


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


NAME
       perlglossary - Perl Glossary

DESCRIPTION
       A glossary of terms (technical and otherwise) used in the
       Perl documentation.  Other useful sources include the Free
       On-Line Dictionary of Computing
       <http://foldoc.doc.ic.ac.uk/foldoc/index.html>, the Jargon
       File <http://catb.org/~esr/jargon/>, and Wikipedia
       <http://www.wikipedia.org/>.

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

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

       alias
           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.

       alternatives
           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



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           bar: "||".  Logical alternatives in "Boolean"
           expressions are separated with either "||" or "or".

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

       architecture
           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".

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

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

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

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

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

       ASCII
           The American Standard Code for Information Interchange
           (a 7-bit character set adequate only for poorly
           representing English text).  Often used loosely to
           describe the lowest 128 values of the various



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           ISO-8859-X character sets, a bunch of mutually
           incompatible 8-bit codes best described as half ASCII.
           See also "Unicode".

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

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

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

       associative array
           See "hash".  Please.

       associativity
           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
           associativity.

       asynchronous
           Said of events or activities whose relative temporal
           ordering is indeterminate because too many things are
           going on at once.  Hence, an asynchronous event is one
           you didn't know when to expect.

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

       atomic operation
           When Democritus gave the word "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.



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

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

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

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

       autosplit
           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.)

       autovivification
           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 "SV".

       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.




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

       backtracking
           The practice of saying, "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.

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

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

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

       binary
           Having to do with numbers represented in base 2.  That
           means 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.




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       binary operator
           An "operator" that takes two operands.

       bind
           To assign a specific "network address" to a "socket".

       bit An integer in the range from 0 to 1, inclusive.  The
           smallest possible unit of information storage.  An
           eighth of a "byte" or of a dollar.  (The term "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 bits".)

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

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

       bless
           In corporate life, to grant official approval to a
           thing, as in, "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.

       block
           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.

       BLOCK
           A syntactic construct consisting of a sequence of Perl
           statements that is delimited by braces.  The "if" and
           "while" statements are defined in terms of 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".



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       Boolean
           A value that is either "true" or "false".

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

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

       broadcast
           To send a "datagram" to multiple destinations
           simultaneously.

       BSD A psychoactive drug, popular in the 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".

       bucket
           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.)

       buffer
           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.

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

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



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

       bytecode
           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
       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".

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

       canonical
           Reduced to a standard form to facilitate comparison.

       capturing
           The use of parentheses around a "subpattern" in a



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           "regular expression" to store the matched "substring"
           as a "backreference".  (Captured strings are also
           returned as a list in "list context".)

       character
           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.

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

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

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

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

       closure
           An "anonymous" subroutine that, when a reference to it
           is generated at run time, keeps track of the
           identities of externally visible lexical variables



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           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.

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

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

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

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

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

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

       command buffering
           A mechanism in Perl that lets you store up the output
           of each Perl "command" and then flush it out as a
           single request to the "operating system".  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 buffering".

       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



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           you tell a "shell" to execute a "command".  These
           values are passed to a Perl program through @ARGV.

       comment
           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 time".

       compiler
           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.

       composer
           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.

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

       conditional
           Something "iffy".  See "Boolean context".



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       connection
           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".

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

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

       context
           The surroundings, or environment.  The context given
           by the surrounding code determines what kind of data a
           particular "expression" is expected to return.  The
           three primary contexts are "list context", "scalar
           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).

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

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

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

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




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       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".

   D
       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".

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

       DBM Stands for "Data Base Management" routines, a set of



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           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 DB_File.

       declaration
           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.

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

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

       defined
           Having a meaning.  Perl thinks that some of the things
           people try to do are devoid of meaning, in particular,
           making use of variables that have never been given a
           "value" and performing certain operations on data that
           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.

       delimiter
           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



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           PODs. Coding practices that misuse features, such as
           "my $foo if 0", can also be deprecated.

       dereference
           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.

       descriptor
           See "file descriptor".

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

       destructor
           A special "method" that is called when an "object" is
           thinking about destroying itself.  A Perl 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.

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

       directive
           A "pod" directive.  See perlpod.

       directory
           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.

       dispatch
           To send something to its correct destination.  Often
           used metaphorically to indicate a transfer of



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           programmatic control to a destination selected
           algorithmically, often by lookup in a table of
           function references or, in the case of object methods,
           by traversing the inheritance tree looking for the
           most specific definition for the method.

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

       dweomer
           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]

       dwimmer
           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".





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

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

       embedding
           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.]

       encapsulation
           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.

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

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

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

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

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





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       error
           See "exception" or "fatal error".

       escape sequence
           See "metasymbol".

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

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

       exec
           To throw away the current "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 "executable".

       execute
           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".

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

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

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




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

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

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

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

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

       file
           A named collection of data, usually stored on disk in
           a "directory" in a "filesystem".  Roughly like a
           document, if 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.



