Provided by: perl-doc_5.26.1-6_all bug

NAME

       IO::Handle - supply object methods for I/O handles

SYNOPSIS

           use IO::Handle;

           $io = IO::Handle->new();
           if ($io->fdopen(fileno(STDIN),"r")) {
               print $io->getline;
               $io->close;
           }

           $io = IO::Handle->new();
           if ($io->fdopen(fileno(STDOUT),"w")) {
               $io->print("Some text\n");
           }

           # setvbuf is not available by default on Perls 5.8.0 and later.
           use IO::Handle '_IOLBF';
           $io->setvbuf($buffer_var, _IOLBF, 1024);

           undef $io;       # automatically closes the file if it's open

           autoflush STDOUT 1;

DESCRIPTION

       "IO::Handle" is the base class for all other IO handle classes. It is not intended that
       objects of "IO::Handle" would be created directly, but instead "IO::Handle" is inherited
       from by several other classes in the IO hierarchy.

       If you are reading this documentation, looking for a replacement for the "FileHandle"
       package, then I suggest you read the documentation for "IO::File" too.

CONSTRUCTOR

       new ()
           Creates a new "IO::Handle" object.

       new_from_fd ( FD, MODE )
           Creates an "IO::Handle" like "new" does.  It requires two parameters, which are passed
           to the method "fdopen"; if the fdopen fails, the object is destroyed. Otherwise, it is
           returned to the caller.

METHODS

       See perlfunc for complete descriptions of each of the following supported "IO::Handle"
       methods, which are just front ends for the corresponding built-in functions:

           $io->close
           $io->eof
           $io->fcntl( FUNCTION, SCALAR )
           $io->fileno
           $io->format_write( [FORMAT_NAME] )
           $io->getc
           $io->ioctl( FUNCTION, SCALAR )
           $io->read ( BUF, LEN, [OFFSET] )
           $io->print ( ARGS )
           $io->printf ( FMT, [ARGS] )
           $io->say ( ARGS )
           $io->stat
           $io->sysread ( BUF, LEN, [OFFSET] )
           $io->syswrite ( BUF, [LEN, [OFFSET]] )
           $io->truncate ( LEN )

       See perlvar for complete descriptions of each of the following supported "IO::Handle"
       methods.  All of them return the previous value of the attribute and takes an optional
       single argument that when given will set the value.  If no argument is given the previous
       value is unchanged (except for $io->autoflush will actually turn ON autoflush by default).

           $io->autoflush ( [BOOL] )                         $|
           $io->format_page_number( [NUM] )                  $%
           $io->format_lines_per_page( [NUM] )               $=
           $io->format_lines_left( [NUM] )                   $-
           $io->format_name( [STR] )                         $~
           $io->format_top_name( [STR] )                     $^
           $io->input_line_number( [NUM])                    $.

       The following methods are not supported on a per-filehandle basis.

           IO::Handle->format_line_break_characters( [STR] ) $:
           IO::Handle->format_formfeed( [STR])               $^L
           IO::Handle->output_field_separator( [STR] )       $,
           IO::Handle->output_record_separator( [STR] )      $\

           IO::Handle->input_record_separator( [STR] )       $/

       Furthermore, for doing normal I/O you might need these:

       $io->fdopen ( FD, MODE )
           "fdopen" is like an ordinary "open" except that its first parameter is not a filename
           but rather a file handle name, an IO::Handle object, or a file descriptor number.
           (For the documentation of the "open" method, see IO::File.)

       $io->opened
           Returns true if the object is currently a valid file descriptor, false otherwise.

       $io->getline
           This works like <$io> described in "I/O Operators" in perlop except that it's more
           readable and can be safely called in a list context but still returns just one line.
           If used as the conditional within a "while" or C-style "for" loop, however, you will
           need to emulate the functionality of <$io> with "defined($_ = $io->getline)".

       $io->getlines
           This works like <$io> when called in a list context to read all the remaining lines in
           a file, except that it's more readable.  It will also croak() if accidentally called
           in a scalar context.

       $io->ungetc ( ORD )
           Pushes a character with the given ordinal value back onto the given handle's input
           stream.  Only one character of pushback per handle is guaranteed.

