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PERLGLOSSARY(1)	       Perl Programmers Reference Guide	       PERLGLOSSARY(1)

       perlglossary - Perl Glossary

       A glossary of terms (technical and otherwise) used in the Perl
       documentation.  Other useful sources include the Free On-Line
       Dictionary of Computing <>,
       the Jargon File <>, and Wikipedia

       accessor methods
	   A "method" used to indirectly inspect or update an "object"'s 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.

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

	   A nickname for something, which behaves in all ways as though you'd
	   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's 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.

	   A list of possible choices from which you may select only one, as
	   in "Would you like door A, B, or C?"	 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".

	   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.

	   The kind of computer you're working on, where one "kind" of
	   computer 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 it's running on than programs in other languages, such
	   as C, that are compiled into machine code.  See also "platform" and
	   "operating system".

	   A piece of data supplied to a program, "subroutine", "function", or
	   "method" to tell it what it's supposed to do.  Also called a

	   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.

	   An ordered sequence of values, stored such that you can easily
	   access any of the values using an integer "subscript" that
	   specifies the value's "offset" in the sequence.

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

	   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".

	   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.

	   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.

	   Determines whether you do the left "operator" first or the right
	   "operator" first when you have "A "operator" B "operator" C" and
	   the two operators are of the same precedence.  Operators like "+"
	   are left associative, while operators like "**" are right
	   associative.	 See perlop for a list of operators and their

	   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 didn't know when to expect.

	   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

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

	   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".

	   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 perlop.

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

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

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

	   A Greco-Roman word meaning "to bring oneself to life".  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 don't have to worry about it.

       AV  Short for "array value", which refers to one of Perl's internal
	   data types that holds an "array".  The "AV" type is a subclass of

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

	   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.

	   The practice of saying, "If I had to do it all over, I'd do it
	   differently," and then actually going back and doing it all over
	   differently.	 Mathematically speaking, it's 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 don't pan out.	See "Backtracking" in perlre.

       backward compatibility
	   Means you can still run your old program because we didn't break
	   any of the features or bugs it was relying on.

	   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 "superclass" by people who respect their ancestors.

	   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-

	   Having to do with numbers represented in base 2.  That means
	   there's basically two numbers, 0 and 1.  Also used to describe a
	   "non-text file", 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.

	   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 "Pieces of Eight" comes from being able to
	   split the old Spanish dollar into 8 bits, each of which still
	   counted for money.  That's why a 25-cent piece today is still "two

       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.

	   In corporate life, to grant official approval to a thing, as in,
	   "The VP of Engineering has blessed our WebCruncher project."
	   Similarly in Perl, to grant official approval to a "referent" so
	   that it can function as an "object", such as a WebCruncher object.
	   See "bless" in perlfunc.

	   What a "process" does when it has to wait for something: "My
	   process blocked waiting for the disk."  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 two such as 512 or
	   8192).  Typically refers to a chunk of data that's coming from or
	   going to a disk file.

	   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 BLOCKs, for instance.  Sometimes we also say
	   "block" to mean a lexical scope; that is, a sequence of statements
	   that act like a "BLOCK", such as within an eval or a file, even
	   though the statements aren't 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".

	   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

	   A spot in your program where you've told the debugger to stop
	   execution so you can poke around and see whether anything is wrong

	   To send a "datagram" to multiple destinations simultaneously.

       BSD A psychoactive drug, popular in the 80s, probably developed at U.
	   C. Berkeley or thereabouts.	Similar in many ways to the
	   prescription-only medication called "System V", but infinitely more
	   useful.  (Or, at least, more fun.)  The full chemical name is
	   "Berkeley Standard Distribution".

	   A location in a "hash table" containing (potentially) multiple
	   entries whose keys "hash" to the same hash value according to its
	   hash function.  (As internal policy, you don't have to worry about
	   it, unless you're into internals, or policy.)

	   A temporary holding location for data.  Block buffering means that
	   the data is passed on to its destination whenever the buffer is
	   full.  Line buffering means that it's passed on whenever a complete
	   line is received.  Command buffering means that it's 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.

	   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::" pseudo-package.

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

	   A piece of data worth eight bits in most places.

