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NAME

       perlglossary - Perl Glossary

VERSION

       version 5.021009

DESCRIPTION

       A glossary of terms (technical and otherwise) used in the Perl documentation, derived from the Glossary
       of Programming Perl, Fourth Edition.  Words or phrases in bold are defined elsewhere in this glossary.

       Other useful sources include the Unicode Glossary <http://unicode.org/glossary/>, the Free On-Line
       Dictionary of Computing <http://foldoc.org/>, the Jargon File <http://catb.org/~esr/jargon/>, and
       Wikipedia <http://www.wikipedia.org/>.

   A
       accessor methods
           A method used to indirectly inspect or update an objectXs state (its instance variables).

       actual arguments
           The scalar values that you supply to a function or subroutine when you call it. For instance, when
           you call "power("puff")", the string "puff" is the actual argument. See also argument and formal
           arguments.

       address operator
           Some languages work directly with the memory addresses of values, but this can be like playing with
           fire. Perl provides a set of asbestos gloves for handling all memory management. The closest to an
           address operator in Perl is the backslash operator, but it gives you a hard reference, which is much
           safer than a memory address.

       algorithm
           A well-defined sequence of steps, explained clearly enough that even a computer could do them.

       alias
           A nickname for something, which behaves in all ways as though youXd used the original name instead of
           the nickname. Temporary aliases are implicitly created in the loop variable for "foreach" loops, in
           the $_ variable for "map" or "grep" operators, in $a and $b during "sort"Xs comparison function, and
           in each element of @_ for the actual arguments of a subroutine call. Permanent aliases are explicitly
           created in packages by importing symbols or by assignment to typeglobs. Lexically scoped aliases for
           package variables are explicitly created by the "our" declaration.

       alphabetic
           The sort of characters we put into words. In Unicode, this is all letters including all ideographs
           and certain diacritics, letter numbers like Roman numerals, and various combining marks.

       alternatives
           A list of possible choices from which you may select only one, as in, XWould you like door A, B, or
           C?X Alternatives in regular expressions are separated with a single vertical bar: "|".  Alternatives
           in normal Perl expressions are separated with a double vertical bar: "||". Logical alternatives in
           Boolean expressions are separated with either "||" or "or".

       anonymous
           Used to describe a referent that is not directly accessible through a named variable. Such a referent
           must be indirectly accessible through at least one hard reference. When the last hard reference goes
           away, the anonymous referent is destroyed without pity.

       application
           A bigger, fancier sort of program with a fancier name so people donXt realize they are using a
           program.

       architecture
           The kind of computer youXre working on, where one Xkind of computerX means all those computers
           sharing a compatible machine language.  Since Perl programs are (typically) simple text files, not
           executable images, a Perl program is much less sensitive to the architecture itXs running on than
           programs in other languages, such as C, that are compiled into machine code. See also platform and
           operating system.

       argument
           A piece of data supplied to a program, subroutine, function, or method to tell it what itXs supposed
           to do. Also called a XparameterX.

       ARGV
           The name of the array containing the argument vector from the command line. If you use the empty "<>"
           operator, "ARGV" is the name of both the filehandle used to traverse the arguments and the scalar
           containing the name of the current input file.

       arithmetical operator
           A symbol such as "+" or "/" that tells Perl to do the arithmetic you were supposed to learn in grade
           school.

       array
           An ordered sequence of values, stored such that you can easily access any of the values using an
           integer subscript that specifies the valueXs offset in the sequence.

       array context
           An archaic expression for what is more correctly referred to as list context.

       Artistic License
           The open source license that Larry Wall created for Perl, maximizing PerlXs usefulness, availability,
           and modifiability. The current version is 2.
           (<http://www.opensource.org/licenses/artistic-license.php>).

       ASCII
           The American Standard Code for Information Interchange (a 7-bit character set adequate only for
           poorly representing English text). Often used loosely to describe the lowest 128 values of the
           various ISO-8859-X character sets, a bunch of mutually incompatible 8-bit codes best described as
           half ASCII. See also Unicode.

       assertion
           A component of a regular expression that must be true for the pattern to match but does not
           necessarily match any characters itself. Often used specifically to mean a zero-width assertion.

       assignment
           An operator whose assigned mission in life is to change the value of a variable.

       assignment operator
           Either a regular assignment or a compound operator composed of an ordinary assignment and some other
           operator, that changes the value of a variable in place; that is, relative to its old value. For
           example, "$a += 2" adds 2 to $a.

       associative array
           See hash. Please. The term associative array is the old Perl 4 term for a hash. Some languages call
           it a dictionary.

       associativity
           Determines whether you do the left operator first or the right operator first when you have XA
           operator B operator CX, and the two operators are of the same precedence. Operators like "+" are left
           associative, while operators like "**" are right associative. See Camel chapter 3, XUnary and Binary
           OperatorsX for a list of operators and their associativity.

       asynchronous
           Said of events or activities whose relative temporal ordering is indeterminate because too many
           things are going on at once. Hence, an asynchronous event is one you didnXt know when to expect.

       atom
           A regular expression component potentially matching a substring containing one or more characters and
           treated as an indivisible syntactic unit by any following quantifier. (Contrast with an assertion
           that matches something of zero width and may not be quantified.)

       atomic operation
           When Democritus gave the word XatomX to the indivisible bits of matter, he meant literally something
           that could not be cut: X- (not) + -XXXXX (cuttable). An atomic operation is an action that canXt be
           interrupted, not one forbidden in a nuclear-free zone.

       attribute
           A new feature that allows the declaration of variables and subroutines with modifiers, as in "sub foo
           : locked method". Also another name for an instance variable of an object.

       autogeneration
           A feature of operator overloading of objects, whereby the behavior of certain operators can be
           reasonably deduced using more fundamental operators. This assumes that the overloaded operators will
           often have the same relationships as the regular operators. See Camel chapter 13, XOverloadingX.

       autoincrement
           To add one to something automatically, hence the name of the "++" operator. To instead subtract one
           from something automatically is known as an XautodecrementX.

       autoload
           To load on demand. (Also called XlazyX loading.)  Specifically, to call an "AUTOLOAD" subroutine on
           behalf of an undefined subroutine.

       autosplit
           To split a string automatically, as the Xa switch does when running under Xp or Xn in order to
           emulate awk. (See also the "AutoSplit" module, which has nothing to do with the "Xa" switch but a lot
           to do with autoloading.)

       autovivification
           A Graeco-Roman word meaning Xto bring oneself to lifeX.  In Perl, storage locations (lvalues)
           spontaneously generate themselves as needed, including the creation of any hard reference values to
           point to the next level of storage. The assignment "$a[5][5][5][5][5] = "quintet"" potentially
           creates five scalar storage locations, plus four references (in the first four scalar locations)
           pointing to four new anonymous arrays (to hold the last four scalar locations). But the point of
           autovivification is that you donXt have to worry about it.

       AV  Short for Xarray valueX, which refers to one of PerlXs internal data types that holds an array. The
           "AV" type is a subclass of SV.

       awk Descriptive editing termXshort for XawkwardX. Also coincidentally refers to a venerable text-
           processing language from which Perl derived some of its high-level ideas.

   B
       backreference
           A substring captured by a subpattern within unadorned parentheses in a regex. Backslashed decimal
           numbers ("\1", "\2", etc.) later in the same pattern refer back to the corresponding subpattern in
           the current match. Outside the pattern, the numbered variables ($1, $2, etc.) continue to refer to
           these same values, as long as the pattern was the last successful match of the current dynamic scope.

       backtracking
           The practice of saying, XIf I had to do it all over, IXd do it differently,X and then actually going
           back and doing it all over differently. Mathematically speaking, itXs returning from an unsuccessful
           recursion on a tree of possibilities. Perl backtracks when it attempts to match patterns with a
           regular expression, and its earlier attempts donXt pan out. See the section XThe Little Engine That
           /Couldn(nXt)X in Camel chapter 5, XPattern MatchingX.

       backward compatibility
           Means you can still run your old program because we didnXt break any of the features or bugs it was
           relying on.

       bareword
           A word sufficiently ambiguous to be deemed illegal under "use strict 'subs'". In the absence of that
           stricture, a bareword is treated as if quotes were around it.

       base class
           A generic object type; that is, a class from which other, more specific classes are derived
           genetically by inheritance. Also called a XsuperclassX by people who respect their ancestors.

       big-endian
           From Swift: someone who eats eggs big end first. Also used of computers that store the most
           significant byte of a word at a lower byte address than the least significant byte. Often considered
           superior to little-endian machines. See also little-endian.

       binary
           Having to do with numbers represented in base 2. That means thereXs basically two numbers: 0 and 1.
           Also used to describe a file of XnontextX, presumably because such a file makes full use of all the
           binary bits in its bytes. With the advent of Unicode, this distinction, already suspect, loses even
           more of its meaning.

       binary operator
           An operator that takes two operands.

       bind
           To assign a specific network address to a socket.

       bit An integer in the range from 0 to 1, inclusive. The smallest possible unit of information storage. An
           eighth of a byte or of a dollar.  (The term XPieces of EightX comes from being able to split the old
           Spanish dollar into 8 bits, each of which still counted for money. ThatXs why a 25- cent piece today
           is still Xtwo bitsX.)

       bit shift
           The movement of bits left or right in a computer word, which has the effect of multiplying or
           dividing by a power of 2.

       bit string
           A sequence of bits that is actually being thought of as a sequence of bits, for once.

       bless
           In corporate life, to grant official approval to a thing, as in, XThe VP of Engineering has blessed
           our WebCruncher project.X Similarly, in Perl, to grant official approval to a referent so that it can
           function as an object, such as a WebCruncher object. See the "bless" function in Camel chapter 27,
           XFunctionsX.

       block
           What a process does when it has to wait for something: XMy process blocked waiting for the disk.X As
           an unrelated noun, it refers to a large chunk of data, of a size that the operating system likes to
           deal with (normally a power of 2 such as 512 or 8192). Typically refers to a chunk of data thatXs
           coming from or going to a disk file.

       BLOCK
           A syntactic construct consisting of a sequence of Perl statements that is delimited by braces.  The
           "if" and "while" statements are defined in terms of "BLOCK"s, for instance. Sometimes we also say
           XblockX to mean a lexical scope; that is, a sequence of statements that acts like a "BLOCK", such as
           within an "eval" or a file, even though the statements arenXt delimited by braces.

       block buffering
           A method of making input and output efficient by passing one block at a time. By default, Perl does
           block buffering to disk files. See buffer and command buffering.

       Boolean
           A value that is either true or false.

       Boolean context
           A special kind of scalar context used in conditionals to decide whether the scalar value returned by
           an expression is true or false. Does not evaluate as either a string or a number. See context.

       breakpoint
           A spot in your program where youXve told the debugger to stop execution so you can poke around and
           see whether anything is wrong yet.

       broadcast
           To send a datagram to multiple destinations simultaneously.

       BSD A psychoactive drug, popular in the X80s, probably developed at UC Berkeley or thereabouts. Similar
           in many ways to the prescription-only medication called XSystem VX, but infinitely more useful. (Or,
           at least, more fun.) The full chemical name is XBerkeley Standard DistributionX.

       bucket
           A location in a hash table containing (potentially) multiple entries whose keys XhashX to the same
           hash value according to its hash function. (As internal policy, you donXt have to worry about it
           unless youXre into internals, or policy.)

       buffer
           A temporary holding location for data. Data that are Block buffering means that the data is passed on
           to its destination whenever the buffer is full. Line buffering means that itXs passed on whenever a
           complete line is received. Command buffering means that itXs passed every time you do a "print"
           command (or equivalent). If your output is unbuffered, the system processes it one byte at a time
           without the use of a holding area. This can be rather inefficient.

       built-in
           A function that is predefined in the language. Even when hidden by overriding, you can always get at
           a built- in function by qualifying its name with the "CORE::" pseudopackage.

       bundle
           A group of related modules on CPAN. (Also sometimes refers to a group of command-line switches
           grouped into one switch cluster.)

       byte
           A piece of data worth eight bits in most places.

       bytecode
           A pidgin-like lingo spoken among Xdroids when they donXt wish to reveal their orientation (see
           endian). Named after some similar languages spoken (for similar reasons) between compilers and
           interpreters in the late 20XX century. These languages are characterized by representing everything
           as a nonarchitecture-dependent sequence of bytes.

