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1=head1 NAME
2
3perlglossary - Perl Glossary
4
5=head1 DESCRIPTION
6
7A glossary of terms (technical and otherwise) used in the Perl documentation.
8Other useful sources include the Free On-Line Dictionary of Computing
9L<http://foldoc.doc.ic.ac.uk/foldoc/index.html>, the Jargon File
10L<http://catb.org/~esr/jargon/>, and Wikipedia L<http://www.wikipedia.org/>.
11
5bbd0522 12=head2 A
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13
14=over 4
15
16=item accessor methods
17
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18A L</method> used to indirectly inspect or update an L</object>'s
19state (its L<instance variables|/instance variable>).
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20
21=item actual arguments
22
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23The L<scalar values|/scalar value> that you supply to a L</function>
24or L</subroutine> when you call it. For instance, when you call
97a1d740 25C<power("puff")>, the string C<"puff"> is the actual argument. See
27ed30b8 26also L</argument> and L</formal arguments>.
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27
28=item address operator
29
30Some languages work directly with the memory addresses of values, but
31this can be like playing with fire. Perl provides a set of asbestos
32gloves for handling all memory management. The closest to an address
27ed30b8 33operator in Perl is the backslash operator, but it gives you a L</hard
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34reference>, which is much safer than a memory address.
35
36=item algorithm
37
38A well-defined sequence of steps, clearly enough explained that even a
39computer could do them.
40
41=item alias
42
43A nickname for something, which behaves in all ways as though you'd
44used the original name instead of the nickname. Temporary aliases are
45implicitly created in the loop variable for C<foreach> loops, in the
46C<$_> variable for L<map|perlfunc/map> or L<grep|perlfunc/grep>
47operators, in C<$a> and C<$b> during L<sort|perlfunc/sort>'s
27ed30b8 48comparison function, and in each element of C<@_> for the L</actual
97a1d740 49arguments> of a subroutine call. Permanent aliases are explicitly
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50created in L<packages|/package> by L<importing|/import> symbols or by
51assignment to L<typeglobs|/typeglob>. Lexically scoped aliases for
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52package variables are explicitly created by the L<our|perlfunc/our>
53declaration.
54
55=item alternatives
56
57A list of possible choices from which you may select only one, as in
58"Would you like door A, B, or C?" Alternatives in regular expressions
59are separated with a single vertical bar: C<|>. Alternatives in
60normal Perl expressions are separated with a double vertical bar:
27ed30b8 61C<||>. Logical alternatives in L</Boolean> expressions are separated
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62with either C<||> or C<or>.
63
64=item anonymous
65
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66Used to describe a L</referent> that is not directly accessible
67through a named L</variable>. Such a referent must be indirectly
68accessible through at least one L</hard reference>. When the last
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69hard reference goes away, the anonymous referent is destroyed without
70pity.
71
72=item architecture
73
d7f8936a 74The kind of computer you're working on, where one "kind" of computer
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75means all those computers sharing a compatible machine language.
76Since Perl programs are (typically) simple text files, not executable
77images, a Perl program is much less sensitive to the architecture it's
78running on than programs in other languages, such as C, that are
27ed30b8 79compiled into machine code. See also L</platform> and L</operating
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80system>.
81
82=item argument
83
84A piece of data supplied to a L<program|/executable file>,
27ed30b8 85L</subroutine>, L</function>, or L</method> to tell it what it's
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86supposed to do. Also called a "parameter".
87
88=item ARGV
89
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90The name of the array containing the L</argument> L</vector> from the
91command line. If you use the empty C<< E<lt>E<gt> >> operator, L</ARGV> is
92the name of both the L</filehandle> used to traverse the arguments and
93the L</scalar> containing the name of the current input file.
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94
95=item arithmetical operator
96
27ed30b8 97A L</symbol> such as C<+> or C</> that tells Perl to do the arithmetic
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98you were supposed to learn in grade school.
99
100=item array
101
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102An ordered sequence of L<values|/value>, stored such that you can
103easily access any of the values using an integer L</subscript>
104that specifies the value's L</offset> in the sequence.
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105
106=item array context
107
108An archaic expression for what is more correctly referred to as
27ed30b8 109L</list context>.
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110
111=item ASCII
112
113The American Standard Code for Information Interchange (a 7-bit
114character set adequate only for poorly representing English text).
115Often used loosely to describe the lowest 128 values of the various
116ISO-8859-X character sets, a bunch of mutually incompatible 8-bit
e1b711da 117codes sometimes described as half ASCII. See also L</Unicode>.
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118
119=item assertion
120
27ed30b8 121A component of a L</regular expression> that must be true for the
97a1d740 122pattern to match but does not necessarily match any characters itself.
27ed30b8 123Often used specifically to mean a L</zero width> assertion.
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124
125=item assignment
126
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127An L</operator> whose assigned mission in life is to change the value
128of a L</variable>.
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129
130=item assignment operator
131
27ed30b8 132Either a regular L</assignment>, or a compound L</operator> composed
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133of an ordinary assignment and some other operator, that changes the
134value of a variable in place, that is, relative to its old value. For
135example, C<$a += 2> adds C<2> to C<$a>.
136
137=item associative array
138
27ed30b8 139See L</hash>. Please.
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140
141=item associativity
142
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143Determines whether you do the left L</operator> first or the right
144L</operator> first when you have "A L</operator> B L</operator> C" and
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145the two operators are of the same precedence. Operators like C<+> are
146left associative, while operators like C<**> are right associative.
147See L<perlop> for a list of operators and their associativity.
148
149=item asynchronous
150
151Said of events or activities whose relative temporal ordering is
152indeterminate because too many things are going on at once. Hence, an
153asynchronous event is one you didn't know when to expect.
154
155=item atom
156
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157A L</regular expression> component potentially matching a
158L</substring> containing one or more characters and treated as an
159indivisible syntactic unit by any following L</quantifier>. (Contrast
160with an L</assertion> that matches something of L</zero width> and may
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161not be quantified.)
162
163=item atomic operation
164
165When Democritus gave the word "atom" to the indivisible bits of
166matter, he meant literally something that could not be cut: I<a->
167(not) + I<tomos> (cuttable). An atomic operation is an action that
168can't be interrupted, not one forbidden in a nuclear-free zone.
169
170=item attribute
171
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172A new feature that allows the declaration of L<variables|/variable>
173and L<subroutines|/subroutine> with modifiers as in C<sub foo : locked
174method>. Also, another name for an L</instance variable> of an
175L</object>.
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176
177=item autogeneration
178
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179A feature of L</operator overloading> of L<objects|/object>, whereby
180the behavior of certain L<operators|/operator> can be reasonably
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181deduced using more fundamental operators. This assumes that the
182overloaded operators will often have the same relationships as the
183regular operators. See L<perlop>.
184
185=item autoincrement
186
cf525c36 187To add one to something automatically, hence the name of the C<++>
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188operator. To instead subtract one from something automatically is
189known as an "autodecrement".
190
191=item autoload
192
193To load on demand. (Also called "lazy" loading.) Specifically, to
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194call an L<AUTOLOAD|perlsub/Autoloading> subroutine on behalf of an
195undefined subroutine.
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196
197=item autosplit
198
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199To split a string automatically, as the B<-a> L</switch> does when
200running under B<-p> or B<-n> in order to emulate L</awk>. (See also
201the L<AutoSplit> module, which has nothing to do with the B<-a>
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202switch, but a lot to do with autoloading.)
203
204=item autovivification
205
206A Greco-Roman word meaning "to bring oneself to life". In Perl,
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207storage locations (L<lvalues|/lvalue>) spontaneously generate
208themselves as needed, including the creation of any L</hard reference>
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209values to point to the next level of storage. The assignment
210C<$a[5][5][5][5][5] = "quintet"> potentially creates five scalar
211storage locations, plus four references (in the first four scalar
212locations) pointing to four new anonymous arrays (to hold the last
213four scalar locations). But the point of autovivification is that you
214don't have to worry about it.
215
216=item AV
217
218Short for "array value", which refers to one of Perl's internal data
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219types that holds an L</array>. The L</AV> type is a subclass of
220L</SV>.
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221
222=item awk
223
224Descriptive editing term--short for "awkward". Also coincidentally
225refers to a venerable text-processing language from which Perl derived
226some of its high-level ideas.
227
228=back
229
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230=head2 B
231
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232=over 4
233
234=item backreference
235
236A substring L<captured|/capturing> by a subpattern within
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237unadorned parentheses in a L</regex>, also referred to as a capture group. The
238sequences (C<\g1>, C<\g2>, etc.) later in the same pattern refer back to
239the corresponding subpattern in the current match. Outside the pattern,
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240the numbered variables (C<$1>, C<$2>, etc.) continue to refer to these
241same values, as long as the pattern was the last successful match of
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242the current dynamic scope. C<\g{-1}> can be used to refer to a group by
243relative rather than absolute position; and groups can be also be named, and
96090e4f 244referred to later by name rather than number. See L<perlre/"Capture groups">.
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245
246=item backtracking
247
248The practice of saying, "If I had to do it all over, I'd do it
249differently," and then actually going back and doing it all over
250differently. Mathematically speaking, it's returning from an
251unsuccessful recursion on a tree of possibilities. Perl backtracks
27ed30b8 252when it attempts to match patterns with a L</regular expression>, and
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253its earlier attempts don't pan out. See L<perlre/Backtracking>.
254
255=item backward compatibility
256
257Means you can still run your old program because we didn't break any
258of the features or bugs it was relying on.
259
260=item bareword
261
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262A word sufficiently ambiguous to be deemed illegal under L<use strict
263'subs'|strict/strict subs>. In the absence of that stricture, a
264bareword is treated as if quotes were around it.
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265
266=item base class
267
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268A generic L</object> type; that is, a L</class> from which other, more
269specific classes are derived genetically by L</inheritance>. Also
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270called a "superclass" by people who respect their ancestors.
271
272=item big-endian
273
274From Swift: someone who eats eggs big end first. Also used of
27ed30b8 275computers that store the most significant L</byte> of a word at a
97a1d740 276lower byte address than the least significant byte. Often considered
27ed30b8 277superior to little-endian machines. See also L</little-endian>.
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278
279=item binary
280
281Having to do with numbers represented in base 2. That means there's
282basically two numbers, 0 and 1. Also used to describe a "non-text
283file", presumably because such a file makes full use of all the binary
27ed30b8 284bits in its bytes. With the advent of L</Unicode>, this distinction,
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285already suspect, loses even more of its meaning.
286
287=item binary operator
288
27ed30b8 289An L</operator> that takes two L<operands|/operand>.
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290
291=item bind
292
27ed30b8 293To assign a specific L</network address> to a L</socket>.
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294
295=item bit
296
297An integer in the range from 0 to 1, inclusive. The smallest possible
27ed30b8 298unit of information storage. An eighth of a L</byte> or of a dollar.