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

       filehandle
           An identifier (not necessarily related to the real
           name of a file) that represents a particular instance
           of opening a file until you close it.  If 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.

       filename
           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.

       filesystem
           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 Unix.

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

       flag
           We tend to avoid this term because it means so many
           things.  It may mean a command-line "switch" that
           takes no argument itself (such as 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.

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




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

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

       formal arguments
           The generic names by which a "subroutine" knows its
           arguments.  In many languages, formal arguments are
           always given individual names, 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".

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

       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.

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

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



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

       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.)

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

       glob
           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".

       global
           Something you can see from anywhere, usually used of
           variables and subroutines that are visible everywhere
           in your program.  In Perl, only certain special
           variables are truly 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.

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





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

       grep
           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.

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

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

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

       handler
           A "subroutine" or "method" that 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 reference".

       hash
           An unordered association of "key"/"value" pairs,
           stored such that you can easily use a string "key" to
           look up its associated data "value".  This glossary is
           like a hash, where the word to be defined is the key,



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           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" instead.

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

       header file
           A file containing certain required definitions that
           you must include "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" mechanism.)

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

       hexadecimal
           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 perlfunc.

       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.)

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

       hubris
           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".




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   I
       identifier
           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" names.)

       impatience
           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".

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

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

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

       indexing
           In olden days, the act of looking up a "key" in an
           actual index (such as a phone book), but now 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 another.

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

       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



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           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";

       indirection
           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.

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

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

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

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

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

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



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

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

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

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

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

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

       IP  Internet Protocol, or Intellectual Property.

       IPC Interprocess Communication.

       is-a
           A relationship between two objects in which one object
           is considered to be a more specific version of the
           other, generic object: "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".





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       iteration
           Doing something repeatedly.

       iterator
           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".

   J
       JAPH
           "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.

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

       keyword
           See "reserved words".

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

       laziness
           The quality that makes you go to great effort to
           reduce overall energy expenditure.  It makes you write
           labor-saving programs that other people will find
           useful, and 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



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           this subject.

       lexeme
           Fancy term for a "token".

       lexer
           Fancy term for a "tokener".

       lexical analysis
           Fancy term for "tokenizing".

       lexical scoping
           Looking at your Oxford English Dictionary through a
           microscope.  (Also known as "static scoping", because
           dictionaries 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 scoping".

       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
           variable.)

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

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

       line
           In Unix, a sequence of zero or more 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



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           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.

       link
           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.

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

       list
           An ordered set of scalar values.

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

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

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

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





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

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

       logical operator
           Symbols representing the concepts "and", "or", "xor",
           and "not".

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

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

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

       loop control statement
           Any statement within the body of a loop that can make
           a loop prematurely stop looping or skip an
           "iteration".  Generally you 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 control.

       lvaluable
           Able to serve as an "lvalue".

       lvalue
           Term used by language lawyers for a storage location
           you can assign a new "value" to, such as a "variable"
           or an element of an "array".  The "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



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           an "lvalue" in some declarative fashion.  Currently
           there are three lvalue modifiers: my, our, and local.

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

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

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

       Makefile
           A file that controls the compilation of a program.
           Perl programs 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.

       manpage
           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.

       matching
           See "pattern matching".

       member data
           See "instance variable".

       memory
           This always means your main memory, not your disk.
           Clouding the issue is the fact that your machine may
           implement "virtual" memory; that is, it will pretend
           that it has more memory than it really does, and it'll
           use disk space to hold inactive bits.  This can make
           it seem like you have a little more memory than you



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           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.

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

       metasymbol
           Something 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.

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

       minimalism
           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.

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

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

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

       modulus
           An integer divisor when you're interested in the



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           remainder instead of the quotient.

       monger
           Short for Perl Monger, a purveyor of Perl.

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

       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.

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

       namespace
           A domain of names.  You 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".

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

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

       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.



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       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 "IV".

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

   O
       object
           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.

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

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

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

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




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

       operating system
           A special program that runs on the bare machine and
           hides the gory details of managing processes and
           devices.  Usually used in a looser sense to indicate a
           particular culture of programming.  The loose sense
           can be used at varying levels of specificity.  At one
           extreme, you might say that all versions of Unix and
           Unix-lookalikes are the same operating system
           (upsetting many people, especially lawyers and other
           advocates).  At the other extreme, you could say this
           particular version of this particular 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".

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

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

       options
           See either switches or "regular expression modifier".

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

       overriding
           Hiding or invalidating some other definition of the
           same name.  (Not to be confused with "overloading",
           which adds definitions that must be disambiguated some
           other way.) To confuse the issue further, we use the
           word with two overloaded definitions: to describe how
           you can define your own "subroutine" to hide a built-
           in "function" of the same name (see "Overriding Built-
           in Functions" in perlsub) and to describe how you can



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           define a replacement "method" in a "derived class" to
           hide a "base class"'s method of the same name (see
           perlobj).

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

   P
       package
           A "namespace" for global variables, subroutines, and
           the like, such that they can be kept separate from
           like-named symbols in other namespaces.  In a sense,
           only the package is global, since the symbols in the
           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".

       parameter
           See "argument".

       parent class
           See "base class".

       parse tree
           See "syntax tree".

