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.\" ========================================================================
.\"
.IX Title "PERLGLOSSARY 1perl"
.TH PERLGLOSSARY 1perl 2024-02-11 "perl v5.38.2" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
perlglossary \- Perl Glossary
.SH VERSION
.IX Header "VERSION"
version 5.20210520
.SH DESCRIPTION
.IX Header "DESCRIPTION"
A glossary of terms (technical and otherwise) used in the Perl
documentation, derived from the Glossary of \fIProgramming
Perl\fR, Fourth Edition.  Words or phrases in bold are defined elsewhere in
this glossary.
.PP
Other useful sources include the Unicode Glossary <http://unicode.org/glossary/>,
the Free On-Line Dictionary of Computing <http://foldoc.org/>,
the Jargon File <http://catb.org/~esr/jargon/>,
and Wikipedia <http://www.wikipedia.org/>.
.SS A
.IX Subsection "A"
.IP "accessor methods" 4
.IX Item "accessor methods"
A \fBmethod\fR used to
indirectly inspect or update an \fBobject\fR’s state (its \fBinstance
variables\fR).
.IX Xref "accessor methods, defined methods, accessor"
.IP "actual arguments" 4
.IX Item "actual arguments"
The \fBscalar values\fR that you supply
to a \fBfunction\fR or \fBsubroutine\fR when you call it. For instance, when you
call \f(CWpower("puff")\fR, the string \f(CW"puff"\fR is the actual argument. See also
\&\fBargument\fR and \fBformal arguments\fR.
.IX Xref "actual arguments arguments, actual"
.IP "address operator" 4
.IX Item "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
\&\fBhard reference\fR, which is much safer than a memory address.
.IX Xref "address operator"
.IP algorithm 4
.IX Item "algorithm"
A well-defined sequence of steps, explained clearly
enough that even a computer could do them.
.IX Xref "algorithms (term)"
.IP alias 4
.IX Item "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 \f(CW\*(C`foreach\*(C'\fR loops, in
the \f(CW$_\fR variable for \f(CW\*(C`map\*(C'\fR or \f(CW\*(C`grep\*(C'\fR operators, in \f(CW$a\fR and \f(CW$b\fR
during \f(CW\*(C`sort\*(C'\fR’s comparison function, and in each element of \f(CW@_\fR for the
\&\fBactual arguments\fR of a subroutine call. Permanent aliases are explicitly
created in \fBpackages\fR by \fBimporting\fR symbols or by assignment to
\&\fBtypeglobs\fR. Lexically scoped aliases for package variables are explicitly
created by the \f(CW\*(C`our\*(C'\fR declaration.
.IX Xref "aliases, defined"
.IP alphabetic 4
.IX Item "alphabetic"
The sort of characters we put into words. In Unicode, this
is all letters including all ideographs and certain diacritics, letter
numbers like Roman numerals, and various combining marks.
.IX Xref "alphabetic sort"
.IP alternatives 4
.IX Item "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: \f(CW\*(C`|\*(C'\fR.
Alternatives in normal Perl expressions are separated with a double vertical
bar: \f(CW\*(C`||\*(C'\fR. Logical alternatives in \fBBoolean\fR expressions are separated
with either \f(CW\*(C`||\*(C'\fR or \f(CW\*(C`or\*(C'\fR.
.IX Xref "alternative characters"
.IP anonymous 4
.IX Item "anonymous"
Used to describe a \fBreferent\fR
that is not directly accessible through a named \fBvariable\fR. Such a referent
must be indirectly accessible through at least one \fBhard reference\fR. When
the last hard reference goes away, the anonymous referent is destroyed
without pity.
.IX Xref "anonymous referents referents, anonymous"
.IP application 4
.IX Item "application"
A bigger, fancier sort of \fBprogram\fR with a fancier
name so people don’t realize they are using a program.
.IX Xref "applications (term)"
.IP architecture 4
.IX Item "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 \fBcompiled\fR
into machine code. See also \fBplatform\fR and \fBoperating system\fR.
.IX Xref "architecture"
.IP argument 4
.IX Item "argument"
A piece of data supplied to a \fBprogram\fR,
\&\fBsubroutine\fR, \fBfunction\fR, or \fBmethod\fR to tell it what it’s supposed to
do. Also called a “parameter”.
.IX Xref "arguments, defined"
.IP ARGV 4
.IX Item "ARGV"
The name of the array containing the \fBargument\fR \fBvector\fR
from the command line. If you use the empty \f(CW\*(C`<>\*(C'\fR operator, \f(CW\*(C`ARGV\*(C'\fR
is the name of both the \fBfilehandle\fR used to traverse the arguments and the
\&\fBscalar\fR containing the name of the current input file.
.IX Xref "ARGV filehandle"
.IP "arithmetical operator" 4
.IX Item "arithmetical operator"
A \fBsymbol\fR such as \f(CW\*(C`+\*(C'\fR or \f(CW\*(C`/\*(C'\fR that tells
Perl to do the arithmetic you were supposed to learn in grade school.
.IX Xref "arithmetic operators, about"
.IP array 4
.IX Item "array"
An ordered sequence of \fBvalues\fR, stored such that you can
easily access any of the values using an \fIinteger subscript\fR that specifies
the value’s \fBoffset\fR in the sequence.
.IX Xref "arrays, defined"
.IP "array context" 4
.IX Item "array context"
An archaic expression for what is more correctly referred to
as \fBlist context\fR.
.IX Xref "array context"
.IP "Artistic License" 4
.IX Item "Artistic License"
The open source license that Larry Wall
created for Perl, maximizing Perl’s usefulness, availability, and
modifiability. The current version is 2. (<http://www.opensource.org/licenses/artistic\-license.php>).
.IX Xref "Artistic License Wall, Larry"
.IP ASCII 4
.IX Item "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 \fBUnicode\fR.
.IX Xref "ASCII (American Standard Code for Information Interchange) American Standard Code for Information Interchange (ASCII)"
.IP assertion 4
.IX Item "assertion"
A component of a \fBregular expression\fR that must be true for the pattern to
match but does not necessarily match any characters itself. Often used
specifically to mean a \fBzero-width\fR assertion.
.IX Xref "assertions (in regexes), defined regular expressions, assertions in"
.IP assignment 4
.IX Item "assignment"
An \fBoperator\fR whose assigned mission in life is to
change the value of a \fBvariable\fR.
.IX Xref "assignments, defined"
.IP "assignment operator" 4
.IX Item "assignment operator"
Either a regular \fBassignment\fR or a compound
\&\fBoperator\fR 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, \f(CW\*(C`$a += 2\*(C'\fR adds \f(CW2\fR to \f(CW$a\fR.
.IX Xref "assignment operators, about"
.IP "associative array" 4
.IX Item "associative array"
See \fBhash\fR. Please. The term associative array is the
old Perl 4 term for a \fBhash\fR. Some languages call it a dictionary.
.IX Xref "associative arrays"
.IP associativity 4
.IX Item "associativity"
Determines whether you do the left \fBoperator\fR first or the
right \fBoperator\fR first when you have “A \fBoperator\fR B \fBoperator\fR C”, and
the two operators are of the same precedence. Operators like \f(CW\*(C`+\*(C'\fR are left
associative, while operators like \f(CW\*(C`**\*(C'\fR are right associative. See Camel
chapter 3, “Unary and Binary Operators” for a list of operators and their
associativity.
.IX Xref "associativity"
.IP asynchronous 4
.IX Item "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.
.IX Xref "asynchronous event processing"
.IP atom 4
.IX Item "atom"
A \fBregular expression\fR component potentially matching a
\&\fBsubstring\fR containing one or more characters and treated as an indivisible
syntactic unit by any following \fBquantifier\fR. (Contrast with an
\&\fBassertion\fR that matches something of \fBzero width\fR and may not be quantified.)
.IX Xref "atoms"
.IP "atomic operation" 4
.IX Item "atomic operation"
When Democritus gave the word “atom” to the indivisible
bits of matter, he meant literally something that could not be cut: \fIἀ\-\fR
(not) + \fI\-τομος\fR (cuttable). An atomic operation is an action that can’t be
interrupted, not one forbidden in a nuclear-free zone.
.IX Xref "atomic operation"
.IP attribute 4
.IX Item "attribute"
A new feature that allows the declaration of
\&\fBvariables\fR and \fBsubroutines\fR with modifiers, as in \f(CW\*(C`sub foo : locked
method\*(C'\fR. Also another name for an \fBinstance variable\fR of an \fBobject\fR.
.IX Xref "attribute feature"
.IP autogeneration 4
.IX Item "autogeneration"
A feature of \fBoperator overloading\fR of \fBobjects\fR,
whereby the behavior of certain \fBoperators\fR can be reasonably deduced using
more fundamental operators. This assumes that the overloaded operators will
often have the same relationships as the regular operators. See Camel
chapter 13, “Overloading”.
.IX Xref "autogeneration, about"
.IP autoincrement 4
.IX Item "autoincrement"
To add one to something automatically, hence the name
of the \f(CW\*(C`++\*(C'\fR operator. To instead subtract one from something automatically
is known as an “autodecrement”.
.IX Xref "autoincrement (term)"
.IP autoload 4
.IX Item "autoload"
To load on demand. (Also called “lazy” loading.)
Specifically, to call an \f(CW\*(C`AUTOLOAD\*(C'\fR subroutine on behalf of an undefined
subroutine.
.IX Xref "autoloading, defined"
.IP autosplit 4
.IX Item "autosplit"
To split a string automatically, as the \fI–a\fR \fBswitch\fR
does when running under \fI–p\fR or \fI–n\fR in order to emulate \fBawk\fR. (See also
the \f(CW\*(C`AutoSplit\*(C'\fR module, which has nothing to do with the
\&\f(CW\*(C`–a\*(C'\fR switch but a lot to do with autoloading.)
.IX Xref "autosplit (term) AutoSplit module"
.IP autovivification 4
.IX Item "autovivification"
A Graeco-Roman word meaning “to bring oneself to life”.
In Perl, storage locations (\fBlvalues\fR) spontaneously generate themselves as
needed, including the creation of any \fBhard reference\fR values to point to
the next level of storage. The assignment \f(CW\*(C`$a[5][5][5][5][5] = "quintet"\*(C'\fR
potentially creates five scalar storage locations, plus four references (in
the first four scalar locations) pointing to four new anonymous arrays (to
hold the last four scalar locations). But the point of autovivification is
that you don’t have to worry about it.
.IX Xref "autovivification"
.IP AV 4
.IX Item "AV"
Short for “array
value”, which refers to one of Perl’s internal data types that holds an
\&\fBarray\fR. The \f(CW\*(C`AV\*(C'\fR type is a subclass of \fBSV\fR.
.IX Xref "AV (array value) array value (AV) values, array"
.IP awk 4
.IX Item "awk"
Descriptive editing term—short for “awkward”. Also
coincidentally refers to a venerable text-processing language from which
Perl derived some of its high-level ideas.
.IX Xref "awk (editing term)"
.SS B
.IX Subsection "B"
.IP backreference 4
.IX Item "backreference"
A substring \fBcaptured\fR
by a subpattern within unadorned parentheses in a \fBregex\fR. Backslashed
decimal numbers (\f(CW\*(C`\e1\*(C'\fR, \f(CW\*(C`\e2\*(C'\fR, etc.) later in the same pattern refer back to
the corresponding subpattern in the current match. Outside the pattern, the
numbered variables (\f(CW$1\fR, \f(CW$2\fR, etc.) continue to refer to these same
values, as long as the pattern was the last successful match of the current
\&\fBdynamic scope\fR.
.IX Xref "backreferences, about references, backreferences"
.IP backtracking 4
.IX Item "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 \fBregular expression\fR, and its earlier attempts don’t
pan out. See the section “The Little Engine That /Couldn(n’t)” in Camel
chapter 5, “Pattern Matching”.
.IX Xref "backtracking"
.IP "backward compatibility" 4
.IX Item "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.
.IX Xref "backward compatibility, defined"
.IP bareword 4
.IX Item "bareword"
A word sufficiently ambiguous to be deemed illegal under
\&\f(CW\*(C`use strict \*(Aqsubs\*(Aq\*(C'\fR. In the absence of that stricture, a bareword is
treated as if quotes were around it.
.IX Xref "barewords, about"
.IP "base class" 4
.IX Item "base class"
A generic \fBobject\fR type; that is, a \fBclass\fR
from which other, more specific classes are derived genetically by
\&\fBinheritance\fR. Also called a
“superclass” by people who respect their ancestors.
.IX Xref "base classes classes, base superclasses classes, superclasses"
.IP big-endian 4
.IX Item "big-endian"
From Swift: someone who
eats eggs big end first. Also used of computers that store the most
significant \fBbyte\fR of a word at a lower byte address than the least
significant byte. Often considered superior to little-endian machines. See
also \fBlittle-endian\fR.
.IX Xref "big–endian, defined endianness, big–endian"
.IP binary 4
.IX Item "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 file of
“nontext”, presumably because such a file makes full use of all the binary
bits in its bytes. With the advent of \fBUnicode\fR, this distinction, already
suspect, loses even more of its meaning.
.IX Xref "binary (term)"
.IP "binary operator" 4
.IX Item "binary operator"
An \fBoperator\fR that takes two \fBoperands\fR.
.IX Xref "binary operators, about"
.IP bind 4
.IX Item "bind"
To assign a specific \fBnetwork address\fR to a \fBsocket\fR.
.IX Xref "bind (term)"
.IP bit 4
.IX Item "bit"
An integer in the range from 0 to 1, inclusive. The smallest
possible unit of information storage. An eighth of a \fBbyte\fR 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”.)
.IX Xref "bits, defined"
.IP "bit shift" 4
.IX Item "bit shift"
The movement of bits left or right in a
computer word, which has the effect of multiplying or dividing by a
power of 2.
.IX Xref "bit–shift operators, defined"
.IP "bit string" 4
.IX Item "bit string"
A sequence of \fBbits\fR that is actually being thought of as a
sequence of bits, for once.
.IX Xref "bit string"
.IP bless 4
.IX Item "bless"
In corporate life, to grant official
approval to a thing, as in, “The VP of Engineering has blessed our
WebCruncher project.” Similarly, in Perl, to grant official approval to a
\&\fBreferent\fR so that it can function as an \fBobject\fR, such as a WebCruncher
object. See the \f(CW\*(C`bless\*(C'\fR function in Camel chapter 27, “Functions”.
.IX Xref "bless function, about bless (term)"
.IP block 4
.IX Item "block"
What a \fBprocess\fR 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 \fBoperating system\fR likes to
deal with (normally a power of 2 such as 512 or 8192). Typically refers to
a chunk of data that’s coming from or going to a disk file.
.IX Xref "blocks, defined"
.IP BLOCK 4
.IX Item "BLOCK"
A syntactic construct
consisting of a sequence of Perl \fBstatements\fR that is delimited by braces.
The \f(CW\*(C`if\*(C'\fR and \f(CW\*(C`while\*(C'\fR statements are defined in terms of \fR\f(CI\*(C`BLOCK\*(C'\fR\fI\fRs, for
instance. Sometimes we also say “block” to mean a lexical scope; that is, a
sequence of statements that acts like a \fI\fR\f(CI\*(C`BLOCK\*(C'\fR\fI\fR, such as within an
\&\f(CW\*(C`eval\*(C'\fR or a file, even though the statements aren’t delimited by braces.
.IX Xref "BLOCK construct, about constructs, BLOCK"
.IP "block buffering" 4
.IX Item "block buffering"
A method of making input and output
efficient by passing one \fBblock\fR at a time. By default, Perl does block
buffering to disk files. See \fBbuffer\fR and \fBcommand buffering\fR.
.IX Xref "block buffering buffering, block"
.IP Boolean 4
.IX Item "Boolean"
A value that is either \fBtrue\fR or
\&\fBfalse\fR.
.IX Xref "Boolean values values, Boolean"
.IP "Boolean context" 4
.IX Item "Boolean context"
A special kind of \fBscalar
context\fR used in conditionals to decide whether the \fBscalar value\fR returned
by an expression is \fBtrue\fR or \fBfalse\fR. Does not evaluate as either a
string or a number. See \fBcontext\fR.
.IX Xref "Boolean context, about context, Boolean"
.IP breakpoint 4
.IX Item "breakpoint"
A spot in your program where you’ve told the debugger
to stop \fBexecution\fR so you can poke around and see whether anything is
wrong yet.
.IX Xref "breakpoints, defined"
.IP broadcast 4
.IX Item "broadcast"
To send a \fBdatagram\fR to multiple destinations
simultaneously.
.IX Xref "broadcast (networking term)"
.IP BSD 4
.IX Item "BSD"
A psychoactive drug, popular in the ’80s, probably developed at UC
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”.
.IX Xref "BSD (Berkeley Standard Distribution) Berkeley Standard Distribution (BSD)"
.IP bucket 4
.IX Item "bucket"
A location in a \fBhash table\fR 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.)
.IX Xref "buckets (term)"
.IP buffer 4
.IX Item "buffer"
A temporary holding location for data. Data that are
\&\fBBlock buffering\fR means that the data is passed on to its destination
whenever the buffer is full. \fBLine buffering\fR means that it’s passed on
whenever a complete line is received. \fBCommand buffering\fR means that it’s
passed every time you do a \f(CW\*(C`print\*(C'\fR 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.
.IX Xref "buffers, defined"
.IP built-in 4
.IX Item "built-in"
A \fBfunction\fR that is predefined in the
language. Even when hidden by \fBoverriding\fR, you can always get at a built\-
in function by \fBqualifying\fR its name with the \f(CW\*(C`CORE::\*(C'\fR pseudopackage.
.IX Xref "built–in functions, about"
.IP bundle 4
.IX Item "bundle"
A group of related modules on \fBCPAN\fR. (Also sometimes
refers to a group of command-line switches grouped into one \fBswitch
cluster\fR.)
.IX Xref "bundles (term)"
.IP byte 4
.IX Item "byte"
A piece of data worth eight \fBbits\fR in most places.
.IX Xref "bytes (term)"
.IP bytecode 4
.IX Item "bytecode"
A pidgin-like lingo spoken among ’droids when they don’t wish to reveal
their orientation (see \fBendian\fR). Named after some similar languages spoken
(for similar reasons) between compilers and interpreters in the late 20ᵗʰ
century. These languages are characterized by representing everything as a
nonarchitecture-dependent sequence of bytes.
.SS C
.IX Subsection "C"
.IP C 4
.IX Item "C"
A language beloved by many for its inside-out \fBtype\fR
definitions, inscrutable \fBprecedence\fR rules, and heavy \fBoverloading\fR of
the function-call mechanism. (Well, actually, people first switched to C
because they found lowercase identifiers easier to read than upper.) Perl is
written in C, so it’s not surprising that Perl borrowed a few ideas from it.