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299(The term "Pieces of Eight" comes from being able to split the old
300Spanish dollar into 8 bits, each of which still counted for money.
301That's why a 25-cent piece today is still "two bits".)
302
303=item bit shift
304
305The movement of bits left or right in a computer word, which has the
306effect of multiplying or dividing by a power of 2.
307
308=item bit string
309
27ed30b8 310A sequence of L<bits|/bit> that is actually being thought of as a
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311sequence of bits, for once.
312
313=item bless
314
315In corporate life, to grant official approval to a thing, as in, "The
316VP of Engineering has blessed our WebCruncher project." Similarly in
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317Perl, to grant official approval to a L</referent> so that it can
318function as an L</object>, such as a WebCruncher object. See
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319L<perlfunc/"bless">.
320
321=item block
322
27ed30b8 323What a L</process> does when it has to wait for something: "My process
97a1d740 324blocked waiting for the disk." As an unrelated noun, it refers to a
27ed30b8 325large chunk of data, of a size that the L</operating system> likes to
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326deal with (normally a power of two such as 512 or 8192). Typically
327refers to a chunk of data that's coming from or going to a disk file.
328
329=item BLOCK
330
331A syntactic construct consisting of a sequence of Perl
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332L<statements|/statement> that is delimited by braces. The C<if> and
333C<while> statements are defined in terms of L<BLOCKs|/BLOCK>, for instance.
97a1d740 334Sometimes we also say "block" to mean a lexical scope; that is, a
27ed30b8 335sequence of statements that act like a L</BLOCK>, such as within an
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336L<eval|perlfunc/eval> or a file, even though the statements aren't
337delimited by braces.
338
339=item block buffering
340
27ed30b8 341A method of making input and output efficient by passing one L</block>
97a1d740 342at a time. By default, Perl does block buffering to disk files. See
27ed30b8 343L</buffer> and L</command buffering>.
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344
345=item Boolean
346
27ed30b8 347A value that is either L</true> or L</false>.
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348
349=item Boolean context
350
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351A special kind of L</scalar context> used in conditionals to decide
352whether the L</scalar value> returned by an expression is L</true> or
353L</false>. Does not evaluate as either a string or a number. See
354L</context>.
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355
356=item breakpoint
357
358A spot in your program where you've told the debugger to stop
359L<execution|/execute> so you can poke around and see whether anything
360is wrong yet.
361
362=item broadcast
363
27ed30b8 364To send a L</datagram> to multiple destinations simultaneously.
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365
366=item BSD
367
368A psychoactive drug, popular in the 80s, probably developed at
369U. C. Berkeley or thereabouts. Similar in many ways to the
370prescription-only medication called "System V", but infinitely more
371useful. (Or, at least, more fun.) The full chemical name is
372"Berkeley Standard Distribution".
373
374=item bucket
375
27ed30b8 376A location in a L</hash table> containing (potentially) multiple
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377entries whose keys "hash" to the same hash value according to its hash
378function. (As internal policy, you don't have to worry about it,
379unless you're into internals, or policy.)
380
381=item buffer
382
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383A temporary holding location for data. L<Block buffering|/block
384buffering> means that the data is passed on to its destination
385whenever the buffer is full. L<Line buffering|/line buffering> means
386that it's passed on whenever a complete line is received. L<Command
387buffering|/command buffering> means that it's passed every time you do
388a L<print|perlfunc/print> command (or equivalent). If your output is
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389unbuffered, the system processes it one byte at a time without the use
390of a holding area. This can be rather inefficient.
391
392=item built-in
393
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394A L</function> that is predefined in the language. Even when hidden
395by L</overriding>, you can always get at a built-in function by
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396L<qualifying|/qualified> its name with the C<CORE::> pseudo-package.
397
398=item bundle
399
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400A group of related modules on L</CPAN>. (Also, sometimes refers to a
401group of command-line switches grouped into one L</switch cluster>.)
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402
403=item byte
404
27ed30b8 405A piece of data worth eight L<bits|/bit> in most places.
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406
407=item bytecode
408
409A pidgin-like language spoken among 'droids when they don't wish to
27ed30b8 410reveal their orientation (see L</endian>). Named after some similar
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411languages spoken (for similar reasons) between compilers and
412interpreters in the late 20th century. These languages are
413characterized by representing everything as a
414non-architecture-dependent sequence of bytes.
415
416=back
417
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418=head2 C
419
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420=over 4
421
422=item C
423
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424A language beloved by many for its inside-out L</type> definitions,
425inscrutable L</precedence> rules, and heavy L</overloading> of the
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426function-call mechanism. (Well, actually, people first switched to C
427because they found lowercase identifiers easier to read than upper.)
428Perl is written in C, so it's not surprising that Perl borrowed a few
429ideas from it.
430
431=item C preprocessor
432
433The typical C compiler's first pass, which processes lines beginning
434with C<#> for conditional compilation and macro definition and does
435various manipulations of the program text based on the current
436definitions. Also known as I<cpp>(1).
437
438=item call by reference
439
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440An L</argument>-passing mechanism in which the L</formal arguments>
441refer directly to the L</actual arguments>, and the L</subroutine> can
97a1d740 442change the actual arguments by changing the formal arguments. That
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443is, the formal argument is an L</alias> for the actual argument. See
444also L</call by value>.
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445
446=item call by value
447
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448An L</argument>-passing mechanism in which the L</formal arguments>
449refer to a copy of the L</actual arguments>, and the L</subroutine>
97a1d740 450cannot change the actual arguments by changing the formal arguments.
27ed30b8 451See also L</call by reference>.
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452
453=item callback
454
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455A L</handler> that you register with some other part of your program
456in the hope that the other part of your program will L</trigger> your
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457handler when some event of interest transpires.
458
459=item canonical
460
461Reduced to a standard form to facilitate comparison.
462
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463=item capture buffer, capture group
464
465These two terms are synonymous:
466a L<captured substring|/capturing> by a regex subpattern.
467
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468=item capturing
469
27ed30b8 470The use of parentheses around a L</subpattern> in a L</regular
c27a5cfe 471expression> to store the matched L</substring> as a L</backreference>
0967016d 472or L<capture group|/capture buffer, capture group>.
27ed30b8 473(Captured strings are also returned as a list in L</list context>.)
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474
475=item character
476
477A small integer representative of a unit of orthography.
478Historically, characters were usually stored as fixed-width integers
479(typically in a byte, or maybe two, depending on the character set),
480but with the advent of UTF-8, characters are often stored in a
481variable number of bytes depending on the size of the integer that
482represents the character. Perl manages this transparently for you,
483for the most part.
484
485=item character class
486
27ed30b8 487A square-bracketed list of characters used in a L</regular expression>
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488to indicate that any character of the set may occur at a given point.
489Loosely, any predefined set of characters so used.
490
491=item character property
492
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493A predefined L</character class> matchable by the C<\p>
494L</metasymbol>. Many standard properties are defined for L</Unicode>.
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495
496=item circumfix operator
497
27ed30b8 498An L</operator> that surrounds its L</operand>, like the angle
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499operator, or parentheses, or a hug.
500
501=item class
502
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503A user-defined L</type>, implemented in Perl via a L</package> that
504provides (either directly or by inheritance) L<methods|/method> (that
505is, L<subroutines|/subroutine>) to handle L<instances|/instance> of
506the class (its L<objects|/object>). See also L</inheritance>.
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507
508=item class method
509
c69ca1d4 510A L</method> whose L</invocand> is a L</package> name, not an
27ed30b8 511L</object> reference. A method associated with the class as a whole.
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512
513=item client
514
27ed30b8 515In networking, a L</process> that initiates contact with a L</server>
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516process in order to exchange data and perhaps receive a service.
517
518=item cloister
519
27ed30b8 520A L</cluster> used to restrict the scope of a L</regular expression
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521modifier>.
522
523=item closure
524
27ed30b8 525An L</anonymous> subroutine that, when a reference to it is generated
97a1d740 526at run time, keeps track of the identities of externally visible
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527L<lexical variables|/lexical variable> even after those lexical
528variables have supposedly gone out of L</scope>. They're called
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529"closures" because this sort of behavior gives mathematicians a sense
530of closure.
531
532=item cluster
533
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534A parenthesized L</subpattern> used to group parts of a L</regular
535expression> into a single L</atom>.
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536
537=item CODE
538
539The word returned by the L<ref|perlfunc/ref> function when you apply
27ed30b8 540it to a reference to a subroutine. See also L</CV>.
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541
542=item code generator
543
544A system that writes code for you in a low-level language, such as
27ed30b8 545code to implement the backend of a compiler. See L</program
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546generator>.
547
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548=item code point
549
550The position of a character in a character set encoding. The character
551C<NULL> is almost certainly at the zeroth position in all character
49cf3968 552sets, so its code point is 0. The code point for the C<SPACE>
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553character in the ASCII character set is 0x20, or 32 decimal; in EBCDIC
554it is 0x40, or 64 decimal. The L<ord|perlfunc/ord> function returns
555the code point of a character.
556
557"code position" and "ordinal" mean the same thing as "code point".
558
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559=item code subpattern
560
27ed30b8 561A L</regular expression> subpattern whose real purpose is to execute
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562some Perl code, for example, the C<(?{...})> and C<(??{...})>
563subpatterns.
564
565=item collating sequence
566
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567The order into which L<characters|/character> sort. This is used by
568L</string> comparison routines to decide, for example, where in this
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569glossary to put "collating sequence".
570
571=item command
572
27ed30b8 573In L</shell> programming, the syntactic combination of a program name
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574and its arguments. More loosely, anything you type to a shell (a
575command interpreter) that starts it doing something. Even more
27ed30b8 576loosely, a Perl L</statement>, which might start with a L</label> and
97a1d740
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577typically ends with a semicolon.
578
579=item command buffering
580
581A mechanism in Perl that lets you store up the output of each Perl
27ed30b8
YST
582L</command> and then flush it out as a single request to the
583L</operating system>. It's enabled by setting the C<$|>
97a1d740
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584(C<$AUTOFLUSH>) variable to a true value. It's used when you don't
585want data sitting around not going where it's supposed to, which may
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586happen because the default on a L</file> or L</pipe> is to use
587L</block buffering>.
97a1d740
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588
589=item command name
590
591The name of the program currently executing, as typed on the command
27ed30b8 592line. In C, the L</command> name is passed to the program as the
97a1d740
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593first command-line argument. In Perl, it comes in separately as
594C<$0>.
595
596=item command-line arguments
597
27ed30b8
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598The L<values|/value> you supply along with a program name when you
599tell a L</shell> to execute a L</command>. These values are passed to
97a1d740
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600a Perl program through C<@ARGV>.
601
602=item comment
603
604A remark that doesn't affect the meaning of the program. In Perl, a
605comment is introduced by a C<#> character and continues to the end of
606the line.
