
               "sleep" is often implemented using "alarm".

               On some older systems, it may sleep up to a full second less
               than what you requested, depending on how it counts seconds.
               Most modern systems always sleep the full amount.  They may
               appear to sleep longer than that, however, because your process
               might not be scheduled right away in a busy multitasking
               system.

               For delays of finer granularity than one second, you may use
               Perl's "syscall" interface to access setitimer(2) if your
               system supports it, or else see "select" above.  The
               Time::HiRes module (from CPAN, and starting from Perl 5.8 part
               of the standard distribution) may also help.

               See also the POSIX module's "pause" function.

       socket SOCKET,DOMAIN,TYPE,PROTOCOL
               Opens a socket of the specified kind and attaches it to
               filehandle SOCKET.  DOMAIN, TYPE, and PROTOCOL are specified
               the same as for the system call of the same name.  You should
               "use Socket" first to get the proper definitions imported.  See
               the examples in "Sockets: Client/Server Communication" in
               perlipc.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptor, as determined
               by the value of $^F.  See "$^F" in perlvar.

       socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
               Creates an unnamed pair of sockets in the specified domain, of
               the specified type.  DOMAIN, TYPE, and PROTOCOL are specified
               the same as for the system call of the same name.  If
               unimplemented, yields a fatal error.  Returns true if
               successful.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptors, as
               determined by the value of $^F.  See "$^F" in perlvar.

               Some systems defined "pipe" in terms of "socketpair", in which
               a call to "pipe(Rdr, Wtr)" is essentially:

                   use Socket;
                   socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
                   shutdown(Rdr, 1);        # no more writing for reader
                   shutdown(Wtr, 0);        # no more reading for writer

               See perlipc for an example of socketpair use.  Perl 5.8 and
               later will emulate socketpair using IP sockets to localhost if
               your system implements sockets but not socketpair.

       sort SUBNAME LIST
       sort BLOCK LIST
       sort LIST
               In list context, this sorts the LIST and returns the sorted
               list value.  In scalar context, the behaviour of "sort()" is
               undefined.

               If SUBNAME or BLOCK is omitted, "sort"s in standard string
               comparison order.  If SUBNAME is specified, it gives the name
               of a subroutine that returns an integer less than, equal to, or
               greater than 0, depending on how the elements of the list are
               to be ordered.  (The "<=>" and "cmp" operators are extremely
               useful in such routines.)  SUBNAME may be a scalar variable
               name (unsubscripted), in which case the value provides the name
               of (or a reference to) the actual subroutine to use.  In place
               of a SUBNAME, you can provide a BLOCK as an anonymous, in-line
               sort subroutine.

               If the subroutine's prototype is "($$)", the elements to be
               compared are passed by reference in @_, as for a normal
               subroutine.  This is slower than unprototyped subroutines,
               where the elements to be compared are passed into the
               subroutine as the package global variables $a and $b (see
               example below).  Note that in the latter case, it is usually
               counter-productive to declare $a and $b as lexicals.

               In either case, the subroutine may not be recursive.  The
               values to be compared are always passed by reference, so don't
               modify them.

               You also cannot exit out of the sort block or subroutine using
               any of the loop control operators described in perlsyn or with
               "goto".

               When "use locale" is in effect, "sort LIST" sorts LIST
               according to the current collation locale.  See perllocale.

               Perl 5.6 and earlier used a quicksort algorithm to implement
               sort.  That algorithm was not stable, and could go quadratic.
               (A stable sort preserves the input order of elements that
               compare equal.  Although quicksort's run time is O(NlogN) when
               averaged over all arrays of length N, the time can be O(N**2),
               quadratic behavior, for some inputs.)  In 5.7, the quicksort
               implementation was replaced with a stable mergesort algorithm
               whose worst case behavior is O(NlogN).  But benchmarks
               indicated that for some inputs, on some platforms, the original
               quicksort was faster.  5.8 has a sort pragma for limited
               control of the sort.  Its rather blunt control of the
               underlying algorithm may not persist into future perls, but the
               ability to characterize the input or output in implementation
               independent ways quite probably will.  See sort.

               Examples:

                   # sort lexically
                   @articles = sort @files;

                   # same thing, but with explicit sort routine
                   @articles = sort {$a cmp $b} @files;

                   # now case-insensitively
                   @articles = sort {uc($a) cmp uc($b)} @files;

                   # same thing in reversed order
                   @articles = sort {$b cmp $a} @files;

                   # sort numerically ascending
                   @articles = sort {$a <=> $b} @files;

                   # sort numerically descending
                   @articles = sort {$b <=> $a} @files;

                   # this sorts the %age hash by value instead of key
                   # using an in-line function
                   @eldest = sort { $age{$b} <=> $age{$a} } keys %age;

                   # sort using explicit subroutine name
                   sub byage {
                       $age{$a} <=> $age{$b};  # presuming numeric
                   }
                   @sortedclass = sort byage @class;

                   sub backwards { $b cmp $a }
                   @harry  = qw(dog cat x Cain Abel);
                   @george = qw(gone chased yz Punished Axed);
                   print sort @harry;
                           # prints AbelCaincatdogx
                   print sort backwards @harry;
                           # prints xdogcatCainAbel
                   print sort @george, 'to', @harry;
                           # prints AbelAxedCainPunishedcatchaseddoggonetoxyz

                   # inefficiently sort by descending numeric compare using
                   # the first integer after the first = sign, or the
                   # whole record case-insensitively otherwise

                   @new = sort {
                       ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
                                           ||
                                   uc($a)  cmp  uc($b)
                   } @old;

                   # same thing, but much more efficiently;
                   # we'll build auxiliary indices instead
                   # for speed
                   @nums = @caps = ();
                   for (@old) {
                       push @nums, /=(\d+)/;
                       push @caps, uc($_);
                   }

                   @new = @old[ sort {
                                       $nums[$b] <=> $nums[$a]
                                                ||
                                       $caps[$a] cmp $caps[$b]
                                      } 0..$#old
                              ];

                   # same thing, but without any temps
                   @new = map { $_->[0] }
                          sort { $b->[1] <=> $a->[1]
                                          ||
                                 $a->[2] cmp $b->[2]
                          } map { [$_, /=(\d+)/, uc($_)] } @old;

                   # using a prototype allows you to use any comparison subroutine
                   # as a sort subroutine (including other package's subroutines)
                   package other;
                   sub backwards ($$) { $_[1] cmp $_[0]; }     # $a and $b are not set here

                   package main;
                   @new = sort other::backwards @old;

                   # guarantee stability, regardless of algorithm
                   use sort 'stable';
                   @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

                   # force use of mergesort (not portable outside Perl 5.8)
                   use sort '_mergesort';  # note discouraging _
                   @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

               If you're using strict, you must not declare $a and $b as
               lexicals.  They are package globals.  That means if you're in
               the "main" package and type

                   @articles = sort {$b <=> $a} @files;

               then $a and $b are $main::a and $main::b (or $::a and $::b),
               but if you're in the "FooPack" package, it's the same as typing

                   @articles = sort {$FooPack::b <=> $FooPack::a} @files;

               The comparison function is required to behave.  If it returns
               inconsistent results (sometimes saying $x[1] is less than $x[2]
               and sometimes saying the opposite, for example) the results are
               not well-defined.

               Because "<=>" returns "undef" when either operand is "NaN"
               (not-a-number), and because "sort" will trigger a fatal error
               unless the result of a comparison is defined, when sorting with
               a comparison function like "$a <=> $b", be careful about lists
               that might contain a "NaN".  The following example takes
               advantage of the fact that "NaN != NaN" to eliminate any "NaN"s
               from the input.

                   @result = sort { $a <=> $b } grep { $_ == $_ } @input;

       splice ARRAY,OFFSET,LENGTH,LIST
       splice ARRAY,OFFSET,LENGTH
       splice ARRAY,OFFSET
       splice ARRAY
               Removes the elements designated by OFFSET and LENGTH from an
               array, and replaces them with the elements of LIST, if any.  In
               list context, returns the elements removed from the array.  In
               scalar context, returns the last element removed, or "undef" if
               no elements are removed.  The array grows or shrinks as
               necessary.  If OFFSET is negative then it starts that far from
               the end of the array.  If LENGTH is omitted, removes everything
               from OFFSET onward.  If LENGTH is negative, removes the
               elements from OFFSET onward except for -LENGTH elements at the
               end of the array.  If both OFFSET and LENGTH are omitted,
               removes everything. If OFFSET is past the end of the array,
               perl issues a warning, and splices at the end of the array.

               The following equivalences hold (assuming "$[ == 0 and $#a >=
               $i" )

                   push(@a,$x,$y)      splice(@a,@a,0,$x,$y)
                   pop(@a)             splice(@a,-1)
                   shift(@a)           splice(@a,0,1)
                   unshift(@a,$x,$y)   splice(@a,0,0,$x,$y)
                   $a[$i] = $y         splice(@a,$i,1,$y)

               Example, assuming array lengths are passed before arrays:

                   sub aeq {   # compare two list values
                       my(@a) = splice(@_,0,shift);
                       my(@b) = splice(@_,0,shift);
                       return 0 unless @a == @b;       # same len?
                       while (@a) {
                           return 0 if pop(@a) ne pop(@b);
                       }
                       return 1;
                   }
                   if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }

       split /PATTERN/,EXPR,LIMIT
       split /PATTERN/,EXPR
       split /PATTERN/
       split   Splits a string into a list of strings and returns that list.
               By default, empty leading fields are preserved, and empty
               trailing ones are deleted.

               In scalar context, returns the number of fields found and
               splits into the @_ array.  Use of split in scalar context is
               deprecated, however, because it clobbers your subroutine
               arguments.

               If EXPR is omitted, splits the $_ string.  If PATTERN is also
               omitted, splits on whitespace (after skipping any leading
               whitespace).  Anything matching PATTERN is taken to be a
               delimiter separating the fields.  (Note that the delimiter may
               be longer than one character.)