.IX Xref "C language, about"
.IP cache 4
.IX Item "cache"
A data repository. Instead of computing expensive answers
several times, compute it once and save the result.
.IX Xref "cache (term)"
.IP callback 4
.IX Item "callback"
A \fBhandler\fR that you register with some other part of your
program in the hope that the other part of your program will \fBtrigger\fR your
handler when some event of interest transpires.
.IX Xref "callbacks"
.IP "call by reference" 4
.IX Item "call by reference"
An \fBargument\fR\-passing mechanism in which the \fBformal arguments\fR refer directly to the
\&\fBactual arguments\fR, and the \fBsubroutine\fR can change the actual arguments
by changing the formal arguments. That is, the formal argument is an
\&\fBalias\fR for the actual argument. See also \fBcall by value\fR.
.IX Xref "call by reference references, call by reference mechanism"
.IP "call by value" 4
.IX Item "call by value"
An \fBargument\fR\-passing mechanism in which the \fBformal
arguments\fR refer to a copy of the \fBactual arguments\fR, and the
\&\fBsubroutine\fR cannot change the actual arguments by changing the formal
arguments. See also \fBcall by reference\fR.
.IX Xref "call by value"
.IP canonical 4
.IX Item "canonical"
Reduced to a standard form to facilitate comparison.
.IX Xref "canonical (term)"
.IP "capture variables" 4
.IX Item "capture variables"
The variables—such as \f(CW$1\fR and
\&\f(CW$2\fR, and \f(CW\*(C`%+\*(C'\fR and \f(CW\*(C`%– \*(C'\fR—that hold the text remembered in a pattern
match. See Camel chapter 5, “Pattern Matching”.
.IX Xref "capture variables variables, capture"
.IP capturing 4
.IX Item "capturing"
The use of parentheses around a \fBsubpattern\fR in a
\&\fBregular expression\fR to store the matched \fBsubstring\fR as a
\&\fBbackreference\fR. (Captured strings are also returned as a list in \fBlist
context\fR.) See Camel chapter 5, “Pattern Matching”.
.IX Xref "capturing in pattern matching subpatterns, capturing pattern matching, capturing in"
.IP "cargo cult" 4
.IX Item "cargo cult"
Copying and pasting code without understanding it, while
superstitiously believing in its value. This term originated from
preindustrial cultures dealing with the detritus of explorers and colonizers
of technologically advanced cultures. See \fIThe Gods Must Be Crazy\fR.
.IX Xref "cargo cult"
.IP case 4
.IX Item "case"
A property of certain
characters. Originally, typesetter stored capital letters in the upper of
two cases and small letters in the lower one. Unicode recognizes three
cases: \fBlowercase\fR (\fBcharacter property\fR \f(CW\*(C`\ep{lower}\*(C'\fR), \fBtitlecase\fR
(\f(CW\*(C`\ep{title}\*(C'\fR), and \fBuppercase\fR (\f(CW\*(C`\ep{upper}\*(C'\fR). A fourth casemapping called
\&\fBfoldcase\fR is not itself a distinct case, but it is used internally to
implement \fBcasefolding\fR. Not all letters have case, and some nonletters
have case.
.IX Xref "case (character) characters, case considerations"
.IP casefolding 4
.IX Item "casefolding"
Comparing or matching a string case-insensitively. In Perl, it
is implemented with the \f(CW\*(C`/i\*(C'\fR pattern modifier, the \f(CW\*(C`fc\*(C'\fR function, and the
\&\f(CW\*(C`\eF\*(C'\fR double-quote translation escape.
.IX Xref "casefolding"
.IP casemapping 4
.IX Item "casemapping"
The process of converting a string to one of the four Unicode
\&\fBcasemaps\fR; in Perl, it is implemented with the \f(CW\*(C`fc\*(C'\fR, \f(CW\*(C`lc\*(C'\fR, \f(CW\*(C`ucfirst\*(C'\fR,
and \f(CW\*(C`uc\*(C'\fR functions.
.IX Xref "casemapping"
.IP character 4
.IX Item "character"
The smallest individual element of a string. Computers
store characters as integers, but Perl lets you operate on them as text. The
integer used to represent a particular character is called that character’s
\&\fBcodepoint\fR.
.IX Xref "characters, defined"
.IP "character class" 4
.IX Item "character class"
A square-bracketed list of
characters used in a \fBregular expression\fR to indicate that any character
of the set may occur at a given point. Loosely, any predefined set of
characters so used.
.IX Xref "character classes, about classes, character"
.IP "character property" 4
.IX Item "character property"
A predefined \fBcharacter class\fR matchable by the \f(CW\*(C`\ep\*(C'\fR
or \f(CW\*(C`\eP\*(C'\fR \fBmetasymbol\fR. \fBUnicode\fR defines hundreds of standard properties
for every possible codepoint, and Perl defines a few of its own, too.
.IX Xref "character property"
.IP "circumfix operator" 4
.IX Item "circumfix operator"
An \fBoperator\fR that surrounds its \fBoperand\fR, like the
angle operator, or parentheses, or a hug.
.IX Xref "circumfix operator"
.IP class 4
.IX Item "class"
A user-defined \fBtype\fR, implemented in Perl via a
\&\fBpackage\fR that provides (either directly or by inheritance) \fBmethods\fR
(that is, \fBsubroutines\fR) to handle \fBinstances\fR of the class (its
\&\fBobjects\fR). See also \fBinheritance\fR.
.IX Xref "classes, defined"
.IP "class method" 4
.IX Item "class method"
A \fBmethod\fR whose \fBinvocant\fR is a
\&\fBpackage\fR name, not an \fBobject\fR reference. A method associated with the
class as a whole. Also see \fBinstance method\fR.
.IX Xref "class methods methods, class"
.IP client 4
.IX Item "client"
In networking, a \fBprocess\fR that
initiates contact with a \fBserver\fR process in order to exchange data and
perhaps receive a service.
.IX Xref "clients, defined processes, client"
.IP closure 4
.IX Item "closure"
An \fBanonymous\fR subroutine
that, when a reference to it is generated at runtime, keeps track of the
identities of externally visible \fBlexical variables\fR, even after those
lexical variables have supposedly gone out of \fBscope\fR. They’re called
“closures” because this sort of behavior gives mathematicians a sense of
closure.
.IX Xref "closure subroutines subroutines, closure"
.IP cluster 4
.IX Item "cluster"
A parenthesized \fBsubpattern\fR
used to group parts of a \fBregular expression\fR into a single \fBatom\fR.
.IX Xref "clusters, defined subpatterns, cluster"
.IP CODE 4
.IX Item "CODE"
The word returned by the \f(CW\*(C`ref\*(C'\fR
function when you apply it to a reference to a subroutine. See also \fBCV\fR.
.IX Xref "CODE (ref function) ref function, about"
.IP "code generator" 4
.IX Item "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 \fBprogram
generator\fR.
.IX Xref "code generators, defined"
.IP codepoint 4
.IX Item "codepoint"
The integer a computer uses to represent a given
character. ASCII codepoints are in the range 0 to 127; Unicode codepoints
are in the range 0 to 0x1F_FFFF; and Perl codepoints are in the range 0 to
2³²−1 or 0 to 2⁶⁴−1, depending on your native integer size. In Perl Culture,
sometimes called \fBordinals\fR.
.IX Xref "codepoints, about"
.IP "code subpattern" 4
.IX Item "code subpattern"
A \fBregular expression\fR subpattern
whose real purpose is to execute some Perl code—for example, the \f(CW\*(C`(?{...})\*(C'\fR
and \f(CW\*(C`(??{...})\*(C'\fR subpatterns.
.IX Xref "code subpatterns subpatterns, code"
.IP "collating sequence" 4
.IX Item "collating sequence"
The order into which \fBcharacters\fR
sort. This is used by \fBstring\fR comparison routines to decide, for example,
where in this glossary to put “collating sequence”.
.IX Xref "collating sequence collating sequence"
.IP co-maintainer 4
.IX Item "co-maintainer"
A person with permissions to index a \fBnamespace\fR in
\&\fBPAUSE\fR. Anyone can upload any namespace, but only primary and
co-maintainers get their contributions indexed.
.IX Xref "co–maintainers"
.IP "combining character" 4
.IX Item "combining character"
Any character with the
General Category of Combining Mark (\f(CW\*(C`\ep{GC=M}\*(C'\fR), which may be spacing or
nonspacing. Some are even invisible. A sequence of combining characters
following a grapheme base character together make up a single user-visible
character called a \fBgrapheme\fR. Most but not all diacritics are combining
characters, and vice versa.
.IX Xref "combining characters characters, combining"
.IP command 4
.IX Item "command"
In \fBshell\fR 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 \fBstatement\fR, which might start with a \fBlabel\fR and typically ends with
a semicolon.
.IX Xref "commands, defined"
.IP "command buffering" 4
.IX Item "command buffering"
A mechanism in Perl that lets you
store up the output of each Perl \fBcommand\fR and then flush it out as a
single request to the \fBoperating system\fR. It’s enabled by setting the \f(CW$|\fR
(\f(CW$AUTOFLUSH\fR) variable to a true value. It’s used when you don’t want data
sitting around, not going where it’s supposed to, which may happen because
the default on a \fBfile\fR or \fBpipe\fR is to use \fBblock buffering\fR.
.IX Xref "command buffering buffering, command"
.IP "command-line arguments" 4
.IX Item "command-line arguments"
The \fBvalues\fR you supply
along with a program name when you tell a \fBshell\fR to execute a \fBcommand\fR.
These values are passed to a Perl program through \f(CW@ARGV\fR.
.IX Xref "command–line arguments arguments, command–line"
.IP "command name" 4
.IX Item "command name"
The name of the program currently executing, as typed on the
command line. In C, the \fBcommand\fR name is passed to the program as the
first command-line argument. In Perl, it comes in separately as \f(CW$0\fR.
.IX Xref "command names"
.IP comment 4
.IX Item "comment"
A remark that doesn’t affect the meaning of the program.
In Perl, a comment is introduced by a \f(CW\*(C`#\*(C'\fR character and continues to the
end of the line.
.IX Xref "comments, defined"
.IP "compilation unit" 4
.IX Item "compilation unit"
The \fBfile\fR (or \fBstring\fR, in the case of \f(CW\*(C`eval\*(C'\fR) that
is currently being \fBcompiled\fR.
.IX Xref "compilation units"
.IP compile 4
.IX Item "compile"
The process of turning source code into a machine-usable form. See \fBcompile
phase\fR.
.IP "compile phase" 4
.IX Item "compile phase"
Any time before Perl starts running your main
program. See also \fBrun phase\fR. Compile phase is mostly spent in \fBcompile
time\fR, but may also be spent in \fBruntime\fR when \f(CW\*(C`BEGIN\*(C'\fR blocks, \f(CW\*(C`use\*(C'\fR or
\&\f(CW\*(C`no\*(C'\fR declarations, or constant subexpressions are being evaluated. The
startup and import code of any \f(CW\*(C`use\*(C'\fR declaration is also run during
compile phase.
.IX Xref "compile phase, defined"
.IP compiler 4
.IX Item "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 \fIperl\fR program is not a compiler by this definition, but it does
contain a kind of compiler that takes a program and turns it into a more
executable form (\fBsyntax trees\fR) within the \fIperl\fR process itself, which
the \fBinterpreter\fR then interprets. There are, however, extension \fBmodules\fR
to get Perl to act more like a “real” compiler. See Camel chapter 16,
“Compiling”.
.IX Xref "compilers and compiling, about"
.IP "compile time" 4
.IX Item "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 \fBruntime\fR.
.IX Xref "compile time, defined"
.IP composer 4
.IX Item "composer"
A “constructor” for a \fBreferent\fR that isn’t really an
\&\fBobject\fR, like an anonymous array or a hash (or a sonata, for that matter).
For example, a pair of braces acts as a composer for a hash, and a pair of
brackets acts as a composer for an array. See the section “Creating
References” in Camel chapter 8, “References”.
.IX Xref "composers, about"
.IP concatenation 4
.IX Item "concatenation"
The process of gluing one
cat’s nose to another cat’s tail. Also a similar operation on two
\&\fBstrings\fR.
.IX Xref "concatenating strings strings, concatenating"
.IP conditional 4
.IX Item "conditional"
Something “iffy”. See \fBBoolean context\fR.
.IX Xref "conditional (term)"
.IP connection 4
.IX Item "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 \fBclient\fR and a \fBserver\fR.
.IX Xref "connections (term)"
.IP construct 4
.IX Item "construct"
As a noun, a piece of syntax made up of smaller
pieces. As a transitive verb, to create an \fBobject\fR using a \fBconstructor\fR.
.IX Xref "constructs, defined"
.IP constructor 4
.IX Item "constructor"
Any \fBclass method\fR, \fBinstance\fR, or \fBsubroutine\fR
that composes, initializes, blesses, and returns an \fBobject\fR. Sometimes we
use the term loosely to mean a \fBcomposer\fR.
.IX Xref "constructors, defined"
.IP context 4
.IX Item "context"
The surroundings or environment. The context given by the
surrounding code determines what kind of data a particular \fBexpression\fR is
expected to return. The three primary contexts are \fBlist context\fR,
\&\fBscalar\fR, and \fBvoid context\fR. Scalar context is sometimes subdivided into
\&\fBBoolean context\fR, \fBnumeric context\fR, \fBstring context\fR, and \fBvoid
context\fR. There’s also a “don’t care” context (which is dealt with in Camel
chapter 2, “Bits and Pieces”, if you care).
.IX Xref "context, about"
.IP continuation 4
.IX Item "continuation"
The treatment of more than one physical \fBline\fR as a
single logical line. \fBMakefile\fR lines are continued by putting a backslash
before the \fBnewline\fR. Mail headers, as defined by RFC 822, are
continued by putting a space or tab \fIafter\fR the newline. In general, lines
in Perl do not need any form of continuation mark, because \fBwhitespace\fR
(including newlines) is gleefully ignored. Usually.
.IX Xref "continuation lines RFC 822"
.IP "core dump" 4
.IX Item "core dump"
The corpse of a \fBprocess\fR, in the form of a file left in the
\&\fBworking directory\fR of the process, usually as a result of certain kinds
of fatal errors.
.IX Xref "core dump"
.IP CPAN 4
.IX Item "CPAN"
The Comprehensive Perl Archive Network. (See the Camel Preface
and Camel chapter 19, “CPAN” for details.)
.IX Xref "Comprehensive Perl Archive Network CPAN (Comprehensive Perl Archive Network), about"
.IP "C preprocessor" 4
.IX Item "C preprocessor"
The typical C compiler’s first pass, which processes lines
beginning with \f(CW\*(C`#\*(C'\fR for conditional compilation and macro definition, and
does various manipulations of the program text based on the current
definitions. Also known as \fIcpp\fR(1).
.IX Xref "C preprocessor"
.IP cracker 4
.IX Item "cracker"
Someone who breaks security on computer systems. A cracker may
be a true \fBhacker\fR or only a \fBscript kiddie\fR.
.IX Xref "crackers"
.IP "currently selected output channel" 4
.IX Item "currently selected output channel"
The last \fBfilehandle\fR that was
designated with \f(CWselect(FILEHANDLE)\fR; \f(CW\*(C`STDOUT\*(C'\fR, if no filehandle has
been selected.
.IX Xref "currently selected output channel"
.IP "current package" 4
.IX Item "current package"
The \fBpackage\fR in which the current statement is
\&\fBcompiled\fR. Scan backward in the text of your program through the current
\&\fBlexical scope\fR or any enclosing lexical scopes until you find a package
declaration. That’s your current package name.
.IX Xref "current package"
.IP "current working directory" 4
.IX Item "current working directory"
See \fBworking directory\fR.
.IX Xref "current working directory"
.IP CV 4
.IX Item "CV"
In academia, a curriculum vitæ, a fancy kind of résumé. In Perl, an internal “code value” typedef holding a
\&\fBsubroutine\fR. The \f(CW\*(C`CV\*(C'\fR type is a subclass of \fBSV\fR.
.IX Xref "CV (code value) code value (CV)"
.SS D
.IX Subsection "D"
.IP "dangling statement" 4
.IX Item "dangling statement"
A bare, single \fBstatement\fR,
without any braces, hanging off an \f(CW\*(C`if\*(C'\fR or \f(CW\*(C`while\*(C'\fR conditional. C allows
them. Perl doesn’t.
.IX Xref "dangling statements statements, dangling"
.IP datagram 4
.IX Item "datagram"
A packet of data, such as a \fBUDP\fR 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 \fBIP\fR level,
but \fBstream\fR protocols such as \fBTCP\fR hide this from your program.)
.IX Xref "datagrams, defined"
.IP "data structure" 4
.IX Item "data structure"
How your various pieces of data relate to each
other and what shape they make when you put them all together, as in a
rectangular table or a triangular tree.
.IX Xref "data structures, defined"
.IP "data type" 4
.IX Item "data type"
A set of possible values, together with all the
operations that know how to deal with those values. For example, a numeric
data type has a certain set of numbers that you can work with, as well as
various mathematical operations that you can do on the numbers, but would
make little sense on, say, a string such as \f(CW"Kilroy"\fR. Strings have their
own operations, such as \fBconcatenation\fR. Compound types made of a number of
smaller pieces generally have operations to compose and decompose them, and
perhaps to rearrange them. \fBObjects\fR 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 \f(CW\*(C`open_door\*(C'\fR
\&\fBmethod\fR.
.IX Xref "data types, defined"
.IP DBM 4
.IX Item "DBM"
Stands for “Database Management” routines, a set of routines that emulate an
\&\fBassociative array\fR using disk files. The routines use a dynamic hashing
scheme to locate any entry with only two disk accesses. DBM files allow a
Perl program to keep a persistent \fBhash\fR across multiple invocations. You
can \f(CW\*(C`tie\*(C'\fR your hash variables to various DBM implementations.
.IX Xref "DBM (Database Management) routines Database Management (DBM) routines"
.IP declaration 4
.IX Item "declaration"
An \fBassertion\fR that states something exists and
perhaps describes what it’s like, without giving any commitment as to how
or where you’ll use it. A declaration is like the part of your recipe that
says, “two cups flour, one large egg, four or five tadpoles…” See
\&\fBstatement\fR for its opposite. Note that some declarations also function
as statements. Subroutine declarations also act as definitions if a body
is supplied.
.IX Xref "declarations, defined"
.IP declarator 4
.IX Item "declarator"
Something that tells your program what sort of variable
you’d like. Perl doesn’t require you to declare variables, but you can use
\&\f(CW\*(C`my\*(C'\fR, \f(CW\*(C`our\*(C'\fR, or \f(CW\*(C`state\*(C'\fR to denote that you want something other than
the default.