	   A pidgin-like language spoken among 'droids when they don't wish to
	   reveal their orientation (see "endian").  Named after some similar
	   languages spoken (for similar reasons) between compilers and
	   interpreters in the late 20th century.  These languages are
	   characterized by representing everything as a non-architecture-
	   dependent sequence of bytes.

       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 it's not surprising that Perl
	   borrowed a few ideas from it.

       C preprocessor
	   The typical C compiler's 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).

       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".

	   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.

	   Reduced to a standard form to facilitate comparison.

	   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".)

	   A small integer representative of a unit of orthography.
	   Historically, characters were usually stored as fixed-width
	   integers (typically in a byte, or maybe two, depending on the
	   character set), but with the advent of UTF-8, characters are often
	   stored in a variable number of bytes depending on the size of the
	   integer that represents the character.  Perl manages this
	   transparently for you, for the most part.

       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" "metasymbol".
	   Many standard properties are defined for "Unicode".

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

	   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.

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

	   A "cluster" used to restrict the scope of a "regular expression

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

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

	   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

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

       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 "collating sequence".

	   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".	It's enabled by setting the $| ($AUTOFLUSH)
	   variable to a true value.  It's used when you don't want data
	   sitting around not going where it's supposed to, which may happen
	   because the default on a "file" or "pipe" is to use "block

       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.

       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.

	   A remark that doesn't 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 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 "run time" when "BEGIN" blocks, use
	   declarations, or constant subexpressions are being evaluated.  The
	   startup and import code of any use declaration is also run during
	   compile phase.

       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 "run

	   Strictly speaking, a program that munches up another program and
	   spits out yet another file containing the program in a "more
	   executable" 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 "real" compiler.
	   See O.

	   A "constructor" for a "referent" that isn't 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 "Making
	   References" in perlref.

	   The process of gluing one cat's nose to another cat's tail.	Also,
	   a similar operation on two strings.

	   Something "iffy".  See "Boolean context".

	   In telephony, the temporary electrical circuit between the caller's
	   and the callee's phone.  In networking, the same kind of temporary
	   circuit between a "client" and a "server".

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

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

	   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 context", and "void context".  Scalar
	   context is sometimes subdivided into "Boolean context", "numeric
	   context", "string context", and "void context".  There's also a
	   "don't care" scalar context (which is dealt with in Programming
	   Perl, Third Edition, Chapter 2, "Bits and Pieces" if you care).

	   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 error.

	   The Comprehensive Perl Archive Network.  (See "What modules and
	   extensions are available for Perl?  What is CPAN?  What does
	   CPAN/src/... mean?" in perlfaq2).

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

       current package
	   The "package" in which the current statement is compiled.  Scan
	   backwards in the text of your program through the current lexical
	   scope or any enclosing lexical scopes till you find a package
	   declaration.	 That's your current package name.

       current working directory
	   See "working directory".

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

       CV  An internal "code value" typedef, holding a "subroutine".  The "CV"
	   type is a subclass of "SV".

       dangling statement
	   A bare, single "statement", without any braces, hanging off an "if"
	   or "while" conditional.  C allows them.  Perl doesn't.

       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-shaped 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 and
	   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".

	   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

       DBM Stands for "Data Base Management" 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--see AnyDBM_File and

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

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

	   A "value" chosen for you if you don't supply a value of your own.

	   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 isn't 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 "defined" in perlfunc.

	   A "character" or "string" that sets bounds to an arbitrarily-sized
	   textual object, not to be confused with a "separator" or
	   "terminator".  "To delimit" really just means "to surround" or "to
	   enclose" (like these parentheses are doing).

       deprecated modules and features
	   Deprecated modules and features are those which were part of a
	   stable release, but later found to be subtly flawed, and which
	   should be avoided.  They are subject to removal and/or bug-
	   incompatible reimplementation in the next major release (but they
	   will be preserved through maintenance releases).  Deprecation
	   warnings are issued under -w or "use diagnostics", and notices are
	   found in perldeltas, as well as various other PODs. Coding
	   practices that misuse features, such as "my $foo if 0", can also be

	   A fancy computer science term meaning "to follow a "reference" to
	   what it points to".	The "de" part of it refers to the fact that
	   you're 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 aren't
	   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.