               If LIMIT is specified and positive, it represents the maximum
               number of fields the EXPR will be split into, though the actual
               number of fields returned depends on the number of times
               PATTERN matches within EXPR.  If LIMIT is unspecified or zero,
               trailing null fields are stripped (which potential users of
               "pop" would do well to remember).  If LIMIT is negative, it is
               treated as if an arbitrarily large LIMIT had been specified.
               Note that splitting an EXPR that evaluates to the empty string
               always returns the empty list, regardless of the LIMIT
               specified.

               A pattern matching the null string (not to be confused with a
               null pattern "//", which is just one member of the set of
               patterns matching a null string) will split the value of EXPR
               into separate characters at each point it matches that way.
               For example:

                   print join(':', split(/ */, 'hi there'));

               produces the output 'h:i:t:h:e:r:e'.

               Using the empty pattern "//" specifically matches the null
               string, and is not be confused with the use of "//" to mean
               "the last successful pattern match".

               Empty leading (or trailing) fields are produced when there are
               positive width matches at the beginning (or end) of the string;
               a zero-width match at the beginning (or end) of the string does
               not produce an empty field.  For example:

                  print join(':', split(/(?=\w)/, 'hi there!'));

               produces the output 'h:i :t:h:e:r:e!'.

               The LIMIT parameter can be used to split a line partially

                   ($login, $passwd, $remainder) = split(/:/, $_, 3);

               When assigning to a list, if LIMIT is omitted, or zero, Perl
               supplies a LIMIT one larger than the number of variables in the
               list, to avoid unnecessary work.  For the list above LIMIT
               would have been 4 by default.  In time critical applications it
               behooves you not to split into more fields than you really
               need.

               If the PATTERN contains parentheses, additional list elements
               are created from each matching substring in the delimiter.

                   split(/([,-])/, "1-10,20", 3);

               produces the list value

                   (1, '-', 10, ',', 20)

               If you had the entire header of a normal Unix email message in
               $header, you could split it up into fields and their values
               this way:

                   $header =~ s/\n\s+/ /g;  # fix continuation lines
                   %hdrs   =  (UNIX_FROM => split /^(\S*?):\s*/m, $header);

               The pattern "/PATTERN/" may be replaced with an expression to
               specify patterns that vary at runtime.  (To do runtime
               compilation only once, use "/$variable/o".)

               As a special case, specifying a PATTERN of space (' ') will
               split on white space just as "split" with no arguments does.
               Thus, "split(' ')" can be used to emulate awk's default
               behavior, whereas "split(/ /)" will give you as many null
               initial fields as there are leading spaces.  A "split" on
               "/\s+/" is like a "split(' ')" except that any leading
               whitespace produces a null first field.  A "split" with no
               arguments really does a "split(' ', $_)" internally.

               A PATTERN of "/^/" is treated as if it were "/^/m", since it
               isn't much use otherwise.

               Example:

                   open(PASSWD, '/etc/passwd');
                   while (<PASSWD>) {
                       chomp;
                       ($login, $passwd, $uid, $gid,
                        $gcos, $home, $shell) = split(/:/);
                       #...
                   }

               As with regular pattern matching, any capturing parentheses
               that are not matched in a "split()" will be set to "undef" when
               returned:

                   @fields = split /(A)|B/, "1A2B3";
                   # @fields is (1, 'A', 2, undef, 3)

       sprintf FORMAT, LIST
               Returns a string formatted by the usual "printf" conventions of
               the C library function "sprintf".  See below for more details
               and see sprintf(3) or printf(3) on your system for an
               explanation of the general principles.

               For example:

                       # Format number with up to 8 leading zeroes
                       $result = sprintf("%08d", $number);

                       # Round number to 3 digits after decimal point
                       $rounded = sprintf("%.3f", $number);

               Perl does its own "sprintf" formatting--it emulates the C
               function "sprintf", but it doesn't use it (except for floating-
               point numbers, and even then only the standard modifiers are
               allowed).  As a result, any non-standard extensions in your
               local "sprintf" are not available from Perl.

               Unlike "printf", "sprintf" does not do what you probably mean
               when you pass it an array as your first argument. The array is
               given scalar context, and instead of using the 0th element of
               the array as the format, Perl will use the count of elements in
               the array as the format, which is almost never useful.

               Perl's "sprintf" permits the following universally-known
               conversions:

                  %%   a percent sign
                  %c   a character with the given number
                  %s   a string
                  %d   a signed integer, in decimal
                  %u   an unsigned integer, in decimal
                  %o   an unsigned integer, in octal
                  %x   an unsigned integer, in hexadecimal
                  %e   a floating-point number, in scientific notation
                  %f   a floating-point number, in fixed decimal notation
                  %g   a floating-point number, in %e or %f notation

               In addition, Perl permits the following widely-supported
               conversions:

                  %X   like %x, but using upper-case letters
                  %E   like %e, but using an upper-case "E"
                  %G   like %g, but with an upper-case "E" (if applicable)
                  %b   an unsigned integer, in binary
                  %p   a pointer (outputs the Perl value's address in hexadecimal)
                  %n   special: *stores* the number of characters output so far
                       into the next variable in the parameter list

               Finally, for backward (and we do mean "backward")
               compatibility, Perl permits these unnecessary but widely-
               supported conversions:

                  %i   a synonym for %d
                  %D   a synonym for %ld
                  %U   a synonym for %lu
                  %O   a synonym for %lo
                  %F   a synonym for %f

               Note that the number of exponent digits in the scientific
               notation produced by %e, %E, %g and %G for numbers with the
               modulus of the exponent less than 100 is system-dependent: it
               may be three or less (zero-padded as necessary).  In other
               words, 1.23 times ten to the 99th may be either "1.23e99" or
               "1.23e099".

               Between the "%" and the format letter, you may specify a number
               of additional attributes controlling the interpretation of the
               format.  In order, these are:

               format parameter index
                   An explicit format parameter index, such as "2$". By
                   default sprintf will format the next unused argument in the
                   list, but this allows you to take the arguments out of
                   order. Eg:

                     printf '%2$d %1$d', 12, 34;      # prints "34 12"
                     printf '%3$d %d %1$d', 1, 2, 3;  # prints "3 1 1"

               flags
                   one or more of:
                      space   prefix positive number with a space
                      +       prefix positive number with a plus sign
                      -       left-justify within the field
                      0       use zeros, not spaces, to right-justify
                      #       prefix non-zero octal with "0", non-zero hex
                   with "0x",
                              non-zero binary with "0b"

                   For example:

                     printf '<% d>', 12;   # prints "< 12>"
                     printf '<%+d>', 12;   # prints "<+12>"
                     printf '<%6s>', 12;   # prints "<    12>"
                     printf '<%-6s>', 12;  # prints "<12    >"
                     printf '<%06s>', 12;  # prints "<000012>"
                     printf '<%#x>', 12;   # prints "<0xc>"

               vector flag
                   The vector flag "v", optionally specifying the join string
                   to use.  This flag tells perl to interpret the supplied
                   string as a vector of integers, one for each character in
                   the string, separated by a given string (a dot "." by
                   default). This can be useful for displaying ordinal values
                   of characters in arbitrary strings:

                     printf "version is v%vd\n", $^V;     # Perl's version

                   Put an asterisk "*" before the "v" to override the string
                   to use to separate the numbers:

                     printf "address is %*vX\n", ":", $addr;   # IPv6 address
                     printf "bits are %0*v8b\n", " ", $bits;   # random bitstring

                   You can also explicitly specify the argument number to use
                   for the join string using eg "*2$v":

                     printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":";   # 3 IPv6 addresses

               (minimum) width
                   Arguments are usually formatted to be only as wide as
                   required to display the given value. You can override the
                   width by putting a number here, or get the width from the
                   next argument (with "*") or from a specified argument (with
                   eg "*2$"):

                     printf '<%s>', "a";       # prints "<a>"
                     printf '<%6s>', "a";      # prints "<     a>"
                     printf '<%*s>', 6, "a";   # prints "<     a>"
                     printf '<%*2$s>', "a", 6; # prints "<     a>"
                     printf '<%2s>', "long";   # prints "<long>" (does not truncate)

                   If a field width obtained through "*" is negative, it has
                   the same effect as the "-" flag: left-justification.

               precision, or maximum width
                   You can specify a precision (for numeric conversions) or a
                   maximum width (for string conversions) by specifying a "."
                   followed by a number.  For floating point formats, with the
                   exception of 'g' and 'G', this specifies the number of
                   decimal places to show (the default being 6), eg:

                     # these examples are subject to system-specific variation
                     printf '<%f>', 1;    # prints "<1.000000>"
                     printf '<%.1f>', 1;  # prints "<1.0>"
                     printf '<%.0f>', 1;  # prints "<1>"
                     printf '<%e>', 10;   # prints "<1.000000e+01>"
                     printf '<%.1e>', 10; # prints "<1.0e+01>"

                   For 'g' and 'G', this specifies the maximum number of
                   digits to show, including prior to the decimal point as
                   well as after it, eg:

                     # these examples are subject to system-specific variation
                     printf '<%g>', 1;        # prints "<1>"
                     printf '<%.10g>', 1;     # prints "<1>"
                     printf '<%g>', 100;      # prints "<100>"
                     printf '<%.1g>', 100;    # prints "<1e+02>"
                     printf '<%.2g>', 100.01; # prints "<1e+02>"
                     printf '<%.5g>', 100.01; # prints "<100.01>"
                     printf '<%.4g>', 100.01; # prints "<100>"

                   For integer conversions, specifying a precision implies
                   that the output of the number itself should be zero-padded
                   to this width:

                     printf '<%.6x>', 1;      # prints "<000001>"
                     printf '<%#.6x>', 1;     # prints "<0x000001>"
                     printf '<%-10.6x>', 1;   # prints "<000001    >"