.IX Xref "declarators"
.IP decrement 4
.IX Item "decrement"
To subtract a value from a
variable, as in “decrement \f(CW$x\fR” (meaning to remove 1 from its value) or
“decrement \f(CW$x\fR by 3”.
.IX Xref "decrementing values values, decrementing"
.IP default 4
.IX Item "default"
A \fBvalue\fR chosen for you if you don’t
supply a value of your own.
.IX Xref "default values values, default"
.IP defined 4
.IX Item "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 \fBvalue\fR 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
\&\fBfalse\fR and the \f(CW\*(C`defined\*(C'\fR entry in Camel chapter 27, “Functions”.
.IX Xref "defined (term)"
.IP delimiter 4
.IX Item "delimiter"
A \fBcharacter\fR or \fBstring\fR that sets bounds to an
arbitrarily sized textual object, not to be confused with a \fBseparator\fR or
\&\fBterminator\fR. “To delimit” really just means “to surround” or “to enclose”
(like these parentheses are doing).
.IX Xref "delimiters (term)"
.IP dereference 4
.IX Item "dereference"
A fancy computer science term
meaning “to follow a \fBreference\fR to what it points to”. The “de” part of it
refers to the fact that you’re taking away one level of \fBindirection\fR.
.IX Xref "dereference (term) references, dereference"
.IP "derived class" 4
.IX Item "derived class"
A \fBclass\fR that defines some of its \fBmethods\fR in terms of a more generic class,
called a \fBbase class\fR. Note that classes aren’t classified exclusively into
base classes or derived classes: a class can function as both a derived
class and a base class simultaneously, which is kind of classy.
.IX Xref "derived classes classes, derived subclasses classes, subclasses"
.IP descriptor 4
.IX Item "descriptor"
See \fBfile descriptor\fR.
.IP destroy 4
.IX Item "destroy"
To deallocate the memory of a \fBreferent\fR (first triggering
its \f(CW\*(C`DESTROY\*(C'\fR method, if it has one).
.IX Xref "destroy (term)"
.IP destructor 4
.IX Item "destructor"
A special \fBmethod\fR that is called
when an \fBobject\fR is thinking about \fBdestroying\fR itself. A Perl program’s
\&\f(CW\*(C`DESTROY\*(C'\fR method doesn’t do the actual destruction; Perl just \fBtriggers\fR
the method in case the \fBclass\fR wants to do any associated cleanup.
.IX Xref "destructor method methods, destructor"
.IP device 4
.IX Item "device"
A whiz-bang hardware gizmo (like a disk or tape drive or a
modem or a joystick or a mouse) attached to your computer, which the
\&\fBoperating system\fR tries to make look like a \fBfile\fR (or a bunch of files).
Under Unix, these fake files tend to live in the \fI/dev\fR directory.
.IX Xref "devices (term)"
.IP directive 4
.IX Item "directive"
A \fBpod\fR directive. See Camel chapter 23, “Plain Old
Documentation”.
.IX Xref "directives, defined"
.IP directory 4
.IX Item "directory"
A special file that contains other files. Some
\&\fBoperating systems\fR call these “folders”, “drawers”, “catalogues”, or
“catalogs”.
.IX Xref "directories, defined"
.IP "directory handle" 4
.IX Item "directory handle"
A name that represents a particular instance of opening a
directory to read it, until you close it. See the \f(CW\*(C`opendir\*(C'\fR function.
.IX Xref "directory handle"
.IP discipline 4
.IX Item "discipline"
Some people need this and some people avoid it.
For Perl, it’s an old way to say \fBI/O layer\fR.
.IX Xref "discipline (I O layer)"
.IP dispatch 4
.IX Item "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
\&\fBreferences\fR or, in the case of object \fBmethods\fR, by traversing the
inheritance tree looking for the most specific definition for the method.
.IX Xref "dispatching"
.IP distribution 4
.IX Item "distribution"
A standard, bundled release of a system of
software. The default usage implies source code is included. If that is not
the case, it will be called a “binary\-only” distribution.
.IX Xref "distributions, defined"
.IP dual-lived 4
.IX Item "dual-lived"
Some modules live both in the
\&\fBStandard Library\fR and on \fBCPAN\fR. These modules might be developed on two
tracks as people modify either version. The trend currently is to untangle
these situations.
.IX Xref "dual–lived modules modules, dual–lived"
.IP dweomer 4
.IX Item "dweomer"
An enchantment, illusion, phantasm, or jugglery. Said when Perl’s
magical \fBdwimmer\fR effects don’t do what you expect, but rather seem to be
the product of arcane \fIdweomercraft\fR, sorcery, or wonder working. [From
Middle English.]
.IX Xref "dweomer"
.IP dwimmer 4
.IX Item "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 \fBdweomer\fR instead.
.IX Xref "DWIM (Do What I Mean) principle Do What I Mean (DWIM) principle dwimming"
.IP "dynamic scoping" 4
.IX Item "dynamic scoping"
Dynamic scoping works over a \fBdynamic
scope\fR, making variables visible throughout the rest of the \fBblock\fR in
which they are first used and in any \fBsubroutines\fR that are called by the
rest of the block. Dynamically scoped variables can have their values
temporarily changed (and implicitly restored later) by a \f(CW\*(C`local\*(C'\fR operator.
(Compare \fBlexical scoping\fR.) Used more loosely to mean how a subroutine
that is in the middle of calling another subroutine “contains” that
subroutine at \fBruntime\fR.
.IX Xref "dynamic scope scopes, dynamic"
.SS E
.IX Subsection "E"
.IP eclectic 4
.IX Item "eclectic"
Derived from many sources. Some would say \fItoo\fR many.
.IX Xref "eclectic (term)"
.IP element 4
.IX Item "element"
A basic building block. When you’re talking about an
\&\fBarray\fR, it’s one of the items that make up the array.
.IX Xref "elements, about"
.IP embedding 4
.IX Item "embedding"
When something is contained in something else,
particularly when that might be considered surprising: “I’ve embedded a
complete Perl interpreter in my editor!”
.IX Xref "embedding (term)"
.IP "empty subclass test" 4
.IX Item "empty subclass test"
The notion that an empty \fBderived class\fR should
behave exactly like its \fBbase class\fR.
.IX Xref "empty subclass test"
.IP encapsulation 4
.IX Item "encapsulation"
The veil of abstraction separating the \fBinterface\fR
from the \fBimplementation\fR (whether enforced or not), which mandates that
all access to an \fBobject\fR’s state be through \fBmethods\fR alone.
.IX Xref "encapsulation (term)"
.IP endian 4
.IX Item "endian"
See \fBlittle-endian\fR and \fBbig-endian\fR.
.IP "en passant" 4
.IX Item "en passant"
When you change a \fBvalue\fR as it is being copied. [From
French “in passing”, as in the exotic pawn-capturing maneuver in chess.]
.IX Xref "en passant (term)"
.IP environment 4
.IX Item "environment"
The collective set of \fBenvironment variables\fR your
\&\fBprocess\fR inherits from its parent. Accessed via \f(CW%ENV\fR.
.IX Xref "environment (term)"
.IP "environment variable" 4
.IX Item "environment variable"
A mechanism by which some high-level agent such as a user can pass its
preferences down to its future offspring (child \fBprocesses\fR, grandchild
processes, great-grandchild processes, and so on). Each environment
variable is a \fBkey\fR/\fBvalue\fR pair, like one entry in a \fBhash\fR.
.IX Xref "environment variables variables, environment environment variables"
.IP EOF 4
.IX Item "EOF"
End of File. Sometimes used
metaphorically as the terminating string of a \fBhere document\fR.
.IX Xref "End of File (EOF) EOF (End of File)"
.IP errno 4
.IX Item "errno"
The error number returned by a
\&\fBsyscall\fR when it fails. Perl refers to the error by the name \f(CW$!\fR (or
\&\f(CW$OS_ERROR\fR if you use the English module).
.IX Xref "errno (error number) error number (errno)"
.IP error 4
.IX Item "error"
See \fBexception\fR or \fBfatal error\fR.
.IP "escape sequence" 4
.IX Item "escape sequence"
See \fBmetasymbol\fR.
.IP exception 4
.IX Item "exception"
A fancy term for an error. See \fBfatal error\fR.
.IP "exception handling" 4
.IX Item "exception handling"
The way a program responds to an error. The
exception-handling mechanism in Perl is the \f(CW\*(C`eval\*(C'\fR operator.
.IX Xref "exception handling, defined"
.IP exec 4
.IX Item "exec"
To throw away the current \fBprocess\fR’s program and replace
it with another, without exiting the process or relinquishing any resources
held (apart from the old memory image).
.IX Xref "exec function"
.IP "executable file" 4
.IX Item "executable file"
A \fBfile\fR that is specially marked to
tell the \fBoperating system\fR that it’s okay to run this file as a program.
Usually shortened to “executable”.
.IX Xref "executable files files, executable"
.IP execute 4
.IX Item "execute"
To run a \fBprogram\fR or \fBsubroutine\fR. (Has nothing to do
with the \f(CW\*(C`kill\*(C'\fR built-in, unless you’re trying to run a \fBsignal handler\fR.)
.IX Xref "execute (term)"
.IP "execute bit" 4
.IX Item "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.
.IX Xref "execute bit"
.IP "exit status" 4
.IX Item "exit status"
See \fBstatus\fR.
.IP exploit 4
.IX Item "exploit"
Used as a noun in this case, this refers to a known way
to compromise a program to get it to do something the author didn’t intend.
Your task is to write unexploitable programs.
.IX Xref "exploits, security"
.IP export 4
.IX Item "export"
To make symbols from a \fBmodule\fR available for
\&\fBimport\fR by other modules.
.IX Xref "exporting, defined"
.IP expression 4
.IX Item "expression"
Anything you can legally say in a spot
where a \fBvalue\fR is required. Typically composed of \fBliterals\fR,
\&\fBvariables\fR, \fBoperators\fR, \fBfunctions\fR, and \fBsubroutine\fR calls, not
necessarily in that order.
.IX Xref "expressions, defined expressions"
.IP extension 4
.IX Item "extension"
A Perl module that also pulls in \fBcompiled\fR C or C++
code. More generally, any experimental option that can be \fBcompiled\fR into
Perl, such as multithreading.
.IX Xref "extensions, defined"
.SS F
.IX Subsection "F"
.IP false 4
.IX Item "false"
In Perl, any value that would look like \f(CW""\fR
or \f(CW"0"\fR if evaluated in a string context. Since undefined values evaluate
to \f(CW""\fR, all undefined values are false, but not all false values are
undefined.
.IX Xref "false values values, false"
.IP FAQ 4
.IX Item "FAQ"
Frequently Asked Question (although not necessarily
frequently answered, especially if the answer appears in the Perl FAQ
shipped standard with Perl).
.IX Xref "FAQ (Frequently Asked Question) Frequently Asked Question (FAQ)"
.IP "fatal error" 4
.IX Item "fatal error"
An uncaught \fBexception\fR, which causes termination of the
\&\fBprocess\fR after printing a message on your \fBstandard error\fR stream. Errors
that happen inside an \f(CW\*(C`eval\*(C'\fR are not fatal. Instead, the \f(CW\*(C`eval\*(C'\fR terminates
after placing the exception message in the \f(CW$@\fR (\f(CW$EVAL_ERROR\fR) variable.
You can try to provoke a fatal error with the \f(CW\*(C`die\*(C'\fR operator (known as
throwing or raising an exception), but this may be caught by a dynamically
enclosing \f(CW\*(C`eval\*(C'\fR. If not caught, the \f(CW\*(C`die\*(C'\fR becomes a fatal error.
.IX Xref "fatal errors"
.IP "feeping creaturism" 4
.IX Item "feeping creaturism"
A spoonerism of “creeping
featurism”, noting the biological urge to add just one more feature to
a program.
.IX Xref "feeping creaturism creeping featurism"
.IP field 4
.IX Item "field"
A single piece of numeric or string data that is part of a
longer \fBstring\fR, \fBrecord\fR, or \fBline\fR. Variable-width fields are usually
split up by \fBseparators\fR (so use \f(CW\*(C`split\*(C'\fR to extract the fields), while
fixed-width fields are usually at fixed positions (so use \f(CW\*(C`unpack\*(C'\fR).
\&\fBInstance variables\fR are also known as “fields”.
.IX Xref "fields (term)"
.IP FIFO 4
.IX Item "FIFO"
First In, First Out. See also \fBLIFO\fR. Also a nickname for a \fBnamed pipe\fR.
.IX Xref "First In, First Out (FIFO) FIFO (First In, First Out)"
.IP file 4
.IX Item "file"
A named collection of data, usually stored on disk in a
\&\fBdirectory\fR in a \fBfilesystem\fR. 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.
.IX Xref "files, defined"
.IP "file descriptor" 4
.IX Item "file descriptor"
The little number the \fBoperating
system\fR uses to keep track of which opened \fBfile\fR you’re talking about.
Perl hides the file descriptor inside a \fBstandard I/O\fR stream and then
attaches the stream to a \fBfilehandle\fR.
.IX Xref "file descriptors descriptors, file"
.IP fileglob 4
.IX Item "fileglob"
A “wildcard” match on \fBfilenames\fR. See the \f(CW\*(C`glob\*(C'\fR function.
.IX Xref "fileglobs"
.IP filehandle 4
.IX Item "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.
.IX Xref "filehandles, about"
.IP filename 4
.IX Item "filename"
One name for a file. This name is listed in a
\&\fBdirectory\fR. You can use it in an \f(CW\*(C`open\*(C'\fR to tell the \fBoperating system\fR
exactly which file you want to open, and associate the file with a
\&\fBfilehandle\fR, which will carry the subsequent identity of that file in
your program, until you close it.
.IX Xref "filenames, about"
.IP filesystem 4
.IX Item "filesystem"
A set of \fBdirectories\fR and \fBfiles\fR 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.
.IX Xref "filesystems, defined"
.IP "file test operator" 4
.IX Item "file test operator"
A built-in unary operator that you use to
determine whether something is \fBtrue\fR about a file, such as \f(CW–o
$filename\fR to test whether you’re the owner of the file.
.IX Xref "file test operators, about"
.IP filter 4
.IX Item "filter"
A program designed to take a \fBstream\fR of input and
transform it into a stream of output.
.IX Xref "filters, defined"
.IP first-come 4
.IX Item "first-come"
The first \fBPAUSE\fR
author to upload a \fBnamespace\fR automatically becomes the \fBprimary
maintainer\fR for that namespace. The “first come” permissions distinguish a
\&\fBprimary maintainer\fR who was assigned that role from one who received it
automatically.
.IX Xref "first–come permissions permissions, first–come"
.IP flag 4
.IX Item "flag"
We tend to avoid this term because it means so many things.
It may mean a command-line \fBswitch\fR that takes no argument itself (such as
Perl’s \f(CW\*(C`–n\*(C'\fR and \f(CW\*(C`–p\*(C'\fR flags) or, less frequently, a single-bit indicator
(such as the \f(CW\*(C`O_CREAT\*(C'\fR and \f(CW\*(C`O_EXCL\*(C'\fR flags used in \f(CW\*(C`sysopen\*(C'\fR). Sometimes
informally used to refer to certain regex modifiers.
.IX Xref "flags (term)"
.IP "floating point" 4
.IX Item "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 \fBintegers\fR. Floating-point numbers are mere
approximations of real numbers.
.IX Xref "floating point methods methods, floating point"
.IP flush 4
.IX Item "flush"
The act of emptying a \fBbuffer\fR,
often before it’s full.
.IX Xref "flushing buffers buffers, flushing"
.IP FMTEYEWTK 4
.IX Item "FMTEYEWTK"
Far More Than Everything You Ever Wanted To Know. An
exhaustive treatise on one narrow topic, something of a super\-\fBFAQ\fR. See
Tom for far more.
.IX Xref "FMTEYEWTK acronym"
.IP foldcase 4
.IX Item "foldcase"
The casemap used in Unicode when comparing or matching
without regard to case. Comparing lower\-, title\-, or uppercase are all
unreliable due to Unicode’s complex, one-to-many case mappings. Foldcase is
a \fBlowercase\fR variant (using a partially decomposed \fBnormalization\fR form
for certain codepoints) created specifically to resolve this.
.IX Xref "foldcase (term)"
.IP fork 4
.IX Item "fork"
To create a child \fBprocess\fR
identical to the parent process at its moment of conception, at least until
it gets ideas of its own. A thread with protected memory.
.IX Xref "forking processes processes, forking"
.IP "formal arguments" 4
.IX Item "formal arguments"
The generic names by which a
\&\fBsubroutine\fR knows its \fBarguments\fR. In many languages, formal arguments
are always given individual names; in Perl, the formal arguments are just
the elements of an array. The formal arguments to a Perl program are
\&\f(CW$ARGV[0]\fR, \f(CW$ARGV[1]\fR, and so on. Similarly, the formal arguments to a
Perl subroutine are \f(CW$_[0]\fR, \f(CW$_[1]\fR, and so on. You may give the
arguments individual names by assigning the values to a \f(CW\*(C`my\*(C'\fR list. See
also \fBactual arguments\fR.
.IX Xref "formal arguments arguments, formal"
.IP format 4
.IX Item "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.
.IX Xref "formats, defined"
.IP "freely available" 4
.IX Item "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).
.IX Xref "freely available (term)"
.IP "freely redistributable" 4
.IX Item "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.
.IX Xref "freely redistributable (term)"
.IP freeware 4
.IX Item "freeware"
Historically, any software that you give away,
particularly if you make the source code available as well. Now often
called \fBopen source software\fR. Recently there has been a trend to use the
term in contradistinction to \fBopen source software\fR, to refer only to free
software released under the Free Software
Foundation’s GPL (General Public License), but this is difficult to justify
etymologically.
.IX Xref "freeware (term) Free Software Foundation"
.IP function 4
.IX Item "function"
Mathematically, a mapping of each of a set of input
values to a particular output value. In computers, refers to a
\&\fBsubroutine\fR or \fBoperator\fR that returns a \fBvalue\fR. It may or may not
have input values (called \fBarguments\fR).
.IX Xref "functions, about"
.IP "funny character" 4
.IX Item "funny character"
Someone like Larry, or one of his
peculiar friends. Also refers to the strange prefixes that Perl requires as
noun markers on its variables.
.IX Xref "funny characters characters, funny"
.SS G
.IX Subsection "G"
.IP "garbage collection" 4
.IX Item "garbage collection"
A misnamed feature—it should be called,
“expecting your mother to pick up after you”. Strictly speaking, Perl
doesn’t do this, but it relies on a reference-counting mechanism to keep
things tidy. However, we rarely speak strictly and will often refer to the
reference-counting scheme as a form of garbage collection. (If it’s any
comfort, when your interpreter exits, a “real” garbage collector runs to
make sure everything is cleaned up if you’ve been messy with circular
references and such.)