	   See "file descriptor".

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

	   A special "method" that is called when an "object" is thinking
	   about destroying itself.  A Perl program's "DESTROY" method doesn't
	   do the actual destruction; Perl just triggers the method in case
	   the "class" wants to do any associated cleanup.

	   A whiz-bang hardware gizmo (like a disk or tape drive or a modem or
	   a joystick or a mouse) attached to your computer, that 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

	   A "pod" directive.  See perlpod.

	   A special file that contains other files.  Some operating systems
	   call these "folders", "drawers", or "catalogs".

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

	   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.

	   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 "binary-only" distribution.

       (to be) dropped modules
	   When Perl 5 was first released (see perlhistory), several modules
	   were included, which have now fallen out of common use.  It has
	   been suggested that these modules should be removed, since the
	   distribution became rather large, and the common criterion for new
	   module additions is now limited to modules that help to build,
	   test, and extend perl itself.  Furthermore, the CPAN (which didn't
	   exist at the time of Perl 5.0) can become the new home of dropped
	   modules. Dropping modules is currently not an option, but further
	   developments may clear the last barriers.

	   An enchantment, illusion, phantasm, or jugglery.  Said when Perl's
	   magical "dwimmer" effects don't do what you expect, but rather seem
	   to be the product of arcane dweomercraft, sorcery, or wonder
	   working.  [From Old English]

	   DWIM is an acronym for "Do What I Mean", 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 "dwimming" is a "dwimmer".
	   Dwimming can require a great deal of behind-the-scenes magic, which
	   (if it doesn't 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 "contains" that subroutine at "run time".

	   Derived from many sources.  Some would say too many.

	   A basic building block.  When you're talking about an "array", it's
	   one of the items that make up the array.

	   When something is contained in something else, particularly when
	   that might be considered surprising: "I've embedded a complete Perl
	   interpreter in my editor!"

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

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

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

	   See "little-endian" and "big-endian".

	   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

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

	   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).

	   See "exception" or "fatal error".

       escape sequence
	   See "metasymbol".

	   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.

	   To throw away the current "process"'s 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 it's okay to run this file as a program.  Usually shortened to

	   To run a program or "subroutine".  (Has nothing to do with the kill
	   built-in, unless you're 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".

	   To make symbols from a "module" available for "import" by other

	   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.

	   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.

	   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.

	   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 fields.

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

	   A named collection of data, usually stored on disk in a "directory"
	   in a "filesystem".  Roughly like a document, if you're 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" you're talking about.  Perl hides the file
	   descriptor inside a "standard I/O" stream and then attaches the
	   stream to a "filehandle".

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

	   A "wildcard" match on filenames.  See the glob function.

	   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 you're going to open and close several different
	   files in succession, it's fine to open each of them with the same
	   filehandle, so you don't have to write out separate code to process
	   each file.

	   One name for a file.	 This name is listed in a "directory", and 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.

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

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

	   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
	   Perl's -n and -p flags) or, less frequently, a single-bit indicator
	   (such as the "O_CREAT" and "O_EXCL" flags used in sysopen).

       floating point
	   A method of storing numbers in "scientific notation", such that the
	   precision of the number is independent of its magnitude (the
	   decimal point "floats").  Perl does its numeric work with floating-
	   point numbers (sometimes called "floats"), when it can't get away
	   with using integers.	 Floating-point numbers are mere
	   approximations of real numbers.

	   The act of emptying a "buffer", often before it's full.

	   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.

	   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,
	   but 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".

	   A specification of how many spaces and digits and things to put
	   somewhere so that whatever you're printing comes out nice and

       freely available
	   Means you don't have to pay money to get it, but the copyright on
	   it may still belong to someone else (like Larry).

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

	   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 Foundation's GPL
	   (General Public License), but this is difficult to justify

	   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

       garbage collection
	   A misnamed feature--it should be called, "expecting your mother to
	   pick up after you".	Strictly speaking, Perl doesn't 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
	   it's any comfort, when your interpreter exits, a "real" garbage
	   collector runs to make sure everything is cleaned up if you've been
	   messy with circular references and such.)

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

	   Strictly, the shell's "*" character, which will match a "glob" of
	   characters when you're 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".