                   For string conversions, specifying a precision truncates
                   the string to fit in the specified width:

                     printf '<%.5s>', "truncated";   # prints "<trunc>"
                     printf '<%10.5s>', "truncated"; # prints "<     trunc>"

                   You can also get the precision from the next argument using
                   ".*":

                     printf '<%.6x>', 1;       # prints "<000001>"
                     printf '<%.*x>', 6, 1;    # prints "<000001>"

                   You cannot currently get the precision from a specified
                   number, but it is intended that this will be possible in
                   the future using eg ".*2$":

                     printf '<%.*2$x>', 1, 6;   # INVALID, but in future will print "<000001>"

               size
                   For numeric conversions, you can specify the size to
                   interpret the number as using "l", "h", "V", "q", "L", or
                   "ll". For integer conversions ("d u o x X b i D U O"),
                   numbers are usually assumed to be whatever the default
                   integer size is on your platform (usually 32 or 64 bits),
                   but you can override this to use instead one of the
                   standard C types, as supported by the compiler used to
                   build Perl:

                      l           interpret integer as C type "long" or "unsigned long"
                      h           interpret integer as C type "short" or "unsigned short"
                      q, L or ll  interpret integer as C type "long long", "unsigned long long".
                                  or "quads" (typically 64-bit integers)

                   The last will produce errors if Perl does not understand
                   "quads" in your installation. (This requires that either
                   the platform natively supports quads or Perl was
                   specifically compiled to support quads.) You can find out
                   whether your Perl supports quads via Config:

                           use Config;
                           ($Config{use64bitint} eq 'define' || $Config{longsize} >= 8) &&
                                   print "quads\n";

                   For floating point conversions ("e f g E F G"), numbers are
                   usually assumed to be the default floating point size on
                   your platform (double or long double), but you can force
                   'long double' with "q", "L", or "ll" if your platform
                   supports them. You can find out whether your Perl supports
                   long doubles via Config:

                           use Config;
                           $Config{d_longdbl} eq 'define' && print "long doubles\n";

                   You can find out whether Perl considers 'long double' to be
                   the default floating point size to use on your platform via
                   Config:

                           use Config;
                           ($Config{uselongdouble} eq 'define') &&
                                   print "long doubles by default\n";

                   It can also be the case that long doubles and doubles are
                   the same thing:

                           use Config;
                           ($Config{doublesize} == $Config{longdblsize}) &&
                                   print "doubles are long doubles\n";

                   The size specifier "V" has no effect for Perl code, but it
                   is supported for compatibility with XS code; it means 'use
                   the standard size for a Perl integer (or floating-point
                   number)', which is already the default for Perl code.

               order of arguments
                   Normally, sprintf takes the next unused argument as the
                   value to format for each format specification. If the
                   format specification uses "*" to require additional
                   arguments, these are consumed from the argument list in the
                   order in which they appear in the format specification
                   before the value to format. Where an argument is specified
                   using an explicit index, this does not affect the normal
                   order for the arguments (even when the explicitly specified
                   index would have been the next argument in any case).

                   So:

                     printf '<%*.*s>', $a, $b, $c;

                   would use $a for the width, $b for the precision and $c as
                   the value to format, while:

                     print '<%*1$.*s>', $a, $b;

                   would use $a for the width and the precision, and $b as the
                   value to format.

                   Here are some more examples - beware that when using an
                   explicit index, the "$" may need to be escaped:

                     printf "%2\$d %d\n",    12, 34;               # will print "34 12\n"
                     printf "%2\$d %d %d\n", 12, 34;               # will print "34 12 34\n"
                     printf "%3\$d %d %d\n", 12, 34, 56;           # will print "56 12 34\n"
                     printf "%2\$*3\$d %d\n", 12, 34, 3;           # will print " 34 12\n"

               If "use locale" is in effect, the character used for the
               decimal point in formatted real numbers is affected by the
               LC_NUMERIC locale.  See perllocale.

       sqrt EXPR
       sqrt    Return the square root of EXPR.  If EXPR is omitted, returns
               square root of $_.  Only works on non-negative operands, unless
               you've loaded the standard Math::Complex module.

                   use Math::Complex;
                   print sqrt(-2);    # prints 1.4142135623731i

       srand EXPR
       srand   Sets the random number seed for the "rand" operator.

               The point of the function is to "seed" the "rand" function so
               that "rand" can produce a different sequence each time you run
               your program.

               If srand() is not called explicitly, it is called implicitly at
               the first use of the "rand" operator.  However, this was not
               the case in versions of Perl before 5.004, so if your script
               will run under older Perl versions, it should call "srand".

               Most programs won't even call srand() at all, except those that
               need a cryptographically-strong starting point rather than the
               generally acceptable default, which is based on time of day,
               process ID, and memory allocation, or the /dev/urandom device,
               if available.

               You can call srand($seed) with the same $seed to reproduce the
               same sequence from rand(), but this is usually reserved for
               generating predictable results for testing or debugging.
               Otherwise, don't call srand() more than once in your program.

               Do not call srand() (i.e. without an argument) more than once
               in a script.  The internal state of the random number generator
               should contain more entropy than can be provided by any seed,
               so calling srand() again actually loses randomness.

               Most implementations of "srand" take an integer and will
               silently truncate decimal numbers.  This means "srand(42)" will
               usually produce the same results as "srand(42.1)".  To be safe,
               always pass "srand" an integer.

               In versions of Perl prior to 5.004 the default seed was just
               the current "time".  This isn't a particularly good seed, so
               many old programs supply their own seed value (often "time ^
               $$" or "time ^ ($$ + ($$ << 15))"), but that isn't necessary
               any more.

               Note that you need something much more random than the default
               seed for cryptographic purposes.  Checksumming the compressed
               output of one or more rapidly changing operating system status
               programs is the usual method.  For example:

                   srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip`);

               If you're particularly concerned with this, see the
               "Math::TrulyRandom" module in CPAN.

               Frequently called programs (like CGI scripts) that simply use

                   time ^ $$

               for a seed can fall prey to the mathematical property that

                   a^b == (a+1)^(b+1)

               one-third of the time.  So don't do that.

       stat FILEHANDLE
       stat EXPR
       stat    Returns a 13-element list giving the status info for a file,
               either the file opened via FILEHANDLE, or named by EXPR.  If
               EXPR is omitted, it stats $_.  Returns a null list if the stat
               fails.  Typically used as follows:

                   ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
                      $atime,$mtime,$ctime,$blksize,$blocks)
                          = stat($filename);

               Not all fields are supported on all filesystem types.  Here are
               the meaning of the fields:

                 0 dev      device number of filesystem
                 1 ino      inode number
                 2 mode     file mode  (type and permissions)
                 3 nlink    number of (hard) links to the file
                 4 uid      numeric user ID of file's owner
                 5 gid      numeric group ID of file's owner
                 6 rdev     the device identifier (special files only)
                 7 size     total size of file, in bytes
                 8 atime    last access time in seconds since the epoch
                 9 mtime    last modify time in seconds since the epoch
                10 ctime    inode change time in seconds since the epoch (*)
                11 blksize  preferred block size for file system I/O
                12 blocks   actual number of blocks allocated

               (The epoch was at 00:00 January 1, 1970 GMT.)

               (*) The ctime field is non-portable, in particular you cannot
               expect it to be a "creation time", see "Files and Filesystems"
               in perlport for details.

               If stat is passed the special filehandle consisting of an
               underline, no stat is done, but the current contents of the
               stat structure from the last stat or filetest are returned.
               Example:

                   if (-x $file && (($d) = stat(_)) && $d < 0) {
                       print "$file is executable NFS file\n";
                   }

               (This works on machines only for which the device number is
               negative under NFS.)

               Because the mode contains both the file type and its
               permissions, you should mask off the file type portion and
               (s)printf using a "%o" if you want to see the real permissions.

                   $mode = (stat($filename))[2];
                   printf "Permissions are %04o\n", $mode & 07777;

               In scalar context, "stat" returns a boolean value indicating
               success or failure, and, if successful, sets the information
               associated with the special filehandle "_".

               The File::stat module provides a convenient, by-name access
               mechanism:

                   use File::stat;
                   $sb = stat($filename);
                   printf "File is %s, size is %s, perm %04o, mtime %s\n",
                       $filename, $sb->size, $sb->mode & 07777,
                       scalar localtime $sb->mtime;

               You can import symbolic mode constants ("S_IF*") and functions
               ("S_IS*") from the Fcntl module:

                   use Fcntl ':mode';

                   $mode = (stat($filename))[2];

                   $user_rwx      = ($mode & S_IRWXU) >> 6;
                   $group_read    = ($mode & S_IRGRP) >> 3;
                   $other_execute =  $mode & S_IXOTH;

                   printf "Permissions are %04o\n", S_IMODE($mode), "\n";

                   $is_setuid     =  $mode & S_ISUID;
                   $is_setgid     =  S_ISDIR($mode);

               You could write the last two using the "-u" and "-d" operators.
               The commonly available S_IF* constants are

                   # Permissions: read, write, execute, for user, group, others.

                   S_IRWXU S_IRUSR S_IWUSR S_IXUSR
                   S_IRWXG S_IRGRP S_IWGRP S_IXGRP
                   S_IRWXO S_IROTH S_IWOTH S_IXOTH

                   # Setuid/Setgid/Stickiness/SaveText.
                   # Note that the exact meaning of these is system dependent.

                   S_ISUID S_ISGID S_ISVTX S_ISTXT

                   # File types.  Not necessarily all are available on your system.

                   S_IFREG S_IFDIR S_IFLNK S_IFBLK S_ISCHR S_IFIFO S_IFSOCK S_IFWHT S_ENFMT

                   # The following are compatibility aliases for S_IRUSR, S_IWUSR, S_IXUSR.

                   S_IREAD S_IWRITE S_IEXEC

               and the S_IF* functions are

                   S_IMODE($mode)      the part of $mode containing the permission bits
                                       and the setuid/setgid/sticky bits

                   S_IFMT($mode)       the part of $mode containing the file type
                                       which can be bit-anded with e.g. S_IFREG
                                       or with the following functions

                   # The operators -f, -d, -l, -b, -c, -p, and -s.

                   S_ISREG($mode) S_ISDIR($mode) S_ISLNK($mode)
                   S_ISBLK($mode) S_ISCHR($mode) S_ISFIFO($mode) S_ISSOCK($mode)

                   # No direct -X operator counterpart, but for the first one
                   # the -g operator is often equivalent.  The ENFMT stands for
                   # record flocking enforcement, a platform-dependent feature.

