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

NAME
       perlglossary - Perl Glossary

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

       A

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       associative array
	   See "hash".	Please.

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

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

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

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

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

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

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

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

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

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

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

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

       B

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

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

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

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

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

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

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

       binary operator
	   An "operator" that takes two operands.

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

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

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

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

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

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

       BLOCK
	   A syntactic construct consisting of a sequence of Perl statements that is delimited by
	   braces.  The "if" and "while" statements are defined in terms of BLOCKs, for instance.
	   Sometimes we also say "block" to mean a lexical scope; that is, a sequence of state-
	   ments 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 buffer-
	   ing".

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

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

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

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

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

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

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

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

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

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

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

       C

       C   A language beloved by many for its inside-out "type" definitions, inscrutable "prece-
	   dence" rules, and heavy "overloading" of the function-call mechanism.  (Well, actu-
	   ally, 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 con-
	   ditional compilation and macro definition and does various manipulations of the pro-
	   gram 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 argu-
	   ment.  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 chang-
	   ing the formal arguments.  See also "call by reference".

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

       canonical
	   Reduced to a standard form to facilitate comparison.

       capturing
	   The use of parentheses around a "subpattern" in a "regular expression" to store the
	   matched "substring" as a "backreference".  (Captured strings are also returned as a
	   list in "list context".)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       current working directory
	   See "working directory".

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

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

       D

       dangling statement
	   A bare, single "statement", without any braces, hanging off an "if" or "while" condi-
	   tional.  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 rear-
	   range them.	Objects that model things in the real world often have operations that
	   correspond to real activities.  For instance, if you model an elevator, your elevator
	   object might have an "open_door()" "method".

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

       DBM Stands for "Data Base Management" routines, a set of routines that emulate an "asso-
	   ciative 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 per-
	   sistent "hash" across multiple invocations.	You can tie your hash variables to vari-
	   ous DBM implementations--see AnyDBM_File and DB_File.

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

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

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

       defined
	   Having a meaning.  Perl thinks that some of the things people try to do are devoid of
	   meaning, in particular, making use of variables that have never been given a "value"
	   and performing certain operations on data that isn't there.	For example, if you try
	   to read data past the end of a file, Perl will hand you back an undefined value.  See
	   also "false" and "defined" in perlfunc.

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

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

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

       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 simul-
	   taneously, which is kind of classy.

       descriptor
	   See "file descriptor".

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

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

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

       directive
	   A "pod" directive.  See perlpod.

       directory
	   A special file that contains other files.  Some operating systems call these "fold-
	   ers", "drawers", or "catalogs".

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

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

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

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

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

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

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

       E

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

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

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

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

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

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

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

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

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

       EOF End of File.  Sometimes used metaphorically as the terminating string of a "here docu-
	   ment".

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

       error
	   See "exception" or "fatal error".

       escape sequence
	   See "metasymbol".

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

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

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

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

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

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

       exit status
	   See "status".

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

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

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

       F

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       G

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

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

       global
	   Something you can see from anywhere, usually used of variables and subroutines that
	   are visible everywhere in your program.  In Perl, only certain special variables are
	   truly global--most variables (and all subroutines) exist only in the current "pack-
	   age".  Global variables can be declared with our.  See "our" in perlfunc.

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

       glue language
	   A language such as Perl that is good at hooking things together that weren't intended
	   to be hooked together.

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

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

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

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

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

       H

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

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

       hard reference
	   A "scalar" "value" containing the actual address of a "referent", such that the refer-
	   ent'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 corre-
	   sponding referent.)	A hard reference is different from a "symbolic reference".

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

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

       header file
	   A file containing certain required definitions that you must include "ahead" of the
	   rest of your program to do certain obscure operations.  A C header file has a .h
	   extension.  Perl doesn't really have header files, though historically Perl has some-
	   times used translated .h files with a .ph extension.  See "require" in perlfunc.
	   (Header files have been superseded by the "module" mechanism.)

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

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

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

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

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

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

       I

       identifier
	   A legally formed name for most anything in which a computer program might be inter-
	   ested.  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 let-
	   ter.  (Perl also has more complicated names, such as "qualified" names.)

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

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

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

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

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

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

       indirect object
	   In English grammar, a short noun phrase between a verb and its direct object indicat-
	   ing 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!";

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

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

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

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

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

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

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

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

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

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

       interpreter
	   Strictly speaking, a program that reads a second program and does what the second pro-
	   gram 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 (syn-
	   tax trees) within the perl process itself, which the Perl "run time" system then
	   interprets.

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

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

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

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

       IP  Internet Protocol, or Intellectual Property.

       IPC Interprocess Communication.

       is-a
	   A relationship between two objects in which one object is considered to be a more spe-
	   cific 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".

       iteration
	   Doing something repeatedly.

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

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

       J

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

       K

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

       keyword
	   See "reserved words".

       L

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

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

       lexeme
	   Fancy term for a "token".

       lexer
	   Fancy term for a "tokener".

       lexical analysis
	   Fancy term for "tokenizing".

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

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

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

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

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

       line buffering
	   Used by a "standard I/O" output stream that flushes its "buffer" after every "new-
	   line".  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) vari-
	   able.  Many error messages report both values, if available.