607
608=item compilation unit
609
27ed30b8 610The L</file> (or L</string>, in the case of L<eval|perlfunc/eval>)
97a1d740
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611that is currently being compiled.
612
613=item compile phase
614
615Any time before Perl starts running your main program. See also
27ed30b8
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616L</run phase>. Compile phase is mostly spent in L</compile time>, but
617may also be spent in L</run time> when C<BEGIN> blocks,
97a1d740
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618L<use|perlfunc/use> declarations, or constant subexpressions are being
619evaluated. The startup and import code of any L<use|perlfunc/use>
620declaration is also run during compile phase.
621
622=item compile time
623
624The time when Perl is trying to make sense of your code, as opposed to
625when it thinks it knows what your code means and is merely trying to
27ed30b8 626do what it thinks your code says to do, which is L</run time>.
97a1d740
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627
628=item compiler
629
630Strictly speaking, a program that munches up another program and spits
631out yet another file containing the program in a "more executable"
632form, typically containing native machine instructions. The I<perl>
633program is not a compiler by this definition, but it does contain a
634kind of compiler that takes a program and turns it into a more
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635executable form (L<syntax trees|/syntax tree>) within the I<perl>
636process itself, which the L</interpreter> then interprets. There are,
637however, extension L<modules|/module> to get Perl to act more like a
97a1d740
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638"real" compiler. See L<O>.
639
640=item composer
641
27ed30b8 642A "constructor" for a L</referent> that isn't really an L</object>,
97a1d740
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643like an anonymous array or a hash (or a sonata, for that matter). For
644example, a pair of braces acts as a composer for a hash, and a pair of
645brackets acts as a composer for an array. See L<perlref/Making
646References>.
647
648=item concatenation
649
650The process of gluing one cat's nose to another cat's tail. Also, a
27ed30b8 651similar operation on two L<strings|/string>.
97a1d740
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652
653=item conditional
654
27ed30b8 655Something "iffy". See L</Boolean context>.
97a1d740
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656
657=item connection
658
659In telephony, the temporary electrical circuit between the caller's
660and the callee's phone. In networking, the same kind of temporary
27ed30b8 661circuit between a L</client> and a L</server>.
97a1d740
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662
663=item construct
664
665As a noun, a piece of syntax made up of smaller pieces. As a
27ed30b8 666transitive verb, to create an L</object> using a L</constructor>.
97a1d740
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667
668=item constructor
669
27ed30b8
YST
670Any L</class method>, instance L</method>, or L</subroutine>
671that composes, initializes, blesses, and returns an L</object>.
672Sometimes we use the term loosely to mean a L</composer>.
97a1d740
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673
674=item context
675
676The surroundings, or environment. The context given by the
677surrounding code determines what kind of data a particular
27ed30b8
YST
678L</expression> is expected to return. The three primary contexts are
679L</list context>, L</scalar context>, and L</void context>. Scalar
680context is sometimes subdivided into L</Boolean context>, L</numeric
681context>, L</string context>, and L</void context>. There's also a
97a1d740
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682"don't care" scalar context (which is dealt with in Programming Perl,
683Third Edition, Chapter 2, "Bits and Pieces" if you care).
684
685=item continuation
686
27ed30b8
YST
687The treatment of more than one physical L</line> as a single logical
688line. L</Makefile> lines are continued by putting a backslash before
689the L</newline>. Mail headers as defined by RFC 822 are continued by
97a1d740 690putting a space or tab I<after> the newline. In general, lines in
27ed30b8 691Perl do not need any form of continuation mark, because L</whitespace>
97a1d740
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692(including newlines) is gleefully ignored. Usually.
693
694=item core dump
695
27ed30b8
YST
696The corpse of a L</process>, in the form of a file left in the
697L</working directory> of the process, usually as a result of certain
97a1d740
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698kinds of fatal error.
699
700=item CPAN
701
702The Comprehensive Perl Archive Network. (See L<perlfaq2/What modules and extensions are available for Perl? What is CPAN? What does CPANE<sol>srcE<sol>... mean?>).
703
704=item cracker
705
706Someone who breaks security on computer systems. A cracker may be a
27ed30b8 707true L</hacker> or only a L</script kiddie>.
97a1d740
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708
709=item current package
710
27ed30b8 711The L</package> in which the current statement is compiled. Scan
97a1d740
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712backwards in the text of your program through the current L<lexical
713scope|/lexical scoping> or any enclosing lexical scopes till you find
714a package declaration. That's your current package name.
715
716=item current working directory
717
27ed30b8 718See L</working directory>.
97a1d740
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719
720=item currently selected output channel
721
27ed30b8
YST
722The last L</filehandle> that was designated with
723L<select|perlfunc/select>(C<FILEHANDLE>); L</STDOUT>, if no filehandle
724has been selected.
97a1d740
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725
726=item CV
727
27ed30b8
YST
728An internal "code value" typedef, holding a L</subroutine>. The L</CV>
729type is a subclass of L</SV>.
97a1d740
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730
731=back
732
5bbd0522
YST
733=head2 D
734
97a1d740
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735=over 4
736
737=item dangling statement
738
27ed30b8 739A bare, single L</statement>, without any braces, hanging off an C<if>
97a1d740
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740or C<while> conditional. C allows them. Perl doesn't.
741
742=item data structure
743
744How your various pieces of data relate to each other and what shape
745they make when you put them all together, as in a rectangular table or
746a triangular-shaped tree.
747
748=item data type
749
750A set of possible values, together with all the operations that know
751how to deal with those values. For example, a numeric data type has a
752certain set of numbers that you can work with and various mathematical
753operations that you can do on the numbers but would make little sense
754on, say, a string such as C<"Kilroy">. Strings have their own
27ed30b8 755operations, such as L</concatenation>. Compound types made of a
97a1d740 756number of smaller pieces generally have operations to compose and
27ed30b8
YST
757decompose them, and perhaps to rearrange them. L<Objects|/object>
758that model things in the real world often have operations that
97a1d740
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759correspond to real activities. For instance, if you model an
760elevator, your elevator object might have an C<open_door()>
27ed30b8 761L</method>.
97a1d740
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762
763=item datagram
764
27ed30b8 765A packet of data, such as a L</UDP> message, that (from the viewpoint
97a1d740 766of the programs involved) can be sent independently over the network.
27ed30b8
YST
767(In fact, all packets are sent independently at the L</IP> level, but
768L</stream> protocols such as L</TCP> hide this from your program.)
97a1d740
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769
770=item DBM
771
772Stands for "Data Base Management" routines, a set of routines that
27ed30b8 773emulate an L</associative array> using disk files. The routines use a
97a1d740
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774dynamic hashing scheme to locate any entry with only two disk
775accesses. DBM files allow a Perl program to keep a persistent
27ed30b8 776L</hash> across multiple invocations. You can L<tie|perlfunc/tie>
97a1d740
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777your hash variables to various DBM implementations--see L<AnyDBM_File>
778and L<DB_File>.
779
780=item declaration
781
27ed30b8 782An L</assertion> that states something exists and perhaps describes
97a1d740
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783what it's like, without giving any commitment as to how or where
784you'll use it. A declaration is like the part of your recipe that
785says, "two cups flour, one large egg, four or five tadpoles..." See
27ed30b8 786L</statement> for its opposite. Note that some declarations also
97a1d740
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787function as statements. Subroutine declarations also act as
788definitions if a body is supplied.
789
790=item decrement
791
792To subtract a value from a variable, as in "decrement C<$x>" (meaning
793to remove 1 from its value) or "decrement C<$x> by 3".
794
795=item default
796
27ed30b8 797A L</value> chosen for you if you don't supply a value of your own.
97a1d740
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798
799=item defined
800
801Having a meaning. Perl thinks that some of the things people try to
802do are devoid of meaning, in particular, making use of variables that
27ed30b8 803have never been given a L</value> and performing certain operations on
97a1d740
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804data that isn't there. For example, if you try to read data past the
805end of a file, Perl will hand you back an undefined value. See also
27ed30b8 806L</false> and L<perlfunc/defined>.
97a1d740
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807
808=item delimiter
809
27ed30b8
YST
810A L</character> or L</string> that sets bounds to an arbitrarily-sized
811textual object, not to be confused with a L</separator> or
812L</terminator>. "To delimit" really just means "to surround" or "to
97a1d740
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813enclose" (like these parentheses are doing).
814
2dd6f5a3
JC
815=item deprecated modules and features
816
817Deprecated modules and features are those which were part of a stable
818release, but later found to be subtly flawed, and which should be avoided.
819They are subject to removal and/or bug-incompatible reimplementation in
353c6505 820the next major release (but they will be preserved through maintenance
2dd6f5a3
JC
821releases). Deprecation warnings are issued under B<-w> or C<use
822diagnostics>, and notices are found in L<perldelta>s, as well as various
823other PODs. Coding practices that misuse features, such as C<my $foo if
8240>, can also be deprecated.
825
97a1d740
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826=item dereference
827
27ed30b8 828A fancy computer science term meaning "to follow a L</reference> to
97a1d740 829what it points to". The "de" part of it refers to the fact that
27ed30b8 830you're taking away one level of L</indirection>.
97a1d740
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831
832=item derived class
833
27ed30b8
YST
834A L</class> that defines some of its L<methods|/method> in terms of a
835more generic class, called a L</base class>. Note that classes aren't
97a1d740
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836classified exclusively into base classes or derived classes: a class
837can function as both a derived class and a base class simultaneously,
838which is kind of classy.
839
840=item descriptor
841
27ed30b8 842See L</file descriptor>.
97a1d740
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843
844=item destroy
845
27ed30b8 846To deallocate the memory of a L</referent> (first triggering its
97a1d740
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847C<DESTROY> method, if it has one).
848
849=item destructor
850
27ed30b8
YST
851A special L</method> that is called when an L</object> is thinking
852about L<destroying|/destroy> itself. A Perl program's C<DESTROY>
97a1d740 853method doesn't do the actual destruction; Perl just
27ed30b8 854L<triggers|/trigger> the method in case the L</class> wants to do any
97a1d740
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855associated cleanup.
856
857=item device
858
859A whiz-bang hardware gizmo (like a disk or tape drive or a modem or a
27ed30b8
YST
860joystick or a mouse) attached to your computer, that the L</operating
861system> tries to make look like a L</file> (or a bunch of files).
97a1d740
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862Under Unix, these fake files tend to live in the I</dev> directory.
863
864=item directive
865
27ed30b8 866A L</pod> directive. See L<perlpod>.
97a1d740
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867
868=item directory
869
870A special file that contains other files. Some L<operating
871systems|/operating system> call these "folders", "drawers", or
872"catalogs".
873
874=item directory handle
875
876A name that represents a particular instance of opening a directory to
877read it, until you close it. See the L<opendir|perlfunc/opendir>
878function.