.IX Xref "garbage collection, defined"
.IP GID 4
.IX Item "GID"
Group ID—in Unix, the numeric group ID
that the \fBoperating system\fR uses to identify you and members of your
\&\fBgroup\fR.
.IX Xref "GID (Group ID) Group ID (GID)"
.IP glob 4
.IX Item "glob"
Strictly, the shell’s \f(CW\*(C`*\*(C'\fR 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 \fBfileglob\fR and \fBtypeglob\fR.
.IX Xref "glob (* character)"
.IP global 4
.IX Item "global"
Something you can see from anywhere, usually used of
\&\fBvariables\fR and \fBsubroutines\fR 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 \fBpackage\fR.
Global variables can be declared with \f(CW\*(C`our\*(C'\fR. See “Global Declarations” in
Camel chapter 4, “Statements and Declarations”.
.IX Xref "global (term)"
.IP "global destruction" 4
.IX Item "global destruction"
The \fBgarbage collection\fR of globals (and the running
of any associated object destructors) that takes place when a Perl
\&\fBinterpreter\fR is being shut down. Global destruction should not be
confused with the Apocalypse, except perhaps when it should.
.IX Xref "global destruction"
.IP "glue language" 4
.IX Item "glue language"
A language such as Perl that is good at hooking things
together that weren’t intended to be hooked together.
.IX Xref "glue language"
.IP granularity 4
.IX Item "granularity"
The size of the pieces you’re dealing with, mentally
speaking.
.IX Xref "granularity"
.IP grapheme 4
.IX Item "grapheme"
A graphene is an allotrope of carbon arranged in a
hexagonal crystal lattice one atom thick. A \fBgrapheme\fR, or more fully, a
\&\fIgrapheme cluster string\fR is a single user-visible \fBcharacter\fR, which may
in turn be several characters (\fBcodepoints\fR) long. For example, a carriage
return plus a line feed is a single grapheme but two characters, while a
“ȫ” is a single grapheme but one, two, or even three characters, depending
on \fBnormalization\fR.
.IX Xref "graphemes, defined"
.IP greedy 4
.IX Item "greedy"
A \fBsubpattern\fR whose
\&\fBquantifier\fR wants to match as many things as possible.
.IX Xref "greedy subpatterns subpatterns, greedy"
.IP grep 4
.IX Item "grep"
Originally from the old Unix editor command for “Globally
search for a Regular Expression and Print it”, now used in the general
sense of any kind of search, especially text searches. Perl has a built-in
\&\f(CW\*(C`grep\*(C'\fR function that searches a list for elements matching any given
criterion, whereas the \fBgrep\fR(1) program searches for lines matching a
\&\fBregular expression\fR in one or more files.
.IX Xref "grep function"
.IP group 4
.IX Item "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.
.IX Xref "groups, defined"
.IP GV 4
.IX Item "GV"
An internal “glob value” typedef,
holding a \fBtypeglob\fR. The \f(CW\*(C`GV\*(C'\fR type is a subclass of \fBSV\fR.
.IX Xref "GV (glob value) glob value (GV)"
.SS H
.IX Subsection "H"
.IP hacker 4
.IX Item "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 \fBcrackers\fR or clueless \fBscript kiddies\fR. If you
confuse them, we will presume that you are either evil or clueless.
.IX Xref "hackers"
.IP handler 4
.IX Item "handler"
A \fBsubroutine\fR or \fBmethod\fR that Perl calls when your
program needs to respond to some internal event, such as a \fBsignal\fR, or an
encounter with an operator subject to \fBoperator overloading\fR. See also
\&\fBcallback\fR.
.IX Xref "handlers, defined"
.IP "hard reference" 4
.IX Item "hard reference"
A \fBscalar\fR \fBvalue\fR containing
the actual address of a \fBreferent\fR, such that the referent’s \fBreference\fR
count accounts for it. (Some hard references are held internally, such as
the implicit reference from one of a \fBtypeglob\fR’s variable slots to its
corresponding referent.) A hard reference is different from a \fBsymbolic
reference\fR.
.IX Xref "hard references, about references, hard"
.IP hash 4
.IX Item "hash"
An unordered association of \fBkey\fR/\fBvalue\fR pairs, stored such that you can easily use a string \fBkey\fR to
look up its associated data \fBvalue\fR. 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.
.IX Xref "hashes, about key value pairs, about"
.IP "hash table" 4
.IX Item "hash table"
A data structure used internally by Perl for implementing
associative arrays (hashes) efficiently. See also \fBbucket\fR.
.IX Xref "hash tables"
.IP "header file" 4
.IX Item "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 \fI.h\fR extension. Perl
doesn’t really have header files, though historically Perl has sometimes
used translated \fI.h\fR files with a \fI.ph\fR extension. See \f(CW\*(C`require\*(C'\fR in
Camel chapter 27, “Functions”. (Header files have been superseded by the
\&\fBmodule\fR mechanism.)
.IX Xref "header files files, header"
.IP "here document" 4
.IX Item "here document"
So called because of a similar construct in \fBshells\fR that
pretends that the \fBlines\fR following the \fBcommand\fR are a separate \fBfile\fR
to be fed to the command, up to some terminating string. In Perl, however,
it’s just a fancy form of quoting.
.IX Xref "here documents"
.IP hexadecimal 4
.IX Item "hexadecimal"
A number in base 16, “hex” for short. The digits for 10
through 15 are customarily represented by the letters \f(CW\*(C`a\*(C'\fR through \f(CW\*(C`f\*(C'\fR.
Hexadecimal constants in Perl start with \f(CW\*(C`0x\*(C'\fR. See also the \f(CW\*(C`hex\*(C'\fR
function in Camel chapter 27, “Functions”.
.IX Xref "hexadecimals"
.IP "home directory" 4
.IX Item "home directory"
The directory you are put into when
you log in. On a Unix system, the name is often placed into \f(CW$ENV{HOME}\fR
or \f(CW$ENV{LOGDIR}\fR by \fIlogin\fR, but you can also find it with
\&\f(CW\*(C`(get\*(C'\fR\f(CW\*(C`pwuid($<))[7]\*(C'\fR. (Some platforms do not have a concept of a
home directory.)
.IX Xref "home directory directories, home"
.IP host 4
.IX Item "host"
The computer on which a program or other data resides.
.IX Xref "host computers"
.IP hubris 4
.IX Item "hubris"
Excessive pride, the sort of thing for which Zeus zaps
you.  Also the quality that makes you write (and maintain) programs that
other people won’t want to say bad things about. Hence, the third great
virtue of a programmer. See also \fBlaziness\fR and \fBimpatience\fR.
.IX Xref "hubris quality"
.IP HV 4
.IX Item "HV"
Short for a “hash value” typedef, which
holds Perl’s internal representation of a hash. The \f(CW\*(C`HV\*(C'\fR type is a
subclass of \fBSV\fR.
.IX Xref "HV (hash value) hash value (HV)"
.SS I
.IX Subsection "I"
.IP identifier 4
.IX Item "identifier"
A legally formed name for most anything in which a
computer program might be interested. Many languages (including Perl) allow
identifiers to start with an alphabetic character, and then contain
alphabetics and digits. Perl also allows connector punctuation like the
underscore character wherever it allows alphabetics. (Perl also has more
complicated names, like \fBqualified\fR names.)
.IX Xref "identifiers, defined"
.IP impatience 4
.IX Item "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 \fBlaziness\fR and \fBhubris\fR.
.IX Xref "impatience quality"
.IP implementation 4
.IX Item "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 \fBinterface\fR.
.IX Xref "implementation (term)"
.IP import 4
.IX Item "import"
To gain access to symbols that are exported from another
module. See \f(CW\*(C`use\*(C'\fR in Camel chapter 27, “Functions”.
.IX Xref "import (term)"
.IP increment 4
.IX Item "increment"
To increase the value of
something by 1 (or by some other number, if so specified).
.IX Xref "incrementing values values, incrementing"
.IP indexing 4
.IX Item "indexing"
In olden days, the act of looking up a \fBkey\fR in an
actual index (such as a phone book). But now it's merely the act of using
any kind of key or position to find the corresponding \fBvalue\fR, even if no
index is involved. Things have degenerated to the point that Perl’s
\&\f(CW\*(C`index\*(C'\fR function merely locates the position (index) of one string in
another.
.IX Xref "indexing (term)"
.IP "indirect filehandle" 4
.IX Item "indirect filehandle"
An \fBexpression\fR that
evaluates to something that can be used as a \fBfilehandle\fR: a \fBstring\fR
(filehandle name), a \fBtypeglob\fR, a typeglob \fBreference\fR, or a low-level
\&\fBIO\fR object.
.IX Xref "indirect filehandles filehandles, indirect"
.IP indirection 4
.IX Item "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 \fBsymbolic references\fR or \fBhard\fR.
.IX Xref "indirection (term)"
.IP "indirect object" 4
.IX Item "indirect object"
In English grammar, a short
noun phrase between a verb and its direct object indicating the beneficiary
or recipient of the action. In Perl, \f(CW\*(C`print STDOUT "$foo\en";\*(C'\fR can be
understood as “verb indirect-object object”, where \f(CW\*(C`STDOUT\*(C'\fR is the
recipient of the \f(CW\*(C`print\*(C'\fR action, and \f(CW"$foo"\fR is the object being
printed.  Similarly, when invoking a \fBmethod\fR, you might place the
invocant in the dative slot between the method and its arguments:
.IX Xref "indirect objects, defined objects, indirect"
.Sp
.Vb 3
\&    $gollum = new Pathetic::Creature "Sméagol";
\&    give $gollum "Fisssssh!";
\&    give $gollum "Precious!";
.Ve
.IP "indirect object slot" 4
.IX Item "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.) \f(CW\*(C`STDERR\*(C'\fR is in the indirect object slot here:
.IX Xref "indirect object slot"
.Sp
.Vb 1
\&    print STDERR "Awake! Awake! Fear, Fire, Foes! Awake!\en";
.Ve
.IP infix 4
.IX Item "infix"
An \fBoperator\fR that comes in between its \fBoperands\fR,
such as multiplication in \f(CW\*(C`24 * 7\*(C'\fR.
.IX Xref "infix operators"
.IP inheritance 4
.IX Item "inheritance"
What you get from your ancestors, genetically or
otherwise. If you happen to be a \fBclass\fR, your ancestors are called \fBbase
classes\fR and your descendants are called \fBderived classes\fR. See \fBsingle
inheritance\fR and \fBmultiple inheritance\fR.
.IX Xref "inheritance, defined"
.IP instance 4
.IX Item "instance"
Short for “an instance of a class”, meaning an \fBobject\fR
of that \fBclass\fR.
.IX Xref "instances (term)"
.IP "instance data" 4
.IX Item "instance data"
See \fBinstance variable\fR.
.IX Xref "instance data"
.IP "instance method" 4
.IX Item "instance method"
A \fBmethod\fR of an \fBobject\fR, as
opposed to a \fBclass method\fR.
.IX Xref "instance methods methods, instance"
.Sp
A \fBmethod\fR whose \fBinvocant\fR is an \fBobject\fR, not a \fBpackage\fR name. Every
object of a class shares all the methods of that class, so an instance
method applies to all instances of the class, rather than applying to a
particular instance. Also see \fBclass method\fR.
.IP "instance variable" 4
.IX Item "instance variable"
An \fBattribute\fR of an \fBobject\fR; data stored with the particular object rather than with the class
as a whole.
.IX Xref "instance variables, defined variables, instance"
.IP integer 4
.IX Item "integer"
A number with no fractional (decimal) part. A counting
number, like 1, 2, 3, and so on, but including 0 and the negatives.
.IX Xref "integers (term)"
.IP interface 4
.IX Item "interface"
The services a piece of code promises to provide
forever, in contrast to its \fBimplementation\fR, which it should feel free to
change whenever it likes.
.IX Xref "interfaces (term)"
.IP interpolation 4
.IX Item "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
\&\fR\f(CI\*(C`LIST\*(C'\fR\fI\fR.
.IX Xref "interpolation, defined"
.IP interpreter 4
.IX Item "interpreter"
Strictly speaking, a program that reads a second
program and does what the second program says directly without turning the
program into a different form first, which is what \fBcompilers\fR 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
(\fBsyntax trees\fR) within the \fIperl\fR process itself, which the Perl
\&\fBruntime\fR system then interprets.
.IX Xref "interpreters, defined"
.IP invocant 4
.IX Item "invocant"
The agent on whose behalf a \fBmethod\fR is invoked. In a
\&\fBclass\fR method, the invocant is a package name. In an \fBinstance\fR method,
the invocant is an object reference.
.IX Xref "invocants, defined"
.IP invocation 4
.IX Item "invocation"
The act of calling up a deity, daemon, program,
method, subroutine, or function to get it to do what you think it’s
supposed to do.  We usually “call” subroutines but “invoke” methods, since
it sounds cooler.
.IX Xref "invocation, method"
.IP I/O 4
.IX Item "I/O"
Input from, or output to, a \fBfile\fR or \fBdevice\fR.
.IX Xref "I O (Input Output), defined Input Output (I O), defined"
.IP IO 4
.IX Item "IO"
An internal I/O object. Can also mean \fBindirect object\fR.
.IP "I/O layer" 4
.IX Item "I/O layer"
One of the filters between the data and what you get as input
or what you end up with as output.
.IX Xref "I O layer"
.IP IPA 4
.IX Item "IPA"
India Pale Ale. Also the International Phonetic Alphabet, the
standard alphabet used for phonetic notation worldwide. Draws heavily on
Unicode, including many combining characters.
.IX Xref "International Phonetic Alphabet (IPA) IPA (International Phonetic Alphabet)"
.IP IP 4
.IX Item "IP"
Internet Protocol, or
Intellectual
Property.
.IX Xref "Internet Protocol (IP) IP (Internet Protocol) IP (Intellectual Property) Intellectual Property (IP)"
.IP IPC 4
.IX Item "IPC"
Interprocess Communication.
.IX Xref "Interprocess Communication IPC (Interprocess Communication), about communication"
.IP is-a 4
.IX Item "is-a"
A relationship between two \fBobjects\fR in which one
object is considered to be a more specific version of the other, generic
object: “A camel is a mammal.” Since the generic object really only exists
in a Platonic sense, we usually add a little abstraction to the notion of
objects and think of the relationship as being between a generic \fBbase
class\fR and a specific \fBderived class\fR. Oddly enough, Platonic classes
don’t always have Platonic relationships—see \fBinheritance\fR.
.IX Xref "is–a relationship"
.IP iteration 4
.IX Item "iteration"
Doing something repeatedly.
.IX Xref "iteration"
.IP iterator 4
.IX Item "iterator"
A special programming gizmo that keeps track of where you are
in something that you’re trying to iterate over. The \f(CW\*(C`foreach\*(C'\fR loop in
Perl contains an iterator; so does a hash, allowing you to \f(CW\*(C`each\*(C'\fR through
it.
.IX Xref "iterators"
.IP IV 4
.IX Item "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 \fBscalar\fR can hold, not to be confused with an \fBNV\fR.
.IX Xref "IV (Integer Value) Integer Value (IV)"
.SS J
.IX Subsection "J"
.IP JAPH 4
.IX Item "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 USENET signatures.
.IX Xref "JAPH acronym"
.SS K
.IX Subsection "K"
.IP key 4
.IX Item "key"
The string index to a \fBhash\fR, used to look up the \fBvalue\fR
associated with that key.
.IX Xref "keys, defined"
.IP keyword 4
.IX Item "keyword"
See \fBreserved words\fR.
.SS L
.IX Subsection "L"
.IP label 4
.IX Item "label"
A name you give to a \fBstatement\fR so that you can talk
about that statement elsewhere in the program.
.IX Xref "labels, defined"
.IP laziness 4
.IX Item "laziness"
The quality that makes you go to great effort to reduce
overall energy expenditure. It makes you write labor-saving programs that
other people will find useful, and then document what you wrote so you
don’t have to answer so many questions about it. Hence, the first great
virtue of a programmer. Also hence, this book. See also \fBimpatience\fR and
\&\fBhubris\fR.
.IX Xref "laziness quality"
.IP "leftmost longest" 4
.IX Item "leftmost longest"
The preference of the \fBregular expression\fR engine to match the
leftmost occurrence of a \fBpattern\fR, then given a position at which a match
will occur, the preference for the longest match (presuming the use of a
\&\fBgreedy\fR quantifier). See Camel chapter 5, “Pattern Matching” for \fImuch\fR
more on this subject.
.IX Xref "leftmost longest preference regular expressions, leftmost longest preference"
.IP "left shift" 4
.IX Item "left shift"
A \fBbit shift\fR that multiplies the
number by some power of 2.
.IX Xref "left shift (<<) bit operator bit–shift operators, left shift << (left shift) bit operator"
.IP lexeme 4
.IX Item "lexeme"
Fancy term for a \fBtoken\fR.
.IX Xref "lexeme (token)"
.IP lexer 4
.IX Item "lexer"
Fancy term for a \fBtokener\fR.
.IX Xref "lexer (tokener)"
.IP "lexical analysis" 4
.IX Item "lexical analysis"
Fancy term for \fBtokenizing\fR.
.IX Xref "lexical analysis"
.IP "lexical scoping" 4
.IX Item "lexical scoping"
Looking at your \fIOxford English
Dictionary\fR through a microscope. (Also known as \fBstatic scoping\fR, 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.
\&\fBstatic scoping\fR. —Ant. \fBdynamic scoping\fR.
.IX Xref "lexical scopes, defined scopes static scopes scopes, static"
.IP "lexical variable" 4
.IX Item "lexical variable"
A \fBvariable\fR subject to
\&\fBlexical scoping\fR, declared by \f(CW\*(C`my\*(C'\fR. Often just called a “lexical”. (The
\&\f(CW\*(C`our\*(C'\fR declaration declares a lexically scoped name for a global variable,
which is not itself a lexical variable.)
.IX Xref "lexical variables, about variables, lexical"
.IP library 4
.IX Item "library"
Generally, a collection of procedures. In ancient
days, referred to a collection of subroutines in a \fI.pl\fR file. In modern
times, refers more often to the entire collection of Perl \fBmodules\fR on
your system.
.IX Xref "libraries, defined"
.IP LIFO 4
.IX Item "LIFO"
Last In, First Out. See also \fBFIFO\fR. A LIFO is usually called a
\&\fBstack\fR.
.IX Xref "Last In, First Out (LIFO) LIFO (Last In, First Out) stacks, defined"
.IP line 4
.IX Item "line"
In Unix, a sequence of zero or more nonnewline characters
terminated with a \fBnewline\fR character. On non-Unix machines, this is
emulated by the C library even if the underlying \fBoperating system\fR has
different ideas.
