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

       accessor methods
           A "method" used to indirectly inspect or update an "object"'s state
           (its instance variables).

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

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

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

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

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

           Used to describe a "referent" that is not directly accessible
           through a named "variable".  Such a referent must be indirectly
           accessible through at least one "hard reference".  When the last
           hard reference goes away, the anonymous referent is destroyed
           A piece of data supplied to a program, "subroutine", "function", or
           "method" to tell it what it's supposed to do.  Also called a

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

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

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

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

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

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

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

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

       associative array
           See "hash".  Please.

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

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

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

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

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

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

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

           A Greco-Roman word meaning "to bring oneself to life".  In Perl,
           storage locations (lvalues) spontaneously generate themselves as
           needed, including the creation of any "hard reference" values to
           point to the next level of storage.  The assignment
           "$a[5][5][5][5][5] = "quintet"" potentially creates five scalar
           storage locations, plus four references (in the first four scalar
           locations) pointing to four new anonymous arrays (to hold the last
           four scalar locations).  But the point of autovivification is that
           you don't have to worry about it.

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

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

           The practice of saying, "If I had to do it all over, I'd do it
           differently," and then actually going back and doing it all over
           differently.  Mathematically speaking, it's returning from an
           unsuccessful recursion on a tree of possibilities.  Perl backtracks
           when it attempts to match patterns with a "regular expression", and
           its earlier attempts don't pan out.  See "Backtracking" in perlre.

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

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

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

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

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

       binary operator
           An "operator" that takes two operands.

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

       bit An integer in the range from 0 to 1, inclusive.  The smallest
           possible unit of information storage.  An eighth of a "byte" or of
           a dollar.  (The term "Pieces of Eight" comes from being able to
           split the old Spanish dollar into 8 bits, each of which still
           counted for money.  That's why a 25-cent piece today is still "two

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

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

           A syntactic construct consisting of a sequence of Perl statements
           that is delimited by braces.  The "if" and "while" statements are
           defined in terms of BLOCKs, for instance.  Sometimes we also say
           "block" to mean a lexical scope; that is, a sequence of statements
           that act like a "BLOCK", such as within an eval or a file, even
           though the statements aren't delimited by braces.

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

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

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

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

           To send a "datagram" to multiple destinations simultaneously.

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

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

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

           A piece of data worth eight bits in most places.

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

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

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

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

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

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

           Reduced to a standard form to facilitate comparison.

       capture buffer, capture group
           These two terms are synonymous: a captured substring by a regex

           The use of parentheses around a "subpattern" in a "regular
           expression" to store the matched "substring" as a "backreference"

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

       character property
           A predefined "character class" matchable by the "\p" "metasymbol".
           Many standard properties are defined for "Unicode".

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

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

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

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

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

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

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

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

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

       code point
           The position of a character in a character set encoding.  The
           character "NULL" is almost certainly at the zeroth position in all

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

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

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

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

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

           A remark that doesn't affect the meaning of the program.  In Perl,
           a comment is introduced by a "#" character and continues to the end
           of the line.

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

       compile phase
           Any time before Perl starts running your main program.  See also
           "run phase".  Compile phase is mostly spent in "compile time", but
           may also be spent in "run time" when "BEGIN" blocks, use
           declarations, or constant subexpressions are being evaluated.  The
           startup and import code of any use declaration is also run during
           compile phase.

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

           A "constructor" for a "referent" that isn't really an "object",
           like an anonymous array or a hash (or a sonata, for that matter).
           For example, a pair of braces acts as a composer for a hash, and a
           pair of brackets acts as a composer for an array.  See "Making
           References" in perlref.

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

           Something "iffy".  See "Boolean context".

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

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

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

           The surroundings, or environment.  The context given by the
           surrounding code determines what kind of data a particular
           "expression" is expected to return.  The three primary contexts are
           "list context", "scalar context", and "void context".  Scalar
           context is sometimes subdivided into "Boolean context", "numeric
           context", "string context", and "void context".  There's also a
           "don't care" scalar context (which is dealt with in Programming
           Perl, Third Edition, Chapter 2, "Bits and Pieces" if you care).

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

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

           The Comprehensive Perl Archive Network.  (See "What modules and
           extensions are available for Perl?  What is CPAN?  What does

       current working directory
           See "working directory".