   C
       C   A language beloved by many for its inside-out type definitions, inscrutable precedence rules, and
           heavy overloading of the function-call mechanism. (Well, actually, people first switched to C because
           they found lowercase identifiers easier to read than upper.) Perl is written in C, so itXs not
           surprising that Perl borrowed a few ideas from it.

       cache
           A data repository. Instead of computing expensive answers several times, compute it once and save the
           result.

       callback
           A handler that you register with some other part of your program in the hope that the other part of
           your program will trigger your handler when some event of interest transpires.

       call by reference
           An argument-passing mechanism in which the formal arguments refer directly to the actual arguments,
           and the subroutine can change the actual arguments by changing the formal arguments. That is, the
           formal argument is an alias for the actual argument. See also call by value.

       call by value
           An argument-passing mechanism in which the formal arguments refer to a copy of the actual arguments,
           and the subroutine cannot change the actual arguments by changing the formal arguments. See also call
           by reference.

       canonical
           Reduced to a standard form to facilitate comparison.

       capture variables
           The variablesXsuch as $1 and $2, and "%+" and %X Xthat hold the text remembered in a pattern match.
           See Camel chapter 5, XPattern MatchingX.

       capturing
           The use of parentheses around a subpattern in a regular expression to store the matched substring as
           a backreference. (Captured strings are also returned as a list in list context.) See Camel chapter 5,
           XPattern MatchingX.

       cargo cult
           Copying and pasting code without understanding it, while superstitiously believing in its value. This
           term originated from preindustrial cultures dealing with the detritus of explorers and colonizers of
           technologically advanced cultures. See The Gods Must Be Crazy.

       case
           A property of certain characters. Originally, typesetter stored capital letters in the upper of two
           cases and small letters in the lower one. Unicode recognizes three cases: lowercase (character
           property "\p{lower}"), titlecase ("\p{title}"), and uppercase ("\p{upper}"). A fourth casemapping
           called foldcase is not itself a distinct case, but it is used internally to implement casefolding.
           Not all letters have case, and some nonletters have case.

       casefolding
           Comparing or matching a string case-insensitively. In Perl, it is implemented with the "/i" pattern
           modifier, the "fc" function, and the "\F" double-quote translation escape.

       casemapping
           The process of converting a string to one of the four Unicode casemaps; in Perl, it is implemented
           with the "fc", "lc", "ucfirst", and "uc" functions.

       character
           The smallest individual element of a string. Computers store characters as integers, but Perl lets
           you operate on them as text. The integer used to represent a particular character is called that
           characterXs codepoint.

       character class
           A square-bracketed list of characters used in a regular expression to indicate that any character of
           the set may occur at a given point. Loosely, any predefined set of characters so used.

       character property
           A predefined character class matchable by the "\p" or "\P" metasymbol. Unicode defines hundreds of
           standard properties for every possible codepoint, and Perl defines a few of its own, too.

       circumfix operator
           An operator that surrounds its operand, like the angle operator, or parentheses, or a hug.

       class
           A user-defined type, implemented in Perl via a package that provides (either directly or by
           inheritance) methods (that is, subroutines) to handle instances of the class (its objects). See also
           inheritance.

       class method
           A method whose invocant is a package name, not an object reference. A method associated with the
           class as a whole. Also see instance method.

       client
           In networking, a process that initiates contact with a server process in order to exchange data and
           perhaps receive a service.

       closure
           An anonymous subroutine that, when a reference to it is generated at runtime, keeps track of the
           identities of externally visible lexical variables, even after those lexical variables have
           supposedly gone out of scope. TheyXre called XclosuresX because this sort of behavior gives
           mathematicians a sense of closure.

       cluster
           A parenthesized subpattern used to group parts of a regular expression into a single atom.

       CODE
           The word returned by the "ref" function when you apply it to a reference to a subroutine. See also
           CV.

       code generator
           A system that writes code for you in a low-level language, such as code to implement the backend of a
           compiler. See program generator.

       codepoint
           The integer a computer uses to represent a given character. ASCII codepoints are in the range 0 to
           127; Unicode codepoints are in the range 0 to 0x1F_FFFF; and Perl codepoints are in the range 0 to
           2XXX1 or 0 to 2XXX1, depending on your native integer size. In Perl Culture, sometimes called
           ordinals.

       code subpattern
           A regular expression subpattern whose real purpose is to execute some Perl codeXfor example, the
           "(?{...})" and "(??{...})" subpatterns.

       collating sequence
           The order into which characters sort. This is used by string comparison routines to decide, for
           example, where in this glossary to put Xcollating sequenceX.

       co-maintainer
           A person with permissions to index a namespace in PAUSE. Anyone can upload any namespace, but only
           primary and co-maintainers get their contributions indexed.

       combining character
           Any character with the General Category of Combining Mark ("\p{GC=M}"), which may be spacing or
           nonspacing. Some are even invisible. A sequence of combining characters following a grapheme base
           character together make up a single user-visible character called a grapheme. Most but not all
           diacritics are combining characters, and vice versa.

       command
           In shell programming, the syntactic combination of a program name and its arguments. More loosely,
           anything you type to a shell (a command interpreter) that starts it doing something. Even more
           loosely, a Perl statement, which might start with a label and typically ends with a semicolon.

       command buffering
           A mechanism in Perl that lets you store up the output of each Perl command and then flush it out as a
           single request to the operating system. ItXs enabled by setting the $| ($AUTOFLUSH) variable to a
           true value. ItXs used when you donXt want data sitting around, not going where itXs supposed to,
           which may happen because the default on a file or pipe is to use block buffering.

       command-line arguments
           The values you supply along with a program name when you tell a shell to execute a command.  These
           values are passed to a Perl program through @ARGV.

       command name
           The name of the program currently executing, as typed on the command line. In C, the command name is
           passed to the program as the first command-line argument. In Perl, it comes in separately as $0.

       comment
           A remark that doesnXt affect the meaning of the program.  In Perl, a comment is introduced by a "#"
           character and continues to the end of the line.

       compilation unit
           The file (or string, in the case of "eval") that is currently being compiled.

       compile
           The process of turning source code into a machine-usable form. See compile phase.

       compile phase
           Any time before Perl starts running your main program. See also run phase. Compile phase is mostly
           spent in compile time, but may also be spent in runtime when "BEGIN" blocks, "use" or "no"
           declarations, or constant subexpressions are being evaluated. The startup and import code of any
           "use" declaration is also run during compile phase.

       compiler
           Strictly speaking, a program that munches up another program and spits out yet another file
           containing the program in a Xmore executableX form, typically containing native machine instructions.
           The perl program is not a compiler by this definition, but it does contain a kind of compiler that
           takes a program and turns it into a more executable form (syntax trees) within the perl process
           itself, which the interpreter then interprets. There are, however, extension modules to get Perl to
           act more like a XrealX compiler. See Camel chapter 16, XCompilingX.

       compile time
           The time when Perl is trying to make sense of your code, as opposed to when it thinks it knows what
           your code means and is merely trying to do what it thinks your code says to do, which is runtime.

       composer
           A XconstructorX for a referent that isnXt really an object, like an anonymous array or a hash (or a
           sonata, for that matter).  For example, a pair of braces acts as a composer for a hash, and a pair of
           brackets acts as a composer for an array. See the section XCreating ReferencesX in Camel chapter 8,
           XReferencesX.

       concatenation
           The process of gluing one catXs nose to another catXs tail. Also a similar operation on two strings.

       conditional
           Something XiffyX. See Boolean context.

       connection
           In telephony, the temporary electrical circuit between the callerXs and the calleeXs phone. In
           networking, the same kind of temporary circuit between a client and a server.

       construct
           As a noun, a piece of syntax made up of smaller pieces. As a transitive verb, to create an object
           using a constructor.

       constructor
           Any class method, instance, or subroutine that composes, initializes, blesses, and returns an object.
           Sometimes we use the term loosely to mean a composer.

       context
           The surroundings or environment. The context given by the surrounding code determines what kind of
           data a particular expression is expected to return. The three primary contexts are list context,
           scalar, and void context. Scalar context is sometimes subdivided into Boolean context, numeric
           context, string context, and void context. ThereXs also a XdonXt careX context (which is dealt with
           in Camel chapter 2, XBits and PiecesX, if you care).

       continuation
           The treatment of more than one physical line as a single logical line. Makefile lines are continued
           by putting a backslash before the newline. Mail headers, as defined by RFC 822, are continued by
           putting a space or tab after the newline. In general, lines in Perl do not need any form of
           continuation mark, because whitespace (including newlines) is gleefully ignored. Usually.

       core dump
           The corpse of a process, in the form of a file left in the working directory of the process, usually
           as a result of certain kinds of fatal errors.

       CPAN
           The Comprehensive Perl Archive Network. (See the Camel Preface and Camel chapter 19, XCPANX for
           details.)

       C preprocessor
           The typical C compilerXs first pass, which processes lines beginning with "#" for conditional
           compilation and macro definition, and does various manipulations of the program text based on the
           current definitions. Also known as cpp(1).

       cracker
           Someone who breaks security on computer systems. A cracker may be a true hacker or only a script
           kiddie.

       currently selected output channel
           The last filehandle that was designated with "select(FILEHANDLE)"; "STDOUT", if no filehandle has
           been selected.

       current package
           The package in which the current statement is compiled. Scan backward in the text of your program
           through the current lexical scope or any enclosing lexical scopes until you find a package
           declaration. ThatXs your current package name.

       current working directory
           See working directory.

       CV  In academia, a curriculum vitae, a fancy kind of resume. In Perl, an internal Xcode valueX typedef
           holding a subroutine. The "CV" type is a subclass of SV.

   D
       dangling statement
           A bare, single statement, without any braces, hanging off an "if" or "while" conditional. C allows
           them. Perl doesnXt.

       datagram
           A packet of data, such as a UDP message, that (from the viewpoint of the programs involved) can be
           sent independently over the network. (In fact, all packets are sent independently at the IP level,
           but stream protocols such as TCP hide this from your program.)

       data structure
           How your various pieces of data relate to each other and what shape they make when you put them all
           together, as in a rectangular table or a triangular tree.

       data type
           A set of possible values, together with all the operations that know how to deal with those values.
           For example, a numeric data type has a certain set of numbers that you can work with, as well as
           various mathematical operations that you can do on the numbers, but would make little sense on, say,
           a string such as "Kilroy". Strings have their own operations, such as concatenation. Compound types
           made of a number of smaller pieces generally have operations to compose and decompose them, and
           perhaps to rearrange them. Objects that model things in the real world often have operations that
           correspond to real activities. For instance, if you model an elevator, your elevator object might
           have an "open_door" method.