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

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

       list
	   An ordered set of scalar values.

       list context
	   The situation in which an "expression" is expected by its surroundings (the code call-
	   ing 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.  Usu-
	   ally used for named built-in operators (such as print, unlink, and system) that do not
	   require parentheses around their "argument" list.

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

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

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

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

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

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

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

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

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

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

       lvaluable
	   Able to serve as an "lvalue".

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

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

       M

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

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

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

       Makefile
	   A file that controls the compilation of a program.  Perl programs don't usually need a
	   "Makefile" because the Perl compiler has plenty of self-control.

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

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

       matching
	   See "pattern matching".

       member data
	   See "instance variable".

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

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

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

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

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

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

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

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

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

       monger
	   Short for Perl Monger, a purveyor of Perl.

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

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

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

       N

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

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

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

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

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

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

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

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

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

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

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

       O

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

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

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

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

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

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

       operating system
	   A special program that runs on the bare machine and hides the gory details of managing
	   processes and devices.  Usually used in a looser sense to indicate a particular cul-
	   ture 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 ven-
	   dor's operating system is different from any other version of this or any other ven-
	   dor's operating system.  Perl is much more portable across operating systems than many
	   other languages.  See also "architecture" and "platform".

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

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

       options
	   See either switches or "regular expression modifier".

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

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

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

       P

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

       pad Short for "scratchpad".

       parameter
	   See "argument".

       parent class
	   See "base class".

       parse tree
	   See "syntax tree".

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

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

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

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

       pattern
	   A template used in "pattern matching".

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

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

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

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

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

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

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

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

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

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

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

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

       POSIX
	   The Portable Operating System Interface specification.

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

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

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

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

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

       preprocessing
	   What some helper "process" did to transform the incoming data into a form more suit-
	   able for the current process.  Often done with an incoming "pipe".  See also "C pre-
	   processor".

       procedure
	   A "subroutine".

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

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

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

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

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

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

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

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

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

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

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

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

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

       Q

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

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

       R

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

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

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

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

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

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

       regex
	   See "regular expression".

       regular expression
	   A single entity with various interpretations, like an elephant.  To a computer scien-
	   tist, 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 insen-
	   sitive.  See also "cloister".

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

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

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

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

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

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

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

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

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

       run time
	   The time when Perl is actually doing what your code says to do, as opposed to the ear-
	   lier 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 yet.

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

       S

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

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

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

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

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

       scope
	   How far away you can see a variable from, looking through one.  Perl has two visibil-
	   ity mechanisms: it does "dynamic scoping" of local variables, meaning that the rest of
	   the "block", and any subroutines that are called by the rest of the block, can see the
	   variables that are local to the block.  Perl does "lexical scoping" of my variables,
	   meaning that the rest of the block can see the variable, but other subroutines called
	   by the block cannot see the variable.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       signal
	   A bolt out of the blue; that is, an event triggered by the "operating system", proba-
	   bly 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.

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

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

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

       soft reference
	   See "symbolic reference".

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

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

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

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

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

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

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

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

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

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

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

       static method
	   No such thing.  See "class method".

       static scoping
	   No such thing.  See "lexical scoping".

       static variable
	   No such thing.  Just use a "lexical variable" in a scope larger than your "subrou-
	   tine".

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

       STDERR
	   See "standard error".

       STDIN
	   See "standard input".

       STDIO
	   See "standard I/O".

       STDOUT
	   See "standard output".

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

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

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

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

       struct
	   C keyword introducing a structure definition or name.

       structure
	   See "data structure".

       subclass
	   See "derived class".

       subpattern
	   A component of a "regular expression" pattern.

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

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

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

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

       superclass
	   See "base class".

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

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

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

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

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

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

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

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

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

       symbolic reference
	   A variable whose value is the name of another variable or subroutine.  By dereferenc-
	   ing the first variable, you can get at the second one.  Symbolic references are ille-
	   gal under use strict 'refs'.

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

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

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

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

       syscall
	   A "function" call directly to the "operating system".  Many of the important subrou-
	   tines 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 actu-
	   ally involves many syscalls.  To avoid any confusion, we nearly always use say
	   "syscall" for something you could call indirectly via Perl's syscall function, and
	   never for something you would call with Perl's system function.

       T

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

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

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

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

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

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

       thread
	   Like a forked process, but without "fork"'s inherent memory protection.  A thread is
	   lighter weight than a full process, in that a process could have multiple threads run-
	   ning 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 perl-
	   func and perltie.

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

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

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

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

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

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

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

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

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

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

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

       type
	   See "data type" and "class".

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

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

       typedef
	   A type definition in the C language.

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

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

       U

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

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

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

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

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

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

	   In ancient times, Unix was also used to refer to some code that a couple of people at
	   Bell Labs wrote to make use of a PDP-7 computer that wasn't doing much of anything
	   else at the time.

       V

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

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

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

       variadic
	   Said of a "function" that happily receives an indeterminate number of "actual argu-
	   ments".

       vector
	   Mathematical jargon for a list of scalar values.

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

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

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

       W

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

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

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

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

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

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

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

       X

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

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

       Y

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

       Z

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

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

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

perl v5.8.9				    2007-11-17				  PERLGLOSSARY(1)
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