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

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

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

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

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

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

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

           An "assertion" that states something exists and perhaps describes
           what it's like, without giving any commitment as to how or where
           you'll use it.  A declaration is like the part of your recipe that
           says, "two cups flour, one large egg, four or five tadpoles..."
           Having a meaning.  Perl thinks that some of the things people try
           to do are devoid of meaning, in particular, making use of variables
           that have never been given a "value" and performing certain
           operations on data that isn't there.  For example, if you try to
           read data past the end of a file, Perl will hand you back an
           undefined value.  See also "false" and "defined" in perlfunc.

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

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

           A fancy computer science term meaning "to follow a "reference" to
           what it points to".  The "de" part of it refers to the fact that
           you're taking away one level of "indirection".

       derived class
           A "class" that defines some of its methods in terms of a more
           generic class, called a "base class".  Note that classes aren't
           classified exclusively into base classes or derived classes: a
           class can function as both a derived class and a base class
           simultaneously, which is kind of classy.

           See "file descriptor".

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

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

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

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

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

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

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

           DWIM is an acronym for "Do What I Mean", the principle that
           something should just do what you want it to do without an undue
           amount of fuss.  A bit of code that does "dwimming" is a "dwimmer".
           Dwimming can require a great deal of behind-the-scenes magic, which
           (if it doesn't stay properly behind the scenes) is called a
           "dweomer" instead.

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

           Derived from many sources.  Some would say too many.

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

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

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

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

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

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

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

           See "exception" or "fatal error".

       escape sequence
           See "metasymbol".

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

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

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

       executable file
           A "file" that is specially marked to tell the "operating system"
           that it's okay to run this file as a program.  Usually shortened to

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

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

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

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

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

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

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

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

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

       file descriptor

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

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

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

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

           We tend to avoid this term because it means so many things.  It may
           mean a command-line "switch" that takes no argument itself (such as
           Perl's -n and -p flags) or, less frequently, a single-bit indicator
           (such as the "O_CREAT" and "O_EXCL" flags used in sysopen).

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

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

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

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

           somewhere so that whatever you're printing comes out nice and

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

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

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

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

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

       garbage collection
           A misnamed feature--it should be called, "expecting your mother to
           pick up after you".  Strictly speaking, Perl doesn't do this, but
           it relies on a reference-counting mechanism to keep things tidy.
           However, we rarely speak strictly and will often refer to the
           reference-counting scheme as a form of garbage collection.  (If
           it's any comfort, when your interpreter exits, a "real" garbage
           collector runs to make sure everything is cleaned up if you've been
           messy with circular references and such.)

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

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

           Something you can see from anywhere, usually used of variables and
           A language such as Perl that is good at hooking things together
           that weren't intended to be hooked together.

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

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

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

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

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

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

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

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

           An unordered association of "key"/"value" pairs, stored such that
           you can easily use a string "key" to look up its associated data
           "value".  This glossary is like a hash, where the word to be
           defined is the key, and the definition is the value.  A hash is
           really have header files, though historically Perl has sometimes
           used translated .h files with a .ph extension.  See "require" in
           perlfunc.  (Header files have been superseded by the "module"

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

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

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

           The computer on which a program or other data resides.

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

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

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

           The anger you feel when the computer is being lazy.  This makes you
           write programs that don't just react to your needs, but actually
           anticipate them.  Or at least that pretend to.  Hence, the second
           great virtue of a programmer.  See also "laziness" and "hubris".

           How a piece of code actually goes about doing its job.  Users of
           the code should not count on implementation details staying the
           same unless they are part of the published "interface".
           key or position to find the corresponding "value", even if no index
           is involved.  Things have degenerated to the point that Perl's
           index function merely locates the position (index) of one string in

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       IP  Internet Protocol, or Intellectual Property.

       IPC Interprocess Communication.

           A relationship between two objects in which one object is
           considered to be a more specific version of the other, generic
           object: "A camel is a mammal."  Since the generic object really
           only exists in a Platonic sense, we usually add a little
           abstraction to the notion of objects and think of the relationship
           as being between a generic "base class" and a specific "derived
           class".  Oddly enough, Platonic classes don't always have Platonic
           relationships--see "inheritance".

           Doing something repeatedly.

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

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

           See "reserved words".

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

           The quality that makes you go to great effort to reduce overall
           energy expenditure.  It makes you write labor-saving programs that
           other people will find useful, and document what you wrote so you
           don't have to answer so many questions about it.  Hence, the first
           great virtue of a programmer.  Also hence, this book.  See also
           "impatience" and "hubris".

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

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

           Fancy term for a "token".