                   S_ISENFMT($mode) S_ISWHT($mode)

               See your native chmod(2) and stat(2) documentation for more
               details about the S_* constants.

               To get status info for a symbolic link instead of the target
               file behind the link, use the "lstat" function, see "stat".

       study SCALAR
       study   Takes extra time to study SCALAR ($_ if unspecified) in
               anticipation of doing many pattern matches on the string before
               it is next modified.  This may or may not save time, depending
               on the nature and number of patterns you are searching on, and
               on the distribution of character frequencies in the string to
               be searched--you probably want to compare run times with and
               without it to see which runs faster.  Those loops which scan
               for many short constant strings (including the constant parts
               of more complex patterns) will benefit most.  You may have only
               one "study" active at a time--if you study a different scalar
               the first is "unstudied".  (The way "study" works is this: a
               linked list of every character in the string to be searched is
               made, so we know, for example, where all the 'k' characters
               are.  From each search string, the rarest character is
               selected, based on some static frequency tables constructed
               from some C programs and English text.  Only those places that
               contain this "rarest" character are examined.)

               For example, here is a loop that inserts index producing
               entries before any line containing a certain pattern:

                   while (<>) {
                       study;
                       print ".IX foo\n"       if /\bfoo\b/;
                       print ".IX bar\n"       if /\bbar\b/;
                       print ".IX blurfl\n"    if /\bblurfl\b/;
                       # ...
                       print;
                   }

               In searching for "/\bfoo\b/", only those locations in $_ that
               contain "f" will be looked at, because "f" is rarer than "o".
               In general, this is a big win except in pathological cases.
               The only question is whether it saves you more time than it
               took to build the linked list in the first place.

               Note that if you have to look for strings that you don't know
               till runtime, you can build an entire loop as a string and
               "eval" that to avoid recompiling all your patterns all the
               time.  Together with undefining $/ to input entire files as one
               record, this can be very fast, often faster than specialized
               programs like fgrep(1).  The following scans a list of files
               (@files) for a list of words (@words), and prints out the names
               of those files that contain a match:

                   $search = 'while (<>) { study;';
                   foreach $word (@words) {
                       $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
                   }
                   $search .= "}";
                   @ARGV = @files;
                   undef $/;
                   eval $search;               # this screams
                   $/ = "\n";          # put back to normal input delimiter
                   foreach $file (sort keys(%seen)) {
                       print $file, "\n";
                   }

       sub NAME BLOCK
       sub NAME (PROTO) BLOCK
       sub NAME : ATTRS BLOCK
       sub NAME (PROTO) : ATTRS BLOCK
               This is subroutine definition, not a real function per se.
               Without a BLOCK it's just a forward declaration.  Without a
               NAME, it's an anonymous function declaration, and does actually
               return a value: the CODE ref of the closure you just created.

               See perlsub and perlref for details about subroutines and
               references, and attributes and Attribute::Handlers for more
               information about attributes.

       substr EXPR,OFFSET,LENGTH,REPLACEMENT
       substr EXPR,OFFSET,LENGTH
       substr EXPR,OFFSET
               Extracts a substring out of EXPR and returns it.  First
               character is at offset 0, or whatever you've set $[ to (but
               don't do that).  If OFFSET is negative (or more precisely, less
               than $[), starts that far from the end of the string.  If
               LENGTH is omitted, returns everything to the end of the string.
               If LENGTH is negative, leaves that many characters off the end
               of the string.

               You can use the substr() function as an lvalue, in which case
               EXPR must itself be an lvalue.  If you assign something shorter
               than LENGTH, the string will shrink, and if you assign
               something longer than LENGTH, the string will grow to
               accommodate it.  To keep the string the same length you may
               need to pad or chop your value using "sprintf".

               If OFFSET and LENGTH specify a substring that is partly outside
               the string, only the part within the string is returned.  If
               the substring is beyond either end of the string, substr()
               returns the undefined value and produces a warning.  When used
               as an lvalue, specifying a substring that is entirely outside
               the string is a fatal error.  Here's an example showing the
               behavior for boundary cases:

                   my $name = 'fred';
                   substr($name, 4) = 'dy';            # $name is now 'freddy'
                   my $null = substr $name, 6, 2;      # returns '' (no warning)
                   my $oops = substr $name, 7;         # returns undef, with warning
                   substr($name, 7) = 'gap';           # fatal error

               An alternative to using substr() as an lvalue is to specify the
               replacement string as the 4th argument.  This allows you to
               replace parts of the EXPR and return what was there before in
               one operation, just as you can with splice().

               If the lvalue returned by substr is used after the EXPR is
               changed in any way, the behaviour may not be as expected and is
               subject to change.  This caveat includes code such as
               "print(substr($foo,$a,$b)=$bar)" or
               "(substr($foo,$a,$b)=$bar)=$fud" (where $foo is changed via the
               substring assignment, and then the substr is used again), or
               where a substr() is aliased via a "foreach" loop or passed as a
               parameter or a reference to it is taken and then the alias,
               parameter, or deref'd reference either is used after the
               original EXPR has been changed or is assigned to and then used
               a second time.

       symlink OLDFILE,NEWFILE
               Creates a new filename symbolically linked to the old filename.
               Returns 1 for success, 0 otherwise.  On systems that don't
               support symbolic links, produces a fatal error at run time.  To
               check for that, use eval:

                   $symlink_exists = eval { symlink("",""); 1 };

       syscall NUMBER, LIST
               Calls the system call specified as the first element of the
               list, passing the remaining elements as arguments to the system
               call.  If unimplemented, produces a fatal error.  The arguments
               are interpreted as follows: if a given argument is numeric, the
               argument is passed as an int.  If not, the pointer to the
               string value is passed.  You are responsible to make sure a
               string is pre-extended long enough to receive any result that
               might be written into a string.  You can't use a string literal
               (or other read-only string) as an argument to "syscall" because
               Perl has to assume that any string pointer might be written
               through.  If your integer arguments are not literals and have
               never been interpreted in a numeric context, you may need to
               add 0 to them to force them to look like numbers.  This
               emulates the "syswrite" function (or vice versa):

                   require 'syscall.ph';               # may need to run h2ph
                   $s = "hi there\n";
                   syscall(&SYS_write, fileno(STDOUT), $s, length $s);

               Note that Perl supports passing of up to only 14 arguments to
               your system call, which in practice should usually suffice.

               Syscall returns whatever value returned by the system call it
               calls.  If the system call fails, "syscall" returns "-1" and
               sets $! (errno).  Note that some system calls can legitimately
               return "-1".  The proper way to handle such calls is to assign
               "$!=0;" before the call and check the value of $! if syscall
               returns "-1".

               There's a problem with "syscall(&SYS_pipe)": it returns the
               file number of the read end of the pipe it creates.  There is
               no way to retrieve the file number of the other end.  You can
               avoid this problem by using "pipe" instead.

       sysopen FILEHANDLE,FILENAME,MODE
       sysopen FILEHANDLE,FILENAME,MODE,PERMS
               Opens the file whose filename is given by FILENAME, and
               associates it with FILEHANDLE.  If FILEHANDLE is an expression,
               its value is used as the name of the real filehandle wanted.
               This function calls the underlying operating system's "open"
               function with the parameters FILENAME, MODE, PERMS.

               The possible values and flag bits of the MODE parameter are
               system-dependent; they are available via the standard module
               "Fcntl".  See the documentation of your operating system's
               "open" to see which values and flag bits are available.  You
               may combine several flags using the "|"-operator.

               Some of the most common values are "O_RDONLY" for opening the
               file in read-only mode, "O_WRONLY" for opening the file in
               write-only mode, and "O_RDWR" for opening the file in read-
               write mode, and.

               For historical reasons, some values work on almost every system
               supported by perl: zero means read-only, one means write-only,
               and two means read/write.  We know that these values do not
               work under OS/390 & VM/ESA Unix and on the Macintosh; you
               probably don't want to use them in new code.

               If the file named by FILENAME does not exist and the "open"
               call creates it (typically because MODE includes the "O_CREAT"
               flag), then the value of PERMS specifies the permissions of the
               newly created file.  If you omit the PERMS argument to
               "sysopen", Perl uses the octal value 0666.  These permission
               values need to be in octal, and are modified by your process's
               current "umask".

               In many systems the "O_EXCL" flag is available for opening
               files in exclusive mode.  This is not locking: exclusiveness
               means here that if the file already exists, sysopen() fails.
               The "O_EXCL" wins "O_TRUNC".

               Sometimes you may want to truncate an already-existing file:
               "O_TRUNC".

               You should seldom if ever use 0644 as argument to "sysopen",
               because that takes away the user's option to have a more
               permissive umask.  Better to omit it.  See the perlfunc(1)
               entry on "umask" for more on this.

               Note that "sysopen" depends on the fdopen() C library function.
               On many UNIX systems, fdopen() is known to fail when file
               descriptors exceed a certain value, typically 255. If you need
               more file descriptors than that, consider rebuilding Perl to
               use the "sfio" library, or perhaps using the POSIX::open()
               function.