879
880=item dispatch
881
882To send something to its correct destination. Often used
883metaphorically to indicate a transfer of programmatic control to a
884destination selected algorithmically, often by lookup in a table of
27ed30b8
YST
885function L<references|/reference> or, in the case of object
886L<methods|/method>, by traversing the inheritance tree looking for the
97a1d740
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887most specific definition for the method.
888
889=item distribution
890
891A standard, bundled release of a system of software. The default
892usage implies source code is included. If that is not the case, it
893will be called a "binary-only" distribution.
894
2dd6f5a3
JC
895=item (to be) dropped modules
896
96090e4f 897When Perl 5 was first released (see L<perlhist>), several modules were
2dd6f5a3
JC
898included, which have now fallen out of common use. It has been suggested
899that these modules should be removed, since the distribution became rather
900large, and the common criterion for new module additions is now limited to
901modules that help to build, test, and extend perl itself. Furthermore,
e6665613
JC
902the CPAN (which didn't exist at the time of Perl 5.0) can become the new
903home of dropped modules. Dropping modules is currently not an option, but
2dd6f5a3
JC
904further developments may clear the last barriers.
905
97a1d740
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906=item dweomer
907
908An enchantment, illusion, phantasm, or jugglery. Said when Perl's
27ed30b8 909magical L</dwimmer> effects don't do what you expect, but rather seem
97a1d740
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910to be the product of arcane dweomercraft, sorcery, or wonder working.
911[From Old English]
912
913=item dwimmer
914
915DWIM is an acronym for "Do What I Mean", the principle that something
916should just do what you want it to do without an undue amount of fuss.
917A bit of code that does "dwimming" is a "dwimmer". Dwimming can
918require a great deal of behind-the-scenes magic, which (if it doesn't
27ed30b8 919stay properly behind the scenes) is called a L</dweomer> instead.
97a1d740
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920
921=item dynamic scoping
922
923Dynamic scoping works over a dynamic scope, making variables visible
27ed30b8
YST
924throughout the rest of the L</block> in which they are first used and
925in any L<subroutines|/subroutine> that are called by the rest of the
97a1d740
YST
926block. Dynamically scoped variables can have their values temporarily
927changed (and implicitly restored later) by a L<local|perlfunc/local>
27ed30b8 928operator. (Compare L</lexical scoping>.) Used more loosely to mean
97a1d740 929how a subroutine that is in the middle of calling another subroutine
27ed30b8 930"contains" that subroutine at L</run time>.
97a1d740
YST
931
932=back
933
5bbd0522
YST
934=head2 E
935
97a1d740
YST
936=over 4
937
938=item eclectic
939
940Derived from many sources. Some would say I<too> many.
941
942=item element
943
27ed30b8 944A basic building block. When you're talking about an L</array>, it's
97a1d740
YST
945one of the items that make up the array.
946
947=item embedding
948
949When something is contained in something else, particularly when that
950might be considered surprising: "I've embedded a complete Perl
951interpreter in my editor!"
952
953=item empty subclass test
954
27ed30b8
YST
955The notion that an empty L</derived class> should behave exactly like
956its L</base class>.
97a1d740
YST
957
958=item en passant
959
27ed30b8 960When you change a L</value> as it is being copied. [From French, "in
97a1d740
YST
961passing", as in the exotic pawn-capturing maneuver in chess.]
962
963=item encapsulation
964
27ed30b8
YST
965The veil of abstraction separating the L</interface> from the
966L</implementation> (whether enforced or not), which mandates that all
967access to an L</object>'s state be through L<methods|/method> alone.
97a1d740
YST
968
969=item endian
970
27ed30b8 971See L</little-endian> and L</big-endian>.
97a1d740
YST
972
973=item environment
974
27ed30b8
YST
975The collective set of L<environment variables|/environment variable>
976your L</process> inherits from its parent. Accessed via C<%ENV>.
97a1d740
YST
977
978=item environment variable
979
980A mechanism by which some high-level agent such as a user can pass its
27ed30b8 981preferences down to its future offspring (child L<processes|/process>,
97a1d740 982grandchild processes, great-grandchild processes, and so on). Each
27ed30b8
YST
983environment variable is a L</key>/L</value> pair, like one entry in a
984L</hash>.
97a1d740
YST
985
986=item EOF
987
988End of File. Sometimes used metaphorically as the terminating string
27ed30b8 989of a L</here document>.
97a1d740
YST
990
991=item errno
992
27ed30b8 993The error number returned by a L</syscall> when it fails. Perl refers
97a1d740
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994to the error by the name C<$!> (or C<$OS_ERROR> if you use the English
995module).
996
997=item error
998
27ed30b8 999See L</exception> or L</fatal error>.
97a1d740
YST
1000
1001=item escape sequence
1002
27ed30b8 1003See L</metasymbol>.
97a1d740
YST
1004
1005=item exception
1006
27ed30b8 1007A fancy term for an error. See L</fatal error>.
97a1d740
YST
1008
1009=item exception handling
1010
1011The way a program responds to an error. The exception handling
1012mechanism in Perl is the L<eval|perlfunc/eval> operator.
1013
1014=item exec
1015
27ed30b8 1016To throw away the current L</process>'s program and replace it with
97a1d740
YST
1017another without exiting the process or relinquishing any resources
1018held (apart from the old memory image).
1019
1020=item executable file
1021
27ed30b8 1022A L</file> that is specially marked to tell the L</operating system>
97a1d740
YST
1023that it's okay to run this file as a program. Usually shortened to
1024"executable".
1025
1026=item execute
1027
27ed30b8 1028To run a L<program|/executable file> or L</subroutine>. (Has nothing
97a1d740 1029to do with the L<kill|perlfunc/kill> built-in, unless you're trying to
27ed30b8 1030run a L</signal handler>.)
97a1d740
YST
1031
1032=item execute bit
1033
1034The special mark that tells the operating system it can run this
1035program. There are actually three execute bits under Unix, and which
1036bit gets used depends on whether you own the file singularly,
1037collectively, or not at all.
1038
1039=item exit status
1040
27ed30b8 1041See L</status>.
97a1d740
YST
1042
1043=item export
1044
27ed30b8 1045To make symbols from a L</module> available for L</import> by other modules.
97a1d740
YST
1046
1047=item expression
1048
27ed30b8
YST
1049Anything you can legally say in a spot where a L</value> is required.
1050Typically composed of L<literals|/literal>, L<variables|/variable>,
1051L<operators|/operator>, L<functions|/function>, and L</subroutine>
97a1d740
YST
1052calls, not necessarily in that order.
1053
1054=item extension
1055
1056A Perl module that also pulls in compiled C or C++ code. More
1057generally, any experimental option that can be compiled into Perl,
1058such as multithreading.
1059
1060=back
1061
5bbd0522
YST
1062=head2 F
1063
97a1d740
YST
1064=over 4
1065
1066=item false
1067
1068In Perl, any value that would look like C<""> or C<"0"> if evaluated
1069in a string context. Since undefined values evaluate to C<"">, all
1070undefined values are false, but not all false values are undefined.
1071
1072=item FAQ
1073
1074Frequently Asked Question (although not necessarily frequently
1075answered, especially if the answer appears in the Perl FAQ shipped
1076standard with Perl).
1077
1078=item fatal error
1079
27ed30b8
YST
1080An uncaught L</exception>, which causes termination of the L</process>
1081after printing a message on your L</standard error> stream. Errors
97a1d740
YST
1082that happen inside an L<eval|perlfunc/eval> are not fatal. Instead,
1083the L<eval|perlfunc/eval> terminates after placing the exception
1084message in the C<$@> (C<$EVAL_ERROR>) variable. You can try to
1085provoke a fatal error with the L<die|perlfunc/die> operator (known as
1086throwing or raising an exception), but this may be caught by a
1087dynamically enclosing L<eval|perlfunc/eval>. If not caught, the
1088L<die|perlfunc/die> becomes a fatal error.
1089
1090=item field
1091
1092A single piece of numeric or string data that is part of a longer
27ed30b8
YST
1093L</string>, L</record>, or L</line>. Variable-width fields are usually
1094split up by L<separators|/separator> (so use L<split|perlfunc/split> to
1095extract the fields), while fixed-width fields are usually at fixed
1096positions (so use L<unpack|perlfunc/unpack>). L<Instance
1097variables|/instance variable> are also known as fields.
97a1d740
YST
1098
1099=item FIFO
1100
27ed30b8
YST
1101First In, First Out. See also L</LIFO>. Also, a nickname for a
1102L</named pipe>.
97a1d740
YST
1103
1104=item file
1105
27ed30b8
YST
1106A named collection of data, usually stored on disk in a L</directory>
1107in a L</filesystem>. Roughly like a document, if you're into office
97a1d740
YST
1108metaphors. In modern filesystems, you can actually give a file more
1109than one name. Some files have special properties, like directories
1110and devices.
1111
1112=item file descriptor
1113
27ed30b8
YST
1114The little number the L</operating system> uses to keep track of which
1115opened L</file> you're talking about. Perl hides the file descriptor
1116inside a L</standard IE<sol>O> stream and then attaches the stream to
1117a L</filehandle>.
97a1d740
YST
1118
1119=item file test operator
1120
1121A built-in unary operator that you use to determine whether something
27ed30b8 1122is L</true> about a file, such as C<-o $filename> to test whether
97a1d740
YST
1123you're the owner of the file.
1124
1125=item fileglob
1126
27ed30b8 1127A "wildcard" match on L<filenames|/filename>. See the
97a1d740
YST
1128L<glob|perlfunc/glob> function.
1129
1130=item filehandle
1131
1132An identifier (not necessarily related to the real name of a file)
1133that represents a particular instance of opening a file until you
1134close it. If you're going to open and close several different files
1135in succession, it's fine to open each of them with the same
1136filehandle, so you don't have to write out separate code to process
1137each file.
1138
1139=item filename
1140
27ed30b8
YST
1141One name for a file. This name is listed in a L</directory>, and you
1142can use it in an L<open|perlfunc/open> to tell the L</operating
97a1d740 1143system> exactly which file you want to open, and associate the file
27ed30b8 1144with a L</filehandle> which will carry the subsequent identity of that
97a1d740
YST
1145file in your program, until you close it.
1146
1147=item filesystem
1148
27ed30b8 1149A set of L<directories|/directory> and L<files|/file> residing on a
97a1d740
YST
1150partition of the disk. Sometimes known as a "partition". You can
1151change the file's name or even move a file around from directory to
1152directory within a filesystem without actually moving the file itself,
1153at least under Unix.
1154
1155=item filter
1156
27ed30b8 1157A program designed to take a L</stream> of input and transform it into
97a1d740
YST
1158a stream of output.