           Fancy term for a "tokener".

       lexical analysis
           Fancy term for "tokenizing".

       lexical scoping
           Looking at your Oxford English Dictionary through a microscope.
           (Also known as "static scoping", because dictionaries don't change
           very fast.)  Similarly, looking at variables stored in a private
           dictionary (namespace) for each scope, which are visible only from
           their point of declaration down to the end of the lexical scope in
           which they are declared.  --Syn. "static scoping".  --Ant. "dynamic

       lexical variable
           A "variable" subject to "lexical scoping", declared by my.  Often
           just called a "lexical".  (The our declaration declares a lexically
           scoped name for a global variable, which is not itself a lexical
           In Unix, a sequence of zero or more non-newline characters
           terminated with a "newline" character.  On non-Unix machines, this
           is emulated by the C library even if the underlying "operating
           system" has different ideas.

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

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

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

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

           An ordered set of scalar values.

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

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

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

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

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

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

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

           A construct that performs something repeatedly, like a roller

       loop control statement
           Any statement within the body of a loop that can make a loop
           prematurely stop looping or skip an "iteration".  Generally you
           shouldn't try this on roller coasters.

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

           Able to serve as an "lvalue".

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

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

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

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

       magical variables
           for you.

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

           See "pattern matching".

       member data
           See "instance variable".

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

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

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

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

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

           In the context of the stat syscall, refers to the field holding the

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

           Short for Perl Monger, a purveyor of Perl.

           A temporary value scheduled to die when the current statement

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

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

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

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

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

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

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

       null character
           A character with the ASCII value of zero.  It's used by C to
           terminate strings, but Perl allows strings to contain a null.

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

       null string

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

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

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

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

           An entire computer program crammed into one line of text.

       open source software
           Programs for which the source code is freely available and freely
           redistributable, with no commercial strings attached.  For a more
           detailed definition, see <>.

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

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

           A gizmo that transforms some number of input values to some number
           of output values, often built into a language with a special syntax

           Another name for "code point"

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

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

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

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

       pad Short for "scratchpad".

           See "argument".

       parent class
           See "base class".

       parse tree
           See "syntax tree".

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

           To fix by applying one, as it were.  In the realm of hackerdom, a
           listing of the differences between two versions of a program as

           A template used in "pattern matching".

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

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

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

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

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

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

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

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

           The notion that you can tell an "object" to do something generic,
           and the object will interpret the command in different ways
           depending on its type.  [<Gk many shapes]
           "platform", where "easily" can be defined however you like, and
           usually is.  Anything may be considered portable if you try hard
           enough.  See mobile home or London Bridge.

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

           The Portable Operating System Interface specification.

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

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

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

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

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

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

           A "subroutine".

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

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

       progressive matching
           Pattern matching that picks up where it left off before.
           parse much like built-in functions.  (Or don't parse, as the case
           may be.)

           A construct that sometimes looks like a function but really isn't.
           Usually reserved for "lvalue" modifiers like my, for "context"
           modifiers like scalar, and for the pick-your-own-quotes constructs,
           "q//", "qq//", "qx//", "qw//", "qr//", "m//", "s///", "y///", and

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

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

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

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

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

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

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

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

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

           The last rites performed by a parent "process" on behalf of a
           which is a naughty no-no in dictionaries but often works out okay
           in computer programs if you're careful not to recurse forever,
           which is like an infinite loop with more spectacular failure modes.

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

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

           See "regular expression".

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

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

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

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

       reserved words
           A word with a specific, built-in meaning to a "compiler", such as
           "if" or delete.  In many languages (not Perl), it's illegal to use
           reserved words to name anything else.  (Which is why they're
           reserved, after all.)  In Perl, you just can't use them to name
           labels or filehandles.  Also called "keywords".

       return value
           The "value" produced by a "subroutine" or "expression" when
           evaluated.  In Perl, a return value may be either a "list" or a
           What you are told when someone thinks you should Read The Fine

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

           Said of a program that runs with the privileges of its "owner"
           rather than (as is usually the case) the privileges of whoever is
           running it.  Also describes the bit in the mode word ("permission
           bits") that controls the feature.  This bit must be explicitly set

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

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

           A bolt out of the blue; that is, an event triggered by the
           "operating system", probably when you're least expecting it.

       signal handler
           A "subroutine" that, instead of being content to be called in the
           normal fashion, sits around waiting for a bolt out of the blue
           before it will deign to "execute".  Under Perl, bolts out of the
           blue are called signals, and you send them with the kill built-in.
           See "%SIG" in perlvar and "Signals" in perlipc.

       single inheritance
           The features you got from your mother, if she told you that you
           don't have a father.  (See also "inheritance" and "multiple
           inheritance".)  In computer languages, the notion that classes
           reproduce asexually so that a given class can only have one direct
           ancestor or "base class".  Perl supplies no such restriction,
           though you may certainly program Perl that way if you like.