               See perlopentut for a kinder, gentler explanation of opening
               files.

       sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
       sysread FILEHANDLE,SCALAR,LENGTH
               Attempts to read LENGTH bytes of data into variable SCALAR from
               the specified FILEHANDLE, using the system call read(2).  It
               bypasses buffered IO, so mixing this with other kinds of reads,
               "print", "write", "seek", "tell", or "eof" can cause confusion
               because the perlio or stdio layers usually buffers data.
               Returns the number of bytes actually read, 0 at end of file, or
               undef if there was an error (in the latter case $! is also
               set).  SCALAR will be grown or shrunk so that the last byte
               actually read is the last byte of the scalar after the read.

               An OFFSET may be specified to place the read data at some place
               in the string other than the beginning.  A negative OFFSET
               specifies placement at that many characters counting backwards
               from the end of the string.  A positive OFFSET greater than the
               length of SCALAR results in the string being padded to the
               required size with "\0" bytes before the result of the read is
               appended.

               There is no syseof() function, which is ok, since eof() doesn't
               work very well on device files (like ttys) anyway.  Use
               sysread() and check for a return value for 0 to decide whether
               you're done.

               Note that if the filehandle has been marked as ":utf8" Unicode
               characters are read instead of bytes (the LENGTH, OFFSET, and
               the return value of sysread() are in Unicode characters).  The
               ":encoding(...)" layer implicitly introduces the ":utf8" layer.
               See "binmode", "open", and the "open" pragma, open.

       sysseek FILEHANDLE,POSITION,WHENCE
               Sets FILEHANDLE's system position in bytes using the system
               call lseek(2).  FILEHANDLE may be an expression whose value
               gives the name of the filehandle.  The values for WHENCE are 0
               to set the new position to POSITION, 1 to set the it to the
               current position plus POSITION, and 2 to set it to EOF plus
               POSITION (typically negative).

               Note the in bytes: even if the filehandle has been set to
               operate on characters (for example by using the ":utf8" I/O
               layer), tell() will return byte offsets, not character offsets
               (because implementing that would render sysseek() very slow).

               sysseek() bypasses normal buffered IO, so mixing this with
               reads (other than "sysread", for example &gt;&lt or read())
               "print", "write", "seek", "tell", or "eof" may cause confusion.

               For WHENCE, you may also use the constants "SEEK_SET",
               "SEEK_CUR", and "SEEK_END" (start of the file, current
               position, end of the file) from the Fcntl module.  Use of the
               constants is also more portable than relying on 0, 1, and 2.
               For example to define a "systell" function:

                       use Fcntl 'SEEK_CUR';
                       sub systell { sysseek($_[0], 0, SEEK_CUR) }

               Returns the new position, or the undefined value on failure.  A
               position of zero is returned as the string "0 but true"; thus
               "sysseek" returns true on success and false on failure, yet you
               can still easily determine the new position.

       system LIST
       system PROGRAM LIST
               Does exactly the same thing as "exec LIST", except that a fork
               is done first, and the parent process waits for the child
               process to complete.  Note that argument processing varies
               depending on the number of arguments.  If there is more than
               one argument in LIST, or if LIST is an array with more than one
               value, starts the program given by the first element of the
               list with arguments given by the rest of the list.  If there is
               only one scalar argument, the argument is checked for shell
               metacharacters, and if there are any, the entire argument is
               passed to the system's command shell for parsing (this is
               "/bin/sh -c" on Unix platforms, but varies on other platforms).
               If there are no shell metacharacters in the argument, it is
               split into words and passed directly to "execvp", which is more
               efficient.

               Beginning with v5.6.0, Perl will attempt to flush all files
               opened for output before any operation that may do a fork, but
               this may not be supported on some platforms (see perlport).  To
               be safe, you may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any open handles.

               The return value is the exit status of the program as returned
               by the "wait" call.  To get the actual exit value shift right
               by eight (see below).  See also "exec".  This is not what you
               want to use to capture the output from a command, for that you
               should use merely backticks or "qx//", as described in
               "`STRING`" in perlop.  Return value of -1 indicates a failure
               to start the program (inspect $! for the reason).

               Like "exec", "system" allows you to lie to a program about its
               name if you use the "system PROGRAM LIST" syntax.  Again, see
               "exec".

               Because "system" and backticks block "SIGINT" and "SIGQUIT",
               killing the program they're running doesn't actually interrupt
               your program.

                   @args = ("command", "arg1", "arg2");
                   system(@args) == 0
                        or die "system @args failed: $?"

               You can check all the failure possibilities by inspecting $?
               like this:

                   if ($? == -1) {
                       print "failed to execute: $!\n";
                   }
                   elsif ($? & 127) {
                       printf "child died with signal %d, %s coredump\n",
                           ($? & 127),  ($? & 128) ? 'with' : 'without';
                   }
                   else {
                       printf "child exited with value %d\n", $? >> 8;
                   }

               or more portably by using the W*() calls of the POSIX
               extension; see perlport for more information.

               When the arguments get executed via the system shell, results
               and return codes will be subject to its quirks and
               capabilities.  See "`STRING`" in perlop and "exec" for details.

       syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
       syswrite FILEHANDLE,SCALAR,LENGTH
       syswrite FILEHANDLE,SCALAR
               Attempts to write LENGTH bytes of data from variable SCALAR to
               the specified FILEHANDLE, using the system call write(2).  If
               LENGTH is not specified, writes whole SCALAR.  It bypasses
               buffered IO, so mixing this with reads (other than sysread()),
               "print", "write", "seek", "tell", or "eof" may cause confusion
               because the perlio and stdio layers usually buffers data.
               Returns the number of bytes actually written, or "undef" if
               there was an error (in this case the errno variable $! is also
               set).  If the LENGTH is greater than the available data in the
               SCALAR after the OFFSET, only as much data as is available will
               be written.

               An OFFSET may be specified to write the data from some part of
               the string other than the beginning.  A negative OFFSET
               specifies writing that many characters counting backwards from
               the end of the string.  In the case the SCALAR is empty you can
               use OFFSET but only zero offset.

               Note that if the filehandle has been marked as ":utf8", Unicode
               characters are written instead of bytes (the LENGTH, OFFSET,
               and the return value of syswrite() are in UTF-8 encoded Unicode
               characters).  The ":encoding(...)" layer implicitly introduces
               the ":utf8" layer.  See "binmode", "open", and the "open"
               pragma, open.

       tell FILEHANDLE
       tell    Returns the current position in bytes for FILEHANDLE, or -1 on
               error.  FILEHANDLE may be an expression whose value gives the
               name of the actual filehandle.  If FILEHANDLE is omitted,
               assumes the file last read.

               Note the in bytes: even if the filehandle has been set to
               operate on characters (for example by using the ":utf8" open
               layer), tell() will return byte offsets, not character offsets
               (because that would render seek() and tell() rather slow).

               The return value of tell() for the standard streams like the
               STDIN depends on the operating system: it may return -1 or
               something else.  tell() on pipes, fifos, and sockets usually
               returns -1.

               There is no "systell" function.  Use "sysseek(FH, 0, 1)" for
               that.

               Do not use tell() on a filehandle that has been opened using
               sysopen(), use sysseek() for that as described above.  Why?
               Because sysopen() creates unbuffered, "raw", filehandles, while
               open() creates buffered filehandles.  sysseek() make sense only
               on the first kind, tell() only makes sense on the second kind.

       telldir DIRHANDLE
               Returns the current position of the "readdir" routines on
               DIRHANDLE.  Value may be given to "seekdir" to access a
               particular location in a directory.  Has the same caveats about
               possible directory compaction as the corresponding system
               library routine.

       tie VARIABLE,CLASSNAME,LIST
               This function binds a variable to a package class that will
               provide the implementation for the variable.  VARIABLE is the
               name of the variable to be enchanted.  CLASSNAME is the name of
               a class implementing objects of correct type.  Any additional
               arguments are passed to the "new" method of the class (meaning
               "TIESCALAR", "TIEHANDLE", "TIEARRAY", or "TIEHASH").  Typically
               these are arguments such as might be passed to the "dbm_open()"
               function of C.  The object returned by the "new" method is also
               returned by the "tie" function, which would be useful if you
               want to access other methods in CLASSNAME.

               Note that functions such as "keys" and "values" may return huge
               lists when used on large objects, like DBM files.  You may
               prefer to use the "each" function to iterate over such.
               Example:

                   # print out history file offsets
                   use NDBM_File;
                   tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
                   while (($key,$val) = each %HIST) {
                       print $key, ' = ', unpack('L',$val), "\n";
                   }
                   untie(%HIST);

               A class implementing a hash should have the following methods:

                   TIEHASH classname, LIST
                   FETCH this, key
                   STORE this, key, value
                   DELETE this, key
                   CLEAR this
                   EXISTS this, key
                   FIRSTKEY this
                   NEXTKEY this, lastkey
                   DESTROY this
                   UNTIE this

               A class implementing an ordinary array should have the
               following methods:

                   TIEARRAY classname, LIST
                   FETCH this, key
                   STORE this, key, value
                   FETCHSIZE this
                   STORESIZE this, count
                   CLEAR this
                   PUSH this, LIST
                   POP this
                   SHIFT this
                   UNSHIFT this, LIST
                   SPLICE this, offset, length, LIST
                   EXTEND this, count
                   DESTROY this
                   UNTIE this

               A class implementing a file handle should have the following
               methods:

                   TIEHANDLE classname, LIST
                   READ this, scalar, length, offset
                   READLINE this
                   GETC this
                   WRITE this, scalar, length, offset
                   PRINT this, LIST
                   PRINTF this, format, LIST
                   BINMODE this
                   EOF this
                   FILENO this
                   SEEK this, position, whence
                   TELL this
                   OPEN this, mode, LIST
                   CLOSE this
                   DESTROY this
                   UNTIE this

               A class implementing a scalar should have the following
               methods:

                   TIESCALAR classname, LIST
                   FETCH this,
                   STORE this, value
                   DESTROY this
                   UNTIE this

               Not all methods indicated above need be implemented.  See
               perltie, Tie::Hash, Tie::Array, Tie::Scalar, and Tie::Handle.