1159
1160=item flag
1161
1162We tend to avoid this term because it means so many things. It may
27ed30b8 1163mean a command-line L</switch> that takes no argument
97a1d740
YST
1164itself (such as Perl's B<-n> and B<-p>
1165flags) or, less frequently, a single-bit indicator (such as the
1166C<O_CREAT> and C<O_EXCL> flags used in
1167L<sysopen|perlfunc/sysopen>).
1168
1169=item floating point
1170
1171A method of storing numbers in "scientific notation", such that the
1172precision of the number is independent of its magnitude (the decimal
1173point "floats"). Perl does its numeric work with floating-point
1174numbers (sometimes called "floats"), when it can't get away with
27ed30b8 1175using L<integers|/integer>. Floating-point numbers are mere
97a1d740
YST
1176approximations of real numbers.
1177
1178=item flush
1179
27ed30b8 1180The act of emptying a L</buffer>, often before it's full.
97a1d740
YST
1181
1182=item FMTEYEWTK
1183
1184Far More Than Everything You Ever Wanted To Know. An exhaustive
27ed30b8 1185treatise on one narrow topic, something of a super-L</FAQ>. See Tom
97a1d740
YST
1186for far more.
1187
1188=item fork
1189
27ed30b8 1190To create a child L</process> identical to the parent process at its
97a1d740
YST
1191moment of conception, at least until it gets ideas of its own. A
1192thread with protected memory.
1193
1194=item formal arguments
1195
27ed30b8
YST
1196The generic names by which a L</subroutine> knows its
1197L<arguments|/argument>. In many languages, formal arguments are
97a1d740
YST
1198always given individual names, but in Perl, the formal arguments are
1199just the elements of an array. The formal arguments to a Perl program
1200are C<$ARGV[0]>, C<$ARGV[1]>, and so on. Similarly, the formal
1201arguments to a Perl subroutine are C<$_[0]>, C<$_[1]>, and so on. You
1202may give the arguments individual names by assigning the values to a
27ed30b8 1203L<my|perlfunc/my> list. See also L</actual arguments>.
97a1d740
YST
1204
1205=item format
1206
1207A specification of how many spaces and digits and things to put
1208somewhere so that whatever you're printing comes out nice and pretty.
1209
1210=item freely available
1211
1212Means you don't have to pay money to get it, but the copyright on it
1213may still belong to someone else (like Larry).
1214
1215=item freely redistributable
1216
1217Means you're not in legal trouble if you give a bootleg copy of it to
1218your friends and we find out about it. In fact, we'd rather you gave
1219a copy to all your friends.
1220
1221=item freeware
1222
1223Historically, any software that you give away, particularly if you
1224make the source code available as well. Now often called C<open
1225source software>. Recently there has been a trend to use the term in
27ed30b8 1226contradistinction to L</open source software>, to refer only to free
97a1d740
YST
1227software released under the Free Software Foundation's GPL (General
1228Public License), but this is difficult to justify etymologically.
1229
1230=item function
1231
1232Mathematically, a mapping of each of a set of input values to a
27ed30b8
YST
1233particular output value. In computers, refers to a L</subroutine> or
1234L</operator> that returns a L</value>. It may or may not have input
1235values (called L<arguments|/argument>).
97a1d740
YST
1236
1237=item funny character
1238
1239Someone like Larry, or one of his peculiar friends. Also refers to
1240the strange prefixes that Perl requires as noun markers on its
1241variables.
1242
043d1e6f
PA
1243=back
1244
1245=head2 G
1246
1247=over 4
1248
97a1d740
YST
1249=item garbage collection
1250
1251A misnamed feature--it should be called, "expecting your mother to
1252pick up after you". Strictly speaking, Perl doesn't do this, but it
1253relies on a reference-counting mechanism to keep things tidy.
1254However, we rarely speak strictly and will often refer to the
1255reference-counting scheme as a form of garbage collection. (If it's
1256any comfort, when your interpreter exits, a "real" garbage collector
1257runs to make sure everything is cleaned up if you've been messy with
1258circular references and such.)
1259
97a1d740
YST
1260=item GID
1261
27ed30b8
YST
1262Group ID--in Unix, the numeric group ID that the L</operating system>
1263uses to identify you and members of your L</group>.
97a1d740
YST
1264
1265=item glob
1266
1267Strictly, the shell's C<*> character, which will match a "glob" of
1268characters when you're trying to generate a list of filenames.
1269Loosely, the act of using globs and similar symbols to do pattern
27ed30b8 1270matching. See also L</fileglob> and L</typeglob>.
97a1d740
YST
1271
1272=item global
1273
1274Something you can see from anywhere, usually used of
27ed30b8 1275L<variables|/variable> and L<subroutines|/subroutine> that are visible
97a1d740
YST
1276everywhere in your program. In Perl, only certain special variables
1277are truly global--most variables (and all subroutines) exist only in
27ed30b8 1278the current L</package>. Global variables can be declared with
97a1d740
YST
1279L<our|perlfunc/our>. See L<perlfunc/our>.
1280
1281=item global destruction
1282
27ed30b8 1283The L</garbage collection> of globals (and the running of any
97a1d740 1284associated object destructors) that takes place when a Perl
27ed30b8 1285L</interpreter> is being shut down. Global destruction should not be
97a1d740
YST
1286confused with the Apocalypse, except perhaps when it should.
1287
1288=item glue language
1289
1290A language such as Perl that is good at hooking things together that
1291weren't intended to be hooked together.
1292
1293=item granularity
1294
1295The size of the pieces you're dealing with, mentally speaking.
1296
1297=item greedy
1298
27ed30b8 1299A L</subpattern> whose L</quantifier> wants to match as many things as
97a1d740
YST
1300possible.
1301
1302=item grep
1303
1304Originally from the old Unix editor command for "Globally search for a
1305Regular Expression and Print it", now used in the general sense of any
1306kind of search, especially text searches. Perl has a built-in
1307L<grep|perlfunc/grep> function that searches a list for elements
27ed30b8
YST
1308matching any given criterion, whereas the I<grep>(1) program searches
1309for lines matching a L</regular expression> in one or more files.
97a1d740
YST
1310
1311=item group
1312
1313A set of users of which you are a member. In some operating systems
1314(like Unix), you can give certain file access permissions to other
1315members of your group.
1316
1317=item GV
1318
27ed30b8
YST
1319An internal "glob value" typedef, holding a L</typeglob>. The L</GV>
1320type is a subclass of L</SV>.
97a1d740
YST
1321
1322=back
1323
5bbd0522
YST
1324=head2 H
1325
97a1d740
YST
1326=over 4
1327
1328=item hacker
1329
1330Someone who is brilliantly persistent in solving technical problems,
1331whether these involve golfing, fighting orcs, or programming. Hacker
1332is a neutral term, morally speaking. Good hackers are not to be
27ed30b8 1333confused with evil L<crackers|/cracker> or clueless L<script
97a1d740
YST
1334kiddies|/script kiddie>. If you confuse them, we will presume that
1335you are either evil or clueless.
1336
1337=item handler
1338
27ed30b8
YST
1339A L</subroutine> or L</method> that is called by Perl when your
1340program needs to respond to some internal event, such as a L</signal>,
1341or an encounter with an operator subject to L</operator overloading>.
1342See also L</callback>.
97a1d740
YST
1343
1344=item hard reference
1345
27ed30b8
YST
1346A L</scalar> L</value> containing the actual address of a
1347L</referent>, such that the referent's L</reference> count accounts
97a1d740 1348for it. (Some hard references are held internally, such as the
27ed30b8 1349implicit reference from one of a L</typeglob>'s variable slots to its
97a1d740 1350corresponding referent.) A hard reference is different from a
27ed30b8 1351L</symbolic reference>.
97a1d740
YST
1352
1353=item hash
1354
27ed30b8
YST
1355An unordered association of L</key>/L</value> pairs, stored such that
1356you can easily use a string L</key> to look up its associated data
1357L</value>. This glossary is like a hash, where the word to be defined
97a1d740
YST
1358is the key, and the definition is the value. A hash is also sometimes
1359septisyllabically called an "associative array", which is a pretty
1360good reason for simply calling it a "hash" instead.
1361
1362=item hash table
1363
1364A data structure used internally by Perl for implementing associative
27ed30b8 1365arrays (hashes) efficiently. See also L</bucket>.
97a1d740
YST
1366
1367=item header file
1368
1369A file containing certain required definitions that you must include
1370"ahead" of the rest of your program to do certain obscure operations.
1371A C header file has a I<.h> extension. Perl doesn't really have
1372header files, though historically Perl has sometimes used translated
1373I<.h> files with a I<.ph> extension. See L<perlfunc/require>.
27ed30b8 1374(Header files have been superseded by the L</module> mechanism.)
97a1d740
YST
1375
1376=item here document
1377
27ed30b8
YST
1378So called because of a similar construct in L<shells|/shell> that
1379pretends that the L<lines|/line> following the L</command> are a
1380separate L</file> to be fed to the command, up to some terminating
97a1d740
YST
1381string. In Perl, however, it's just a fancy form of quoting.
1382
1383=item hexadecimal
1384
1385A number in base 16, "hex" for short. The digits for 10 through 16
1386are customarily represented by the letters C<a> through C<f>.
1387Hexadecimal constants in Perl start with C<0x>. See also
27ed30b8 1388L<perlfunc/hex>.
97a1d740
YST
1389
1390=item home directory
1391
1392The directory you are put into when you log in. On a Unix system, the
1393name is often placed into C<$ENV{HOME}> or C<$ENV{LOGDIR}> by
1394I<login>, but you can also find it with C<(getpwuid($E<lt>))[7]>.
1395(Some platforms do not have a concept of a home directory.)
1396
1397=item host
1398
1399The computer on which a program or other data resides.
1400
1401=item hubris
1402
1403Excessive pride, the sort of thing Zeus zaps you for. Also the
1404quality that makes you write (and maintain) programs that other people
1405won't want to say bad things about. Hence, the third great virtue of
27ed30b8 1406a programmer. See also L</laziness> and L</impatience>.
97a1d740
YST
1407
1408=item HV
1409
1410Short for a "hash value" typedef, which holds Perl's internal
27ed30b8 1411representation of a hash. The L</HV> type is a subclass of L</SV>.
97a1d740
YST
1412
1413=back
1414
5bbd0522
YST
1415=head2 I
1416
97a1d740
YST
1417=over 4
1418
1419=item identifier
1420
1421A legally formed name for most anything in which a computer program
1422might be interested. Many languages (including Perl) allow
1423identifiers that start with a letter and contain letters and digits.
1424Perl also counts the underscore character as a valid letter. (Perl
27ed30b8 1425also has more complicated names, such as L</qualified> names.)
97a1d740
YST
1426
1427=item impatience
1428
1429The anger you feel when the computer is being lazy. This makes you
1430write programs that don't just react to your needs, but actually
1431anticipate them. Or at least that pretend to. Hence, the second
27ed30b8 1432great virtue of a programmer. See also L</laziness> and L</hubris>.