	   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 global--most variables
	   (and all subroutines) exist only in the current "package".  Global
	   variables can be declared with our.	See "our" in perlfunc.

       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 weren't intended to be hooked together.

	   The size of the pieces you're dealing with, mentally speaking.

	   A "subpattern" whose "quantifier" wants to match as many things as

	   Originally from the old Unix editor command for "Globally search
	   for a Regular Expression and Print it", 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.

	   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 "glob value" typedef, holding a "typeglob".  The "GV"
	   type is a subclass of "SV".

	   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.

	   A "subroutine" or "method" that is called by Perl 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 referent's "reference" count accounts for it.	(Some
	   hard references are held internally, such as the implicit reference
	   from one of a "typeglob"'s variable slots to its corresponding
	   referent.)  A hard reference is different from a "symbolic

	   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 "associative array",
	   which is a pretty good reason for simply calling it a "hash"

       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 "ahead" of the rest of your program to do certain obscure
	   operations.	A C header file has a .h extension.  Perl doesn't
	   really have header files, though historically Perl has sometimes
	   used translated .h files with a .ph extension.  See "require" in
	   perlfunc.  (Header files have been superseded by the "module"

       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, it's just a fancy form of quoting.

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

       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 $ENV{LOGDIR} by login,
	   but you can also find it with "(getpwuid($<))[7]".  (Some platforms
	   do not have a concept of a home directory.)

	   The computer on which a program or other data resides.

	   Excessive pride, the sort of thing Zeus zaps you for.  Also the
	   quality that makes you write (and maintain) programs that other
	   people won't want to say bad things about.  Hence, the third great
	   virtue of a programmer.  See also "laziness" and "impatience".

       HV  Short for a "hash value" typedef, which holds Perl's internal
	   representation of a hash.  The "HV" type is a subclass of "SV".

	   A legally formed name for most anything in which a computer program
	   might be interested.	 Many languages (including Perl) allow
	   identifiers that start with a letter and contain letters and
	   digits.  Perl also counts the underscore character as a valid
	   letter.  (Perl also has more complicated names, such as "qualified"

	   The anger you feel when the computer is being lazy.	This makes you
	   write programs that don't 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".

	   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".

	   To gain access to symbols that are exported from another module.
	   See "use" in perlfunc.

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

	   In olden days, the act of looking up a "key" in an actual index
	   (such as a phone book), but now 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 Perl's
	   index function merely locates the position (index) of one string in

       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.

       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 "$foo\n";" can be understood as
	   "verb indirect-object object" where "STDOUT" is the recipient of
	   the print action, and "$foo" is the object being printed.
	   Similarly, when invoking a "method", you might place the invocant
	   between the method and its arguments:

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

	   In modern Perl, calling methods this way is often considered bad
	   practice and to be avoided.

       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";

	   If something in a program isn't the value you're looking for but
	   indicates where the value is, that's indirection.  This can be done
	   with either symbolic references or hard references.

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

	   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".

	   Short for "an instance of a class", meaning an "object" of that

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

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

	   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.

	   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".

	   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 "run time" system then interprets.

	   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.

	   The act of calling up a deity, daemon, program, method, subroutine,
	   or function to get it do what you think it's supposed to do.	 We
	   usually "call" subroutines but "invoke" methods, since it sounds

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

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

       IP  Internet Protocol, or Intellectual Property.

       IPC Interprocess Communication.

	   A relationship between two objects in which one object is
	   considered to be a more specific version of the other, generic
	   object: "A camel is a mammal."  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 don't always have Platonic
	   relationships--see "inheritance".

	   Doing something repeatedly.

	   A special programming gizmo that keeps track of where you are in
	   something that you're 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, Tom's favorite
	   editor.  IV also means an internal Integer Value of the type a
	   "scalar" can hold, not to be confused with an "NV".

	   "Just Another Perl Hacker," 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 Usenix signatures.

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

	   See "reserved words".

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

	   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 document what you wrote so you
	   don't 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".

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

       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 perlre for much more on
	   this subject.

	   Fancy term for a "token".

	   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 don't 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.  --Syn. "static scoping".  --Ant. "dynamic

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

	   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

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

	   In Unix, a sequence of zero or more non-newline 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.