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

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

           An endpoint for network communication among multiple processes that
           works much like a telephone or a post office box.  The most
           important thing about a socket is its "network address" (like a
           phone number).  Different kinds of sockets have different kinds of
           addresses--some look like filenames, and some don't.

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

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

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

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

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

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

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

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

           Varying slowly compared to something else.  (Unfortunately,
           everything is relatively stable compared to something else, except
           for certain elementary particles, and we're not so sure about
           them.)  In computers, where things are supposed to vary rapidly,
           "static" has a derogatory connotation, indicating a slightly
           dysfunctional "variable", "subroutine", or "method".  In Perl
           culture, the word is politely avoided.
           The "value" returned to the parent "process" when one of its child
           processes dies.  This value is placed in the special variable $?.
           Its upper eight bits are the exit status of the defunct process,
           and its lower eight bits identify the signal (if any) that the
           process died from.  On Unix systems, this status value is the same
           as the status word returned by wait(2).  See "system" in perlfunc.

           See "standard error".

           See "standard input".

           See "standard I/O".

           See "standard output".

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

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

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

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

           C keyword introducing a structure definition or name.

           See "data structure".

           See "derived class".

           A component of a "regular expression" pattern.

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

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

           See "base class".

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

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

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

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

       switch statement
           A program technique that lets you evaluate an "expression" and
           then, based on the value of the expression, do a multiway branch to
           the appropriate piece of code for that value.  Also called a "case
           structure", named after the similar Pascal construct.  See "Switch
           statements" in perlsyn.

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

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

       symbolic debugger
           A program that lets you step through the execution of your program,
           stopping or printing things out here and there to see whether
           subroutine.  By dereferencing the first variable, you can get at
           the second one.  Symbolic references are illegal under use strict

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

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

           From Greek, "with-arrangement".  How things (particularly symbols)
           are put together with each other.

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

           A "function" call directly to the "operating system".  Many of the
           important subroutines and functions you use aren't direct system
           calls, but are built up in one or more layers above the system call
           level.  In general, Perl programmers don't need to worry about the
           distinction.  However, if you do happen to know which Perl
           functions are really syscalls, you can predict which of these will
           set the $!  ($ERRNO) variable on failure.  Unfortunately, beginning
           programmers often confusingly employ the term "system call" to mean
           what happens when you call the Perl system function, which actually
           involves many syscalls.  To avoid any confusion, we nearly always
           use say "syscall" for something you could call indirectly via
           Perl's syscall function, and never for something you would call
           with Perl's system function.

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

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

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

           A "character" or "string" that marks the end of another string.

           Like a forked process, but without "fork"'s inherent memory
           protection.  A thread is lighter weight than a full process, in
           that a process could have multiple threads running around in it,
           all fighting over the same process's memory space unless steps are
           taken to protect threads from each other.  See threads.

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

           There's More Than One Way To Do It, the Perl Motto.  The notion
           that there can be more than one valid path to solving a programming
           problem in context.  (This doesn't mean that more ways are always
           better or that all possible paths are equally desirable--just that
           there need not be One True Way.)  Pronounced TimToady.

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

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

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

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

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

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

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

           A venerable typesetting language from which Perl derives the name
           of its $% variable and which is secretly used in the production of
           Camel books.
           Converting data from one type to another.  C permits this.  Perl
           does not need it.  Nor want it.

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

           A type definition in the C language.

           Use of a single identifier, prefixed with "*".  For example, *name
           stands for any or all of $name, @name, %name, &name, or just
           "name".  How you use it determines whether it is interpreted as all
           or only one of them.  See "Typeglobs and Filehandles" in perldata.

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

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

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

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

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

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

           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.

           "value", as your program sees fit.

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

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

           Mathematical jargon for a list of scalar values.

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

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

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

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

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

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

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

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

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

           An external "subroutine" defined in "XS".

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

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

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

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

perl v5.14.2                      2016-03-01                   PERLGLOSSARY(1)
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