       DBM Stands for XDatabase ManagementX routines, a set of routines that emulate an associative array using
           disk files. The routines use a dynamic hashing scheme to locate any entry with only two disk
           accesses. DBM files allow a Perl program to keep a persistent hash across multiple invocations. You
           can "tie" your hash variables to various DBM implementations.

       declaration
           An assertion that states something exists and perhaps describes what itXs like, without giving any
           commitment as to how or where youXll use it. A declaration is like the part of your recipe that says,
           Xtwo cups flour, one large egg, four or five tadpolesXX See statement for its opposite. Note that
           some declarations also function as statements. Subroutine declarations also act as definitions if a
           body is supplied.

       declarator
           Something that tells your program what sort of variable youXd like. Perl doesnXt require you to
           declare variables, but you can use "my", "our", or "state" to denote that you want something other
           than the default.

       decrement
           To subtract a value from a variable, as in Xdecrement $xX (meaning to remove 1 from its value) or
           Xdecrement $x by 3X.

       default
           A value chosen for you if you donXt supply a value of your own.

       defined
           Having a meaning. Perl thinks that some of the things people try to do are devoid of meaning; in
           particular, making use of variables that have never been given a value and performing certain
           operations on data that isnXt there. For example, if you try to read data past the end of a file,
           Perl will hand you back an undefined value. See also false and the "defined" entry in Camel chapter
           27, XFunctionsX.

       delimiter
           A character or string that sets bounds to an arbitrarily sized textual object, not to be confused
           with a separator or terminator. XTo delimitX really just means Xto surroundX or Xto encloseX (like
           these parentheses are doing).

       dereference
           A fancy computer science term meaning Xto follow a reference to what it points toX. The XdeX part of
           it refers to the fact that youXre taking away one level of indirection.

       derived class
           A class that defines some of its methods in terms of a more generic class, called a base class. Note
           that classes arenXt classified exclusively into base classes or derived classes: a class can function
           as both a derived class and a base class simultaneously, which is kind of classy.

       descriptor
           See file descriptor.

       destroy
           To deallocate the memory of a referent (first triggering its "DESTROY" method, if it has one).

       destructor
           A special method that is called when an object is thinking about destroying itself. A Perl programXs
           "DESTROY" method doesnXt do the actual destruction; Perl just triggers the method in case the class
           wants to do any associated cleanup.

       device
           A whiz-bang hardware gizmo (like a disk or tape drive or a modem or a joystick or a mouse) attached
           to your computer, which the operating system tries to make look like a file (or a bunch of files).
           Under Unix, these fake files tend to live in the /dev directory.

       directive
           A pod directive. See Camel chapter 23, XPlain Old DocumentationX.

       directory
           A special file that contains other files. Some operating systems call these XfoldersX, XdrawersX,
           XcataloguesX, or XcatalogsX.

       directory handle
           A name that represents a particular instance of opening a directory to read it, until you close it.
           See the "opendir" function.

       discipline
           Some people need this and some people avoid it.  For Perl, itXs an old way to say I/O layer.

       dispatch
           To send something to its correct destination. Often used metaphorically to indicate a transfer of
           programmatic control to a destination selected algorithmically, often by lookup in a table of
           function references or, in the case of object methods, by traversing the inheritance tree looking for
           the most specific definition for the method.

       distribution
           A standard, bundled release of a system of software. The default usage implies source code is
           included. If that is not the case, it will be called a Xbinary-onlyX distribution.

       dual-lived
           Some modules live both in the Standard Library and on CPAN. These modules might be developed on two
           tracks as people modify either version. The trend currently is to untangle these situations.

       dweomer
           An enchantment, illusion, phantasm, or jugglery. Said when PerlXs magical dwimmer effects donXt do
           what you expect, but rather seem to be the product of arcane dweomercraft, sorcery, or wonder
           working. [From Middle English.]

       dwimmer
           DWIM is an acronym for XDo What I MeanX, the principle that something should just do what you want it
           to do without an undue amount of fuss. A bit of code that does XdwimmingX is a XdwimmerX. Dwimming
           can require a great deal of behind-the-scenes magic, which (if it doesnXt stay properly behind the
           scenes) is called a dweomer instead.

       dynamic scoping
           Dynamic scoping works over a dynamic scope, making variables visible throughout the rest of the block
           in which they are first used and in any subroutines that are called by the rest of the block.
           Dynamically scoped variables can have their values temporarily changed (and implicitly restored
           later) by a "local" operator.  (Compare lexical scoping.) Used more loosely to mean how a subroutine
           that is in the middle of calling another subroutine XcontainsX that subroutine at runtime.

   E
       eclectic
           Derived from many sources. Some would say too many.

       element
           A basic building block. When youXre talking about an array, itXs one of the items that make up the
           array.

       embedding
           When something is contained in something else, particularly when that might be considered surprising:
           XIXve embedded a complete Perl interpreter in my editor!X

       empty subclass test
           The notion that an empty derived class should behave exactly like its base class.

       encapsulation
           The veil of abstraction separating the interface from the implementation (whether enforced or not),
           which mandates that all access to an objectXs state be through methods alone.

       endian
           See little-endian and big-endian.

       en passant
           When you change a value as it is being copied. [From French Xin passingX, as in the exotic pawn-
           capturing maneuver in chess.]

       environment
           The collective set of environment variables your process inherits from its parent. Accessed via %ENV.

       environment variable
           A mechanism by which some high-level agent such as a user can pass its preferences down to its future
           offspring (child processes, grandchild processes, great-grandchild processes, and so on). Each
           environment variable is a key/value pair, like one entry in a hash.

       EOF End of File. Sometimes used metaphorically as the terminating string of a here document.

       errno
           The error number returned by a syscall when it fails. Perl refers to the error by the name $! (or
           $OS_ERROR if you use the English module).

       error
           See exception or fatal error.

       escape sequence
           See metasymbol.

       exception
           A fancy term for an error. See fatal error.

       exception handling
           The way a program responds to an error. The exception-handling mechanism in Perl is the "eval"
           operator.

       exec
           To throw away the current processXs program and replace it with another, without exiting the process
           or relinquishing any resources held (apart from the old memory image).

       executable file
           A file that is specially marked to tell the operating system that itXs okay to run this file as a
           program.  Usually shortened to XexecutableX.

       execute
           To run a program or subroutine. (Has nothing to do with the "kill" built-in, unless youXre trying to
           run a signal handler.)

       execute bit
           The special mark that tells the operating system it can run this program. There are actually three
           execute bits under Unix, and which bit gets used depends on whether you own the file singularly,
           collectively, or not at all.

       exit status
           See status.

       exploit
           Used as a noun in this case, this refers to a known way to compromise a program to get it to do
           something the author didnXt intend.  Your task is to write unexploitable programs.

       export
           To make symbols from a module available for import by other modules.

       expression
           Anything you can legally say in a spot where a value is required. Typically composed of literals,
           variables, operators, functions, and subroutine calls, not necessarily in that order.

       extension
           A Perl module that also pulls in compiled C or C++ code. More generally, any experimental option that
           can be compiled into Perl, such as multithreading.

   F
       false
           In Perl, any value that would look like "" or "0" if evaluated in a string context. Since undefined
           values evaluate to "", all undefined values are false, but not all false values are undefined.

       FAQ Frequently Asked Question (although not necessarily frequently answered, especially if the answer
           appears in the Perl FAQ shipped standard with Perl).

       fatal error
           An uncaught exception, which causes termination of the process after printing a message on your
           standard error stream. Errors that happen inside an "eval" are not fatal. Instead, the "eval"
           terminates after placing the exception message in the $@ ($EVAL_ERROR) variable.  You can try to
           provoke a fatal error with the "die" operator (known as throwing or raising an exception), but this
           may be caught by a dynamically enclosing "eval". If not caught, the "die" becomes a fatal error.

       feeping creaturism
           A spoonerism of Xcreeping featurismX, noting the biological urge to add just one more feature to a
           program.

       field
           A single piece of numeric or string data that is part of a longer string, record, or line. Variable-
           width fields are usually split up by separators (so use "split" to extract the fields), while fixed-
           width fields are usually at fixed positions (so use "unpack").  Instance variables are also known as
           XfieldsX.

       FIFO
           First In, First Out. See also LIFO. Also a nickname for a named pipe.

       file
           A named collection of data, usually stored on disk in a directory in a filesystem. Roughly like a
           document, if youXre into office metaphors. In modern filesystems, you can actually give a file more
           than one name. Some files have special properties, like directories and devices.

       file descriptor
           The little number the operating system uses to keep track of which opened file youXre talking about.
           Perl hides the file descriptor inside a standard I/O stream and then attaches the stream to a
           filehandle.

       fileglob
           A XwildcardX match on filenames. See the "glob" function.

       filehandle
           An identifier (not necessarily related to the real name of a file) that represents a particular
           instance of opening a file, until you close it. If youXre going to open and close several different
           files in succession, itXs fine to open each of them with the same filehandle, so you donXt have to
           write out separate code to process each file.

       filename
           One name for a file. This name is listed in a directory. You can use it in an "open" to tell the
           operating system exactly which file you want to open, and associate the file with a filehandle, which
           will carry the subsequent identity of that file in your program, until you close it.

       filesystem
           A set of directories and files residing on a partition of the disk. Sometimes known as a XpartitionX.
           You can change the fileXs name or even move a file around from directory to directory within a
           filesystem without actually moving the file itself, at least under Unix.

       file test operator
           A built-in unary operator that you use to determine whether something is true about a file, such as
           "Xo $filename" to test whether youXre the owner of the file.

       filter
           A program designed to take a stream of input and transform it into a stream of output.

       first-come
           The first PAUSE author to upload a namespace automatically becomes the primary maintainer for that
           namespace. The Xfirst comeX permissions distinguish a primary maintainer who was assigned that role
           from one who received it automatically.

       flag
           We tend to avoid this term because it means so many things.  It may mean a command-line switch that
           takes no argument itself (such as PerlXs "Xn" and "Xp" flags) or, less frequently, a single-bit
           indicator (such as the "O_CREAT" and "O_EXCL" flags used in "sysopen"). Sometimes informally used to
           refer to certain regex modifiers.

       floating point
           A method of storing numbers in Xscientific notationX, such that the precision of the number is
           independent of its magnitude (the decimal point XfloatsX). Perl does its numeric work with floating-
           point numbers (sometimes called XfloatsX) when it canXt get away with using integers. Floating-point
           numbers are mere approximations of real numbers.

       flush
           The act of emptying a buffer, often before itXs full.

       FMTEYEWTK
           Far More Than Everything You Ever Wanted To Know. An exhaustive treatise on one narrow topic,
           something of a super-FAQ. See Tom for far more.

       foldcase
           The casemap used in Unicode when comparing or matching without regard to case. Comparing lower-,
           title-, or uppercase are all unreliable due to UnicodeXs complex, one-to-many case mappings. Foldcase
           is a lowercase variant (using a partially decomposed normalization form for certain codepoints)
           created specifically to resolve this.

       fork
           To create a child process identical to the parent process at its moment of conception, at least until
           it gets ideas of its own. A thread with protected memory.

       formal arguments
           The generic names by which a subroutine knows its arguments. In many languages, formal arguments are
           always given individual names; in Perl, the formal arguments are just the elements of an array. The
           formal arguments to a Perl program are $ARGV[0], $ARGV[1], and so on. Similarly, the formal arguments
           to a Perl subroutine are $_[0], $_[1], and so on. You may give the arguments individual names by
           assigning the values to a "my" list. See also actual arguments.

       format
           A specification of how many spaces and digits and things to put somewhere so that whatever youXre
           printing comes out nice and pretty.

       freely available
           Means you donXt have to pay money to get it, but the copyright on it may still belong to someone else
           (like Larry).

       freely redistributable
           Means youXre not in legal trouble if you give a bootleg copy of it to your friends and we find out
           about it. In fact, weXd rather you gave a copy to all your friends.

       freeware
           Historically, any software that you give away, particularly if you make the source code available as
           well. Now often called open source software. Recently there has been a trend to use the term in
           contradistinction to open source software, to refer only to free software released under the Free
           Software FoundationXs GPL (General Public License), but this is difficult to justify etymologically.

       function
           Mathematically, a mapping of each of a set of input values to a particular output value. In
           computers, refers to a subroutine or operator that returns a value. It may or may not have input
           values (called arguments).

       funny character
           Someone like Larry, or one of his peculiar friends. Also refers to the strange prefixes that Perl
           requires as noun markers on its variables.