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

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

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

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




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       pattern
           A template used in "pattern matching".

       pattern matching
           Taking a pattern, usually a "regular expression", and
           trying the pattern various ways on a string to see
           whether 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.

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

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

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

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

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

       pointer
           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



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           pointers and do in fact contain pointers).

       polymorphism
           The notion that you can tell an "object" to do
           something generic, and the object will interpret the
           command in different ways depending on its type.  [<Gk
           many shapes]

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

       portable
           Once upon a time, C code compilable under both BSD and
           SysV.  In general, code that can be easily converted
           to run on another "platform", where "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.

       porter
           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.

       POSIX
           The Portable Operating System Interface specification.

       postfix
           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.

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

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





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

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

       procedure
           A "subroutine".

       process
           An instance of a running program.  Under multitasking
           systems like Unix, two or more separate processes
           could be running the same program independently at the
           same 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.

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

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

       prototype
           An optional part of a "subroutine" declaration telling
           the Perl compiler how many and what flavor of
           arguments may be passed as "actual arguments", so that
           you can write subroutine calls that parse much like
           built-in functions.  (Or don't parse, as the case may
           be.)

       pseudofunction
           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



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           "tr///".

       pseudohash
           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.

       pseudoliteral
           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 redistributable".

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

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

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

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

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

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

       reaping
           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.




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       record
           A set of related data values in a "file" or "stream",
           often associated with a unique "key" field.  In Unix,
           often commensurate with a "line", or a blank-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.

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

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

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

       regex
           See "regular expression".

       regular expression
           A single entity with various interpretations, like an
           elephant.  To a computer scientist, 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" file.




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       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 "scalar".

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

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

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

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

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



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           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 yet.

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

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

       scalar context
           The situation in which an "expression" is expected by
           its surroundings (the code calling it) to return a
           single "value" rather than a "list" of values.  See
           also "context" and "list context".  A scalar context
           sometimes imposes additional constraints on the return
           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 false.

       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.

       scope
           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
           variable.





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

       script
           A text "file" that is a program intended to be
           executed directly rather than compiled to another form
           of file before execution.  Also, in the context of
           "Unicode", a writing system for a particular language
           or group of languages, such as Greek, Bengali, or
           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 ideas.

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

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

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

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

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

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



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           "group" privileges.

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

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

       shebang
           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.

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

       signal
           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



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           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.

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

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

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

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

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

       standard error
           The default output "stream" for nasty remarks that
           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



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           automatically.

       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.

       statement
           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.

       static
           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



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           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".

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

       STDERR
           See "standard error".

       STDIN
           See "standard input".

       STDIO
           See "standard I/O".

       STDOUT
           See "standard output".

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

       string
           A sequence of characters such as "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".

       stringification
           The process of producing a "string" representation of



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           an abstract object.

       struct
           C keyword introducing a structure definition or name.

       structure
           See "data structure".

       subclass
           See "derived class".

       subpattern
           A component of a "regular expression" pattern.

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

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

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

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

       superclass
           See "base class".

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

       SV  Short for "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



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           "subroutine".

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

       switch cluster
           The combination of multiple command-line switches
           (e.g., -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.

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

       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



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           or subroutine.  By dereferencing the first variable,
           you can get at the second one.  Symbolic references
           are illegal under use strict 'refs'.

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

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

       syntax
           From Greek, "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.

       syscall
           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.

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

       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.)




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       term
           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.

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

       ternary
           An "operator" taking three operands.  Sometimes
           pronounced "trinary".

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

       thread
           Like a forked process, but without "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.

       TMTOWTDI
           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.

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

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

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




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       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.

       transliterate
           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 perlop.

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

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

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

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

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

       type
           See "data type" and "class".

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

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

       typedef
           A type definition in the C language.

       typeglob
           Use of a single identifier, prefixed with "*".  For
           example, *name stands for any or all of $name, @name,
           %name, &name, or just "name".  How you use it



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           determines whether it is interpreted as all or only
           one of them.  See "Typeglobs and Filehandles" in
           perldata.

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

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

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

       umask
           A mask of those "permission bits" that should be
           forced off when creating files or directories, in
           order to establish a policy of whom 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.)

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

       Unix
           A very large and constantly evolving language with
           several alternative and largely incompatible syntaxes,
           in which anyone can define anything any way they
           choose, and usually do.  Speakers of this language
           think 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.




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

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

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

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

       vector
           Mathematical jargon for a list of scalar values.

       virtual
           Providing the appearance of something without the
           reality, as in: virtual memory is not real memory.
           (See also "memory".)  The opposite of "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.

       v-string
           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.)

   W
       warning
           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.




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


       whitespace
           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.

       word
           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 boundaries.

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

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

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

   X
       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.

       XSUB
           An external "subroutine" defined in "XS".

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





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


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

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

AUTHOR AND COPYRIGHT
       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.







































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