.IX Xref "line (term)"
.IP linebreak 4
.IX Item "linebreak"
A \fBgrapheme\fR consisting of either a carriage return followed
by a line feed or any character with the Unicode Vertical Space \fBcharacter
property\fR.
.IX Xref "linebreaks"
.IP "line buffering" 4
.IX Item "line buffering"
Used by a \fBstandard I/O\fR output stream that
flushes its \fBbuffer\fR after every \fBnewline\fR. Many standard I/O libraries
automatically set up line buffering on output that is going to the terminal.
.IX Xref "line buffering buffering, line"
.IP "line number" 4
.IX Item "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 \f(CW\*(C`_\|_LINE_\|_\*(C'\fR. The
current input line number (for the file that was most recently read via
\&\f(CW\*(C`<FH>\*(C'\fR) is represented by the \f(CW$.\fR (\f(CW$INPUT_LINE_NUMBER\fR)
variable. Many error messages report both values, if available.
.IX Xref "line number"
.IP link 4
.IX Item "link"
Used as a noun, a name in a \fBdirectory\fR that represents a
\&\fBfile\fR. 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 \fBcompiled\fR 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.
.IX Xref "links, defined"
.IP LIST 4
.IX Item "LIST"
A syntactic construct representing a
comma\- separated list of expressions, evaluated to produce a \fBlist value\fR.
Each \fBexpression\fR in a \fR\f(CI\*(C`LIST\*(C'\fR\fI\fR is evaluated in \fBlist context\fR and
interpolated into the list value.
.IX Xref "LIST construct constructs, LIST"
.IP list 4
.IX Item "list"
An ordered set of scalar values.
.IX Xref "lists, defined"
.IP "list context" 4
.IX Item "list context"
The situation in which an \fBexpression\fR is
expected by its surroundings (the code calling it) to return a list of
values rather than a single value. Functions that want a \fR\f(CI\*(C`LIST\*(C'\fR\fI\fR of
arguments tell those arguments that they should produce a list value. See
also \fBcontext\fR.
.IX Xref "list context context, list"
.IP "list operator" 4
.IX Item "list operator"
An \fBoperator\fR that does something with a list of
values, such as \f(CW\*(C`join\*(C'\fR or \f(CW\*(C`grep\*(C'\fR. Usually used for named built-in
operators (such as \f(CW\*(C`print\*(C'\fR, \f(CW\*(C`unlink\*(C'\fR, and \f(CW\*(C`system\*(C'\fR) that do not require
parentheses around their \fBargument\fR list.
.IX Xref "list operators, about"
.IP "list value" 4
.IX Item "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 \fBlist context\fR.
.IX Xref "list values, about values, list"
.IP literal 4
.IX Item "literal"
A token in a programming language, such as a number or
\&\fBstring\fR, that gives you an actual \fBvalue\fR instead of merely representing
possible values as a \fBvariable\fR does.
.IX Xref "literals, defined"
.IP little-endian 4
.IX Item "little-endian"
From Swift: someone
who eats eggs little end first. Also used of computers that store the least
significant \fBbyte\fR of a word at a lower byte address than the most
significant byte. Often considered superior to big-endian machines. See
also \fBbig-endian\fR.
.IX Xref "little–endian, defined endianness, little–endian"
.IP local 4
.IX Item "local"
Not meaning the same thing everywhere. A global
variable in Perl can be localized inside a \fBdynamic scope\fR via the
\&\f(CW\*(C`local\*(C'\fR operator.
.IX Xref "local operator, about"
.IP "logical operator" 4
.IX Item "logical operator"
Symbols representing the concepts “and”, “or”,
“xor”, and “not”.
.IX Xref "logical operators, about"
.IP lookahead 4
.IX Item "lookahead"
An \fBassertion\fR that peeks at the string to the right of the current match location.
.IX Xref "lookahead assertions assertions (in regexes), lookahead"
.IP lookbehind 4
.IX Item "lookbehind"
An \fBassertion\fR that peeks at the string to the left of the current match
location.
.IX Xref "lookbehind assertions assertions (in regexes), lookbehind"
.IP loop 4
.IX Item "loop"
A construct that
performs something repeatedly, like a roller coaster.
.IX Xref "loop constructs and statements, about constructs, loop"
.IP "loop control statement" 4
.IX Item "loop control statement"
Any statement within the body of a loop that can
make a loop prematurely stop looping or skip an \fBiteration\fR. Generally,
you shouldn’t try this on roller coasters.
.IX Xref "statements, loop control"
.IP "loop label" 4
.IX Item "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.
.IX Xref "loop labels labels, loop"
.IP lowercase 4
.IX Item "lowercase"
In Unicode, not just
characters with the General Category of Lowercase Letter, but any character
with the Lowercase property, including Modifier Letters, Letter Numbers,
some Other Symbols, and one Combining Mark.
.IX Xref "lowercase characters characters, lowercase"
.IP lvaluable 4
.IX Item "lvaluable"
Able to serve as an \fBlvalue\fR.
.IX Xref "lvaluable function functions, lvaluable"
.IP lvalue 4
.IX Item "lvalue"
Term used by language lawyers for a
storage location you can assign a new \fBvalue\fR to, such as a \fBvariable\fR or
an element of an \fBarray\fR. The “l” is short for “left”, as in the left side
of an assignment, a typical place for lvalues. An \fBlvaluable\fR function or
expression is one to which a value may be assigned, as in \f(CW\*(C`pos($x) = 10\*(C'\fR.
.IX Xref "lvalue (term) values, lvalue"
.IP "lvalue modifier" 4
.IX Item "lvalue modifier"
An adjectival pseudofunction that
warps the meaning of an \fBlvalue\fR in some declarative fashion. Currently
there are three lvalue modifiers: \f(CW\*(C`my\*(C'\fR, \f(CW\*(C`our\*(C'\fR, and \f(CW\*(C`local\*(C'\fR.
.IX Xref "lvalue modifier modifiers, lvalue"
.SS M
.IX Subsection "M"
.IP magic 4
.IX Item "magic"
Technically speaking, any extra semantics attached to a
variable such as \f(CW$!\fR, \f(CW$0\fR, \f(CW%ENV\fR, or \f(CW%SIG\fR, or to any tied
variable.  Magical things happen when you diddle those variables.
.IX Xref "magic (term)"
.IP "magical increment" 4
.IX Item "magical increment"
An \fBincrement\fR operator that knows how to
bump up ASCII alphabetics as well as numbers.
.IX Xref "magical increment operator"
.IP "magical variables" 4
.IX Item "magical variables"
Special variables that have side
effects when you access them or assign to them. For example, in Perl,
changing elements of the \f(CW%ENV\fR array also changes the corresponding
environment variables that subprocesses will use. Reading the \f(CW$!\fR
variable gives you the current system error number or message.
.IX Xref "magical variables variables, magical"
.IP Makefile 4
.IX Item "Makefile"
A file that controls the compilation of a program. Perl programs
don’t usually need a \fBMakefile\fR because the Perl compiler has plenty of
self-control.
.IX Xref "Makefile"
.IP man 4
.IX Item "man"
The Unix program that displays online documentation
(manual pages) for you.
.IX Xref "man program (Unix)"
.IP manpage 4
.IX Item "manpage"
A “page” from the manuals, typically accessed via the
\&\fIman\fR(1) command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of
BUGS, and so on, and is typically longer than a page. There are manpages
documenting \fBcommands\fR, \fBsyscalls\fR, \fBlibrary\fR \fBfunctions\fR, \fBdevices\fR,
\&\fBprotocols\fR, \fBfiles\fR, 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.
.IX Xref "manpages, defined"
.IP matching 4
.IX Item "matching"
See \fBpattern matching\fR.
.IX Xref "matching"
.IP "member data" 4
.IX Item "member data"
See \fBinstance variable\fR.
.IX Xref "member data"
.IP memory 4
.IX Item "memory"
This always means your main memory, not your disk.
Clouding the issue is the fact that your machine may implement
\&\fBvirtual\fR 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.
.IX Xref "memory, defined"
.IP metacharacter 4
.IX Item "metacharacter"
A \fBcharacter\fR that is \fInot\fR supposed to be treated normally. Which characters
are to be treated specially as metacharacters varies greatly from context to
context. Your \fBshell\fR will have certain metacharacters, double-quoted Perl
\&\fBstrings\fR have other metacharacters,
and \fBregular expression\fR patterns have all the double-quote metacharacters plus
some extra ones of their own.
.IX Xref "metacharacters, about characters, regex metacharacters regular expressions, metacharacters and"
.IP metasymbol 4
.IX Item "metasymbol"
Something we’d call a
\&\fBmetacharacter\fR except that it’s a sequence of more than one character.
Generally, the first character in the sequence must be a true metacharacter
to get the other characters in the metasymbol to misbehave along with it.
.IX Xref "metasymbols, about escape sequences"
.IP method 4
.IX Item "method"
A kind of action that an \fBobject\fR can take if you tell
it to. See Camel chapter 12, “Objects”.
.IX Xref "methods, defined"
.IP "method resolution order" 4
.IX Item "method resolution order"
The path Perl takes through \f(CW@INC\fR. By default, this is a double depth first
search, once looking for defined methods and once for \f(CW\*(C`AUTOLOAD\*(C'\fR. However,
Perl lets you configure this with \f(CW\*(C`mro\*(C'\fR.
.IX Xref "method resolution order (mro) mro (method resolution order)"
.IP minicpan 4
.IX Item "minicpan"
A CPAN mirror that includes just the latest versions for each
distribution, probably created with \f(CW\*(C`CPAN::Mini\*(C'\fR. See
Camel chapter 19, “CPAN”.
.IX Xref "minicpan, defined CPAN (Comprehensive Perl Archive Network), minicpan and CPAN::Mini module"
.IP minimalism 4
.IX Item "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.
.IX Xref "minimalism"
.IP mode 4
.IX Item "mode"
In the context of the \fIstat\fR(2) syscall, refers to the field
holding the \fBpermission bits\fR and the type of the \fBfile\fR.
.IX Xref "mode"
.IP modifier 4
.IX Item "modifier"
See \fBstatement modifier\fR, \fBregular expression\fR, and
\&\fBlvalue\fR, not necessarily in that order.
.IX Xref "modifiers, defined"
.IP module 4
.IX Item "module"
A \fBfile\fR that defines a \fBpackage\fR of (almost) the same
name, which can either \fBexport\fR symbols or function as an \fBobject\fR class.
(A module’s main \fI.pm\fR file may also load in other files in support of the
module.) See the \f(CW\*(C`use\*(C'\fR built-in.
.IX Xref "modules, defined"
.IP modulus 4
.IX Item "modulus"
An integer divisor when
you’re interested in the remainder instead of the quotient.
.IX Xref "modulus (%) operator % (modulus) operator"
.IP mojibake 4
.IX Item "mojibake"
When you speak one language and the computer thinks you’re
speaking another. You’ll see odd translations when you send UTF‑8, for
instance, but the computer thinks you sent Latin\-1, showing all sorts of
weird characters instead. The term is written 「文字化け」in Japanese and
means “character rot”, an apt description. Pronounced [\f(CW\*(C`modʑibake\*(C'\fR] in
standard \fBIPA\fR phonetics, or approximately “moh\-jee\-bah\-keh”.
.IX Xref "mojibake"
.IP monger 4
.IX Item "monger"
Short for one member of \fBPerl mongers\fR, a
purveyor of Perl.
.IX Xref "mongers, Perl Perl mongers"
.IP mortal 4
.IX Item "mortal"
A temporary value scheduled to die when the
current statement finishes.
.IX Xref "mortal value values, mortal"
.IP mro 4
.IX Item "mro"
See \fBmethod resolution order\fR.
.IP "multidimensional array" 4
.IX Item "multidimensional array"
An array with multiple
subscripts for finding a single element. Perl implements these using
\&\fBreferences\fR—see Camel chapter 9, “Data Structures”.
.IX Xref "multidimensional arrays arrays, multidimensional"
.IP "multiple inheritance" 4
.IX Item "multiple inheritance"
The features you got from
your mother and father, mixed together unpredictably. (See also
\&\fBinheritance\fR and \fBsingle inheritance\fR.) In computer languages (including
Perl), it is the notion that a given class may have multiple direct
ancestors or \fBbase classes\fR.
.IX Xref "multiple inheritance inheritance, multiple"
.SS N
.IX Subsection "N"
.IP "named pipe" 4
.IX Item "named pipe"
A \fBpipe\fR with a name embedded in the
\&\fBfilesystem\fR so that it can be accessed by two unrelated \fBprocesses\fR.
.IX Xref "named pipes pipes, names"
.IP namespace 4
.IX Item "namespace"
A domain of names. You needn’t worry about whether the
names in one such domain have been used in another. See \fBpackage\fR.
.IX Xref "namespaces, about"
.IP NaN 4
.IX Item "NaN"
Not a number. The value Perl uses
for certain invalid or inexpressible floating-point operations.
.IX Xref "NaN (not a number) not a number (NaN)"
.IP "network address" 4
.IX Item "network address"
The most important attribute of a socket, like your
telephone’s telephone number. Typically an IP address. See also \fBport\fR.
.IX Xref "network address"
.IP newline 4
.IX Item "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 \f(CW\*(C`\en\*(C'\fR 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.
.IX Xref "newline character characters, newline"
.IP NFS 4
.IX Item "NFS"
Network File System, which allows you to mount a remote filesystem as if it were local.
.IX Xref "NFS (Network File System) Network File System (NFS)"
.IP normalization 4
.IX Item "normalization"
Converting a text string into an alternate but equivalent
\&\fBcanonical\fR (or compatible) representation that can then be compared for
equivalence. Unicode recognizes four different normalization forms: NFD,
NFC, NFKD, and NFKC.
.IX Xref "normalization"
.IP "null character" 4
.IX Item "null character"
A character with the numeric value of
zero. It’s used by C to terminate strings, but Perl allows strings to
contain a null.
.IX Xref "null character characters, null"
.IP "null list" 4
.IX Item "null list"
A \fBlist value\fR with zero elements, represented
in Perl by \f(CW\*(C`()\*(C'\fR.
.IX Xref "null lists lists, null"
.IP "null string" 4
.IX Item "null string"
A \fBstring\fR containing no characters, not to
be confused with a string containing a \fBnull character\fR, which has a
positive length and is \fBtrue\fR.
.IX Xref "null strings strings, null"
.IP "numeric context" 4
.IX Item "numeric context"
The situation in which an expression
is expected by its surroundings (the code calling it) to return a number.
See also \fBcontext\fR and \fBstring context\fR.
.IX Xref "numeric context context, numeric"
.IP numification 4
.IX Item "numification"
(Sometimes spelled \fInummification\fR and \fInummify\fR.) Perl lingo
for implicit conversion into a number; the related verb is \fInumify\fR.
\&\fINumification\fR is intended to rhyme with \fImummification\fR, and \fInumify\fR with
\&\fImummify\fR. It is unrelated to English \fInumen\fR, \fInumina\fR, \fInuminous\fR. We
originally forgot the extra \fIm\fR a long time ago, and some people got used to
our funny spelling, and so just as with \f(CW\*(C`HTTP_REFERER\*(C'\fR’s own missing letter,
our weird spelling has stuck around.
.IX Xref "numification"
.IP NV 4
.IX Item "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 \fBscalar\fR can hold, not to be
confused with an \fBIV\fR.
.IX Xref "Numeric Value (NV) NV (Numeric Value)"
.IP nybble 4
.IX Item "nybble"
Half a \fBbyte\fR, equivalent to one \fBhexadecimal\fR digit, and worth
four \fBbits\fR.
.IX Xref "nybble"
.SS O
.IX Subsection "O"
.IP object 4
.IX Item "object"
An \fBinstance\fR of a \fBclass\fR. 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.
.IX Xref "objects, defined"
.IP octal 4
.IX Item "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 \f(CW\*(C`oct\*(C'\fR function.
.IX Xref "octals"
.IP offset 4
.IX Item "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.
.IX Xref "offsets in strings strings, offsets in"
.IP one-liner 4
.IX Item "one-liner"
An entire computer program crammed into one line of
text.
.IX Xref "one–liner programs"
.IP "open source software" 4
.IX Item "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>.
.IX Xref "open source software"
.IP operand 4
.IX Item "operand"
An \fBexpression\fR that yields a \fBvalue\fR that an
\&\fBoperator\fR operates on. See also \fBprecedence\fR.
.IX Xref "operands (term)"
.IP "operating system" 4
.IX Item "operating system"
A special program that runs on the bare
machine and hides the gory details of managing \fBprocesses\fR and \fBdevices\fR.
Usually used in a looser sense to indicate a particular culture of
programming. The loose sense can be used at varying levels of specificity.
At one extreme, you might say that all versions of Unix and Unix-lookalikes
are the same operating system (upsetting many people, especially lawyers
and other advocates). At the other extreme, you could say this particular
version of this particular vendor’s operating system is different from any
other version of this or any other vendor’s operating system. Perl is much
more portable across operating systems than many other languages. See also
\&\fBarchitecture\fR and \fBplatform\fR.
.IX Xref "operating systems, defined"
.IP operator 4
.IX Item "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 \fBtypes\fR of data you give as its arguments (\fBoperands\fR) and what type
of data you want back from it.
.IX Xref "operators, about"
.IP "operator overloading" 4
.IX Item "operator overloading"
A kind of
\&\fBoverloading\fR that you can do on built-in \fBoperators\fR to make them work
on \fBobjects\fR 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 \fBpragma\fR—see Camel chapter 13, “Overloading”.
.IX Xref "operator overloading, about overloading, operator"
.IP options 4
.IX Item "options"
See either \fBswitches\fR or \fBregular expression modifiers\fR.
.IX Xref "options"
.IP ordinal 4
.IX Item "ordinal"
An abstract character’s integer value. Same thing as
\&\fBcodepoint\fR.
.IX Xref "ordinals (term)"
.IP overloading 4
.IX Item "overloading"
Giving additional meanings to a symbol or construct.
Actually, all languages do overloading to one extent or another, since
people are good at figuring out things from \fBcontext\fR.
.IX Xref "overloading, defined"
.IP overriding 4
.IX Item "overriding"
Hiding or invalidating some other definition of the
same name. (Not to be confused with \fBoverloading\fR, 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 \fBsubroutine\fR to hide a built-in \fBfunction\fR of the same
name (see the section “Overriding Built-in Functions” in Camel chapter 11,
“Modules”), and to describe how you can define a replacement \fBmethod\fR in a
\&\fBderived class\fR to hide a \fBbase class\fR’s method of the same name (see
Camel chapter 12, “Objects”).
.IX Xref "overriding, defined"
.IP owner 4
.IX Item "owner"
The one user (apart from the
superuser) who has absolute control over a \fBfile\fR. A file may also have a
\&\fBgroup\fR of users who may exercise joint ownership if the real owner
permits it. See \fBpermission bits\fR.