   G
       garbage collection
           A misnamed featureXit should be called, Xexpecting your mother to pick up after youX. Strictly
           speaking, Perl doesnXt do this, but it relies on a reference-counting mechanism to keep things tidy.
           However, we rarely speak strictly and will often refer to the reference-counting scheme as a form of
           garbage collection. (If itXs any comfort, when your interpreter exits, a XrealX garbage collector
           runs to make sure everything is cleaned up if youXve been messy with circular references and such.)

       GID Group IDXin Unix, the numeric group ID that the operating system uses to identify you and members of
           your group.

       glob
           Strictly, the shellXs "*" character, which will match a XglobX of characters when youXre trying to
           generate a list of filenames.  Loosely, the act of using globs and similar symbols to do pattern
           matching.  See also fileglob and typeglob.

       global
           Something you can see from anywhere, usually used of variables and subroutines that are visible
           everywhere in your program.  In Perl, only certain special variables are truly globalXmost variables
           (and all subroutines) exist only in the current package.  Global variables can be declared with
           "our". See XGlobal DeclarationsX in Camel chapter 4, XStatements and DeclarationsX.

       global destruction
           The garbage collection of globals (and the running of any associated object destructors) that takes
           place when a Perl interpreter is being shut down. Global destruction should not be confused with the
           Apocalypse, except perhaps when it should.

       glue language
           A language such as Perl that is good at hooking things together that werenXt intended to be hooked
           together.

       granularity
           The size of the pieces youXre dealing with, mentally speaking.

       grapheme
           A graphene is an allotrope of carbon arranged in a hexagonal crystal lattice one atom thick. A
           grapheme, or more fully, a grapheme cluster string is a single user-visible character, which may in
           turn be several characters (codepoints) long. For example, a carriage return plus a line feed is a
           single grapheme but two characters, while a XXX is a single grapheme but one, two, or even three
           characters, depending on normalization.

       greedy
           A subpattern whose quantifier wants to match as many things as possible.

       grep
           Originally from the old Unix editor command for XGlobally search for a Regular Expression and Print
           itX, now used in the general sense of any kind of search, especially text searches. Perl has a built-
           in "grep" function that searches a list for elements matching any given criterion, whereas the
           grep(1) program searches for lines matching a regular expression in one or more files.

       group
           A set of users of which you are a member. In some operating systems (like Unix), you can give certain
           file access permissions to other members of your group.

       GV  An internal Xglob valueX typedef, holding a typeglob. The "GV" type is a subclass of SV.

   H
       hacker
           Someone who is brilliantly persistent in solving technical problems, whether these involve golfing,
           fighting orcs, or programming.  Hacker is a neutral term, morally speaking. Good hackers are not to
           be confused with evil crackers or clueless script kiddies. If you confuse them, we will presume that
           you are either evil or clueless.

       handler
           A subroutine or method that Perl calls when your program needs to respond to some internal event,
           such as a signal, or an encounter with an operator subject to operator overloading. See also
           callback.

       hard reference
           A scalar value containing the actual address of a referent, such that the referentXs reference count
           accounts for it. (Some hard references are held internally, such as the implicit reference from one
           of a typeglobXs variable slots to its corresponding referent.) A hard reference is different from a
           symbolic reference.

       hash
           An unordered association of key/value pairs, stored such that you can easily use a string key to look
           up its associated data value. This glossary is like a hash, where the word to be defined is the key
           and the definition is the value. A hash is also sometimes septisyllabically called an Xassociative
           arrayX, which is a pretty good reason for simply calling it a XhashX instead.

       hash table
           A data structure used internally by Perl for implementing associative arrays (hashes) efficiently.
           See also bucket.

       header file
           A file containing certain required definitions that you must include XaheadX of the rest of your
           program to do certain obscure operations. A C header file has a .h extension. Perl doesnXt really
           have header files, though historically Perl has sometimes used translated .h files with a .ph
           extension. See "require" in Camel chapter 27, XFunctionsX. (Header files have been superseded by the
           module mechanism.)

       here document
           So called because of a similar construct in shells that pretends that the lines following the command
           are a separate file to be fed to the command, up to some terminating string. In Perl, however, itXs
           just a fancy form of quoting.

       hexadecimal
           A number in base 16, XhexX for short. The digits for 10 through 15 are customarily represented by the
           letters "a" through "f".  Hexadecimal constants in Perl start with "0x". See also the "hex" function
           in Camel chapter 27, XFunctionsX.

       home directory
           The directory you are put into when you log in. On a Unix system, the name is often placed into
           $ENV{HOME} or $ENV{LOGDIR} by login, but you can also find it with "(get""pwuid($<))[7]". (Some
           platforms do not have a concept of a home directory.)

       host
           The computer on which a program or other data resides.

       hubris
           Excessive pride, the sort of thing for which Zeus zaps you.  Also the quality that makes you write
           (and maintain) programs that other people wonXt want to say bad things about. Hence, the third great
           virtue of a programmer. See also laziness and impatience.

       HV  Short for a Xhash valueX typedef, which holds PerlXs internal representation of a hash. The "HV" type
           is a subclass of SV.

   I
       identifier
           A legally formed name for most anything in which a computer program might be interested. Many
           languages (including Perl) allow identifiers to start with an alphabetic character, and then contain
           alphabetics and digits. Perl also allows connector punctuation like the underscore character wherever
           it allows alphabetics. (Perl also has more complicated names, like qualified names.)

       impatience
           The anger you feel when the computer is being lazy.  This makes you write programs that donXt just
           react to your needs, but actually anticipate them. Or at least that pretend to. Hence, the second
           great virtue of a programmer. See also laziness and hubris.

       implementation
           How a piece of code actually goes about doing its job. Users of the code should not count on
           implementation details staying the same unless they are part of the published interface.

       import
           To gain access to symbols that are exported from another module. See "use" in Camel chapter 27,
           XFunctionsX.

       increment
           To increase the value of something by 1 (or by some other number, if so specified).

       indexing
           In olden days, the act of looking up a key in an actual index (such as a phone book). But now it's
           merely the act of using any kind of key or position to find the corresponding value, even if no index
           is involved. Things have degenerated to the point that PerlXs "index" function merely locates the
           position (index) of one string in another.

       indirect filehandle
           An expression that evaluates to something that can be used as a filehandle: a string (filehandle
           name), a typeglob, a typeglob reference, or a low-level IO object.

       indirection
           If something in a program isnXt the value youXre looking for but indicates where the value is, thatXs
           indirection. This can be done with either symbolic references or hard.

       indirect object
           In English grammar, a short noun phrase between a verb and its direct object indicating the
           beneficiary or recipient of the action. In Perl, "print STDOUT "$foo\n";" can be understood as Xverb
           indirect-object objectX, where "STDOUT" is the recipient of the "print" action, and "$foo" is the
           object being printed.  Similarly, when invoking a method, you might place the invocant in the dative
           slot between the method and its arguments:

               $gollum = new Pathetic::Creature "Smeagol";
               give $gollum "Fisssssh!";
               give $gollum "Precious!";

       indirect object slot
           The syntactic position falling between a method call and its arguments when using the indirect object
           invocation syntax. (The slot is distinguished by the absence of a comma between it and the next
           argument.) "STDERR" is in the indirect object slot here:

               print STDERR "Awake! Awake! Fear, Fire, Foes! Awake!\n";

       infix
           An operator that comes in between its operands, such as multiplication in "24 * 7".

       inheritance
           What you get from your ancestors, genetically or otherwise. If you happen to be a class, your
           ancestors are called base classes and your descendants are called derived classes. See single
           inheritance and multiple inheritance.

       instance
           Short for Xan instance of a classX, meaning an object of that class.

       instance data
           See instance variable.

       instance method
           A method of an object, as opposed to a class method.

           A method whose invocant is an object, not a package name. Every object of a class shares all the
           methods of that class, so an instance method applies to all instances of the class, rather than
           applying to a particular instance. Also see class method.

       instance variable
           An attribute of an object; data stored with the particular object rather than with the class as a
           whole.

       integer
           A number with no fractional (decimal) part. A counting number, like 1, 2, 3, and so on, but including
           0 and the negatives.

       interface
           The services a piece of code promises to provide forever, in contrast to its implementation, which it
           should feel free to change whenever it likes.

       interpolation
           The insertion of a scalar or list value somewhere in the middle of another value, such that it
           appears to have been there all along. In Perl, variable interpolation happens in double-quoted
           strings and patterns, and list interpolation occurs when constructing the list of values to pass to a
           list operator or other such construct that takes a "LIST".

       interpreter
           Strictly speaking, a program that reads a second program and does what the second program says
           directly without turning the program into a different form first, which is what compilers do. Perl is
           not an interpreter by this definition, because it contains a kind of compiler that takes a program
           and turns it into a more executable form (syntax trees) within the perl process itself, which the
           Perl runtime system then interprets.

       invocant
           The agent on whose behalf a method is invoked. In a class method, the invocant is a package name. In
           an instance method, the invocant is an object reference.

       invocation
           The act of calling up a deity, daemon, program, method, subroutine, or function to get it to do what
           you think itXs supposed to do.  We usually XcallX subroutines but XinvokeX methods, since it sounds
           cooler.

       I/O Input from, or output to, a file or device.

       IO  An internal I/O object. Can also mean indirect object.

       I/O layer
           One of the filters between the data and what you get as input or what you end up with as output.

       IPA India Pale Ale. Also the International Phonetic Alphabet, the standard alphabet used for phonetic
           notation worldwide. Draws heavily on Unicode, including many combining characters.

       IP  Internet Protocol, or Intellectual Property.

       IPC Interprocess Communication.

       is-a
           A relationship between two objects in which one object is considered to be a more specific version of
           the other, generic object: XA camel is a mammal.X Since the generic object really only exists in a
           Platonic sense, we usually add a little abstraction to the notion of objects and think of the
           relationship as being between a generic base class and a specific derived class. Oddly enough,
           Platonic classes donXt always have Platonic relationshipsXsee inheritance.

       iteration
           Doing something repeatedly.

       iterator
           A special programming gizmo that keeps track of where you are in something that youXre trying to
           iterate over. The "foreach" loop in Perl contains an iterator; so does a hash, allowing you to "each"
           through it.

       IV  The integer four, not to be confused with six, TomXs favorite editor. IV also means an internal
           Integer Value of the type a scalar can hold, not to be confused with an NV.

   J
       JAPH
           XJust Another Perl HackerX, a clever but cryptic bit of Perl code that, when executed, evaluates to
           that string. Often used to illustrate a particular Perl feature, and something of an ongoing
           Obfuscated Perl Contest seen in USENET signatures.

   K
       key The string index to a hash, used to look up the value associated with that key.

       keyword
           See reserved words.