       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 file's 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.

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

	   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.

	   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".

	   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.

	   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".

	   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 "and", "or", "xor", and "not".

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

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

	   A construct that performs something repeatedly, like a roller

       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
	   shouldn't 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

	   Able to serve as an "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 "l" is short for "left", 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.

	   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 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.

	   A file that controls the compilation of a program.  Perl programs
	   don't 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.

	   A "page" 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 it's installed in on your system.

	   See "pattern matching".

       member data
	   See "instance variable".

	   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 it'll use disk space to hold inactive bits.  This can
	   make it seem like you have a little more memory than you really do,
	   but it's 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 too, if you haven't thrashed your disk to death first.

	   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.

	   Something we'd call a "metacharacter" except that it's 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.

	   A kind of action that an "object" can take if you tell it to.  See

	   The belief that "small is beautiful."  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.

	   In the context of the stat syscall, refers to the field holding the
	   "permission bits" and the type of the "file".

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

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

	   An integer divisor when you're interested in the remainder instead
	   of the quotient.

	   Short for Perl Monger, a purveyor of Perl.

	   A temporary value scheduled to die when the current statement

       multidimensional array
	   An array with multiple subscripts for finding a single element.
	   Perl implements these using references--see perllol and perldsc.

       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), the notion that a given
	   class may have multiple direct ancestors or base classes.

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

	   A domain of names.  You needn't worry about whether the names in
	   one such domain have been used in another.  See "package".

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

	   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

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

       null character
	   A character with the ASCII value of zero.  It's 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".

       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

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

	   An "instance" of a "class".	Something that "knows" 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.

	   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

	   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 don't skip
	   anything to get to the first item.

	   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 <>.

	   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 vendor's
	   operating system is different from any other version of this or any
	   other vendor's operating system.  Perl is much more portable across
	   operating systems than many other languages.	 See also
	   "architecture" and "platform".

	   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 "pragma".

	   See either switches or "regular expression modifier".

	   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".

	   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 "Overriding Built-in Functions"
	   in perlsub) and to describe how you can define a replacement
	   "method" in a "derived class" to hide a "base class"'s method of
	   the same name (see perlobj).

	   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".

	   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 package's symbol table are only accessible from code
	   compiled outside the package by naming the package.	But in another
	   sense, all package symbols are also globals--they're just well-
	   organized globals.

       pad Short for "scratchpad".

	   See "argument".

       parent class
	   See "base class".

       parse tree
	   See "syntax tree".

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

	   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.

	   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}.

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

	   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 there's any way to
	   make it fit.	 Often used to pick interesting tidbits out of a file.

       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.

	   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.

	   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.

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

	   The entire hardware and software context in which a program runs.
	    program written in a platform-dependent language might break if
	   you change any of: 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-

       pod The markup used to embed documentation into your Perl code.	See

	   A "variable" in a language like C that contains the exact memory
	   location of some other item.	 Perl handles pointers internally so
	   you don't have to worry about them.	Instead, you just use symbolic
	   pointers in the form of keys and "variable" names, or hard
	   references, which aren't pointers (but act like pointers and do in
	   fact contain pointers).

	   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.  [<Gk many shapes]

	   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.

	   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 "easily" can be defined however you like, and
	   usually is.	Anything may be considered portable if you try hard
	   enough.  See mobile home or London Bridge.

	   Someone who "carries" 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.

	   The Portable Operating System Interface specification.

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

       pp  An internal shorthand for a "push-pop" code, that is, C code
	   implementing Perl's stack machine.

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

	   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.

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

	   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".

	   A "subroutine".

	   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 time--in fact, the fork function
	   is designed to bring about this happy state of affairs.  Under
	   other operating systems, processes are sometimes called "threads",
	   "tasks", or "jobs", often with slight nuances in meaning.

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

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

	   See either "instance variable" or "character property".

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

	   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 that you can write subroutine calls that
	   parse much like built-in functions.	(Or don't parse, as the case
	   may be.)

	   A construct that sometimes looks like a function but really isn't.
	   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

	   A reference to an array whose initial element happens to hold a
	   reference to a hash.	 You can treat a pseudohash reference as
	   either an array reference or a hash reference.