.IX Xref "ownership, file files, ownership of"
.SS P
.IX Subsection "P"
.IP package 4
.IX Item "package"
A \fBnamespace\fR for global \fBvariables\fR, \fBsubroutines\fR,
and the like, such that they can be kept separate from like-named
\&\fBsymbols\fR in other namespaces. In a sense, only the package is global,
since the symbols in the package’s symbol table are only accessible from
code \fBcompiled\fR outside the package by naming the package. But in another
sense, all package symbols are also globals—they’re just well-organized
globals.
.IX Xref "packages, defined"
.IP pad 4
.IX Item "pad"
Short for \fBscratchpad\fR.
.IX Xref "pads (scratchpads)"
.IP parameter 4
.IX Item "parameter"
See \fBargument\fR.
.IX Xref "parameters"
.IP "parent class" 4
.IX Item "parent class"
See \fBbase class\fR.
.IX Xref "parent classes classes, parent"
.IP "parse tree" 4
.IX Item "parse tree"
See \fBsyntax tree\fR.
.IX Xref "parse tree"
.IP parsing 4
.IX Item "parsing"
The subtle but sometimes brutal art of attempting to turn
your possibly malformed program into a valid \fBsyntax tree\fR.
.IX Xref "parsing, about"
.IP patch 4
.IX Item "patch"
To fix by applying one, as it were. In the realm of hackerdom, a
listing of the differences between two versions of a program as might be
applied by the \fBpatch\fR(1) program when you want to fix a bug or upgrade
your old version.
.IX Xref "patches"
.IP PATH 4
.IX Item "PATH"
The list of
\&\fBdirectories\fR the system searches to find a program you want to
\&\fBexecute\fR.  The list is stored as one of your \fBenvironment variables\fR,
accessible in Perl as \f(CW$ENV{PATH}\fR.
.IX Xref "PATH environment variable variables, environment"
.IP pathname 4
.IX Item "pathname"
A fully qualified filename such as \fI/usr/bin/perl\fR. Sometimes
confused with \f(CW\*(C`PATH\*(C'\fR.
.IX Xref "pathname"
.IP pattern 4
.IX Item "pattern"
A template used in \fBpattern matching\fR.
.IX Xref "patterns, defined"
.IP "pattern matching" 4
.IX Item "pattern matching"
Taking a pattern, usually a \fBregular
expression\fR, and trying the pattern various ways on a string to see whether
there’s any way to make it fit. Often used to pick interesting tidbits out
of a file.
.IX Xref "pattern matching, about"
.IP PAUSE 4
.IX Item "PAUSE"
The Perl Authors Upload SErver (<http://pause.perl.org>), the gateway
for \fBmodules\fR on their way to \fBCPAN\fR.
.IX Xref "Perl Authors Upload SErver (PAUSE) PAUSE (Perl Authors Upload SErver)"
.IP "Perl mongers" 4
.IX Item "Perl mongers"
A Perl user group, taking the form of its
name from the New York Perl mongers, the first Perl user group. Find one
near you at <http://www.pm.org>.
.IX Xref "Perl mongers mongers, Perl"
.IP "permission bits" 4
.IX Item "permission bits"
Bits that the \fBowner\fR of a file sets
or unsets to allow or disallow access to other people. These flag bits are
part of the \fBmode\fR word returned by the \f(CW\*(C`stat\*(C'\fR built-in when you ask
about a file. On Unix systems, you can check the \fIls\fR(1) manpage for more
information.
.IX Xref "permission bits bits, permission"
.IP Pern 4
.IX Item "Pern"
What you get when you do \f(CW\*(C`Perl++\*(C'\fR twice. Doing it only once
will curl your hair. You have to increment it eight times to shampoo your
hair. Lather, rinse, iterate.
.IX Xref "Pern (term)"
.IP pipe 4
.IX Item "pipe"
A direct \fBconnection\fR that carries the output of one
\&\fBprocess\fR 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.
.IX Xref "pipes, defined"
.IP pipeline 4
.IX Item "pipeline"
A series of \fBprocesses\fR all in a row, linked by \fBpipes\fR, where
each passes its output stream to the next.
.IX Xref "pipeline"
.IP platform 4
.IX Item "platform"
The entire hardware and software context in which a
program runs. A program written in a platform-dependent language might
break if you change any of the following: machine, operating system,
libraries, compiler, or system configuration. The \fIperl\fR interpreter has
to be \fBcompiled\fR differently for each platform because it is implemented
in C, but programs written in the Perl language are largely platform
independent.
.IX Xref "platforms, defined"
.IP pod 4
.IX Item "pod"
The markup
used to embed documentation into your Perl code. Pod stands for “Plain old
documentation”. See Camel chapter 23, “Plain Old Documentation”.
.IX Xref "pod (plain old documentation), about plain old documentation"
.IP "pod command" 4
.IX Item "pod command"
A sequence, such as \f(CW\*(C`=head1\*(C'\fR, that denotes
the start of a \fBpod\fR section.
.IX Xref "pod commands commands, pod"
.IP pointer 4
.IX Item "pointer"
A \fBvariable\fR 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 \fBkeys\fR and \fBvariable\fR names, or \fBhard references\fR, which
aren’t pointers (but act like pointers and do in fact contain pointers).
.IX Xref "pointers"
.IP polymorphism 4
.IX Item "polymorphism"
The notion that you can tell an \fBobject\fR to do something
generic, and the object will interpret the command in different ways
depending on its type. [< Greek πολυ\- + μορϕή, many forms.]
.IX Xref "polymorphism"
.IP port 4
.IX Item "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.
.IX Xref "ports (term)"
.IP portable 4
.IX Item "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
\&\fBplatform\fR, where “easily” can be defined however you like, and usually
is.  Anything may be considered portable if you try hard enough, such as a
mobile home or London Bridge.
.IX Xref "portability, about"
.IP porter 4
.IX Item "porter"
Someone who “carries” software from one \fBplatform\fR to another.
Porting programs written in platform-dependent languages such as C can be
difficult work, but porting programs like Perl is very much worth the
agony.
.IX Xref "porters"
.IP possessive 4
.IX Item "possessive"
Said of quantifiers and groups in patterns that refuse
to give up anything once they’ve gotten their mitts on it. Catchier and
easier to say than the even more formal \fInonbacktrackable\fR.
.IX Xref "possessive (term)"
.IP POSIX 4
.IX Item "POSIX"
The Portable Operating System Interface
specification.
.IX Xref "Portable Operating System Interface (POSIX), about POSIX (Portable Operating System Interface), about"
.IP postfix 4
.IX Item "postfix"
An \fBoperator\fR that follows its \fBoperand\fR, as in
\&\f(CW\*(C`$x++\*(C'\fR.
.IX Xref "postfix operator"
.IP pp 4
.IX Item "pp"
An internal shorthand for a
“push\- pop” code; that is, C code implementing Perl’s stack machine.
.IX Xref "pp (push–pop) code push–pop (pp) code"
.IP pragma 4
.IX Item "pragma"
A standard module whose practical hints and
suggestions are received (and possibly ignored) at compile time. Pragmas
are named in all lowercase.
.IX Xref "pragmas, about modules"
.IP precedence 4
.IX Item "precedence"
The rules of
conduct that, in the absence of other guidance, determine what should
happen first.  For example, in the absence of parentheses, you always do
multiplication before addition.
.IX Xref "precedence rules, about operators, precedence rules"
.IP prefix 4
.IX Item "prefix"
An \fBoperator\fR that precedes its \fBoperand\fR, as in
\&\f(CW\*(C`++$x\*(C'\fR.
.IX Xref "prefix operators"
.IP preprocessing 4
.IX Item "preprocessing"
What some helper \fBprocess\fR did to transform the incoming
data into a form more suitable for the current process. Often done with an
incoming \fBpipe\fR. See also \fBC preprocessor\fR.
.IX Xref "preprocessing"
.IP "primary maintainer" 4
.IX Item "primary maintainer"
The author that PAUSE allows to assign \fBco-maintainer\fR
permissions to a \fBnamespace\fR. A primary maintainer can give up this
distinction by assigning it to another PAUSE author. See Camel chapter 19,
“CPAN”.
.IX Xref "primary maintainer"
.IP procedure 4
.IX Item "procedure"
A \fBsubroutine\fR.
.IX Xref "procedures, defined"
.IP process 4
.IX Item "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 \f(CW\*(C`fork\*(C'\fR 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.
.IX Xref "processes, defined"
.IP program 4
.IX Item "program"
See \fBscript\fR.
.IP "program generator" 4
.IX Item "program generator"
A system that algorithmically writes code for you in a
high-level language. See also \fBcode generator\fR.
.IX Xref "program generators"
.IP "progressive matching" 4
.IX Item "progressive matching"
\&\fBPattern matching\fR  matching>that picks up where it left off before.
.IX Xref "progressive matching pattern matching, progressive matching"
.IP property 4
.IX Item "property"
See either \fBinstance variable\fR or \fBcharacter property\fR.
.IX Xref "property"
.IP protocol 4
.IX Item "protocol"
In networking, an agreed-upon way of sending messages
back and forth so that neither correspondent will get too confused.
.IX Xref "protocols (term)"
.IP prototype 4
.IX Item "prototype"
An optional part of a \fBsubroutine\fR declaration telling
the Perl compiler how many and what flavor of arguments may be passed as
\&\fBactual arguments\fR, so you can write subroutine calls that parse much like
built-in functions. (Or don’t parse, as the case may be.)
.IX Xref "prototypes, about"
.IP pseudofunction 4
.IX Item "pseudofunction"
A construct that sometimes looks like a function but really
isn’t. Usually reserved for \fBlvalue\fR modifiers like \f(CW\*(C`my\*(C'\fR, for \fBcontext\fR
modifiers like \f(CW\*(C`scalar\*(C'\fR, and for the pick-your-own-quotes constructs,
\&\f(CW\*(C`q//\*(C'\fR, \f(CW\*(C`qq//\*(C'\fR, \f(CW\*(C`qx//\*(C'\fR, \f(CW\*(C`qw//\*(C'\fR, \f(CW\*(C`qr//\*(C'\fR, \f(CW\*(C`m//\*(C'\fR, \f(CW\*(C`s///\*(C'\fR, \f(CW\*(C`y///\*(C'\fR, and
\&\f(CW\*(C`tr///\*(C'\fR.
.IX Xref "pseudofunctions constructs, pseudofunctions functions, pseudofunctions"
.IP pseudohash 4
.IX Item "pseudohash"
Formerly, a reference to an array
whose initial element happens to hold a reference to a hash. You used to be
able to treat a pseudohash reference as either an array reference or a hash
reference. Pseudohashes are no longer supported.
.IX Xref "pseudohashes hashes, pseudohashes"
.IP pseudoliteral 4
.IX Item "pseudoliteral"
An \fBoperator\fR X\f(CW\*(C`that looks something like a \fR\f(CBliteral\fR\f(CW,
such as the output\-grabbing operator, <literal
moreinfo="none"\*(C'\fR`>\fR\f(CI\*(C`command\*(C'\fR\fI\fR\f(CW\*(C`\`\*(C'\fR.
.IX Xref "pseudoliterals"
.IP "public domain" 4
.IX Item "public domain"
Something not owned by anybody. Perl is copyrighted and is
thus \fInot\fR in the public domain—it’s just \fBfreely available\fR and \fBfreely
redistributable\fR.
.IX Xref "public domain"
.IP pumpkin 4
.IX Item "pumpkin"
A notional “baton” handed around the Perl community
indicating who is the lead integrator in some arena of development.
.IX Xref "pumpkin (term)"
.IP pumpking 4
.IX Item "pumpking"
A \fBpumpkin\fR 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.
.IX Xref "pumpking"
.IP PV 4
.IX Item "PV"
A “pointer value”, which is Perl
Internals Talk for a \f(CW\*(C`char*\*(C'\fR.
.IX Xref "PV (pointer value) pointer value (PV)"
.SS Q
.IX Subsection "Q"
.IP qualified 4
.IX Item "qualified"
Possessing a complete name. The symbol \f(CW$Ent::moot\fR is
qualified; \f(CW$moot\fR is unqualified. A fully qualified filename is specified
from the top-level directory.
.IX Xref "qualified (term)"
.IP quantifier 4
.IX Item "quantifier"
A component of a \fBregular expression\fR specifying how
many times the foregoing \fBatom\fR may occur.
.IX Xref "quantifiers, about"
.SS R
.IX Subsection "R"
.IP "race condition" 4
.IX Item "race condition"
A race condition exists when the result of
several interrelated events depends on the ordering of those events, but
that order cannot be guaranteed due to nondeterministic timing effects. If
two or more programs, or parts of the same program, try to go through the
same series of events, one might interrupt the work of the other. This is a
good way to find an \fBexploit\fR.
.IX Xref "race conditions, defined"
.IP readable 4
.IX Item "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.
.IX Xref "readable (term)"
.IP reaping 4
.IX Item "reaping"
The last rites performed by a parent \fBprocess\fR
on behalf of a deceased child process so that it doesn’t remain a
\&\fBzombie\fR.  See the \f(CW\*(C`wait\*(C'\fR and \f(CW\*(C`waitpid\*(C'\fR function calls.
.IX Xref "reaping zombie processes"
.IP record 4
.IX Item "record"
A set of related data values in a \fBfile\fR or \fBstream\fR,
often associated with a unique \fBkey\fR field. In Unix, often commensurate
with a \fBline\fR, or a blank\-line–terminated set of lines (a “paragraph”).
Each line of the \fI/etc/passwd\fR file is a record, keyed on login name,
containing information about that user.
.IX Xref "records, defined"
.IP recursion 4
.IX Item "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).
.IX Xref "recursion, defined"
.IP reference 4
.IX Item "reference"
Where you look to find a pointer to information
somewhere else. (See \fBindirection\fR.) References come in two flavors:
\&\fBsymbolic references\fR and \fBhard references\fR.
.IX Xref "references, about"
.IP referent 4
.IX Item "referent"
Whatever a reference refers to, which may or may not
have a name. Common types of referents include scalars, arrays, hashes, and
subroutines.
.IX Xref "referents, defined"
.IP regex 4
.IX Item "regex"
See \fBregular expression\fR.
.IP "regular expression" 4
.IX Item "regular expression"
A single entity with various
interpretations, like an elephant. To a computer scientist, it’s a grammar
for a little language in which some strings are legal and others aren’t. To
normal people, it’s a pattern you can use to find what you’re looking for
when it varies from case to case. Perl’s regular expressions are far from
regular in the theoretical sense, but in regular use they work quite well.
Here’s a regular expression: \f(CW\*(C`/Oh s.*t./\*(C'\fR. This will match strings like
“\f(CW\*(C`Oh say can you see by the dawn\*(Aqs early light\*(C'\fR” and “\f(CW\*(C`Oh sit!\*(C'\fR”. See
Camel chapter 5, “Pattern Matching”.
.IX Xref "regular expressions, defined"
.IP "regular expression modifier" 4
.IX Item "regular expression modifier"
An option on a pattern or substitution, such as \f(CW\*(C`/i\*(C'\fR to render the pattern
case\- insensitive.
.IX Xref "regular expression modifiers modifiers, regular expression"
.IP "regular file" 4
.IX Item "regular file"
A \fBfile\fR that’s not a \fBdirectory\fR, a
\&\fBdevice\fR, a named \fBpipe\fR or \fBsocket\fR, or a \fBsymbolic link\fR. Perl uses
the \f(CW\*(C`–f\*(C'\fR file test operator to identify regular files. Sometimes called a
“plain” file.
.IX Xref "regular files files, regular"
.IP "relational operator" 4
.IX Item "relational operator"
An \fBoperator\fR that says whether a particular
ordering relationship is \fBtrue\fR about a pair of \fBoperands\fR. Perl has both
numeric and string relational operators. See \fBcollating sequence\fR.
.IX Xref "relational operators"
.IP "reserved words" 4
.IX Item "reserved words"
A word with a specific, built-in meaning
to a \fBcompiler\fR, such as \f(CW\*(C`if\*(C'\fR or \f(CW\*(C`delete\*(C'\fR. 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
\&\fBlabels\fR or \fBfilehandles\fR. Also called “keywords”.
.IX Xref "reserved words keywords (term)"
.IP "return value" 4
.IX Item "return value"
The \fBvalue\fR produced by a \fBsubroutine\fR
or \fBexpression\fR when evaluated. In Perl, a return value may be either a
\&\fBlist\fR or a \fBscalar\fR.
.IX Xref "return values values, return"
.IP RFC 4
.IX Item "RFC"
Request For Comment, which despite the timid connotations is the name of a series of
important standards documents.
.IX Xref "Request For Comment (RFC) RFC (Request For Comment)"
.IP "right shift" 4
.IX Item "right shift"
A \fBbit shift\fR that divides
a number by some power of 2.
.IX Xref "right shift (>>) bit operator bit–shift operators, right shift >> (right shift) bit operator"
.IP role 4
.IX Item "role"
A name for a concrete set of behaviors. A role is a way to
add behavior to a class without inheritance.
.IX Xref "roles (term)"
.IP root 4
.IX Item "root"
The superuser (\f(CW\*(C`UID\*(C'\fR == 0). Also the top-level directory of
the filesystem.
.IX Xref "root (term)"
.IP RTFM 4
.IX Item "RTFM"
What you are told when someone thinks you should Read The
Fine Manual.
.IX Xref "RTFM acronym"
.IP "run phase" 4
.IX Item "run phase"
Any time after Perl starts running your main program.
See also \fBcompile phase\fR. Run phase is mostly spent in \fBruntime\fR but may
also be spent in \fBcompile time\fR when \f(CW\*(C`require\*(C'\fR, \f(CW\*(C`do\*(C'\fR \fR\f(CI\*(C`FILE\*(C'\fR\fI\fR, or
\&\f(CW\*(C`eval\*(C'\fR \fI\fR\f(CI\*(C`STRING\*(C'\fR\fI\fR operators are executed, or when a substitution uses
the \f(CW\*(C`/ee\*(C'\fR modifier.
.IX Xref "run phase, defined"
.IP runtime 4
.IX Item "runtime"
The time when Perl is actually doing what your
code says to do, as opposed to the earlier period of time when it was
trying to figure out whether what you said made any sense whatsoever, which
is \fBcompile time\fR.
.IX Xref "runtime (term), defined"
.IP "runtime pattern" 4
.IX Item "runtime pattern"
A pattern that contains one or more
variables to be interpolated before parsing the pattern as a \fBregular
expression\fR, and that therefore cannot be analyzed at compile time, but
must be reanalyzed each time the pattern match operator is evaluated.
Runtime patterns are useful but expensive.