   L
       label
           A name you give to a statement so that you can talk about that statement elsewhere in the program.

       laziness
           The quality that makes you go to great effort to reduce overall energy expenditure. It makes you
           write labor-saving programs that other people will find useful, and then document what you wrote so
           you donXt have to answer so many questions about it. Hence, the first great virtue of a programmer.
           Also hence, this book. See also impatience and hubris.

       leftmost longest
           The preference of the regular expression engine to match the leftmost occurrence of a pattern, then
           given a position at which a match will occur, the preference for the longest match (presuming the use
           of a greedy quantifier). See Camel chapter 5, XPattern MatchingX for much more on this subject.

       left shift
           A bit shift that multiplies the number by some power of 2.

       lexeme
           Fancy term for a token.

       lexer
           Fancy term for a tokener.

       lexical analysis
           Fancy term for tokenizing.

       lexical scoping
           Looking at your Oxford English Dictionary through a microscope. (Also known as static scoping,
           because dictionaries donXt change very fast.) Similarly, looking at variables stored in a private
           dictionary (namespace) for each scope, which are visible only from their point of declaration down to
           the end of the lexical scope in which they are declared. XSyn.  static scoping. XAnt. dynamic
           scoping.

       lexical variable
           A variable subject to lexical scoping, declared by "my". Often just called a XlexicalX. (The "our"
           declaration declares a lexically scoped name for a global variable, which is not itself a lexical
           variable.)

       library
           Generally, a collection of procedures. In ancient days, referred to a collection of subroutines in a
           .pl file. In modern times, refers more often to the entire collection of Perl modules on your system.

       LIFO
           Last In, First Out. See also FIFO. A LIFO is usually called a stack.

       line
           In Unix, a sequence of zero or more nonnewline characters terminated with a newline character. On
           non-Unix machines, this is emulated by the C library even if the underlying operating system has
           different ideas.

       linebreak
           A grapheme consisting of either a carriage return followed by a line feed or any character with the
           Unicode Vertical Space character property.

       line buffering
           Used by a standard I/O output stream that flushes its buffer after every newline. Many standard I/O
           libraries automatically set up line buffering on output that is going to the terminal.

       line number
           The number of lines read previous to this one, plus 1. Perl keeps a separate line number for each
           source or input file it opens. The current source fileXs line number is represented by "__LINE__".
           The current input line number (for the file that was most recently read via "<FH>") is represented by
           the $. ($INPUT_LINE_NUMBER) variable. Many error messages report both values, if available.

       link
           Used as a noun, a name in a directory that represents a file. A given file can have multiple links to
           it. ItXs like having the same phone number listed in the phone directory under different names. As a
           verb, to resolve a partially compiled fileXs unresolved symbols into a (nearly) executable image.
           Linking can generally be static or dynamic, which has nothing to do with static or dynamic scoping.

       LIST
           A syntactic construct representing a comma- separated list of expressions, evaluated to produce a
           list value.  Each expression in a "LIST" is evaluated in list context and interpolated into the list
           value.

       list
           An ordered set of scalar values.

       list context
           The situation in which an expression is expected by its surroundings (the code calling it) to return
           a list of values rather than a single value. Functions that want a "LIST" of arguments tell those
           arguments that they should produce a list value. See also context.

       list operator
           An operator that does something with a list of values, such as "join" or "grep". Usually used for
           named built-in operators (such as "print", "unlink", and "system") that do not require parentheses
           around their argument list.

       list value
           An unnamed list of temporary scalar values that may be passed around within a program from any list-
           generating function to any function or construct that provides a list context.

       literal
           A token in a programming language, such as a number or string, that gives you an actual value instead
           of merely representing possible values as a variable does.

       little-endian
           From Swift: someone who eats eggs little end first. Also used of computers that store the least
           significant byte of a word at a lower byte address than the most significant byte. Often considered
           superior to big-endian machines. See also big-endian.

       local
           Not meaning the same thing everywhere. A global variable in Perl can be localized inside a dynamic
           scope via the "local" operator.

       logical operator
           Symbols representing the concepts XandX, XorX, XxorX, and XnotX.

       lookahead
           An assertion that peeks at the string to the right of the current match location.

       lookbehind
           An assertion that peeks at the string to the left of the current match location.

       loop
           A construct that performs something repeatedly, like a roller coaster.

       loop control statement
           Any statement within the body of a loop that can make a loop prematurely stop looping or skip an
           iteration. Generally, you shouldnXt try this on roller coasters.

       loop label
           A kind of key or name attached to a loop (or roller coaster) so that loop control statements can talk
           about which loop they want to control.

       lowercase
           In Unicode, not just characters with the General Category of Lowercase Letter, but any character with
           the Lowercase property, including Modifier Letters, Letter Numbers, some Other Symbols, and one
           Combining Mark.

       lvaluable
           Able to serve as an lvalue.

       lvalue
           Term used by language lawyers for a storage location you can assign a new value to, such as a
           variable or an element of an array. The XlX is short for XleftX, as in the left side of an
           assignment, a typical place for lvalues. An lvaluable function or expression is one to which a value
           may be assigned, as in "pos($x) = 10".

       lvalue modifier
           An adjectival pseudofunction that warps the meaning of an lvalue in some declarative fashion.
           Currently there are three lvalue modifiers: "my", "our", and "local".

   M
       magic
           Technically speaking, any extra semantics attached to a variable such as $!, $0, %ENV, or %SIG, or to
           any tied variable.  Magical things happen when you diddle those variables.

       magical increment
           An increment operator that knows how to bump up ASCII alphabetics as well as numbers.

       magical variables
           Special variables that have side effects when you access them or assign to them. For example, in
           Perl, changing elements of the %ENV array also changes the corresponding environment variables that
           subprocesses will use. Reading the $!  variable gives you the current system error number or message.

       Makefile
           A file that controls the compilation of a program. Perl programs donXt usually need a Makefile
           because the Perl compiler has plenty of self-control.

       man The Unix program that displays online documentation (manual pages) for you.

       manpage
           A XpageX from the manuals, typically accessed via the man(1) command. A manpage contains a SYNOPSIS,
           a DESCRIPTION, a list of BUGS, and so on, and is typically longer than a page. There are manpages
           documenting commands, syscalls, library functions, devices, protocols, files, and such. In this book,
           we call any piece of standard Perl documentation (like perlop or perldelta) a manpage, no matter what
           format itXs installed in on your system.

       matching
           See pattern matching.

       member data
           See instance variable.

       memory
           This always means your main memory, not your disk.  Clouding the issue is the fact that your machine
           may implement virtual memory; that is, it will pretend that it has more memory than it really does,
           and itXll use disk space to hold inactive bits. This can make it seem like you have a little more
           memory than you really do, but itXs not a substitute for real memory. The best thing that can be said
           about virtual memory is that it lets your performance degrade gradually rather than suddenly when you
           run out of real memory. But your program can die when you run out of virtual memory, tooXif you
           havenXt thrashed your disk to death first.

       metacharacter
           A character that is not supposed to be treated normally. Which characters are to be treated specially
           as metacharacters varies greatly from context to context. Your shell will have certain
           metacharacters, double-quoted Perl strings have other metacharacters, and regular expression patterns
           have all the double-quote metacharacters plus some extra ones of their own.

       metasymbol
           Something weXd call a metacharacter except that itXs a sequence of more than one character.
           Generally, the first character in the sequence must be a true metacharacter to get the other
           characters in the metasymbol to misbehave along with it.

       method
           A kind of action that an object can take if you tell it to. See Camel chapter 12, XObjectsX.

       method resolution order
           The path Perl takes through @INC. By default, this is a double depth first search, once looking for
           defined methods and once for "AUTOLOAD". However, Perl lets you configure this with "mro".

       minicpan
           A CPAN mirror that includes just the latest versions for each distribution, probably created with
           "CPAN::Mini". See Camel chapter 19, XCPANX.

       minimalism
           The belief that Xsmall is beautifulX. Paradoxically, if you say something in a small language, it
           turns out big, and if you say it in a big language, it turns out small. Go figure.

       mode
           In the context of the stat(2) syscall, refers to the field holding the permission bits and the type
           of the file.

       modifier
           See statement modifier, regular expression, and lvalue, not necessarily in that order.

       module
           A file that defines a package of (almost) the same name, which can either export symbols or function
           as an object class.  (A moduleXs main .pm file may also load in other files in support of the
           module.) See the "use" built-in.

       modulus
           An integer divisor when youXre interested in the remainder instead of the quotient.

       mojibake
           When you speak one language and the computer thinks youXre speaking another. YouXll see odd
           translations when you send UTFX8, for instance, but the computer thinks you sent Latin-1, showing all
           sorts of weird characters instead. The term is written XXXXXXin Japanese and means Xcharacter rotX,
           an apt description. Pronounced ["modXibake"] in standard IPA phonetics, or approximately Xmoh-jee-
           bah-kehX.

       monger
           Short for one member of Perl mongers, a purveyor of Perl.

       mortal
           A temporary value scheduled to die when the current statement finishes.

       mro See method resolution order.

       multidimensional array
           An array with multiple subscripts for finding a single element. Perl implements these using
           referencesXsee Camel chapter 9, XData StructuresX.

       multiple inheritance
           The features you got from your mother and father, mixed together unpredictably. (See also inheritance
           and single inheritance.) In computer languages (including Perl), it is the notion that a given class
           may have multiple direct ancestors or base classes.

   N
       named pipe
           A pipe with a name embedded in the filesystem so that it can be accessed by two unrelated processes.

       namespace
           A domain of names. You neednXt worry about whether the names in one such domain have been used in
           another. See package.

       NaN Not a number. The value Perl uses for certain invalid or inexpressible floating-point operations.

       network address
           The most important attribute of a socket, like your telephoneXs telephone number. Typically an IP
           address. See also port.

       newline
           A single character that represents the end of a line, with the ASCII value of 012 octal under Unix
           (but 015 on a Mac), and represented by "\n" in Perl strings. For Windows machines writing text files,
           and for certain physical devices like terminals, the single newline gets automatically translated by
           your C library into a line feed and a carriage return, but normally, no translation is done.

       NFS Network File System, which allows you to mount a remote filesystem as if it were local.

       normalization
           Converting a text string into an alternate but equivalent canonical (or compatible) representation
           that can then be compared for equivalence. Unicode recognizes four different normalization forms:
           NFD, NFC, NFKD, and NFKC.

       null character
           A character with the numeric value of zero. ItXs used by C to terminate strings, but Perl allows
           strings to contain a null.

       null list
           A list value with zero elements, represented in Perl by "()".

       null string
           A string containing no characters, not to be confused with a string containing a null character,
           which has a positive length and is true.

       numeric context
           The situation in which an expression is expected by its surroundings (the code calling it) to return
           a number.  See also context and string context.

       numification
           (Sometimes spelled nummification and nummify.) Perl lingo for implicit conversion into a number; the
           related verb is numify.  Numification is intended to rhyme with mummification, and numify with
           mummify. It is unrelated to English numen, numina, numinous. We originally forgot the extra m a long
           time ago, and some people got used to our funny spelling, and so just as with "HTTP_REFERER"Xs own
           missing letter, our weird spelling has stuck around.

       NV  Short for Nevada, no part of which will ever be confused with civilization. NV also means an internal
           floating- point Numeric Value of the type a scalar can hold, not to be confused with an IV.

       nybble
           Half a byte, equivalent to one hexadecimal digit, and worth four bits.