       $io->write ( BUF, LEN [, OFFSET ] )
           This "write" is somewhat like "write" found in C, in that it is the opposite of read.
           The wrapper for the perl "write" function is called "format_write". However, whilst
           the C "write" function returns the number of bytes written, this "write" function
           simply returns true if successful (like "print"). A more C-like "write" is "syswrite"
           (see above).

       $io->error
           Returns a true value if the given handle has experienced any errors since it was
           opened or since the last call to "clearerr", or if the handle is invalid. It only
           returns false for a valid handle with no outstanding errors.

       $io->clearerr
           Clear the given handle's error indicator. Returns -1 if the handle is invalid, 0
           otherwise.

       $io->sync
           "sync" synchronizes a file's in-memory state  with  that  on the physical medium.
           "sync" does not operate at the perlio api level, but operates on the file descriptor
           (similar to sysread, sysseek and systell). This means that any data held at the perlio
           api level will not be synchronized. To synchronize data that is buffered at the perlio
           api level you must use the flush method. "sync" is not implemented on all platforms.
           Returns "0 but true" on success, "undef" on error, "undef" for an invalid handle. See
           fsync(3c).

       $io->flush
           "flush" causes perl to flush any buffered data at the perlio api level.  Any unread
           data in the buffer will be discarded, and any unwritten data will be written to the
           underlying file descriptor. Returns "0 but true" on success, "undef" on error.

       $io->printflush ( ARGS )
           Turns on autoflush, print ARGS and then restores the autoflush status of the
           "IO::Handle" object. Returns the return value from print.

       $io->blocking ( [ BOOL ] )
           If called with an argument "blocking" will turn on non-blocking IO if "BOOL" is false,
           and turn it off if "BOOL" is true.

           "blocking" will return the value of the previous setting, or the current setting if
           "BOOL" is not given.

           If an error occurs "blocking" will return undef and $! will be set.

       If the C functions setbuf() and/or setvbuf() are available, then "IO::Handle::setbuf" and
       "IO::Handle::setvbuf" set the buffering policy for an IO::Handle.  The calling sequences
       for the Perl functions are the same as their C counterparts--including the constants
       "_IOFBF", "_IOLBF", and "_IONBF" for setvbuf()--except that the buffer parameter specifies
       a scalar variable to use as a buffer. You should only change the buffer before any I/O, or
       immediately after calling flush.

       WARNING: The IO::Handle::setvbuf() is not available by default on Perls 5.8.0 and later
       because setvbuf() is rather specific to using the stdio library, while Perl prefers the
       new perlio subsystem instead.

       WARNING: A variable used as a buffer by "setbuf" or "setvbuf" must not be modified in any
       way until the IO::Handle is closed or "setbuf" or "setvbuf" is called again, or memory
       corruption may result! Remember that the order of global destruction is undefined, so even
       if your buffer variable remains in scope until program termination, it may be undefined
       before the file IO::Handle is closed. Note that you need to import the constants "_IOFBF",
       "_IOLBF", and "_IONBF" explicitly. Like C, setbuf returns nothing. setvbuf returns "0 but
       true", on success, "undef" on failure.

       Lastly, there is a special method for working under -T and setuid/gid scripts:

       $io->untaint
           Marks the object as taint-clean, and as such data read from it will also be considered
           taint-clean. Note that this is a very trusting action to take, and appropriate
           consideration for the data source and potential vulnerability should be kept in mind.
           Returns 0 on success, -1 if setting the taint-clean flag failed. (eg invalid handle)

NOTE

       An "IO::Handle" object is a reference to a symbol/GLOB reference (see the "Symbol"
       package).  Some modules that inherit from "IO::Handle" may want to keep object related
       variables in the hash table part of the GLOB. In an attempt to prevent modules trampling
       on each other I propose the that any such module should prefix its variables with its own
       name separated by _'s. For example the IO::Socket module keeps a "timeout" variable in
       'io_socket_timeout'.

SEE ALSO

       perlfunc, "I/O Operators" in perlop, IO::File

BUGS

       Due to backwards compatibility, all filehandles resemble objects of class "IO::Handle", or
       actually classes derived from that class.  They actually aren't.  Which means you can't
       derive your own class from "IO::Handle" and inherit those methods.

HISTORY

       Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>