.IX Xref "runtime patterns patterns, runtime"
.IP RV 4
.IX Item "RV"
A recreational vehicle, not
to be confused with vehicular recreation. RV also means an internal
Reference Value of the type a \fBscalar\fR can hold. See also \fBIV\fR and \fBNV\fR
if you’re not confused yet.
.IX Xref "Reference Value (RV) RV (Reference Value)"
.IP rvalue 4
.IX Item "rvalue"
A \fBvalue\fR that you might find on the
right side of an \fBassignment\fR. See also \fBlvalue\fR.
.IX Xref "rvalue (term) values, rvalue"
.SS S
.IX Subsection "S"
.IP sandbox 4
.IX Item "sandbox"
A walled off area that’s not supposed to affect beyond
its walls. You let kids play in the sandbox instead of running in the road.
See Camel chapter 20, “Security”.
.IX Xref "sandbox, defined"
.IP scalar 4
.IX Item "scalar"
A simple, singular value; a number, \fBstring\fR, or
\&\fBreference\fR.
.IX Xref "scalars, defined"
.IP "scalar context" 4
.IX Item "scalar context"
The situation in which an
\&\fBexpression\fR is expected by its surroundings (the code calling it) to
return a single \fBvalue\fR rather than a \fBlist\fR of values. See also
\&\fBcontext\fR and \fBlist context\fR. A scalar context sometimes imposes
additional constraints on the return value—see \fBstring context\fR and
\&\fBnumeric context\fR. Sometimes we talk about a \fBBoolean context\fR inside
conditionals, but this imposes no additional constraints, since any scalar
value, whether numeric or \fBstring\fR, is already true or false.
.IX Xref "scalar context, about context, scalar"
.IP "scalar literal" 4
.IX Item "scalar literal"
A number or quoted \fBstring\fR—an actual
\&\fBvalue\fR in the text of your program, as opposed to a \fBvariable\fR.
.IX Xref "scalar literals literals, scalar"
.IP "scalar value" 4
.IX Item "scalar value"
A value that happens to be a
\&\fBscalar\fR as opposed to a \fBlist\fR.
.IX Xref "scalar values, about values, scalar SV"
.IP "scalar variable" 4
.IX Item "scalar variable"
A \fBvariable\fR prefixed with
\&\f(CW\*(C`$\*(C'\fR that holds a single value.
.IX Xref "scalar variables, defined variables, scalar"
.IP scope 4
.IX Item "scope"
From how far away you can see a variable, looking through
one. Perl has two visibility mechanisms. It does \fBdynamic scoping\fR of
\&\f(CW\*(C`local\*(C'\fR \fBvariables\fR, meaning that the rest of the \fBblock\fR, and any
\&\fBsubroutines\fR that are called by the rest of the block, can see the
variables that are local to the block. Perl does \fBlexical scoping\fR of
\&\f(CW\*(C`my\*(C'\fR variables, meaning that the rest of the block can see the variable,
but other subroutines called by the block \fIcannot\fR see the variable.
.IX Xref "scopes, defined"
.IP scratchpad 4
.IX Item "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.
.IX Xref "scratchpads"
.IP script 4
.IX Item "script"
A text \fBfile\fR that is a program
intended to be \fBexecuted\fR directly rather than \fBcompiled\fR to another form
of file before \fBexecution\fR.
.IX Xref "scripts (term) programs, defined"
.Sp
Also, in the context of \fBUnicode\fR, a writing system for a particular
language or group of languages, such as Greek, Bengali, or Tengwar.
.IP "script kiddie" 4
.IX Item "script kiddie"
A \fBcracker\fR who is not a \fBhacker\fR but knows just enough
to run canned scripts. A \fBcargo-cult\fR programmer.
.IX Xref "script kiddie"
.IP sed 4
.IX Item "sed"
A venerable Stream EDitor from
which Perl derives some of its ideas.
.IX Xref "sed (Stream EDitor) Stream EDitor (sed)"
.IP semaphore 4
.IX Item "semaphore"
A fancy kind of interlock that prevents multiple \fBthreads\fR or
\&\fBprocesses\fR from using up the same resources simultaneously.
.IX Xref "semaphore"
.IP separator 4
.IX Item "separator"
A \fBcharacter\fR or \fBstring\fR that keeps two surrounding strings from being
confused with each other. The \f(CW\*(C`split\*(C'\fR function works on separators. Not to be confused with \fBdelimiters\fR
or \fBterminators\fR. The “or” in the previous sentence separated the two
alternatives.
.IX Xref "separators characters, separators strings, separators split function, separators and"
.IP serialization 4
.IX Item "serialization"
Putting a fancy \fBdata structure\fR into
linear order so that it can be stored as a \fBstring\fR in a disk file or
database, or sent through a \fBpipe\fR. Also called marshalling.
.IX Xref "serialization marshalling (term)"
.IP server 4
.IX Item "server"
In networking, a \fBprocess\fR that
either advertises a \fBservice\fR or just hangs around at a known location and
waits for \fBclients\fR who need service to get in touch with it.
.IX Xref "servers, defined processes, server"
.IP service 4
.IX Item "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 \f(CW\*(C`getservent\*(C'\fR
function.
.IX Xref "services (term) getservent function"
.IP setgid 4
.IX Item "setgid"
Same as \fBsetuid\fR, only having to do with giving
away \fBgroup\fR privileges.
.IX Xref "setgid program, about"
.IP setuid 4
.IX Item "setuid"
Said of a program that runs with the privileges of
its \fBowner\fR rather than (as is usually the case) the privileges of whoever
is running it. Also describes the bit in the mode word (\fBpermission bits\fR)
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.
.IX Xref "setuid program, about"
.IP "shared memory" 4
.IX Item "shared memory"
A piece of \fBmemory\fR accessible by two
different \fBprocesses\fR who otherwise would not see each other’s memory.
.IX Xref "shared memory memory, shared"
.IP shebang 4
.IX Item "shebang"
Irish for the whole McGillicuddy. In Perl culture, a
portmanteau of “sharp” and “bang”, meaning the \f(CW\*(C`#!\*(C'\fR sequence that tells
the system where to find the interpreter.
.IX Xref "shebang (term)"
.IP shell 4
.IX Item "shell"
A \fBcommand\fR\-line \fBinterpreter\fR. The program that
interactively gives you a prompt, accepts one or more \fBlines\fR of input,
and executes the programs you mentioned, feeding each of them their proper
\&\fBarguments\fR and input data. Shells can also execute scripts containing
such commands. Under Unix, typical shells include the Bourne shell
(\fI/bin/sh\fR), the C shell (\fI/bin/csh\fR), and the Korn shell (\fI/bin/ksh\fR).
Perl is not strictly a shell because it’s not interactive (although Perl
programs can be interactive).
.IX Xref "shell program, defined"
.IP "side effects" 4
.IX Item "side effects"
Something extra that happens when you evaluate an
\&\fBexpression\fR. 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 \f(CW$|\fR (\f(CW$AUTOFLUSH\fR) has the side effect of forcing a
flush after every \f(CW\*(C`write\*(C'\fR or \f(CW\*(C`print\*(C'\fR on the currently selected
filehandle.
.IX Xref "side effects"
.IP sigil 4
.IX Item "sigil"
A glyph used in magic. Or, for Perl, the symbol in front
of a variable name, such as \f(CW\*(C`$\*(C'\fR, \f(CW\*(C`@\*(C'\fR, and \f(CW\*(C`%\*(C'\fR.
.IX Xref "sigils, defined"
.IP signal 4
.IX Item "signal"
A bolt out of the blue; that is, an
event triggered by the \fBoperating system\fR, probably when you’re least
expecting it.
.IX Xref "signals and signal handling, about"
.IP "signal handler" 4
.IX Item "signal handler"
A \fBsubroutine\fR 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 \fBexecute\fR. Under Perl, bolts out of the blue
are called signals, and you send them with the \f(CW\*(C`kill\*(C'\fR built-in. See the
\&\f(CW%SIG\fR hash in Camel chapter 25, “Special Names” and the section “Signals”
in Camel chapter 15, “Interprocess Communication”.
.IX Xref "handlers, signal"
.IP "single inheritance" 4
.IX Item "single inheritance"
The features you got from your
mother, if she told you that you don’t have a father. (See also
\&\fBinheritance\fR and \fBmultiple inheritance\fR.) In computer languages, the
idea that \fBclasses\fR reproduce asexually so that a given class can only
have one direct ancestor or \fBbase class\fR. Perl supplies no such
restriction, though you may certainly program Perl that way if you like.
.IX Xref "single inheritance inheritance, single"
.IP slice 4
.IX Item "slice"
A selection of any number of
\&\fBelements\fR from a \fBlist\fR, \fBarray\fR, or \fBhash\fR.
.IX Xref "slices of elements elements, slices of"
.IP slurp 4
.IX Item "slurp"
To read an entire \fBfile\fR into a \fBstring\fR in one operation.
.IX Xref "slurp (term)"
.IP socket 4
.IX Item "socket"
An endpoint for network communication among multiple
\&\fBprocesses\fR that works much like a telephone or a post office box. The
most important thing about a socket is its \fBnetwork address\fR (like a phone
number). Different kinds of sockets have different kinds of addresses—some
look like filenames, and some don’t.
.IX Xref "sockets, defined"
.IP "soft reference" 4
.IX Item "soft reference"
See \fBsymbolic reference\fR.
.IX Xref "soft references references, soft"
.IP "source filter" 4
.IX Item "source filter"
A special kind of \fBmodule\fR that does
\&\fBpreprocessing\fR on your script just before it gets to the \fBtokener\fR.
.IX Xref "source filters filters, source"
.IP stack 4
.IX Item "stack"
A device you can put things on the top of, and later take
them back off in the opposite order in which you put them on. See \fBLIFO\fR.
.IX Xref "stacks, defined"
.IP standard 4
.IX Item "standard"
Included in the official Perl distribution, as in a
standard module, a standard tool, or a standard Perl \fBmanpage\fR.
.IX Xref "standard (term)"
.IP "standard error" 4
.IX Item "standard error"
The default output \fBstream\fR for nasty remarks that don’t belong in
\&\fBstandard output\fR. Represented within a Perl program by the output>  \fBfilehandle\fR \f(CW\*(C`STDERR\*(C'\fR. You can use this
stream explicitly, but the \f(CW\*(C`die\*(C'\fR and \f(CW\*(C`warn\*(C'\fR built-ins write to your
standard error stream automatically (unless trapped or otherwise
intercepted).
.IX Xref "STDERR filehandle, about"
.IP "standard input" 4
.IX Item "standard input"
The default input \fBstream\fR for your program,
which if possible shouldn’t care where its data is coming from. Represented
within a Perl program by the \fBfilehandle\fR \f(CW\*(C`STDIN\*(C'\fR.
.IX Xref "STDIN filehandle, about"
.IP "standard I/O" 4
.IX Item "standard I/O"
A standard C library for doing \fBbuffered\fR input
and output to the \fBoperating system\fR. (The “standard” of standard I/O is
at most marginally related to the “standard” of standard input and output.)
In general, Perl relies on whatever implementation of standard I/O a given
operating system supplies, so the buffering characteristics of a Perl
program on one machine may not exactly match those on another machine.
Normally this only influences efficiency, not semantics. If your standard
I/O package is doing block buffering and you want it to \fBflush\fR the buffer
more often, just set the \f(CW$|\fR variable to a true value.
.IX Xref "standard I O I O (Input Output), standard Input Output (I O), standard STDIO filehandle"
.IP "Standard Library" 4
.IX Item "Standard Library"
Everything that comes with the official
\&\fIperl\fR distribution. Some vendor versions of \fIperl\fR change their
distributions, leaving out some parts or including extras. See also
\&\fBdual-lived\fR.
.IX Xref "Standard Perl Library, about"
.IP "standard output" 4
.IX Item "standard output"
The default output \fBstream\fR for your program,
which if possible shouldn’t care where its data is going. Represented
within a Perl program by the \fBfilehandle\fR \f(CW\*(C`STDOUT\*(C'\fR.
.IX Xref "STDOUT filehandle, about"
.IP statement 4
.IX Item "statement"
A \fBcommand\fR to the computer about what to do next,
like a step in a recipe: “Add marmalade to batter and mix until mixed.” A
statement is distinguished from a \fBdeclaration\fR, which doesn’t tell the
computer to do anything, but just to learn something.
.IX Xref "statements, about"
.IP "statement modifier" 4
.IX Item "statement modifier"
A \fBconditional\fR or
\&\fBloop\fR that you put after the \fBstatement\fR instead of before, if you know
what we mean.
.IX Xref "statement modifiers, about modifiers, statement"
.IP static 4
.IX Item "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 \fBvariable\fR,
\&\fBsubroutine\fR, or \fBmethod\fR. In Perl culture, the word is politely avoided.
.IX Xref "static (term)"
.Sp
If you’re a C or C++ programmer, you might be looking for Perl’s \f(CW\*(C`state\*(C'\fR
keyword.
.IP "static method" 4
.IX Item "static method"
No such thing. See \fBclass method\fR.
.IX Xref "static methods methods, static"
.IP "static scoping" 4
.IX Item "static scoping"
No such thing. See \fBlexical scoping\fR.
.IP "static variable" 4
.IX Item "static variable"
No such thing. Just use a \fBlexical
variable\fR in a scope larger than your \fBsubroutine\fR, or declare it with
\&\f(CW\*(C`state\*(C'\fR instead of with \f(CW\*(C`my\*(C'\fR.
.IX Xref "static variables variables, static"
.IP "stat structure" 4
.IX Item "stat structure"
A special internal spot
in which Perl keeps the information about the last \fBfile\fR on which you
requested information.
.IX Xref "stat structure data structures, stat structure"
.IP status 4
.IX Item "status"
The \fBvalue\fR returned to the
parent \fBprocess\fR when one of its child processes dies. This value is
placed in the special variable \f(CW$?\fR. Its upper eight \fBbits\fR 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 \fIwait\fR(2). See \f(CW\*(C`system\*(C'\fR in Camel
chapter 27, “Functions”.
.IX Xref "status value values, status exit status"
.IP STDERR 4
.IX Item "STDERR"
See \fBstandard error\fR.
.IP STDIN 4
.IX Item "STDIN"
See \fBstandard input\fR.
.IP STDIO 4
.IX Item "STDIO"
See \fBstandard I/O\fR.
.IP STDOUT 4
.IX Item "STDOUT"
See \fBstandard output\fR.
.IP stream 4
.IX Item "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
\&\fBinterface\fR—the underlying \fBimplementation\fR may well break your data up
into separate packets for delivery, but this is hidden from you.
.IX Xref "streaming data processes, streaming data"
.IP string 4
.IX Item "string"
A sequence of characters such as “He said !@#*&%@#*?!”.
A string does not have to be entirely printable.
.IX Xref "strings, defined"
.IP "string context" 4
.IX Item "string context"
The situation in which an expression is
expected by its surroundings (the code calling it) to return a \fBstring\fR.
See also \fBcontext\fR and \fBnumeric context\fR.
.IX Xref "string context context, string"
.IP stringification 4
.IX Item "stringification"
The process of producing a \fBstring\fR representation of an
abstract object.
.IX Xref "stringification"
.IP struct 4
.IX Item "struct"
C keyword introducing a structure definition or name.
.IX Xref "struct keyword"
.IP structure 4
.IX Item "structure"
See \fBdata structure\fR.
.IX Xref "structures"
.IP subclass 4
.IX Item "subclass"
See \fBderived class\fR.
.IP subpattern 4
.IX Item "subpattern"
A component of a \fBregular expression\fR pattern.
.IX Xref "subpatterns, defined"
.IP subroutine 4
.IX Item "subroutine"
A named or otherwise accessible piece of program
that can be invoked from elsewhere in the program in order to accomplish
some subgoal of the program. A subroutine is often parameterized to
accomplish different but related things depending on its input
\&\fBarguments\fR. If the subroutine returns a meaningful \fBvalue\fR, it is also
called a \fBfunction\fR.
.IX Xref "subroutines, defined"
.IP subscript 4
.IX Item "subscript"
A \fBvalue\fR that indicates the position of a particular
\&\fBarray\fR \fBelement\fR in an array.
.IX Xref "subscripts"
.IP substitution 4
.IX Item "substitution"
Changing parts of a string via the \f(CW\*(C`s///\*(C'\fR
operator. (We avoid use of this term to mean \fBvariable interpolation\fR.)
.IX Xref "substitution (s ) operator, about strings, substitution in s (substitution) operator, about"
.IP substring 4
.IX Item "substring"
A portion of a \fBstring\fR, starting at a certain
\&\fBcharacter\fR position (\fBoffset\fR) and proceeding for a certain number of
characters.
.IX Xref "substrings (term)"
.IP superclass 4
.IX Item "superclass"
See \fBbase class\fR.
.IP superuser 4
.IX Item "superuser"
The person whom the \fBoperating system\fR will let do almost
anything. Typically your system administrator or someone pretending to be
your system administrator. On Unix systems, the \fBroot\fR user. On Windows
systems, usually the Administrator user.
.IX Xref "superusers"
.IP SV 4
.IX Item "SV"
Short for “scalar value”. But
within the Perl interpreter, every \fBreferent\fR is treated as a member of a
class derived from SV, in an object-oriented sort of way. Every \fBvalue\fR
inside Perl is passed around as a C language \f(CW\*(C`SV*\*(C'\fR pointer. The SV
\&\fBstruct\fR knows its own “referent type”, and the code is smart enough (we
hope) not to try to call a \fBhash\fR function on a \fBsubroutine\fR.
.IX Xref "scalar values, about values, scalar"
.IP switch 4
.IX Item "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 \fBswitch statement\fR.
.IX Xref "switches, about switches"
.IP "switch cluster" 4
.IX Item "switch cluster"
The combination of multiple command\-
line switches (\fIe.g.\fR, \f(CW\*(C`–a –b –c\*(C'\fR) into one switch (\fIe.g.\fR, \f(CW\*(C`–abc\*(C'\fR).
Any switch with an additional \fBargument\fR must be the last switch in a
cluster.
.IX Xref "switch clusters clusters, switch"
.IP "switch statement" 4
.IX Item "switch statement"
A program technique that lets you
evaluate an \fBexpression\fR 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 \f(CW\*(C`given\*(C'\fR. See “The \f(CW\*(C`given\*(C'\fR
statement” in Camel chapter 4, “Statements and Declarations”.
.IX Xref "switch statement statements, switch"
.IP symbol 4
.IX Item "symbol"
Generally, any \fBtoken\fR or \fBmetasymbol\fR. Often used
more specifically to mean the sort of name you might find in a \fBsymbol
table\fR.