   O
       object
           An instance of a class. Something that XknowsX what user-defined type (class) it is, and what it can
           do because of what class it is. Your program can request an object to do things, but the object gets
           to decide whether it wants to do them or not. Some objects are more accommodating than others.

       octal
           A number in base 8. Only the digits 0 through 7 are allowed. Octal constants in Perl start with 0, as
           in 013. See also the "oct" function.

       offset
           How many things you have to skip over when moving from the beginning of a string or array to a
           specific position within it. Thus, the minimum offset is zero, not one, because you donXt skip
           anything to get to the first item.

       one-liner
           An entire computer program crammed into one line of text.

       open source software
           Programs for which the source code is freely available and freely redistributable, with no commercial
           strings attached.  For a more detailed definition, see <http://www.opensource.org/osd.html>.

       operand
           An expression that yields a value that an operator operates on. See also precedence.

       operating system
           A special program that runs on the bare machine and hides the gory details of managing processes and
           devices.  Usually used in a looser sense to indicate a particular culture of programming. The loose
           sense can be used at varying levels of specificity.  At one extreme, you might say that all versions
           of Unix and Unix-lookalikes are the same operating system (upsetting many people, especially lawyers
           and other advocates). At the other extreme, you could say this particular version of this particular
           vendorXs operating system is different from any other version of this or any other vendorXs operating
           system. Perl is much more portable across operating systems than many other languages. See also
           architecture and platform.

       operator
           A gizmo that transforms some number of input values to some number of output values, often built into
           a language with a special syntax or symbol. A given operator may have specific expectations about
           what types of data you give as its arguments (operands) and what type of data you want back from it.

       operator overloading
           A kind of overloading that you can do on built-in operators to make them work on objects as if the
           objects were ordinary scalar values, but with the actual semantics supplied by the object class. This
           is set up with the overload pragmaXsee Camel chapter 13, XOverloadingX.

       options
           See either switches or regular expression modifiers.

       ordinal
           An abstract characterXs integer value. Same thing as codepoint.

       overloading
           Giving additional meanings to a symbol or construct.  Actually, all languages do overloading to one
           extent or another, since people are good at figuring out things from context.

       overriding
           Hiding or invalidating some other definition of the same name. (Not to be confused with overloading,
           which adds definitions that must be disambiguated some other way.) To confuse the issue further, we
           use the word with two overloaded definitions: to describe how you can define your own subroutine to
           hide a built-in function of the same name (see the section XOverriding Built-in FunctionsX in Camel
           chapter 11, XModulesX), and to describe how you can define a replacement method in a derived class to
           hide a base classXs method of the same name (see Camel chapter 12, XObjectsX).

       owner
           The one user (apart from the superuser) who has absolute control over a file. A file may also have a
           group of users who may exercise joint ownership if the real owner permits it. See permission bits.

   P
       package
           A namespace for global variables, subroutines, and the like, such that they can be kept separate from
           like-named symbols in other namespaces. In a sense, only the package is global, since the symbols in
           the packageXs symbol table are only accessible from code compiled outside the package by naming the
           package. But in another sense, all package symbols are also globalsXtheyXre just well-organized
           globals.

       pad Short for scratchpad.

       parameter
           See argument.

       parent class
           See base class.

       parse tree
           See syntax tree.

       parsing
           The subtle but sometimes brutal art of attempting to turn your possibly malformed program into a
           valid syntax tree.

       patch
           To fix by applying one, as it were. In the realm of hackerdom, a listing of the differences between
           two versions of a program as might be applied by the patch(1) program when you want to fix a bug or
           upgrade your old version.

       PATH
           The list of directories the system searches to find a program you want to execute.  The list is
           stored as one of your environment variables, accessible in Perl as $ENV{PATH}.

       pathname
           A fully qualified filename such as /usr/bin/perl. Sometimes confused with "PATH".

       pattern
           A template used in pattern matching.

       pattern matching
           Taking a pattern, usually a regular expression, and trying the pattern various ways on a string to
           see whether thereXs any way to make it fit. Often used to pick interesting tidbits out of a file.

       PAUSE
           The Perl Authors Upload SErver (<http://pause.perl.org>), the gateway for modules on their way to
           CPAN.

       Perl mongers
           A Perl user group, taking the form of its name from the New York Perl mongers, the first Perl user
           group. Find one near you at <http://www.pm.org>.

       permission bits
           Bits that the owner of a file sets or unsets to allow or disallow access to other people. These flag
           bits are part of the mode word returned by the "stat" built-in when you ask about a file. On Unix
           systems, you can check the ls(1) manpage for more information.

       Pern
           What you get when you do "Perl++" twice. Doing it only once will curl your hair. You have to
           increment it eight times to shampoo your hair. Lather, rinse, iterate.

       pipe
           A direct connection that carries the output of one process to the input of another without an
           intermediate temporary file.  Once the pipe is set up, the two processes in question can read and
           write as if they were talking to a normal file, with some caveats.

       pipeline
           A series of processes all in a row, linked by pipes, where each passes its output stream to the next.

       platform
           The entire hardware and software context in which a program runs. A program written in a platform-
           dependent language might break if you change any of the following: machine, operating system,
           libraries, compiler, or system configuration. The perl interpreter has to be compiled differently for
           each platform because it is implemented in C, but programs written in the Perl language are largely
           platform independent.

       pod The markup used to embed documentation into your Perl code. Pod stands for XPlain old documentationX.
           See Camel chapter 23, XPlain Old DocumentationX.

       pod command
           A sequence, such as "=head1", that denotes the start of a pod section.

       pointer
           A variable in a language like C that contains the exact memory location of some other item. Perl
           handles pointers internally so you donXt have to worry about them. Instead, you just use symbolic
           pointers in the form of keys and variable names, or hard references, which arenXt pointers (but act
           like pointers and do in fact contain pointers).

       polymorphism
           The notion that you can tell an object to do something generic, and the object will interpret the
           command in different ways depending on its type. [< Greek XXXX- + XXXXX, many forms.]

       port
           The part of the address of a TCP or UDP socket that directs packets to the correct process after
           finding the right machine, something like the phone extension you give when you reach the company
           operator. Also the result of converting code to run on a different platform than originally intended,
           or the verb denoting this conversion.

       portable
           Once upon a time, C code compilable under both BSD and SysV. In general, code that can be easily
           converted to run on another platform, where XeasilyX can be defined however you like, and usually is.
           Anything may be considered portable if you try hard enough, such as a mobile home or London Bridge.

       porter
           Someone who XcarriesX software from one platform to another.  Porting programs written in platform-
           dependent languages such as C can be difficult work, but porting programs like Perl is very much
           worth the agony.

       possessive
           Said of quantifiers and groups in patterns that refuse to give up anything once theyXve gotten their
           mitts on it. Catchier and easier to say than the even more formal nonbacktrackable.

       POSIX
           The Portable Operating System Interface specification.

       postfix
           An operator that follows its operand, as in "$x++".

       pp  An internal shorthand for a Xpush- popX code; that is, C code implementing PerlXs stack machine.

       pragma
           A standard module whose practical hints and suggestions are received (and possibly ignored) at
           compile time. Pragmas are named in all lowercase.

       precedence
           The rules of conduct that, in the absence of other guidance, determine what should happen first.  For
           example, in the absence of parentheses, you always do multiplication before addition.

       prefix
           An operator that precedes its operand, as in "++$x".

       preprocessing
           What some helper process did to transform the incoming data into a form more suitable for the current
           process. Often done with an incoming pipe. See also C preprocessor.

       primary maintainer
           The author that PAUSE allows to assign co-maintainer permissions to a namespace. A primary maintainer
           can give up this distinction by assigning it to another PAUSE author. See Camel chapter 19, XCPANX.

       procedure
           A subroutine.

       process
           An instance of a running program. Under multitasking systems like Unix, two or more separate
           processes could be running the same program independently at the same timeXin fact, the "fork"
           function is designed to bring about this happy state of affairs. Under other operating systems,
           processes are sometimes called XthreadsX, XtasksX, or XjobsX, often with slight nuances in meaning.

       program
           See script.

       program generator
           A system that algorithmically writes code for you in a high-level language. See also code generator.

       progressive matching
           Pattern matching  matching>that picks up where it left off before.

       property
           See either instance variable or character property.

       protocol
           In networking, an agreed-upon way of sending messages back and forth so that neither correspondent
           will get too confused.

       prototype
           An optional part of a subroutine declaration telling the Perl compiler how many and what flavor of
           arguments may be passed as actual arguments, so you can write subroutine calls that parse much like
           built-in functions. (Or donXt parse, as the case may be.)

       pseudofunction
           A construct that sometimes looks like a function but really isnXt. Usually reserved for lvalue
           modifiers like "my", for context modifiers like "scalar", and for the pick-your-own-quotes
           constructs, "q//", "qq//", "qx//", "qw//", "qr//", "m//", "s///", "y///", and "tr///".

       pseudohash
           Formerly, a reference to an array whose initial element happens to hold a reference to a hash. You
           used to be able to treat a pseudohash reference as either an array reference or a hash reference.
           Pseduohashes are no longer supported.

       pseudoliteral
           An operator X"that looks something like a literal, such as the output-grabbing operator, <literal
           moreinfo="none""`>"command""`".

       public domain
           Something not owned by anybody. Perl is copyrighted and is thus not in the public domainXitXs just
           freely available and freely redistributable.

       pumpkin
           A notional XbatonX handed around the Perl community indicating who is the lead integrator in some
           arena of development.

       pumpking
           A pumpkin holder, the person in charge of pumping the pump, or at least priming it. Must be willing
           to play the part of the Great Pumpkin now and then.

       PV  A Xpointer valueX, which is Perl Internals Talk for a "char*".

   Q
       qualified
           Possessing a complete name. The symbol $Ent::moot is qualified; $moot is unqualified. A fully
           qualified filename is specified from the top-level directory.

       quantifier
           A component of a regular expression specifying how many times the foregoing atom may occur.

   R
       race condition
           A race condition exists when the result of several interrelated events depends on the ordering of
           those events, but that order cannot be guaranteed due to nondeterministic timing effects. If two or
           more programs, or parts of the same program, try to go through the same series of events, one might
           interrupt the work of the other. This is a good way to find an exploit.

       readable
           With respect to files, one that has the proper permission bit set to let you access the file. With
           respect to computer programs, one thatXs written well enough that someone has a chance of figuring
           out what itXs trying to do.

       reaping
           The last rites performed by a parent process on behalf of a deceased child process so that it doesnXt
           remain a zombie.  See the "wait" and "waitpid" function calls.

       record
           A set of related data values in a file or stream, often associated with a unique key field. In Unix,
           often commensurate with a line, or a blank-lineXterminated set of lines (a XparagraphX).  Each line
           of the /etc/passwd file is a record, keyed on login name, containing information about that user.

       recursion
           The art of defining something (at least partly) in terms of itself, which is a naughty no-no in
           dictionaries but often works out okay in computer programs if youXre careful not to recurse forever
           (which is like an infinite loop with more spectacular failure modes).

       reference
           Where you look to find a pointer to information somewhere else. (See indirection.) References come in
           two flavors: symbolic references and hard references.

       referent
           Whatever a reference refers to, which may or may not have a name. Common types of referents include
           scalars, arrays, hashes, and subroutines.

       regex
           See regular expression.

       regular expression
           A single entity with various interpretations, like an elephant. To a computer scientist, itXs a
           grammar for a little language in which some strings are legal and others arenXt. To normal people,
           itXs a pattern you can use to find what youXre looking for when it varies from case to case. PerlXs
           regular expressions are far from regular in the theoretical sense, but in regular use they work quite
           well.  HereXs a regular expression: "/Oh s.*t./". This will match strings like X"Oh say can you see
           by the dawn's early light"X and X"Oh sit!"X. See Camel chapter 5, XPattern MatchingX.

       regular expression modifier
           An option on a pattern or substitution, such as "/i" to render the pattern case- insensitive.

       regular file
           A file thatXs not a directory, a device, a named pipe or socket, or a symbolic link. Perl uses the
           "Xf" file test operator to identify regular files. Sometimes called a XplainX file.

       relational operator
           An operator that says whether a particular ordering relationship is true about a pair of operands.
           Perl has both numeric and string relational operators. See collating sequence.

       reserved words
           A word with a specific, built-in meaning to a compiler, such as "if" or "delete". In many languages
           (not Perl), itXs illegal to use reserved words to name anything else. (Which is why theyXre reserved,
           after all.) In Perl, you just canXt use them to name labels or filehandles. Also called XkeywordsX.

       return value
           The value produced by a subroutine or expression when evaluated. In Perl, a return value may be
           either a list or a scalar.