97a1d740
YST
1433
1434=item implementation
1435
1436How a piece of code actually goes about doing its job. Users of the
1437code should not count on implementation details staying the same
27ed30b8 1438unless they are part of the published L</interface>.
97a1d740
YST
1439
1440=item import
1441
1442To gain access to symbols that are exported from another module. See
1443L<perlfunc/use>.
1444
1445=item increment
1446
1447To increase the value of something by 1 (or by some other number, if
1448so specified).
1449
1450=item indexing
1451
27ed30b8 1452In olden days, the act of looking up a L</key> in an actual index
97a1d740 1453(such as a phone book), but now merely the act of using any kind of
27ed30b8 1454key or position to find the corresponding L</value>, even if no index
97a1d740
YST
1455is involved. Things have degenerated to the point that Perl's
1456L<index|perlfunc/index> function merely locates the position (index)
1457of one string in another.
1458
1459=item indirect filehandle
1460
27ed30b8
YST
1461An L</expression> that evaluates to something that can be used as a
1462L</filehandle>: a L</string> (filehandle name), a L</typeglob>, a
1463typeglob L</reference>, or a low-level L</IO> object.
97a1d740
YST
1464
1465=item indirect object
1466
1467In English grammar, a short noun phrase between a verb and its direct
1468object indicating the beneficiary or recipient of the action. In
1469Perl, C<print STDOUT "$foo\n";> can be understood as "verb
27ed30b8 1470indirect-object object" where L</STDOUT> is the recipient of the
97a1d740 1471L<print|perlfunc/print> action, and C<"$foo"> is the object being
27ed30b8 1472printed. Similarly, when invoking a L</method>, you might place the
c69ca1d4 1473invocand between the method and its arguments:
97a1d740
YST
1474
1475 $gollum = new Pathetic::Creature "Smeagol";
1476 give $gollum "Fisssssh!";
1477 give $gollum "Precious!";
1478
797f796a
RS
1479In modern Perl, calling methods this way is often considered bad practice and
1480to be avoided.
1481
97a1d740
YST
1482=item indirect object slot
1483
1484The syntactic position falling between a method call and its arguments
1485when using the indirect object invocation syntax. (The slot is
1486distinguished by the absence of a comma between it and the next
27ed30b8 1487argument.) L</STDERR> is in the indirect object slot here:
97a1d740
YST
1488
1489 print STDERR "Awake! Awake! Fear, Fire,
1490 Foes! Awake!\n";
1491
1492=item indirection
1493
1494If something in a program isn't the value you're looking for but
1495indicates where the value is, that's indirection. This can be done
27ed30b8 1496with either L<symbolic references|/symbolic reference> or L<hard
97a1d740
YST
1497references|/hard reference>.
1498
1499=item infix
1500
27ed30b8 1501An L</operator> that comes in between its L<operands|/operand>, such
97a1d740
YST
1502as multiplication in C<24 * 7>.
1503
1504=item inheritance
1505
1506What you get from your ancestors, genetically or otherwise. If you
27ed30b8 1507happen to be a L</class>, your ancestors are called L<base
97a1d740 1508classes|/base class> and your descendants are called L<derived
27ed30b8 1509classes|/derived class>. See L</single inheritance> and L</multiple
97a1d740
YST
1510inheritance>.
1511
1512=item instance
1513
27ed30b8 1514Short for "an instance of a class", meaning an L</object> of that L</class>.
97a1d740
YST
1515
1516=item instance variable
1517
27ed30b8 1518An L</attribute> of an L</object>; data stored with the particular
97a1d740
YST
1519object rather than with the class as a whole.
1520
1521=item integer
1522
1523A number with no fractional (decimal) part. A counting number, like
15241, 2, 3, and so on, but including 0 and the negatives.
1525
1526=item interface
1527
1528The services a piece of code promises to provide forever, in contrast to
27ed30b8 1529its L</implementation>, which it should feel free to change whenever it
97a1d740
YST
1530likes.
1531
1532=item interpolation
1533
1534The insertion of a scalar or list value somewhere in the middle of
1535another value, such that it appears to have been there all along. In
1536Perl, variable interpolation happens in double-quoted strings and
1537patterns, and list interpolation occurs when constructing the list of
1538values to pass to a list operator or other such construct that takes a
27ed30b8 1539L</LIST>.
97a1d740
YST
1540
1541=item interpreter
1542
1543Strictly speaking, a program that reads a second program and does what
1544the second program says directly without turning the program into a
27ed30b8 1545different form first, which is what L<compilers|/compiler> do. Perl
97a1d740
YST
1546is not an interpreter by this definition, because it contains a kind
1547of compiler that takes a program and turns it into a more executable
27ed30b8
YST
1548form (L<syntax trees|/syntax tree>) within the I<perl> process itself,
1549which the Perl L</run time> system then interprets.
97a1d740 1550
c69ca1d4 1551=item invocand
97a1d740 1552
27ed30b8 1553The agent on whose behalf a L</method> is invoked. In a L</class>
c69ca1d4
PAR
1554method, the invocand is a package name. In an L</instance> method,
1555the invocand is an object reference.
97a1d740
YST
1556
1557=item invocation
1558
1559The act of calling up a deity, daemon, program, method, subroutine, or
1560function to get it do what you think it's supposed to do. We usually
1561"call" subroutines but "invoke" methods, since it sounds cooler.
1562
1563=item I/O
1564
27ed30b8 1565Input from, or output to, a L</file> or L</device>.
97a1d740
YST
1566
1567=item IO
1568
27ed30b8 1569An internal I/O object. Can also mean L</indirect object>.
97a1d740
YST
1570
1571=item IP
1572
1573Internet Protocol, or Intellectual Property.
1574
1575=item IPC
1576
1577Interprocess Communication.
1578
1579=item is-a
1580
27ed30b8 1581A relationship between two L<objects|/object> in which one object is
97a1d740
YST
1582considered to be a more specific version of the other, generic object:
1583"A camel is a mammal." Since the generic object really only exists in
1584a Platonic sense, we usually add a little abstraction to the notion of
1585objects and think of the relationship as being between a generic
27ed30b8 1586L</base class> and a specific L</derived class>. Oddly enough,
97a1d740 1587Platonic classes don't always have Platonic relationships--see
27ed30b8 1588L</inheritance>.
97a1d740
YST
1589
1590=item iteration
1591
1592Doing something repeatedly.
1593
1594=item iterator
1595
1596A special programming gizmo that keeps track of where you are in
1597something that you're trying to iterate over. The C<foreach> loop in
1598Perl contains an iterator; so does a hash, allowing you to
1599L<each|perlfunc/each> through it.
1600
1601=item IV
1602
1603The integer four, not to be confused with six, Tom's favorite editor.
27ed30b8
YST
1604IV also means an internal Integer Value of the type a L</scalar> can
1605hold, not to be confused with an L</NV>.
97a1d740
YST
1606
1607=back
1608
5bbd0522
YST
1609=head2 J
1610
97a1d740
YST
1611=over 4
1612
1613=item JAPH
1614
1615"Just Another Perl Hacker," a clever but cryptic bit of Perl code that
1616when executed, evaluates to that string. Often used to illustrate a
353c6505 1617particular Perl feature, and something of an ongoing Obfuscated Perl
97a1d740
YST
1618Contest seen in Usenix signatures.
1619
1620=back
1621
5bbd0522
YST
1622=head2 K
1623
97a1d740
YST
1624=over 4
1625
1626=item key
1627
27ed30b8 1628The string index to a L</hash>, used to look up the L</value>
97a1d740
YST
1629associated with that key.
1630
1631=item keyword
1632
27ed30b8 1633See L</reserved words>.
97a1d740
YST
1634
1635=back
1636
5bbd0522
YST
1637=head2 L
1638
97a1d740
YST
1639=over 4
1640
1641=item label
1642
27ed30b8 1643A name you give to a L</statement> so that you can talk about that
97a1d740
YST
1644statement elsewhere in the program.
1645
1646=item laziness
1647
1648The quality that makes you go to great effort to reduce overall energy
1649expenditure. It makes you write labor-saving programs that other
1650people will find useful, and document what you wrote so you don't have
1651to answer so many questions about it. Hence, the first great virtue
27ed30b8
YST
1652of a programmer. Also hence, this book. See also L</impatience> and
1653L</hubris>.
97a1d740
YST
1654
1655=item left shift
1656
27ed30b8 1657A L</bit shift> that multiplies the number by some power of 2.
97a1d740
YST
1658
1659=item leftmost longest
1660
27ed30b8
YST
1661The preference of the L</regular expression> engine to match the
1662leftmost occurrence of a L</pattern>, then given a position at which a
97a1d740 1663match will occur, the preference for the longest match (presuming the
27ed30b8 1664use of a L</greedy> quantifier). See L<perlre> for I<much> more on
97a1d740
YST
1665this subject.
1666
1667=item lexeme
1668
27ed30b8 1669Fancy term for a L</token>.
97a1d740
YST
1670
1671=item lexer
1672
27ed30b8 1673Fancy term for a L</tokener>.
97a1d740
YST
1674
1675=item lexical analysis
1676
27ed30b8 1677Fancy term for L</tokenizing>.
97a1d740
YST
1678
1679=item lexical scoping
1680
1681Looking at your I<Oxford English Dictionary> through a microscope.
27ed30b8 1682(Also known as L</static scoping>, because dictionaries don't change
97a1d740
YST
1683very fast.) Similarly, looking at variables stored in a private
1684dictionary (namespace) for each scope, which are visible only from
1685their point of declaration down to the end of the lexical scope in
27ed30b8
YST
1686which they are declared. --Syn. L</static scoping>.
1687--Ant. L</dynamic scoping>.
97a1d740
YST
1688
1689=item lexical variable
1690
27ed30b8 1691A L</variable> subject to L</lexical scoping>, declared by
97a1d740
YST
1692L<my|perlfunc/my>. Often just called a "lexical". (The
1693L<our|perlfunc/our> declaration declares a lexically scoped name for a
1694global variable, which is not itself a lexical variable.)
1695
1696=item library
1697
1698Generally, a collection of procedures. In ancient days, referred to a
1699collection of subroutines in a I<.pl> file. In modern times, refers
27ed30b8 1700more often to the entire collection of Perl L<modules|/module> on your
97a1d740
YST
1701system.
1702
1703=item LIFO
1704
27ed30b8
YST
1705Last In, First Out. See also L</FIFO>. A LIFO is usually called a
1706L</stack>.
97a1d740
YST
1707
1708=item line
1709
1710In Unix, a sequence of zero or more non-newline characters terminated
27ed30b8
YST
1711with a L</newline> character. On non-Unix machines, this is emulated
1712by the C library even if the underlying L</operating system> has
97a1d740
YST
1713different ideas.