.IX Xref "symbols symbols"
.IP "symbolic debugger" 4
.IX Item "symbolic debugger"
A program that lets you step through
the \fBexecution\fR of your program, stopping or printing things out here and
there to see whether anything has gone wrong, and, if so, what. The
“symbolic” part just means that you can talk to the debugger using the same
symbols with which your program is written.
.IX Xref "symbolic debugger debugger, about"
.IP "symbolic link" 4
.IX Item "symbolic link"
An alternate filename that points to the
real \fBfilename\fR, which in turn points to the real \fBfile\fR. Whenever the
\&\fBoperating system\fR is trying to parse a \fBpathname\fR containing a symbolic
link, it merely substitutes the new name and continues parsing.
.IX Xref "symbolic links links, symbolic"
.IP "symbolic reference" 4
.IX Item "symbolic reference"
A variable whose value is the
name of another variable or subroutine. By \fBdereferencing\fR the first
variable, you can get at the second one. Symbolic references are illegal
under \f(CW\*(C`use strict "refs"\*(C'\fR.
.IX Xref "symbolic references references, symbolic"
.IP "symbol table" 4
.IX Item "symbol table"
Where a \fBcompiler\fR remembers symbols. A program
like Perl must somehow remember all the names of all the \fBvariables\fR,
\&\fBfilehandles\fR, and \fBsubroutines\fR you’ve used. It does this by placing the
names in a symbol table, which is implemented in Perl using a \fBhash
table\fR. There is a separate symbol table for each \fBpackage\fR to give each
package its own \fBnamespace\fR.
.IX Xref "symbol tables, about"
.IP synchronous 4
.IX Item "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.
.IX Xref "synchronous (term)"
.IP "syntactic sugar" 4
.IX Item "syntactic sugar"
An alternative way of writing something more easily; a
shortcut.
.IX Xref "syntactic sugar"
.IP syntax 4
.IX Item "syntax"
From Greek σύνταξις, “with\-arrangement”. How things
(particularly symbols) are put together with each other.
.IX Xref "syntax, about"
.IP "syntax tree" 4
.IX Item "syntax tree"
An internal representation of your program wherein
lower-level \fBconstructs\fR dangle off the higher-level constructs enclosing
them.
.IX Xref "syntax tree"
.IP syscall 4
.IX Item "syscall"
A \fBfunction\fR call directly to the \fBoperating
system\fR. Many of the important subroutines and functions you use aren’t
direct system calls, but are built up in one or more layers above the
system call level. In general, Perl programmers don’t need to worry about
the distinction. However, if you do happen to know which Perl functions are
really syscalls, you can predict which of these will set the \f(CW$!\fR
(\f(CW$ERRNO\fR) variable on failure. Unfortunately, beginning programmers often
confusingly employ the term “system call” to mean what happens when you
call the Perl \f(CW\*(C`system\*(C'\fR function, which actually involves many syscalls. To
avoid any confusion, we nearly always say “syscall” for something you could
call indirectly via Perl’s \f(CW\*(C`syscall\*(C'\fR function, and never for something you
would call with Perl’s \f(CW\*(C`system\*(C'\fR function.
.IX Xref "syscall function, about"
.SS T
.IX Subsection "T"
.IP "taint checks" 4
.IX Item "taint checks"
The special bookkeeping Perl does to track the flow
of external data through your program and disallow their use in system
commands.
.IX Xref "taint checks, about"
.IP tainted 4
.IX Item "tainted"
Said of data derived from the grubby hands of a user,
and thus unsafe for a secure program to rely on. Perl does taint checks if
you run a \fBsetuid\fR (or \fBsetgid\fR) program, or if you use the \f(CW\*(C`–T\*(C'\fR switch.
.IX Xref "tainted data, about"
.IP "taint mode" 4
.IX Item "taint mode"
Running under the \f(CW\*(C`–T\*(C'\fR switch, marking all external data as
suspect and refusing to use it with system commands. See Camel chapter 20,
“Security”.
.IX Xref "taint mode"
.IP TCP 4
.IX Item "TCP"
Short for Transmission Control Protocol. A protocol wrapped around the
Internet Protocol to make an unreliable packet transmission mechanism
appear to the application program to be a reliable \fBstream\fR of bytes.
(Usually.)
.IX Xref "TCP (Transmission Control Protocol) Transmission Control Protocol (TCP)"
.IP term 4
.IX Item "term"
Short for a “terminal”—that is, a leaf node of a \fBsyntax
tree\fR. A thing that functions grammatically as an \fBoperand\fR for the
operators in an expression.
.IX Xref "terms, defined"
.IP terminator 4
.IX Item "terminator"
A \fBcharacter\fR or \fBstring\fR that marks the end of another string. The \f(CW$/\fR
variable contains the string that terminates a \f(CW\*(C`readline\*(C'\fR operation, which
\&\f(CW\*(C`chomp\*(C'\fR deletes from the end. Not to be confused with \fBdelimiters\fR or
\&\fBseparators\fR. The period at the end of this sentence is a terminator.
.IX Xref "terminators (term) characters, terminators strings, terminators in"
.IP ternary 4
.IX Item "ternary"
An \fBoperator\fR taking three \fBoperands\fR. Sometimes
pronounced \fBtrinary\fR.
.IX Xref "ternary operators"
.IP text 4
.IX Item "text"
A \fBstring\fR or \fBfile\fR containing primarily printable characters.
.IX Xref "text, defined strings, text files, text text"
.IP thread 4
.IX Item "thread"
Like a forked process, but without \fBfork\fR’s inherent
memory protection. A thread is lighter weight than a full process, in that
a process could have multiple threads running around in it, all fighting
over the same process’s memory space unless steps are taken to protect
threads from one another.
.IX Xref "threads (term)"
.IP tie 4
.IX Item "tie"
The bond between a magical variable and its
implementation class. See the \f(CW\*(C`tie\*(C'\fR function in Camel chapter 27,
“Functions” and Camel chapter 14, “Tied Variables”.
.IX Xref "tied variables, about"
.IP titlecase 4
.IX Item "titlecase"
The case used for capitals
that are followed by lowercase characters instead of by more capitals.
Sometimes called sentence case or headline case. English doesn’t use
Unicode titlecase, but casing rules for English titles are more complicated
than simply capitalizing each word’s first character.
.IX Xref "titlecase characters characters, titlecase"
.IP TMTOWTDI 4
.IX Item "TMTOWTDI"
There’s More Than One Way To Do It, the Perl Motto. The
notion that there can be more than one valid path to solving a programming
problem in context. (This doesn’t mean that more ways are always better or
that all possible paths are equally desirable—just that there need not be
One True Way.)
.IX Xref "TMTOWTDI acronym"
.IP token 4
.IX Item "token"
A morpheme in a programming language, the smallest unit
of text with semantic significance.
.IX Xref "tokens, defined"
.IP tokener 4
.IX Item "tokener"
A module that breaks a program text into a sequence of
\&\fBtokens\fR for later analysis by a parser.
.IX Xref "tokeners, defined"
.IP tokenizing 4
.IX Item "tokenizing"
Splitting up a program text into \fBtokens\fR. Also known as
“lexing”, in which case you get “lexemes” instead of tokens.
.IX Xref "tokenizing"
.IP "toolbox approach" 4
.IX Item "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.
.IX Xref "toolbox approach"
.IP topic 4
.IX Item "topic"
The thing you’re working on. Structures like
\&\f(CWwhile(<>)\fR, \f(CW\*(C`for\*(C'\fR, \f(CW\*(C`foreach\*(C'\fR, and \f(CW\*(C`given\*(C'\fR set the topic for
you by assigning to \f(CW$_\fR, the default (\fItopic\fR) variable.
.IX Xref "topics (term)"
.IP transliterate 4
.IX Item "transliterate"
To turn one string
representation into another by mapping each character of the source string
to its corresponding character in the result string. Not to be confused
with translation: for example, Greek \fIπολύχρωμος\fR transliterates into
\&\fIpolychromos\fR but translates into \fImany-colored\fR. See the \f(CW\*(C`tr///\*(C'\fR
operator in Camel chapter 5, “Pattern Matching”.
.IX Xref "tr (transliteration) operator, about strings, transliteration of transliteration (tr ) operator, about"
.IP trigger 4
.IX Item "trigger"
An event that causes a \fBhandler\fR to be run.
.IX Xref "triggers (term)"
.IP trinary 4
.IX Item "trinary"
Not a stellar system with three stars, but an
\&\fBoperator\fR taking three \fBoperands\fR. Sometimes pronounced \fBternary\fR.
.IX Xref "trinary operators"
.IP troff 4
.IX Item "troff"
A venerable typesetting language from which Perl derives
the name of its \f(CW$%\fR variable and which is secretly used in the production
of Camel books.
.IX Xref "troff language"
.IP true 4
.IX Item "true"
Any scalar value that doesn’t evaluate to 0 or
\&\f(CW""\fR.
.IX Xref "true values values, true"
.IP truncating 4
.IX Item "truncating"
Emptying a file of existing
contents, either automatically when opening a file for writing or
explicitly via the \f(CW\*(C`truncate\*(C'\fR function.
.IX Xref "truncate function files, truncating"
.IP type 4
.IX Item "type"
See \fBdata type\fR and \fBclass\fR.
.IX Xref "type"
.IP "type casting" 4
.IX Item "type casting"
Converting data from one type to another. C permits this.
Perl does not need it. Nor want it.
.IX Xref "type casting"
.IP typedef 4
.IX Item "typedef"
A type definition in the C and C++ languages.
.IX Xref "typedef"
.IP "typed lexical" 4
.IX Item "typed lexical"
A \fBlexical variable\fR  lexical>that is declared with a \fBclass\fR
type: \f(CW\*(C`my Pony $bill\*(C'\fR.
.IX Xref "typed lexicals lexical variables, typed lexicals variables, variable"
.IP typeglob 4
.IX Item "typeglob"
Use of a single identifier, prefixed with \f(CW\*(C`*\*(C'\fR. For
example, \f(CW*name\fR stands for any or all of \f(CW$name\fR, \f(CW@name\fR, \f(CW%name\fR,
\&\f(CW&name\fR, or just \f(CW\*(C`name\*(C'\fR. How you use it determines whether it is
interpreted as all or only one of them. See “Typeglobs and Filehandles” in
Camel chapter 2, “Bits and Pieces”.
.IX Xref "typeglobs, defined"
.IP typemap 4
.IX Item "typemap"
A description of how C types may be transformed to and from Perl
types within an \fBextension\fR module written in \fBXS\fR.
.IX Xref "typemap"
.SS U
.IX Subsection "U"
.IP UDP 4
.IX Item "UDP"
User Datagram Protocol, the typical way to send
\&\fBdatagrams\fR over the Internet.
.IX Xref "User Datagram Protocol (UDP) UDP (User Datagram Protocol) datagrams, UDP support"
.IP UID 4
.IX Item "UID"
A user ID. Often used in the context of
\&\fBfile\fR or \fBprocess\fR ownership.
.IX Xref "UID (user ID) user ID (UID)"
.IP umask 4
.IX Item "umask"
A mask of those \fBpermission bits\fR 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 \f(CW\*(C`umask\*(C'\fR function.
.IX Xref "umask function"
.IP "unary operator" 4
.IX Item "unary operator"
An operator with only one \fBoperand\fR, like \f(CW\*(C`!\*(C'\fR or
\&\f(CW\*(C`chdir\*(C'\fR. Unary operators are usually prefix operators; that is, they
precede their operand. The \f(CW\*(C`++\*(C'\fR and \f(CW\*(C`––\*(C'\fR operators can be either prefix
or postfix. (Their position \fIdoes\fR change their meanings.)
.IX Xref "unary operators, about"
.IP Unicode 4
.IX Item "Unicode"
A character set comprising all the major character sets of
the world, more or less. See <http://www.unicode.org>.
.IX Xref "Unicode, about"
.IP Unix 4
.IX Item "Unix"
A very large and constantly evolving language with several
alternative and largely incompatible syntaxes, in which anyone can define
anything any way they choose, and usually do. Speakers of this language
think it’s easy to learn because it’s so easily twisted to one’s own ends,
but dialectical differences make tribal intercommunication nearly
impossible, and travelers are often reduced to a pidgin-like subset of the
language. To be universally understood, a Unix shell programmer must spend
years of study in the art. Many have abandoned this discipline and now
communicate via an Esperanto-like language called Perl.
.IX Xref "Unix language"
.Sp
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.
.IP uppercase 4
.IX Item "uppercase"
In Unicode, not just
characters with the General Category of Uppercase Letter, but any character
with the Uppercase property, including some Letter Numbers and Symbols. Not
to be confused with \fBtitlecase\fR.
.IX Xref "uppercase characters characters, uppercase"
.SS V
.IX Subsection "V"
.IP value 4
.IX Item "value"
An actual piece of data, in contrast to all the
variables, references, keys, indices, operators, and whatnot that you need
to access the value.
.IX Xref "values, defined"
.IP variable 4
.IX Item "variable"
A named storage location that can hold any
of various kinds of \fBvalue\fR, as your program sees fit.
.IX Xref "variables, defined variables"
.IP "variable interpolation" 4
.IX Item "variable interpolation"
The \fBinterpolation\fR of
a scalar or array variable into a string.
.IX Xref "variable interpolation interpolation, variable"
.IP variadic 4
.IX Item "variadic"
Said of a \fBfunction\fR that happily receives an
indeterminate number of \fBactual arguments\fR.
.IX Xref "variadic (term)"
.IP vector 4
.IX Item "vector"
Mathematical jargon for a list of \fBscalar values\fR.
.IX Xref "vectors"
.IP virtual 4
.IX Item "virtual"
Providing the appearance of something without the reality,
as in: virtual memory is not real memory. (See also \fBmemory\fR.) 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.
.IX Xref "virtual (term)"
.IP "void context" 4
.IX Item "void context"
A form of \fBscalar context\fR in which an
\&\fBexpression\fR is not expected to return any \fBvalue\fR at all and is
evaluated for its \fBside effects\fR alone.
.IX Xref "void context context, void"
.IP v\-string 4
.IX Item "v-string"
A “version” or “vector” \fBstring\fR
specified with a \f(CW\*(C`v\*(C'\fR followed by a series of decimal integers in dot
notation, for instance, \f(CW\*(C`v1.20.300.4000\*(C'\fR. Each number turns into a
\&\fBcharacter\fR with the specified ordinal value. (The \f(CW\*(C`v\*(C'\fR is optional when
there are at least three integers.)
.IX Xref "v–strings strings, v–strings"
.SS W
.IX Subsection "W"
.IP warning 4
.IX Item "warning"
A message printed to the \f(CW\*(C`STDERR\*(C'\fR stream to the effect that something might be
wrong but isn’t worth blowing up over. See \f(CW\*(C`warn\*(C'\fR in Camel chapter 27,
“Functions” and the \f(CW\*(C`warnings\*(C'\fR pragma in Camel chapter 28, “Pragmantic
Modules”.
.IX Xref "warning messages STDERR filehandle, warning messages and"
.IP "watch expression" 4
.IX Item "watch expression"
An expression which, when its value
changes, causes a breakpoint in the Perl debugger.
.IX Xref "watch expression expressions, watch"
.IP "weak reference" 4
.IX Item "weak reference"
A reference that doesn’t get counted
normally. When all the normal references to data disappear, the data
disappears. These are useful for circular references that would never
disappear otherwise.
.IX Xref "weak references references, weak"
.IP whitespace 4
.IX Item "whitespace"
A \fBcharacter\fR that moves
your cursor but doesn’t otherwise put anything on your screen. Typically
refers to any of: space, tab, line feed, carriage return, or form feed. In
Unicode, matches many other characters that Unicode considers whitespace,
including the ɴ\-ʙʀ .
.IX Xref "whitespace characters characters, whitespace"
.IP word 4
.IX Item "word"
In normal “computerese”, the piece of data of the size most
efficiently handled by your computer, typically 32 bits or so, give or take a
few powers of 2. In Perl culture, it more often refers to an alphanumeric
\&\fBidentifier\fR (including underscores), or to a string of nonwhitespace
\&\fBcharacters\fR bounded by whitespace or string boundaries.
.IX Xref "words (term)"
.IP "working directory" 4
.IX Item "working directory"
Your current \fBdirectory\fR, from
which relative pathnames are interpreted by the \fBoperating system\fR. The
operating system knows your current directory because you told it with a
\&\f(CW\*(C`chdir\*(C'\fR, or because you started out in the place where your parent
\&\fBprocess\fR was when you were born.
.IX Xref "working directory directories, working"
.IP wrapper 4
.IX Item "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.
.IX Xref "wrappers (term)"
.IP WYSIWYG 4
.IX Item "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
\&\f(CW\*(C`format\*(C'\fR declarations. Also used to mean the opposite of magic because
everything works exactly as it appears, as in the three\- argument form of
\&\f(CW\*(C`open\*(C'\fR.
.IX Xref "WYSIWYG acronym"
.SS X
.IX Subsection "X"
.IP XS 4
.IX Item "XS"
An extraordinarily
exported, expeditiously excellent, expressly eXternal Subroutine, executed
in existing C or C++ or in an exciting extension language called
(exasperatingly) XS.
.IX Xref "XS (eXternal Subroutine) eXternal Subroutine (XS)"
.IP XSUB 4
.IX Item "XSUB"
An external \fBsubroutine\fR defined in \fBXS\fR.
.IX Xref "XSUB (term)"
.SS Y
.IX Subsection "Y"
.IP yacc 4
.IX Item "yacc"
Yet Another Compiler Compiler. A parser generator without
which Perl probably would not have existed. See the file \fIperly.y\fR in the
Perl source distribution.
.IX Xref "yacc acronym"
.SS Z
.IX Subsection "Z"
.IP "zero width" 4
.IX Item "zero width"
A subpattern \fBassertion\fR matching the \fBnull
string\fR between \fBcharacters\fR.
.IX Xref "zero–width assertions subpatterns, zero–width assertions assertions (in regexes), zero–width"
.IP zombie 4
.IX Item "zombie"
A process that has died (exited) but
whose parent has not yet received proper notification of its demise by
virtue of having called \f(CW\*(C`wait\*(C'\fR or \f(CW\*(C`waitpid\*(C'\fR. If you \f(CW\*(C`fork\*(C'\fR, you must
clean up after your child processes when they exit; otherwise, the process
table will fill up and your system administrator will Not Be Happy with
you.
.IX Xref "zombie processes processes, zombie"
.SH "AUTHOR AND COPYRIGHT"
.IX Header "AUTHOR AND COPYRIGHT"
Based on the Glossary of \fIProgramming Perl\fR, Fourth Edition,
by Tom Christiansen, brian d foy, Larry Wall, & Jon Orwant.
Copyright (c) 2000, 1996, 1991, 2012 O'Reilly Media, Inc.
This document may be distributed under the same terms as Perl itself.