               Unlike "dbmopen", the "tie" function will not use or require a
               module for you--you need to do that explicitly yourself.  See
               DB_File or the Config module for interesting "tie"
               implementations.

               For further details see perltie, "tied VARIABLE".

       tied VARIABLE
               Returns a reference to the object underlying VARIABLE (the same
               value that was originally returned by the "tie" call that bound
               the variable to a package.)  Returns the undefined value if
               VARIABLE isn't tied to a package.

       time    Returns the number of non-leap seconds since whatever time the
               system considers to be the epoch (that's 00:00:00, January 1,
               1904 for Mac OS, and 00:00:00 UTC, January 1, 1970 for most
               other systems).  Suitable for feeding to "gmtime" and
               "localtime".

               For measuring time in better granularity than one second, you
               may use either the Time::HiRes module (from CPAN, and starting
               from Perl 5.8 part of the standard distribution), or if you
               have gettimeofday(2), you may be able to use the "syscall"
               interface of Perl.  See perlfaq8 for details.

       times   Returns a four-element list giving the user and system times,
               in seconds, for this process and the children of this process.

                   ($user,$system,$cuser,$csystem) = times;

               In scalar context, "times" returns $user.

       tr///   The transliteration operator.  Same as "y///".  See perlop.

       truncate FILEHANDLE,LENGTH
       truncate EXPR,LENGTH
               Truncates the file opened on FILEHANDLE, or named by EXPR, to
               the specified length.  Produces a fatal error if truncate isn't
               implemented on your system.  Returns true if successful, the
               undefined value otherwise.

               The behavior is undefined if LENGTH is greater than the length
               of the file.

       uc EXPR
       uc      Returns an uppercased version of EXPR.  This is the internal
               function implementing the "\U" escape in double-quoted strings.
               Respects current LC_CTYPE locale if "use locale" in force.  See
               perllocale and perlunicode for more details about locale and
               Unicode support.  It does not attempt to do titlecase mapping
               on initial letters.  See "ucfirst" for that.

               If EXPR is omitted, uses $_.

       ucfirst EXPR
       ucfirst Returns the value of EXPR with the first character in uppercase
               (titlecase in Unicode).  This is the internal function
               implementing the "\u" escape in double-quoted strings.
               Respects current LC_CTYPE locale if "use locale" in force.  See
               perllocale and perlunicode for more details about locale and
               Unicode support.

               If EXPR is omitted, uses $_.

       umask EXPR
       umask   Sets the umask for the process to EXPR and returns the previous
               value.  If EXPR is omitted, merely returns the current umask.

               The Unix permission "rwxr-x---" is represented as three sets of
               three bits, or three octal digits: 0750 (the leading 0
               indicates octal and isn't one of the digits).  The "umask"
               value is such a number representing disabled permissions bits.
               The permission (or "mode") values you pass "mkdir" or "sysopen"
               are modified by your umask, so even if you tell "sysopen" to
               create a file with permissions 0777, if your umask is 0022 then
               the file will actually be created with permissions 0755.  If
               your "umask" were 0027 (group can't write; others can't read,
               write, or execute), then passing "sysopen" 0666 would create a
               file with mode 0640 ("0666 &~ 027" is 0640).

               Here's some advice: supply a creation mode of 0666 for regular
               files (in "sysopen") and one of 0777 for directories (in
               "mkdir") and executable files.  This gives users the freedom of
               choice: if they want protected files, they might choose process
               umasks of 022, 027, or even the particularly antisocial mask of
               077.  Programs should rarely if ever make policy decisions
               better left to the user.  The exception to this is when writing
               files that should be kept private: mail files, web browser
               cookies, .rhosts files, and so on.

               If umask(2) is not implemented on your system and you are
               trying to restrict access for yourself (i.e., (EXPR & 0700) >
               0), produces a fatal error at run time.  If umask(2) is not
               implemented and you are not trying to restrict access for
               yourself, returns "undef".

               Remember that a umask is a number, usually given in octal; it
               is not a string of octal digits.  See also "oct", if all you
               have is a string.

       undef EXPR
       undef   Undefines the value of EXPR, which must be an lvalue.  Use only
               on a scalar value, an array (using "@"), a hash (using "%"), a
               subroutine (using "&"), or a typeglob (using "*").  (Saying
               "undef $hash{$key}" will probably not do what you expect on
               most predefined variables or DBM list values, so don't do that;
               see delete.)  Always returns the undefined value.  You can omit
               the EXPR, in which case nothing is undefined, but you still get
               an undefined value that you could, for instance, return from a
               subroutine, assign to a variable or pass as a parameter.
               Examples:

                   undef $foo;
                   undef $bar{'blurfl'};      # Compare to: delete $bar{'blurfl'};
                   undef @ary;
                   undef %hash;
                   undef &mysub;
                   undef *xyz;       # destroys $xyz, @xyz, %xyz, &xyz, etc.
                   return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
                   select undef, undef, undef, 0.25;
                   ($a, $b, undef, $c) = &foo;       # Ignore third value returned

               Note that this is a unary operator, not a list operator.

       unlink LIST
       unlink  Deletes a list of files.  Returns the number of files
               successfully deleted.

                   $cnt = unlink 'a', 'b', 'c';
                   unlink @goners;
                   unlink <*.bak>;

               Note: "unlink" will not delete directories unless you are
               superuser and the -U flag is supplied to Perl.  Even if these
               conditions are met, be warned that unlinking a directory can
               inflict damage on your filesystem.  Use "rmdir" instead.

               If LIST is omitted, uses $_.

       unpack TEMPLATE,EXPR
               "unpack" does the reverse of "pack": it takes a string and
               expands it out into a list of values.  (In scalar context, it
               returns merely the first value produced.)

               The string is broken into chunks described by the TEMPLATE.
               Each chunk is converted separately to a value.  Typically,
               either the string is a result of "pack", or the bytes of the
               string represent a C structure of some kind.

               The TEMPLATE has the same format as in the "pack" function.
               Here's a subroutine that does substring:

                   sub substr {
                       my($what,$where,$howmuch) = @_;
                       unpack("x$where a$howmuch", $what);
                   }

               and then there's

                   sub ordinal { unpack("c",$_[0]); } # same as ord()

               In addition to fields allowed in pack(), you may prefix a field
               with a %<number> to indicate that you want a <number>-bit
               checksum of the items instead of the items themselves.  Default
               is a 16-bit checksum.  Checksum is calculated by summing
               numeric values of expanded values (for string fields the sum of
               "ord($char)" is taken, for bit fields the sum of zeroes and
               ones).

               For example, the following computes the same number as the
               System V sum program:

                   $checksum = do {
                       local $/;  # slurp!
                       unpack("%32C*",<>) % 65535;
                   };

               The following efficiently counts the number of set bits in a
               bit vector:

                   $setbits = unpack("%32b*", $selectmask);

               The "p" and "P" formats should be used with care.  Since Perl
               has no way of checking whether the value passed to "unpack()"
               corresponds to a valid memory location, passing a pointer value
               that's not known to be valid is likely to have disastrous
               consequences.

               If there are more pack codes or if the repeat count of a field
               or a group is larger than what the remainder of the input
               string allows, the result is not well defined: in some cases,
               the repeat count is decreased, or "unpack()" will produce null
               strings or zeroes, or terminate with an error. If the input
               string is longer than one described by the TEMPLATE, the rest
               is ignored.

               See "pack" for more examples and notes.

       untie VARIABLE
               Breaks the binding between a variable and a package.  (See
               "tie".)  Has no effect if the variable is not tied.

       unshift ARRAY,LIST
               Does the opposite of a "shift".  Or the opposite of a "push",
               depending on how you look at it.  Prepends list to the front of
               the array, and returns the new number of elements in the array.

                   unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;

               Note the LIST is prepended whole, not one element at a time, so
               the prepended elements stay in the same order.  Use "reverse"
               to do the reverse.

       use Module VERSION LIST
       use Module VERSION
       use Module LIST
       use Module
       use VERSION
               Imports some semantics into the current package from the named
               module, generally by aliasing certain subroutine or variable
               names into your package.  It is exactly equivalent to

                   BEGIN { require Module; import Module LIST; }

               except that Module must be a bareword.

               VERSION may be either a numeric argument such as 5.006, which
               will be compared to $], or a literal of the form v5.6.1, which
               will be compared to $^V (aka $PERL_VERSION.  A fatal error is
               produced if VERSION is greater than the version of the current
               Perl interpreter; Perl will not attempt to parse the rest of
               the file.  Compare with "require", which can do a similar check
               at run time.

               Specifying VERSION as a literal of the form v5.6.1 should
               generally be avoided, because it leads to misleading error
               messages under earlier versions of Perl which do not support
               this syntax.  The equivalent numeric version should be used
               instead.

                   use v5.6.1;         # compile time version check
                   use 5.6.1;          # ditto
                   use 5.006_001;      # ditto; preferred for backwards compatibility

               This is often useful if you need to check the current Perl
               version before "use"ing library modules that have changed in
               incompatible ways from older versions of Perl.  (We try not to
               do this more than we have to.)

               The "BEGIN" forces the "require" and "import" to happen at
               compile time.  The "require" makes sure the module is loaded
               into memory if it hasn't been yet.  The "import" is not a
               builtin--it's just an ordinary static method call into the
               "Module" package to tell the module to import the list of
               features back into the current package.  The module can
               implement its "import" method any way it likes, though most
               modules just choose to derive their "import" method via
               inheritance from the "Exporter" class that is defined in the
               "Exporter" module.  See Exporter.  If no "import" method can be
               found then the call is skipped.

               If you do not want to call the package's "import" method (for
               instance, to stop your namespace from being altered),
               explicitly supply the empty list:

                   use Module ();

               That is exactly equivalent to

                   BEGIN { require Module }

               If the VERSION argument is present between Module and LIST,
               then the "use" will call the VERSION method in class Module
               with the given version as an argument.  The default VERSION
               method, inherited from the UNIVERSAL class, croaks if the given
               version is larger than the value of the variable
               $Module::VERSION.