       RFC Request For Comment, which despite the timid connotations is the name of a series of important
           standards documents.

       right shift
           A bit shift that divides a number by some power of 2.

       role
           A name for a concrete set of behaviors. A role is a way to add behavior to a class without
           inheritance.

       root
           The superuser ("UID" == 0). Also the top-level directory of the filesystem.

       RTFM
           What you are told when someone thinks you should Read The Fine Manual.

       run phase
           Any time after Perl starts running your main program.  See also compile phase. Run phase is mostly
           spent in runtime but may also be spent in compile time when "require", "do" "FILE", or "eval"
           "STRING" operators are executed, or when a substitution uses the "/ee" modifier.

       runtime
           The time when Perl is actually doing what your code says to do, as opposed to the earlier period of
           time when it was trying to figure out whether what you said made any sense whatsoever, which is
           compile time.

       runtime pattern
           A pattern that contains one or more variables to be interpolated before parsing the pattern as a
           regular expression, and that therefore cannot be analyzed at compile time, but must be reanalyzed
           each time the pattern match operator is evaluated.  Runtime patterns are useful but expensive.

       RV  A recreational vehicle, not to be confused with vehicular recreation. RV also means an internal
           Reference Value of the type a scalar can hold. See also IV and NV if youXre not confused yet.

       rvalue
           A value that you might find on the right side of an assignment. See also lvalue.

   S
       sandbox
           A walled off area thatXs not supposed to affect beyond its walls. You let kids play in the sandbox
           instead of running in the road.  See Camel chapter 20, XSecurityX.

       scalar
           A simple, singular value; a number, string, or reference.

       scalar context
           The situation in which an expression is expected by its surroundings (the code calling it) to return
           a single value rather than a list of values. See also context and list context. A scalar context
           sometimes imposes additional constraints on the return valueXsee string context and numeric context.
           Sometimes we talk about a Boolean context inside conditionals, but this imposes no additional
           constraints, since any scalar value, whether numeric or string, is already true or false.

       scalar literal
           A number or quoted stringXan actual value in the text of your program, as opposed to a variable.

       scalar value
           A value that happens to be a scalar as opposed to a list.

       scalar variable
           A variable prefixed with "$" that holds a single value.

       scope
           From how far away you can see a variable, looking through one. Perl has two visibility mechanisms. It
           does dynamic scoping of "local" variables, meaning that the rest of the block, and any subroutines
           that are called by the rest of the block, can see the variables that are local to the block. Perl
           does lexical scoping of "my" variables, meaning that the rest of the block can see the variable, but
           other subroutines called by the block cannot see the variable.

       scratchpad
           The area in which a particular invocation of a particular file or subroutine keeps some of its
           temporary values, including any lexically scoped variables.

       script
           A text file that is a program intended to be executed directly rather than compiled to another form
           of file before execution.

           Also, in the context of Unicode, a writing system for a particular language or group of languages,
           such as Greek, Bengali, or Tengwar.

       script kiddie
           A cracker who is not a hacker but knows just enough to run canned scripts. A cargo-cult programmer.

       sed A venerable Stream EDitor from which Perl derives some of its ideas.

       semaphore
           A fancy kind of interlock that prevents multiple threads or processes from using up the same
           resources simultaneously.

       separator
           A character or string that keeps two surrounding strings from being confused with each other. The
           "split" function works on separators. Not to be confused with delimiters or terminators. The XorX in
           the previous sentence separated the two alternatives.

       serialization
           Putting a fancy data structure into linear order so that it can be stored as a string in a disk file
           or database, or sent through a pipe. Also called marshalling.

       server
           In networking, a process that either advertises a service or just hangs around at a known location
           and waits for clients who need service to get in touch with it.

       service
           Something you do for someone else to make them happy, like giving them the time of day (or of their
           life). On some machines, well-known services are listed by the "getservent" function.

       setgid
           Same as setuid, only having to do with giving away group privileges.

       setuid
           Said of a program that runs with the privileges of its owner rather than (as is usually the case) the
           privileges of whoever is running it. Also describes the bit in the mode word (permission bits) that
           controls the feature. This bit must be explicitly set by the owner to enable this feature, and the
           program must be carefully written not to give away more privileges than it ought to.

       shared memory
           A piece of memory accessible by two different processes who otherwise would not see each otherXs
           memory.

       shebang
           Irish for the whole McGillicuddy. In Perl culture, a portmanteau of XsharpX and XbangX, meaning the
           "#!" sequence that tells the system where to find the interpreter.

       shell
           A command-line interpreter. The program that interactively gives you a prompt, accepts one or more
           lines of input, and executes the programs you mentioned, feeding each of them their proper arguments
           and input data. Shells can also execute scripts containing such commands. Under Unix, typical shells
           include the Bourne shell (/bin/sh), the C shell (/bin/csh), and the Korn shell (/bin/ksh).  Perl is
           not strictly a shell because itXs not interactive (although Perl programs can be interactive).

       side effects
           Something extra that happens when you evaluate an expression. Nowadays it can refer to almost
           anything. For example, evaluating a simple assignment statement typically has the Xside effectX of
           assigning a value to a variable. (And you thought assigning the value was your primary intent in the
           first place!) Likewise, assigning a value to the special variable $| ($AUTOFLUSH) has the side effect
           of forcing a flush after every "write" or "print" on the currently selected filehandle.

       sigil
           A glyph used in magic. Or, for Perl, the symbol in front of a variable name, such as "$", "@", and
           "%".

       signal
           A bolt out of the blue; that is, an event triggered by the operating system, probably when youXre
           least expecting it.

       signal handler
           A subroutine that, instead of being content to be called in the normal fashion, sits around waiting
           for a bolt out of the blue before it will deign to execute. Under Perl, bolts out of the blue are
           called signals, and you send them with the "kill" built-in. See the %SIG hash in Camel chapter 25,
           XSpecial NamesX and the section XSignalsX in Camel chapter 15, XInterprocess CommunicationX.

       single inheritance
           The features you got from your mother, if she told you that you donXt have a father. (See also
           inheritance and multiple inheritance.) In computer languages, the idea that classes reproduce
           asexually so that a given class can only have one direct ancestor or base class. Perl supplies no
           such restriction, though you may certainly program Perl that way if you like.

       slice
           A selection of any number of elements from a list, array, or hash.

       slurp
           To read an entire file into a string in one operation.

       socket
           An endpoint for network communication among multiple processes that works much like a telephone or a
           post office box. The most important thing about a socket is its network address (like a phone
           number). Different kinds of sockets have different kinds of addressesXsome look like filenames, and
           some donXt.

       soft reference
           See symbolic reference.

       source filter
           A special kind of module that does preprocessing on your script just before it gets to the tokener.

       stack
           A device you can put things on the top of, and later take them back off in the opposite order in
           which you put them on. See LIFO.

       standard
           Included in the official Perl distribution, as in a standard module, a standard tool, or a standard
           Perl manpage.

       standard error
           The default output stream for nasty remarks that donXt belong in standard output. Represented within
           a Perl program by the output>  filehandle "STDERR". You can use this stream explicitly, but the "die"
           and "warn" built-ins write to your standard error stream automatically (unless trapped or otherwise
           intercepted).

       standard input
           The default input stream for your program, which if possible shouldnXt care where its data is coming
           from. Represented within a Perl program by the filehandle "STDIN".

       standard I/O
           A standard C library for doing buffered input and output to the operating system. (The XstandardX of
           standard I/O is at most marginally related to the XstandardX of standard input and output.)  In
           general, Perl relies on whatever implementation of standard I/O a given operating system supplies, so
           the buffering characteristics of a Perl program on one machine may not exactly match those on another
           machine.  Normally this only influences efficiency, not semantics. If your standard I/O package is
           doing block buffering and you want it to flush the buffer more often, just set the $| variable to a
           true value.

       Standard Library
           Everything that comes with the official perl distribution. Some vendor versions of perl change their
           distributions, leaving out some parts or including extras. See also dual-lived.

       standard output
           The default output stream for your program, which if possible shouldnXt care where its data is going.
           Represented within a Perl program by the filehandle "STDOUT".

       statement
           A command to the computer about what to do next, like a step in a recipe: XAdd marmalade to batter
           and mix until mixed.X A statement is distinguished from a declaration, which doesnXt tell the
           computer to do anything, but just to learn something.

       statement modifier
           A conditional or loop that you put after the statement instead of before, if you know what we mean.

       static
           Varying slowly compared to something else. (Unfortunately, everything is relatively stable compared
           to something else, except for certain elementary particles, and weXre not so sure about them.) In
           computers, where things are supposed to vary rapidly, XstaticX has a derogatory connotation,
           indicating a slightly dysfunctional variable, subroutine, or method. In Perl culture, the word is
           politely avoided.

           If youXre a C or C++ programmer, you might be looking for PerlXs "state" keyword.

       static method
           No such thing. See class method.

       static scoping
           No such thing. See lexical scoping.

       static variable
           No such thing. Just use a lexical variable in a scope larger than your subroutine, or declare it with
           "state" instead of with "my".

       stat structure
           A special internal spot in which Perl keeps the information about the last file on which you
           requested information.

       status
           The value returned to the parent process when one of its child processes dies. This value is placed
           in the special variable $?. Its upper eight bits are the exit status of the defunct process, and its
           lower eight bits identify the signal (if any) that the process died from. On Unix systems, this
           status value is the same as the status word returned by wait(2). See "system" in Camel chapter 27,
           XFunctionsX.

       STDERR
           See standard error.

       STDIN
           See standard input.

       STDIO
           See standard I/O.

       STDOUT
           See standard output.

       stream
           A flow of data into or out of a process as a steady sequence of bytes or characters, without the
           appearance of being broken up into packets. This is a kind of interfaceXthe underlying implementation
           may well break your data up into separate packets for delivery, but this is hidden from you.

       string
           A sequence of characters such as XHe said !@#*&%@#*?!X.  A string does not have to be entirely
           printable.

       string context
           The situation in which an expression is expected by its surroundings (the code calling it) to return
           a string.  See also context and numeric context.

       stringification
           The process of producing a string representation of an abstract object.

       struct
           C keyword introducing a structure definition or name.

       structure
           See data structure.

       subclass
           See derived class.

       subpattern
           A component of a regular expression pattern.

       subroutine
           A named or otherwise accessible piece of program that can be invoked from elsewhere in the program in
           order to accomplish some subgoal of the program. A subroutine is often parameterized to accomplish
           different but related things depending on its input arguments. If the subroutine returns a meaningful
           value, it is also called a function.

       subscript
           A value that indicates the position of a particular array element in an array.

       substitution
           Changing parts of a string via the "s///" operator. (We avoid use of this term to mean variable
           interpolation.)

       substring
           A portion of a string, starting at a certain character position (offset) and proceeding for a certain
           number of characters.

       superclass
           See base class.

       superuser
           The person whom the operating system will let do almost anything. Typically your system administrator
           or someone pretending to be your system administrator. On Unix systems, the root user. On Windows
           systems, usually the Administrator user.