	   An "operator" that looks something like a "literal", such as the
	   output-grabbing operator, "`""command""`".

       public domain
	   Something not owned by anybody.  Perl is copyrighted and is thus
	   not in the public domain--it's just "freely available" and "freely

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

	   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 "pointer value", which is Perl Internals Talk for a "char*".

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

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

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

	   The last rites performed by a parent "process" on behalf of a
	   deceased child process so that it doesn't remain a "zombie".	 See
	   the wait and waitpid function calls.

	   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-line-terminated set of lines (a
	   "paragraph").  Each line of the /etc/passwd file is a record, keyed
	   on login name, containing information about that user.

	   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 you're careful not to recurse forever,
	   which is like an infinite loop with more spectacular failure modes.

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

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

	   See "regular expression".

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

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

       regular file
	   A "file" that's not a "directory", a "device", a named "pipe" or
	   "socket", or a "symbolic link".  Perl uses the "-f" file test
	   operator to identify regular files.	Sometimes called a "plain"

       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), it's illegal to use
	   reserved words to name anything else.  (Which is why they're
	   reserved, after all.)  In Perl, you just can't use them to name
	   labels or filehandles.  Also called "keywords".

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

       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.

	   The superuser (UID == 0).  Also, the top-level directory of the

	   What you are told when someone thinks you should Read The Fine

       run phase
	   Any time after Perl starts running your main program.  See also
	   "compile phase".  Run phase is mostly spent in "run time" 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.

       run time
	   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".

       run-time 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 re-
	   analyzed each time the pattern match operator is evaluated.	Run-
	   time 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 you're not confused

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

	   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 value--see "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

       scalar literal
	   A number or quoted "string"--an 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.

	   How far away you can see a variable from, 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

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

	   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 Klingon.

       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

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

	   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 "or" in the previous sentence separated the two alternatives.

	   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.

	   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.

	   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.

	   Same as "setuid", only having to do with giving away "group"

	   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

       shared memory
	   A piece of "memory" accessible by two different processes who
	   otherwise would not see each other's memory.

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

	   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 it's 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 "side effect" 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.

	   A bolt out of the blue; that is, an event triggered by the
	   "operating system", probably when you're 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 "%SIG" in perlvar and "Signals" in perlipc.

       single inheritance
	   The features you got from your mother, if she told you that you
	   don't have a father.	 (See also "inheritance" and "multiple
	   inheritance".)  In computer languages, the notion 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.

	   A selection of any number of elements from a "list", "array", or

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

	   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
	   addresses--some look like filenames, and some don't.

       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".

	   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".

	   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 don't belong in
	   "standard output".  Represented within a Perl program by the
	   "filehandle" "STDERR".  You can use this stream explicitly, but the
	   die and warn built-ins write to your standard error stream

       standard I/O
	   A standard C library for doing buffered input and output to the
	   "operating system".	(The "standard" of standard I/O is only
	   marginally related to the "standard" 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 input
	   The default input "stream" for your program, which if possible
	   shouldn't care where its data is coming from.  Represented within a
	   Perl program by the "filehandle" "STDIN".

       standard output
	   The default output "stream" for your program, which if possible
	   shouldn't care where its data is going.  Represented within a Perl
	   program by the "filehandle" "STDOUT".

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

	   A "command" to the computer about what to do next, like a step in a
	   recipe: "Add marmalade to batter and mix until mixed."  A statement
	   is distinguished from a "declaration", which doesn't 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.

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

       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".

	   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 perlfunc.

	   See "standard error".

	   See "standard input".

	   See "standard I/O".

	   See "standard output".

	   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 "interface"--the underlying
	   "implementation" may well break your data up into separate packets
	   for delivery, but this is hidden from you.

	   A sequence of characters such as "He said !@#*&%@#*?!".  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".

	   The process of producing a "string" representation of an abstract

	   C keyword introducing a structure definition or name.

	   See "data structure".

	   See "derived class".

	   A component of a "regular expression" pattern.

	   A named or otherwise accessible piece of program that can be
	   invoked from elsewhere in the program in order to accomplish some
	   sub-goal 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".

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

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

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

	   See "base class".