1714
1715=item line buffering
1716
27ed30b8
YST
1717Used by a L</standard IE<sol>O> output stream that flushes its
1718L</buffer> after every L</newline>. Many standard I/O libraries
97a1d740
YST
1719automatically set up line buffering on output that is going to the
1720terminal.
1721
1722=item line number
1723
1724The number of lines read previous to this one, plus 1. Perl keeps a
1725separate line number for each source or input file it opens. The
1726current source file's line number is represented by C<__LINE__>. The
1727current input line number (for the file that was most recently read
27ed30b8 1728via C<< E<lt>FHE<gt> >>) is represented by the C<$.>
97a1d740
YST
1729(C<$INPUT_LINE_NUMBER>) variable. Many error messages report both
1730values, if available.
1731
1732=item link
1733
27ed30b8 1734Used as a noun, a name in a L</directory>, representing a L</file>. A
97a1d740
YST
1735given file can have multiple links to it. It's like having the same
1736phone number listed in the phone directory under different names. As
1737a verb, to resolve a partially compiled file's unresolved symbols into
1738a (nearly) executable image. Linking can generally be static or
1739dynamic, which has nothing to do with static or dynamic scoping.
1740
1741=item LIST
1742
1743A syntactic construct representing a comma-separated list of
27ed30b8
YST
1744expressions, evaluated to produce a L</list value>. Each
1745L</expression> in a L</LIST> is evaluated in L</list context> and
97a1d740
YST
1746interpolated into the list value.
1747
1748=item list
1749
1750An ordered set of scalar values.
1751
1752=item list context
1753
27ed30b8 1754The situation in which an L</expression> is expected by its
97a1d740 1755surroundings (the code calling it) to return a list of values rather
27ed30b8 1756than a single value. Functions that want a L</LIST> of arguments tell
97a1d740 1757those arguments that they should produce a list value. See also
27ed30b8 1758L</context>.
97a1d740
YST
1759
1760=item list operator
1761
27ed30b8 1762An L</operator> that does something with a list of values, such as
97a1d740
YST
1763L<join|perlfunc/join> or L<grep|perlfunc/grep>. Usually used for
1764named built-in operators (such as L<print|perlfunc/print>,
1765L<unlink|perlfunc/unlink>, and L<system|perlfunc/system>) that do not
27ed30b8 1766require parentheses around their L</argument> list.
97a1d740
YST
1767
1768=item list value
1769
1770An unnamed list of temporary scalar values that may be passed around
1771within a program from any list-generating function to any function or
27ed30b8 1772construct that provides a L</list context>.
97a1d740
YST
1773
1774=item literal
1775
27ed30b8
YST
1776A token in a programming language such as a number or L</string> that
1777gives you an actual L</value> instead of merely representing possible
1778values as a L</variable> does.
97a1d740
YST
1779
1780=item little-endian
1781
1782From Swift: someone who eats eggs little end first. Also used of
27ed30b8 1783computers that store the least significant L</byte> of a word at a
97a1d740 1784lower byte address than the most significant byte. Often considered
27ed30b8 1785superior to big-endian machines. See also L</big-endian>.
97a1d740
YST
1786
1787=item local
1788
1789Not meaning the same thing everywhere. A global variable in Perl can
1790be localized inside a L<dynamic scope|/dynamic scoping> via the
1791L<local|perlfunc/local> operator.
1792
1793=item logical operator
1794
1795Symbols representing the concepts "and", "or", "xor", and "not".
1796
1797=item lookahead
1798
27ed30b8 1799An L</assertion> that peeks at the string to the right of the current
97a1d740
YST
1800match location.
1801
1802=item lookbehind
1803
27ed30b8 1804An L</assertion> that peeks at the string to the left of the current
97a1d740
YST
1805match location.
1806
1807=item loop
1808
1809A construct that performs something repeatedly, like a roller coaster.
1810
1811=item loop control statement
1812
1813Any statement within the body of a loop that can make a loop
27ed30b8 1814prematurely stop looping or skip an L</iteration>. Generally you
97a1d740
YST
1815shouldn't try this on roller coasters.
1816
1817=item loop label
1818
1819A kind of key or name attached to a loop (or roller coaster) so that
1820loop control statements can talk about which loop they want to
1821control.
1822
1823=item lvaluable
1824
27ed30b8 1825Able to serve as an L</lvalue>.
97a1d740
YST
1826
1827=item lvalue
1828
1829Term used by language lawyers for a storage location you can assign a
27ed30b8
YST
1830new L</value> to, such as a L</variable> or an element of an
1831L</array>. The "l" is short for "left", as in the left side of an
1832assignment, a typical place for lvalues. An L</lvaluable> function or
97a1d740
YST
1833expression is one to which a value may be assigned, as in C<pos($x) =
183410>.
1835
1836=item lvalue modifier
1837
27ed30b8 1838An adjectival pseudofunction that warps the meaning of an L</lvalue>
97a1d740
YST
1839in some declarative fashion. Currently there are three lvalue
1840modifiers: L<my|perlfunc/my>, L<our|perlfunc/our>, and
1841L<local|perlfunc/local>.
1842
1843=back
1844
5bbd0522
YST
1845=head2 M
1846
97a1d740
YST
1847=over 4
1848
1849=item magic
1850
1851Technically speaking, any extra semantics attached to a variable such
1852as C<$!>, C<$0>, C<%ENV>, or C<%SIG>, or to any tied variable.
1853Magical things happen when you diddle those variables.
1854
1855=item magical increment
1856
27ed30b8 1857An L</increment> operator that knows how to bump up alphabetics as
97a1d740
YST
1858well as numbers.
1859
1860=item magical variables
1861
1862Special variables that have side effects when you access them or
1863assign to them. For example, in Perl, changing elements of the
1864C<%ENV> array also changes the corresponding environment variables
1865that subprocesses will use. Reading the C<$!> variable gives you the
1866current system error number or message.
1867
1868=item Makefile
1869
1870A file that controls the compilation of a program. Perl programs
27ed30b8 1871don't usually need a L</Makefile> because the Perl compiler has plenty
97a1d740
YST
1872of self-control.
1873
1874=item man
1875
1876The Unix program that displays online documentation (manual pages) for
1877you.
1878
1879=item manpage
1880
27ed30b8 1881A "page" from the manuals, typically accessed via the I<man>(1)
97a1d740
YST
1882command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of
1883BUGS, and so on, and is typically longer than a page. There are
27ed30b8
YST
1884manpages documenting L<commands|/command>, L<syscalls|/syscall>,
1885L</library> L<functions|/function>, L<devices|/device>,
1886L<protocols|/protocol>, L<files|/file>, and such. In this book, we
97a1d740
YST
1887call any piece of standard Perl documentation (like I<perlop> or
1888I<perldelta>) a manpage, no matter what format it's installed in on
1889your system.
1890
1891=item matching
1892
27ed30b8 1893See L</pattern matching>.
97a1d740
YST
1894
1895=item member data
1896
27ed30b8 1897See L</instance variable>.
97a1d740
YST
1898
1899=item memory
1900
1901This always means your main memory, not your disk. Clouding the issue
27ed30b8 1902is the fact that your machine may implement L</virtual> memory; that
97a1d740
YST
1903is, it will pretend that it has more memory than it really does, and
1904it'll use disk space to hold inactive bits. This can make it seem
1905like you have a little more memory than you really do, but it's not a
1906substitute for real memory. The best thing that can be said about
1907virtual memory is that it lets your performance degrade gradually
1908rather than suddenly when you run out of real memory. But your
1909program can die when you run out of virtual memory too, if you haven't
1910thrashed your disk to death first.
1911
1912=item metacharacter
1913
27ed30b8 1914A L</character> that is I<not> supposed to be treated normally. Which
97a1d740 1915characters are to be treated specially as metacharacters varies
27ed30b8
YST
1916greatly from context to context. Your L</shell> will have certain
1917metacharacters, double-quoted Perl L<strings|/string> have other
1918metacharacters, and L</regular expression> patterns have all the
97a1d740
YST
1919double-quote metacharacters plus some extra ones of their own.
1920
1921=item metasymbol
1922
27ed30b8 1923Something we'd call a L</metacharacter> except that it's a sequence of
97a1d740
YST
1924more than one character. Generally, the first character in the
1925sequence must be a true metacharacter to get the other characters in
1926the metasymbol to misbehave along with it.
1927
1928=item method
1929
27ed30b8 1930A kind of action that an L</object> can take if you tell it to. See
97a1d740
YST
1931L<perlobj>.
1932
1933=item minimalism
1934
1935The belief that "small is beautiful." Paradoxically, if you say
1936something in a small language, it turns out big, and if you say it in
1937a big language, it turns out small. Go figure.
1938
1939=item mode
1940
dfcceb59 1941In the context of the L<stat(2)> syscall, refers to the field holding
27ed30b8 1942the L</permission bits> and the type of the L</file>.
97a1d740
YST
1943
1944=item modifier
1945
27ed30b8
YST
1946See L</statement modifier>, L</regular expression modifier>, and
1947L</lvalue modifier>, not necessarily in that order.
97a1d740
YST
1948
1949=item module
1950
27ed30b8
YST
1951A L</file> that defines a L</package> of (almost) the same name, which
1952can either L</export> symbols or function as an L</object> class. (A
97a1d740
YST
1953module's main I<.pm> file may also load in other files in support of
1954the module.) See the L<use|perlfunc/use> built-in.
1955
1956=item modulus
1957
1958An integer divisor when you're interested in the remainder instead of
1959the quotient.
1960
1961=item monger
1962
1963Short for Perl Monger, a purveyor of Perl.
1964
1965=item mortal
1966
1967A temporary value scheduled to die when the current statement
1968finishes.
1969
1970=item multidimensional array
1971
1972An array with multiple subscripts for finding a single element. Perl
27ed30b8 1973implements these using L<references|/reference>--see L<perllol> and
97a1d740
YST
1974L<perldsc>.
1975
1976=item multiple inheritance
1977
1978The features you got from your mother and father, mixed together
27ed30b8 1979unpredictably. (See also L</inheritance>, and L</single
97a1d740
YST
1980inheritance>.) In computer languages (including Perl), the notion
1981that a given class may have multiple direct ancestors or L<base
1982classes|/base class>.
1983
1984=back
1985
5bbd0522
YST
1986=head2 N
1987
97a1d740
YST
1988=over 4
1989
1990=item named pipe
1991
27ed30b8
YST
1992A L</pipe> with a name embedded in the L</filesystem> so that it can
1993be accessed by two unrelated L<processes|/process>.
97a1d740
YST
1994
1995=item namespace
1996
1997A domain of names. You needn't worry about whether the names in one
27ed30b8 1998such domain have been used in another. See L</package>.