       SV  Short for Xscalar valueX. But within the Perl interpreter, every referent is treated as a member of a
           class derived from SV, in an object-oriented sort of way. Every value inside Perl is passed around as
           a C language "SV*" pointer. The SV struct knows its own Xreferent typeX, and the code is smart enough
           (we hope) not to try to call a hash function on a subroutine.

       switch
           An option you give on a command line to influence the way your program works, usually introduced with
           a minus sign.  The word is also used as a nickname for a switch statement.

       switch cluster
           The combination of multiple command- line switches (e.g., "Xa Xb Xc") into one switch (e.g., "Xabc").
           Any switch with an additional argument must be the last switch in a cluster.

       switch statement
           A program technique that lets you evaluate an expression and then, based on the value of the
           expression, do a multiway branch to the appropriate piece of code for that value. Also called a Xcase
           structureX, named after the similar Pascal construct. Most switch statements in Perl are spelled
           "given". See XThe "given" statementX in Camel chapter 4, XStatements and DeclarationsX.

       symbol
           Generally, any token or metasymbol. Often used more specifically to mean the sort of name you might
           find in a symbol table.

       symbolic debugger
           A program that lets you step through the execution of your program, stopping or printing things out
           here and there to see whether anything has gone wrong, and, if so, what. The XsymbolicX part just
           means that you can talk to the debugger using the same symbols with which your program is written.

       symbolic link
           An alternate filename that points to the real filename, which in turn points to the real file.
           Whenever the operating system is trying to parse a pathname containing a symbolic link, it merely
           substitutes the new name and continues parsing.

       symbolic reference
           A variable whose value is the name of another variable or subroutine. By dereferencing the first
           variable, you can get at the second one. Symbolic references are illegal under "use strict "refs"".

       symbol table
           Where a compiler remembers symbols. A program like Perl must somehow remember all the names of all
           the variables, filehandles, and subroutines youXve used. It does this by placing the names in a
           symbol table, which is implemented in Perl using a hash table. There is a separate symbol table for
           each package to give each package its own namespace.

       synchronous
           Programming in which the orderly sequence of events can be determined; that is, when things happen
           one after the other, not at the same time.

       syntactic sugar
           An alternative way of writing something more easily; a shortcut.

       syntax
           From Greek XXXXXXXX, Xwith-arrangementX. How things (particularly symbols) are put together with each
           other.

       syntax tree
           An internal representation of your program wherein lower-level constructs dangle off the higher-level
           constructs enclosing them.

       syscall
           A function call directly to the operating system. Many of the important subroutines and functions you
           use arenXt direct system calls, but are built up in one or more layers above the system call level.
           In general, Perl programmers donXt need to worry about the distinction. However, if you do happen to
           know which Perl functions are really syscalls, you can predict which of these will set the $!
           ($ERRNO) variable on failure. Unfortunately, beginning programmers often confusingly employ the term
           Xsystem callX to mean what happens when you call the Perl "system" function, which actually involves
           many syscalls. To avoid any confusion, we nearly always say XsyscallX for something you could call
           indirectly via PerlXs "syscall" function, and never for something you would call with PerlXs "system"
           function.

   T
       taint checks
           The special bookkeeping Perl does to track the flow of external data through your program and
           disallow their use in system commands.

       tainted
           Said of data derived from the grubby hands of a user, and thus unsafe for a secure program to rely
           on. Perl does taint checks if you run a setuid (or setgid) program, or if you use the "XT" switch.

       taint mode
           Running under the "XT" switch, marking all external data as suspect and refusing to use it with
           system commands. See Camel chapter 20, XSecurityX.

       TCP Short for Transmission Control Protocol. A protocol wrapped around the Internet Protocol to make an
           unreliable packet transmission mechanism appear to the application program to be a reliable stream of
           bytes.  (Usually.)

       term
           Short for a XterminalXXthat is, a leaf node of a syntax tree. A thing that functions grammatically as
           an operand for the operators in an expression.

       terminator
           A character or string that marks the end of another string. The $/ variable contains the string that
           terminates a "readline" operation, which "chomp" deletes from the end. Not to be confused with
           delimiters or separators. The period at the end of this sentence is a terminator.

       ternary
           An operator taking three operands. Sometimes pronounced trinary.

       text
           A string or file containing primarily printable characters.

       thread
           Like a forked process, but without forkXs inherent memory protection. A thread is lighter weight than
           a full process, in that a process could have multiple threads running around in it, all fighting over
           the same processXs memory space unless steps are taken to protect threads from one another.

       tie The bond between a magical variable and its implementation class. See the "tie" function in Camel
           chapter 27, XFunctionsX and Camel chapter 14, XTied VariablesX.

       titlecase
           The case used for capitals that are followed by lowercase characters instead of by more capitals.
           Sometimes called sentence case or headline case. English doesnXt use Unicode titlecase, but casing
           rules for English titles are more complicated than simply capitalizing each wordXs first character.

       TMTOWTDI
           ThereXs More Than One Way To Do It, the Perl Motto. The notion that there can be more than one valid
           path to solving a programming problem in context. (This doesnXt mean that more ways are always better
           or that all possible paths are equally desirableXjust that there need not be One True Way.)

       token
           A morpheme in a programming language, the smallest unit of text with semantic significance.

       tokener
           A module that breaks a program text into a sequence of tokens for later analysis by a parser.

       tokenizing
           Splitting up a program text into tokens. Also known as XlexingX, in which case you get XlexemesX
           instead of tokens.

       toolbox approach
           The notion that, with a complete set of simple tools that work well together, you can build almost
           anything you want. Which is fine if youXre assembling a tricycle, but if youXre building a
           defranishizing comboflux regurgalator, you really want your own machine shop in which to build
           special tools. Perl is sort of a machine shop.

       topic
           The thing youXre working on. Structures like "while(<>)", "for", "foreach", and "given" set the topic
           for you by assigning to $_, the default (topic) variable.

       transliterate
           To turn one string representation into another by mapping each character of the source string to its
           corresponding character in the result string. Not to be confused with translation: for example, Greek
           XXXXXXXXXX transliterates into polychromos but translates into many-colored. See the "tr///" operator
           in Camel chapter 5, XPattern MatchingX.

       trigger
           An event that causes a handler to be run.

       trinary
           Not a stellar system with three stars, but an operator taking three operands. Sometimes pronounced
           ternary.

       troff
           A venerable typesetting language from which Perl derives the name of its $% variable and which is
           secretly used in the production of Camel books.

       true
           Any scalar value that doesnXt evaluate to 0 or "".

       truncating
           Emptying a file of existing contents, either automatically when opening a file for writing or
           explicitly via the "truncate" function.

       type
           See data type and class.

       type casting
           Converting data from one type to another. C permits this.  Perl does not need it. Nor want it.

       typedef
           A type definition in the C and C++ languages.

       typed lexical
           A lexical variable  lexical>that is declared with a class type: "my Pony $bill".

       typeglob
           Use of a single identifier, prefixed with "*". For example, *name stands for any or all of $name,
           @name, %name, &name, or just "name". How you use it determines whether it is interpreted as all or
           only one of them. See XTypeglobs and FilehandlesX in Camel chapter 2, XBits and PiecesX.

       typemap
           A description of how C types may be transformed to and from Perl types within an extension module
           written in XS.

   U
       UDP User Datagram Protocol, the typical way to send datagrams over the Internet.

       UID A user ID. Often used in the context of file or process ownership.

       umask
           A mask of those permission bits that should be forced off when creating files or directories, in
           order to establish a policy of whom youXll ordinarily deny access to. See the "umask" function.

       unary operator
           An operator with only one operand, like "!" or "chdir". Unary operators are usually prefix operators;
           that is, they precede their operand. The "++" and "XX" operators can be either prefix or postfix.
           (Their position does change their meanings.)

       Unicode
           A character set comprising all the major character sets of the world, more or less. See
           <http://www.unicode.org>.

       Unix
           A very large and constantly evolving language with several alternative and largely incompatible
           syntaxes, in which anyone can define anything any way they choose, and usually do. Speakers of this
           language think itXs easy to learn because itXs so easily twisted to oneXs own ends, but dialectical
           differences make tribal intercommunication nearly impossible, and travelers are often reduced to a
           pidgin-like subset of the language. To be universally understood, a Unix shell programmer must spend
           years of study in the art. Many have abandoned this discipline and now communicate via an Esperanto-
           like language called Perl.

           In ancient times, Unix was also used to refer to some code that a couple of people at Bell Labs wrote
           to make use of a PDP-7 computer that wasnXt doing much of anything else at the time.

       uppercase
           In Unicode, not just characters with the General Category of Uppercase Letter, but any character with
           the Uppercase property, including some Letter Numbers and Symbols. Not to be confused with titlecase.

   V
       value
           An actual piece of data, in contrast to all the variables, references, keys, indices, operators, and
           whatnot that you need to access the value.

       variable
           A named storage location that can hold any of various kinds of value, as your program sees fit.

       variable interpolation
           The interpolation of a scalar or array variable into a string.

       variadic
           Said of a function that happily receives an indeterminate number of actual arguments.

       vector
           Mathematical jargon for a list of scalar values.

       virtual
           Providing the appearance of something without the reality, as in: virtual memory is not real memory.
           (See also memory.) The opposite of XvirtualX is XtransparentX, which means providing the reality of
           something without the appearance, as in: Perl handles the variable-length UTFX8 character encoding
           transparently.

       void context
           A form of scalar context in which an expression is not expected to return any value at all and is
           evaluated for its side effects alone.

       v-string
           A XversionX or XvectorX string specified with a "v" followed by a series of decimal integers in dot
           notation, for instance, "v1.20.300.4000". Each number turns into a character with the specified
           ordinal value. (The "v" is optional when there are at least three integers.)

   W
       warning
           A message printed to the "STDERR" stream to the effect that something might be wrong but isnXt worth
           blowing up over. See "warn" in Camel chapter 27, XFunctionsX and the "warnings" pragma in Camel
           chapter 28, XPragmantic ModulesX.

       watch expression
           An expression which, when its value changes, causes a breakpoint in the Perl debugger.

       weak reference
           A reference that doesnXt get counted normally. When all the normal references to data disappear, the
           data disappears. These are useful for circular references that would never disappear otherwise.

       whitespace
           A character that moves your cursor but doesnXt otherwise put anything on your screen. Typically
           refers to any of: space, tab, line feed, carriage return, or form feed. In Unicode, matches many
           other characters that Unicode considers whitespace, including the X-XX .

       word
           In normal XcomputereseX, the piece of data of the size most efficiently handled by your computer,
           typically 32 bits or so, give or take a few powers of 2. In Perl culture, it more often refers to an
           alphanumeric identifier (including underscores), or to a string of nonwhitespace characters bounded
           by whitespace or string boundaries.

       working directory
           Your current directory, from which relative pathnames are interpreted by the operating system. The
           operating system knows your current directory because you told it with a "chdir", or because you
           started out in the place where your parent process was when you were born.

       wrapper
           A program or subroutine that runs some other program or subroutine for you, modifying some of its
           input or output to better suit your purposes.

       WYSIWYG
           What You See Is What You Get. Usually used when something that appears on the screen matches how it
           will eventually look, like PerlXs "format" declarations. Also used to mean the opposite of magic
           because everything works exactly as it appears, as in the three- argument form of "open".

   X
       XS  An extraordinarily exported, expeditiously excellent, expressly eXternal Subroutine, executed in
           existing C or C++ or in an exciting extension language called (exasperatingly) XS.

       XSUB
           An external subroutine defined in XS.

   Y
       yacc
           Yet Another Compiler Compiler. A parser generator without which Perl probably would not have existed.
           See the file perly.y in the Perl source distribution.

   Z
       zero width
           A subpattern assertion matching the null string between characters.

       zombie
           A process that has died (exited) but whose parent has not yet received proper notification of its
           demise by virtue of having called "wait" or "waitpid". If you "fork", you must clean up after your
           child processes when they exit; otherwise, the process table will fill up and your system
           administrator will Not Be Happy with you.

       Based on the Glossary of Programming Perl, Fourth Edition, by Tom Christiansen, brian d foy, Larry Wall,
       & Jon Orwant.  Copyright (c) 2000, 1996, 1991, 2012 O'Reilly Media, Inc.  This document may be
       distributed under the same terms as Perl itself.