	   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 "scalar value".  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 "referent type", and the code is smart enough (we hope) not to
	   try to call a "hash" function on a "subroutine".

	   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., -a -b -c)
	   into one switch (e.g., -abc).  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 "case
	   structure", named after the similar Pascal construct.  Most switch
	   statements in Perl are spelled "for".  See "Basic BLOCKs and Switch
	   Statements" in perlsyn.

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

       symbol table
	   Where a "compiler" remembers symbols.  A program like Perl must
	   somehow remember all the names of all the variables, filehandles,
	   and subroutines you've 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".

       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 "symbolic" 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

	   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.

	   From Greek, "with-arrangement".  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.

	   A "function" call directly to the "operating system".  Many of the
	   important subroutines and functions you use aren't direct system
	   calls, but are built up in one or more layers above the system call
	   level.  In general, Perl programmers don't 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 "system call" to mean
	   what happens when you call the Perl system function, which actually
	   involves many syscalls.  To avoid any confusion, we nearly always
	   use say "syscall" for something you could call indirectly via
	   Perl's syscall function, and never for something you would call
	   with Perl's system function.

	   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 -T

       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.)

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

	   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.

	   An "operator" taking three operands.	 Sometimes pronounced

	   A "string" or "file" containing primarily printable characters.

	   Like a forked process, but without "fork"'s 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 process's memory space unless steps are
	   taken to protect threads from each other.  See threads.

       tie The bond between a magical variable and its implementation class.
	   See "tie" in perlfunc and perltie.

	   There's 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 doesn't mean that more ways are always
	   better or that all possible paths are equally desirable--just that
	   there need not be One True Way.)  Pronounced TimToady.

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

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

	   Splitting up a program text into tokens.  Also known as "lexing",
	   in which case you get "lexemes" 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
	   you're assembling a tricycle, but if you're 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.

	   To turn one string representation into another by mapping each
	   character of the source string to its corresponding character in
	   the result string.  See "tr/SEARCHLIST/REPLACEMENTLIST/cds" in

	   An event that causes a "handler" to be run.

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

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

	   Any scalar value that doesn't evaluate to 0 or "".

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

	   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.

       typed lexical
	   A "lexical variable" that is declared with a "class" type: "my Pony

	   A type definition in the C language.

	   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 "Typeglobs and Filehandles" in perldata.

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

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

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

	   A mask of those "permission bits" that should be forced off when
	   creating files or directories, in order to establish a policy of
	   whom you'll 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 "--" operators can be either prefix or
	   postfix.  (Their position does change their meanings.)

	   A character set comprising all the major character sets of the
	   world, more or less.	 See <>.

	   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 it's easy to learn because it's so easily
	   twisted to one's 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 wasn't doing much of anything else at the time.

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

	   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.

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

	   Mathematical jargon for a list of scalar values.

	   Providing the appearance of something without the reality, as in:
	   virtual memory is not real memory.  (See also "memory".)  The
	   opposite of "virtual" is "transparent", which means providing the
	   reality of something without the appearance, as in: Perl handles
	   the variable-length UTF-8 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.

	   A "version" or "vector" "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.)

	   A message printed to the "STDERR" stream to the effect that
	   something might be wrong but isn't worth blowing up over.  See
	   "warn" in perlfunc and the warnings pragma.

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

	   A "character" that moves your cursor but doesn't otherwise put
	   anything on your screen.  Typically refers to any of: space, tab,
	   line feed, carriage return, or form feed.

	   In normal "computerese", 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

       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.

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

	   What You See Is What You Get.  Usually used when something that
	   appears on the screen matches how it will eventually look, like
	   Perl's 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.

       XS  An extraordinarily exported, expeditiously excellent, expressly
	   eXternal Subroutine, executed in existing C or C++ or in an
	   exciting new extension language called (exasperatingly) XS.
	   Examine perlxs for the exact explanation or perlxstut for an
	   exemplary unexacting one.

	   An external "subroutine" defined in "XS".

	   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.

       zero width
	   A subpattern "assertion" matching the "null string" between

	   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, or else the process table will fill
	   up and your system administrator will Not Be Happy with you.

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

perl v5.10.1			  2009-04-12		       PERLGLOSSARY(1)

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