               Again, there is a distinction between omitting LIST ("import"
               called with no arguments) and an explicit empty LIST "()"
               ("import" not called).  Note that there is no comma after
               VERSION!

               Because this is a wide-open interface, pragmas (compiler
               directives) are also implemented this way.  Currently
               implemented pragmas are:

                   use constant;
                   use diagnostics;
                   use integer;
                   use sigtrap  qw(SEGV BUS);
                   use strict   qw(subs vars refs);
                   use subs     qw(afunc blurfl);
                   use warnings qw(all);
                   use sort     qw(stable _quicksort _mergesort);

               Some of these pseudo-modules import semantics into the current
               block scope (like "strict" or "integer", unlike ordinary
               modules, which import symbols into the current package (which
               are effective through the end of the file).

               There's a corresponding "no" command that unimports meanings
               imported by "use", i.e., it calls "unimport Module LIST"
               instead of "import".

                   no integer;
                   no strict 'refs';
                   no warnings;

               See perlmodlib for a list of standard modules and pragmas.  See
               perlrun for the "-M" and "-m" command-line options to perl that
               give "use" functionality from the command-line.

       utime LIST
               Changes the access and modification times on each file of a
               list of files.  The first two elements of the list must be the
               NUMERICAL access and modification times, in that order.
               Returns the number of files successfully changed.  The inode
               change time of each file is set to the current time.  For
               example, this code has the same effect as the Unix touch(1)
               command when the files already exist.

                   #!/usr/bin/perl
                   $now = time;
                   utime $now, $now, @ARGV;

               Note:  Under NFS, touch(1) uses the time of the NFS server, not
               the time of the local machine.  If there is a time
               synchronization problem, the NFS server and local machine will
               have different times.

               Since perl 5.7.2, if the first two elements of the list are
               "undef", then the utime(2) function in the C library will be
               called with a null second argument. On most systems, this will
               set the file's access and modification times to the current
               time (i.e. equivalent to the example above.)

                   utime undef, undef, @ARGV;

       values HASH
               Returns a list consisting of all the values of the named hash.
               (In a scalar context, returns the number of values.)

               The values are returned in an apparently random order.  The
               actual random order is subject to change in future versions of
               perl, but it is guaranteed to be the same order as either the
               "keys" or "each" function would produce on the same
               (unmodified) hash.  Since Perl 5.8.1 the ordering is different
               even between different runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in perlsec).

               As a side effect, calling values() resets the HASH's internal
               iterator, see "each".

               Note that the values are not copied, which means modifying them
               will modify the contents of the hash:

                   for (values %hash)      { s/foo/bar/g }   # modifies %hash values
                   for (@hash{keys %hash}) { s/foo/bar/g }   # same

               See also "keys", "each", and "sort".

       vec EXPR,OFFSET,BITS
               Treats the string in EXPR as a bit vector made up of elements
               of width BITS, and returns the value of the element specified
               by OFFSET as an unsigned integer.  BITS therefore specifies the
               number of bits that are reserved for each element in the bit
               vector.  This must be a power of two from 1 to 32 (or 64, if
               your platform supports that).

               If BITS is 8, "elements" coincide with bytes of the input
               string.

               If BITS is 16 or more, bytes of the input string are grouped
               into chunks of size BITS/8, and each group is converted to a
               number as with pack()/unpack() with big-endian formats "n"/"N"
               (and analogously for BITS==64).  See "pack" for details.

               If bits is 4 or less, the string is broken into bytes, then the
               bits of each byte are broken into 8/BITS groups.  Bits of a
               byte are numbered in a little-endian-ish way, as in 0x01, 0x02,
               0x04, 0x08, 0x10, 0x20, 0x40, 0x80.  For example, breaking the
               single input byte "chr(0x36)" into two groups gives a list
               "(0x6, 0x3)"; breaking it into 4 groups gives "(0x2, 0x1, 0x3,
               0x0)".

               "vec" may also be assigned to, in which case parentheses are
               needed to give the expression the correct precedence as in

                   vec($image, $max_x * $x + $y, 8) = 3;

               If the selected element is outside the string, the value 0 is
               returned.  If an element off the end of the string is written
               to, Perl will first extend the string with sufficiently many
               zero bytes.   It is an error to try to write off the beginning
               of the string (i.e. negative OFFSET).

               The string should not contain any character with the value >
               255 (which can only happen if you're using UTF-8 encoding).  If
               it does, it will be treated as something which is not UTF-8
               encoded.  When the "vec" was assigned to, other parts of your
               program will also no longer consider the string to be UTF-8
               encoded.  In other words, if you do have such characters in
               your string, vec() will operate on the actual byte string, and
               not the conceptual character string.

               Strings created with "vec" can also be manipulated with the
               logical operators "|", "&", "^", and "~".  These operators will
               assume a bit vector operation is desired when both operands are
               strings.  See "Bitwise String Operators" in perlop.

               The following code will build up an ASCII string saying
               'PerlPerlPerl'.  The comments show the string after each step.
               Note that this code works in the same way on big-endian or
               little-endian machines.

                   my $foo = '';
                   vec($foo,  0, 32) = 0x5065726C;     # 'Perl'

                   # $foo eq "Perl" eq "\x50\x65\x72\x6C", 32 bits
                   print vec($foo, 0, 8);              # prints 80 == 0x50 == ord('P')

                   vec($foo,  2, 16) = 0x5065;         # 'PerlPe'
                   vec($foo,  3, 16) = 0x726C;         # 'PerlPerl'
                   vec($foo,  8,  8) = 0x50;           # 'PerlPerlP'
                   vec($foo,  9,  8) = 0x65;           # 'PerlPerlPe'
                   vec($foo, 20,  4) = 2;              # 'PerlPerlPe'   . "\x02"
                   vec($foo, 21,  4) = 7;              # 'PerlPerlPer'
                                                       # 'r' is "\x72"
                   vec($foo, 45,  2) = 3;              # 'PerlPerlPer'  . "\x0c"
                   vec($foo, 93,  1) = 1;              # 'PerlPerlPer'  . "\x2c"
                   vec($foo, 94,  1) = 1;              # 'PerlPerlPerl'
                                                       # 'l' is "\x6c"

               To transform a bit vector into a string or list of 0's and 1's,
               use these:

                   $bits = unpack("b*", $vector);
                   @bits = split(//, unpack("b*", $vector));

               If you know the exact length in bits, it can be used in place
               of the "*".

               Here is an example to illustrate how the bits actually fall in
               place:

                   #!/usr/bin/perl -wl

                   print <<'EOT';
                                                     0         1         2         3
                                      unpack("V",$_) 01234567890123456789012345678901
                   ------------------------------------------------------------------
                   EOT

                   for $w (0..3) {
                       $width = 2**$w;
                       for ($shift=0; $shift < $width; ++$shift) {
                           for ($off=0; $off < 32/$width; ++$off) {
                               $str = pack("B*", "0"x32);
                               $bits = (1<<$shift);
                               vec($str, $off, $width) = $bits;
                               $res = unpack("b*",$str);
                               $val = unpack("V", $str);
                               write;
                           }
                       }
                   }

                   format STDOUT =
                   vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
                   $off, $width, $bits, $val, $res
                   .
                   __END__

               Regardless of the machine architecture on which it is run, the
               above example should print the following table:

                                                     0         1         2         3
                                      unpack("V",$_) 01234567890123456789012345678901
                   ------------------------------------------------------------------
                   vec($_, 0, 1) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 1) = 1   ==          2 01000000000000000000000000000000
                   vec($_, 2, 1) = 1   ==          4 00100000000000000000000000000000
                   vec($_, 3, 1) = 1   ==          8 00010000000000000000000000000000
                   vec($_, 4, 1) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 5, 1) = 1   ==         32 00000100000000000000000000000000
                   vec($_, 6, 1) = 1   ==         64 00000010000000000000000000000000
                   vec($_, 7, 1) = 1   ==        128 00000001000000000000000000000000
                   vec($_, 8, 1) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 9, 1) = 1   ==        512 00000000010000000000000000000000
                   vec($_,10, 1) = 1   ==       1024 00000000001000000000000000000000
                   vec($_,11, 1) = 1   ==       2048 00000000000100000000000000000000
                   vec($_,12, 1) = 1   ==       4096 00000000000010000000000000000000
                   vec($_,13, 1) = 1   ==       8192 00000000000001000000000000000000
                   vec($_,14, 1) = 1   ==      16384 00000000000000100000000000000000
                   vec($_,15, 1) = 1   ==      32768 00000000000000010000000000000000
                   vec($_,16, 1) = 1   ==      65536 00000000000000001000000000000000
                   vec($_,17, 1) = 1   ==     131072 00000000000000000100000000000000
                   vec($_,18, 1) = 1   ==     262144 00000000000000000010000000000000
                   vec($_,19, 1) = 1   ==     524288 00000000000000000001000000000000
                   vec($_,20, 1) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_,21, 1) = 1   ==    2097152 00000000000000000000010000000000
                   vec($_,22, 1) = 1   ==    4194304 00000000000000000000001000000000
                   vec($_,23, 1) = 1   ==    8388608 00000000000000000000000100000000
                   vec($_,24, 1) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_,25, 1) = 1   ==   33554432 00000000000000000000000001000000
                   vec($_,26, 1) = 1   ==   67108864 00000000000000000000000000100000
                   vec($_,27, 1) = 1   ==  134217728 00000000000000000000000000010000
                   vec($_,28, 1) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_,29, 1) = 1   ==  536870912 00000000000000000000000000000100
                   vec($_,30, 1) = 1   == 1073741824 00000000000000000000000000000010
                   vec($_,31, 1) = 1   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 2) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 2) = 1   ==          4 00100000000000000000000000000000
                   vec($_, 2, 2) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 3, 2) = 1   ==         64 00000010000000000000000000000000
                   vec($_, 4, 2) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 5, 2) = 1   ==       1024 00000000001000000000000000000000
                   vec($_, 6, 2) = 1   ==       4096 00000000000010000000000000000000
                   vec($_, 7, 2) = 1   ==      16384 00000000000000100000000000000000
                   vec($_, 8, 2) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 9, 2) = 1   ==     262144 00000000000000000010000000000000
                   vec($_,10, 2) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_,11, 2) = 1   ==    4194304 00000000000000000000001000000000
                   vec($_,12, 2) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_,13, 2) = 1   ==   67108864 00000000000000000000000000100000
                   vec($_,14, 2) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_,15, 2) = 1   == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 2) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 2) = 2   ==          8 00010000000000000000000000000000
                   vec($_, 2, 2) = 2   ==         32 00000100000000000000000000000000
                   vec($_, 3, 2) = 2   ==        128 00000001000000000000000000000000
                   vec($_, 4, 2) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 5, 2) = 2   ==       2048 00000000000100000000000000000000
                   vec($_, 6, 2) = 2   ==       8192 00000000000001000000000000000000
                   vec($_, 7, 2) = 2   ==      32768 00000000000000010000000000000000
                   vec($_, 8, 2) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 9, 2) = 2   ==     524288 00000000000000000001000000000000
                   vec($_,10, 2) = 2   ==    2097152 00000000000000000000010000000000
                   vec($_,11, 2) = 2   ==    8388608 00000000000000000000000100000000
                   vec($_,12, 2) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_,13, 2) = 2   ==  134217728 00000000000000000000000000010000
                   vec($_,14, 2) = 2   ==  536870912 00000000000000000000000000000100
                   vec($_,15, 2) = 2   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 4) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 4) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 2, 4) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 3, 4) = 1   ==       4096 00000000000010000000000000000000
                   vec($_, 4, 4) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 5, 4) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_, 6, 4) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_, 7, 4) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_, 0, 4) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 4) = 2   ==         32 00000100000000000000000000000000
                   vec($_, 2, 4) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 3, 4) = 2   ==       8192 00000000000001000000000000000000
                   vec($_, 4, 4) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 5, 4) = 2   ==    2097152 00000000000000000000010000000000
                   vec($_, 6, 4) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_, 7, 4) = 2   ==  536870912 00000000000000000000000000000100
                   vec($_, 0, 4) = 4   ==          4 00100000000000000000000000000000
                   vec($_, 1, 4) = 4   ==         64 00000010000000000000000000000000
                   vec($_, 2, 4) = 4   ==       1024 00000000001000000000000000000000
                   vec($_, 3, 4) = 4   ==      16384 00000000000000100000000000000000
                   vec($_, 4, 4) = 4   ==     262144 00000000000000000010000000000000
                   vec($_, 5, 4) = 4   ==    4194304 00000000000000000000001000000000
                   vec($_, 6, 4) = 4   ==   67108864 00000000000000000000000000100000
                   vec($_, 7, 4) = 4   == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 4) = 8   ==          8 00010000000000000000000000000000
                   vec($_, 1, 4) = 8   ==        128 00000001000000000000000000000000
                   vec($_, 2, 4) = 8   ==       2048 00000000000100000000000000000000
                   vec($_, 3, 4) = 8   ==      32768 00000000000000010000000000000000
                   vec($_, 4, 4) = 8   ==     524288 00000000000000000001000000000000
                   vec($_, 5, 4) = 8   ==    8388608 00000000000000000000000100000000
                   vec($_, 6, 4) = 8   ==  134217728 00000000000000000000000000010000
                   vec($_, 7, 4) = 8   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 8) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 8) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 2, 8) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 3, 8) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_, 0, 8) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 8) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 2, 8) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 3, 8) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_, 0, 8) = 4   ==          4 00100000000000000000000000000000
                   vec($_, 1, 8) = 4   ==       1024 00000000001000000000000000000000
                   vec($_, 2, 8) = 4   ==     262144 00000000000000000010000000000000
                   vec($_, 3, 8) = 4   ==   67108864 00000000000000000000000000100000
                   vec($_, 0, 8) = 8   ==          8 00010000000000000000000000000000
                   vec($_, 1, 8) = 8   ==       2048 00000000000100000000000000000000
                   vec($_, 2, 8) = 8   ==     524288 00000000000000000001000000000000
                   vec($_, 3, 8) = 8   ==  134217728 00000000000000000000000000010000
                   vec($_, 0, 8) = 16  ==         16 00001000000000000000000000000000
                   vec($_, 1, 8) = 16  ==       4096 00000000000010000000000000000000
                   vec($_, 2, 8) = 16  ==    1048576 00000000000000000000100000000000
                   vec($_, 3, 8) = 16  ==  268435456 00000000000000000000000000001000
                   vec($_, 0, 8) = 32  ==         32 00000100000000000000000000000000
                   vec($_, 1, 8) = 32  ==       8192 00000000000001000000000000000000
                   vec($_, 2, 8) = 32  ==    2097152 00000000000000000000010000000000
                   vec($_, 3, 8) = 32  ==  536870912 00000000000000000000000000000100
                   vec($_, 0, 8) = 64  ==         64 00000010000000000000000000000000
                   vec($_, 1, 8) = 64  ==      16384 00000000000000100000000000000000
                   vec($_, 2, 8) = 64  ==    4194304 00000000000000000000001000000000
                   vec($_, 3, 8) = 64  == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 8) = 128 ==        128 00000001000000000000000000000000
                   vec($_, 1, 8) = 128 ==      32768 00000000000000010000000000000000
                   vec($_, 2, 8) = 128 ==    8388608 00000000000000000000000100000000
                   vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001

       wait    Behaves like the wait(2) system call on your system: it waits
               for a child process to terminate and returns the pid of the
               deceased process, or "-1" if there are no child processes.  The
               status is returned in $?.  Note that a return value of "-1"
               could mean that child processes are being automatically reaped,
               as described in perlipc.

       waitpid PID,FLAGS
               Waits for a particular child process to terminate and returns
               the pid of the deceased process, or "-1" if there is no such
               child process.  On some systems, a value of 0 indicates that
               there are processes still running.  The status is returned in
               $?.  If you say

                   use POSIX ":sys_wait_h";
                   #...
                   do {
                       $kid = waitpid(-1, WNOHANG);
                   } until $kid > 0;

               then you can do a non-blocking wait for all pending zombie
               processes.  Non-blocking wait is available on machines
               supporting either the waitpid(2) or wait4(2) system calls.
               However, waiting for a particular pid with FLAGS of 0 is
               implemented everywhere.  (Perl emulates the system call by
               remembering the status values of processes that have exited but
               have not been harvested by the Perl script yet.)

               Note that on some systems, a return value of "-1" could mean
               that child processes are being automatically reaped.  See
               perlipc for details, and for other examples.

       wantarray
               Returns true if the context of the currently executing
               subroutine is looking for a list value.  Returns false if the
               context is looking for a scalar.  Returns the undefined value
               if the context is looking for no value (void context).

                   return unless defined wantarray;    # don't bother doing more
                   my @a = complex_calculation();
                   return wantarray ? @a : "@a";

               This function should have been named wantlist() instead.

       warn LIST
               Produces a message on STDERR just like "die", but doesn't exit
               or throw an exception.

               If LIST is empty and $@ already contains a value (typically
               from a previous eval) that value is used after appending
               "\t...caught" to $@.  This is useful for staying almost, but
               not entirely similar to "die".

               If $@ is empty then the string "Warning: Something's wrong" is
               used.

               No message is printed if there is a $SIG{__WARN__} handler
               installed.  It is the handler's responsibility to deal with the
               message as it sees fit (like, for instance, converting it into
               a "die").  Most handlers must therefore make arrangements to
               actually display the warnings that they are not prepared to
               deal with, by calling "warn" again in the handler.  Note that
               this is quite safe and will not produce an endless loop, since
               "__WARN__" hooks are not called from inside one.

               You will find this behavior is slightly different from that of
               $SIG{__DIE__} handlers (which don't suppress the error text,
               but can instead call "die" again to change it).

               Using a "__WARN__" handler provides a powerful way to silence
               all warnings (even the so-called mandatory ones).  An example:

                   # wipe out *all* compile-time warnings
                   BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } }
                   my $foo = 10;
                   my $foo = 20;          # no warning about duplicate my $foo,
                                          # but hey, you asked for it!
                   # no compile-time or run-time warnings before here
                   $DOWARN = 1;

                   # run-time warnings enabled after here
                   warn "\$foo is alive and $foo!";     # does show up

               See perlvar for details on setting %SIG entries, and for more
               examples.  See the Carp module for other kinds of warnings
               using its carp() and cluck() functions.

       write FILEHANDLE
       write EXPR
       write   Writes a formatted record (possibly multi-line) to the
               specified FILEHANDLE, using the format associated with that
               file.  By default the format for a file is the one having the
               same name as the filehandle, but the format for the current
               output channel (see the "select" function) may be set
               explicitly by assigning the name of the format to the $~
               variable.

               Top of form processing is handled automatically:  if there is
               insufficient room on the current page for the formatted record,
               the page is advanced by writing a form feed, a special top-of-
               page format is used to format the new page header, and then the
               record is written.  By default the top-of-page format is the
               name of the filehandle with "_TOP" appended, but it may be
               dynamically set to the format of your choice by assigning the
               name to the $^ variable while the filehandle is selected.  The
               number of lines remaining on the current page is in variable
               "$-", which can be set to 0 to force a new page.

               If FILEHANDLE is unspecified, output goes to the current
               default output channel, which starts out as STDOUT but may be
               changed by the "select" operator.  If the FILEHANDLE is an
               EXPR, then the expression is evaluated and the resulting string
               is used to look up the name of the FILEHANDLE at run time.  For
               more on formats, see perlform.

               Note that write is not the opposite of "read".  Unfortunately.

       y///    The transliteration operator.  Same as "tr///".  See perlop.