97a1d740
YST
1999
2000=item network address
2001
2002The most important attribute of a socket, like your telephone's
27ed30b8 2003telephone number. Typically an IP address. See also L</port>.
97a1d740
YST
2004
2005=item newline
2006
2007A single character that represents the end of a line, with the ASCII
2008value of 012 octal under Unix (but 015 on a Mac), and represented by
2009C<\n> in Perl strings. For Windows machines writing text files, and
2010for certain physical devices like terminals, the single newline gets
2011automatically translated by your C library into a line feed and a
2012carriage return, but normally, no translation is done.
2013
2014=item NFS
2015
2016Network File System, which allows you to mount a remote filesystem as
2017if it were local.
2018
2019=item null character
2020
2021A character with the ASCII value of zero. It's used by C to terminate
2022strings, but Perl allows strings to contain a null.
2023
2024=item null list
2025
27ed30b8 2026A L</list value> with zero elements, represented in Perl by C<()>.
97a1d740
YST
2027
2028=item null string
2029
27ed30b8
YST
2030A L</string> containing no characters, not to be confused with a
2031string containing a L</null character>, which has a positive length
2032and is L</true>.
97a1d740
YST
2033
2034=item numeric context
2035
2036The situation in which an expression is expected by its surroundings
27ed30b8
YST
2037(the code calling it) to return a number. See also L</context> and
2038L</string context>.
97a1d740
YST
2039
2040=item NV
2041
2042Short for Nevada, no part of which will ever be confused with
2043civilization. NV also means an internal floating-point Numeric Value
27ed30b8 2044of the type a L</scalar> can hold, not to be confused with an L</IV>.
97a1d740
YST
2045
2046=item nybble
2047
27ed30b8
YST
2048Half a L</byte>, equivalent to one L</hexadecimal> digit, and worth
2049four L<bits|/bit>.
97a1d740
YST
2050
2051=back
2052
5bbd0522
YST
2053=head2 O
2054
97a1d740
YST
2055=over 4
2056
2057=item object
2058
27ed30b8 2059An L</instance> of a L</class>. Something that "knows" what
97a1d740
YST
2060user-defined type (class) it is, and what it can do because of what
2061class it is. Your program can request an object to do things, but the
2062object gets to decide whether it wants to do them or not. Some
2063objects are more accommodating than others.
2064
2065=item octal
2066
2067A number in base 8. Only the digits 0 through 7 are allowed. Octal
2068constants in Perl start with 0, as in 013. See also the
2069L<oct|perlfunc/oct> function.
2070
2071=item offset
2072
2073How many things you have to skip over when moving from the beginning
2074of a string or array to a specific position within it. Thus, the
2075minimum offset is zero, not one, because you don't skip anything to
2076get to the first item.
2077
2078=item one-liner
2079
2080An entire computer program crammed into one line of text.
2081
2082=item open source software
2083
2084Programs for which the source code is freely available and freely
2085redistributable, with no commercial strings attached. For a more
2086detailed definition, see L<http://www.opensource.org/osd.html>.
2087
2088=item operand
2089
27ed30b8
YST
2090An L</expression> that yields a L</value> that an L</operator>
2091operates on. See also L</precedence>.
97a1d740
YST
2092
2093=item operating system
2094
2095A special program that runs on the bare machine and hides the gory
27ed30b8 2096details of managing L<processes|/process> and L<devices|/device>.
97a1d740
YST
2097Usually used in a looser sense to indicate a particular culture of
2098programming. The loose sense can be used at varying levels of
2099specificity. At one extreme, you might say that all versions of Unix
2100and Unix-lookalikes are the same operating system (upsetting many
2101people, especially lawyers and other advocates). At the other
2102extreme, you could say this particular version of this particular
2103vendor's operating system is different from any other version of this
2104or any other vendor's operating system. Perl is much more portable
2105across operating systems than many other languages. See also
27ed30b8 2106L</architecture> and L</platform>.
97a1d740
YST
2107
2108=item operator
2109
2110A gizmo that transforms some number of input values to some number of
2111output values, often built into a language with a special syntax or
2112symbol. A given operator may have specific expectations about what
27ed30b8
YST
2113L<types|/type> of data you give as its arguments
2114(L<operands|/operand>) and what type of data you want back from it.
97a1d740
YST
2115
2116=item operator overloading
2117
27ed30b8
YST
2118A kind of L</overloading> that you can do on built-in
2119L<operators|/operator> to make them work on L<objects|/object> as if
97a1d740
YST
2120the objects were ordinary scalar values, but with the actual semantics
2121supplied by the object class. This is set up with the L<overload>
27ed30b8 2122L</pragma>.
97a1d740
YST
2123
2124=item options
2125
27ed30b8 2126See either L<switches|/switch> or L</regular expression modifier>.
97a1d740 2127
1ab74a36
KW
2128=item ordinal
2129
2130Another name for L</code point>
2131
97a1d740
YST
2132=item overloading
2133
2134Giving additional meanings to a symbol or construct. Actually, all
2135languages do overloading to one extent or another, since people are
27ed30b8 2136good at figuring out things from L</context>.
97a1d740
YST
2137
2138=item overriding
2139
2140Hiding or invalidating some other definition of the same name. (Not
27ed30b8 2141to be confused with L</overloading>, which adds definitions that must
97a1d740
YST
2142be disambiguated some other way.) To confuse the issue further, we use
2143the word with two overloaded definitions: to describe how you can
27ed30b8 2144define your own L</subroutine> to hide a built-in L</function> of the
97a1d740 2145same name (see L<perlsub/Overriding Built-in Functions>) and to
27ed30b8
YST
2146describe how you can define a replacement L</method> in a L</derived
2147class> to hide a L</base class>'s method of the same name (see
97a1d740
YST
2148L<perlobj>).
2149
2150=item owner
2151
2152The one user (apart from the superuser) who has absolute control over
27ed30b8 2153a L</file>. A file may also have a L</group> of users who may
97a1d740 2154exercise joint ownership if the real owner permits it. See
27ed30b8 2155L</permission bits>.
97a1d740
YST
2156
2157=back
2158
5bbd0522
YST
2159=head2 P
2160
97a1d740
YST
2161=over 4
2162
2163=item package
2164
27ed30b8
YST
2165A L</namespace> for global L<variables|/variable>,
2166L<subroutines|/subroutine>, and the like, such that they can be kept
2167separate from like-named L<symbols|/symbol> in other namespaces. In a
97a1d740
YST
2168sense, only the package is global, since the symbols in the package's
2169symbol table are only accessible from code compiled outside the
2170package by naming the package. But in another sense, all package
2171symbols are also globals--they're just well-organized globals.
2172
2173=item pad
2174
27ed30b8 2175Short for L</scratchpad>.
97a1d740
YST
2176
2177=item parameter
2178
27ed30b8 2179See L</argument>.
97a1d740
YST
2180
2181=item parent class
2182
27ed30b8 2183See L</base class>.
97a1d740
YST
2184
2185=item parse tree
2186
27ed30b8 2187See L</syntax tree>.
97a1d740
YST
2188
2189=item parsing
2190
2191The subtle but sometimes brutal art of attempting to turn your
27ed30b8 2192possibly malformed program into a valid L</syntax tree>.
97a1d740
YST
2193
2194=item patch
2195
2196To fix by applying one, as it were. In the realm of hackerdom, a
2197listing of the differences between two versions of a program as might
27ed30b8 2198be applied by the I<patch>(1) program when you want to fix a bug or
97a1d740
YST
2199upgrade your old version.
2200
2201=item PATH
2202
2203The list of L<directories|/directory> the system searches to find a
27ed30b8
YST
2204program you want to L</execute>. The list is stored as one of your
2205L<environment variables|/environment variable>, accessible in Perl as
97a1d740
YST
2206C<$ENV{PATH}>.
2207
2208=item pathname
2209
2210A fully qualified filename such as I</usr/bin/perl>. Sometimes
27ed30b8 2211confused with L</PATH>.
97a1d740
YST
2212
2213=item pattern
2214
27ed30b8 2215A template used in L</pattern matching>.
97a1d740
YST
2216
2217=item pattern matching
2218
27ed30b8 2219Taking a pattern, usually a L</regular expression>, and trying the
97a1d740
YST
2220pattern various ways on a string to see whether there's any way to
2221make it fit. Often used to pick interesting tidbits out of a file.
2222
2223=item permission bits
2224
27ed30b8
YST
2225Bits that the L</owner> of a file sets or unsets to allow or disallow
2226access to other people. These flag bits are part of the L</mode> word
97a1d740
YST
2227returned by the L<stat|perlfunc/stat> built-in when you ask about a
2228file. On Unix systems, you can check the I<ls>(1) manpage for more
2229information.
2230
2231=item Pern
2232
2233What you get when you do C<Perl++> twice. Doing it only once will
2234curl your hair. You have to increment it eight times to shampoo your
2235hair. Lather, rinse, iterate.
2236
2237=item pipe
2238
27ed30b8 2239A direct L</connection> that carries the output of one L</process> to
97a1d740
YST
2240the input of another without an intermediate temporary file. Once the
2241pipe is set up, the two processes in question can read and write as if
2242they were talking to a normal file, with some caveats.
2243
2244=item pipeline
2245
27ed30b8
YST
2246A series of L<processes|/process> all in a row, linked by
2247L<pipes|/pipe>, where each passes its output stream to the next.
97a1d740
YST
2248
2249=item platform
2250
2251The entire hardware and software context in which a program runs. A
2252 program written in a platform-dependent language might break if you
2253change any of: machine, operating system, libraries, compiler, or
2254system configuration. The I<perl> interpreter has to be compiled
2255differently for each platform because it is implemented in C, but
2256programs written in the Perl language are largely
2257platform-independent.
2258
2259=item pod
2260
2261The markup used to embed documentation into your Perl code. See
2262L<perlpod>.
2263
2264=item pointer
2265
27ed30b8 2266A L</variable> in a language like C that contains the exact memory
97a1d740
YST
2267location of some other item. Perl handles pointers internally so you
2268don't have to worry about them. Instead, you just use symbolic
27ed30b8 2269pointers in the form of L<keys|/key> and L</variable> names, or L<hard
97a1d740
YST
2270references|/hard reference>, which aren't pointers (but act like
2271pointers and do in fact contain pointers).
2272
2273=item polymorphism
2274
27ed30b8 2275The notion that you can tell an L</object> to do something generic,
97a1d740
YST
2276and the object will interpret the command in different ways depending
2277on its type. [E<lt>Gk many shapes]
2278
2279=item port
2280
2281The part of the address of a TCP or UDP socket that directs packets to
2282the correct process after finding the right machine, something like
2283the phone extension you give when you reach the company operator.
2284Also, the result of converting code to run on a different platform
2285than originally intended, or the verb denoting this conversion.
2286
2287=item portable
2288
2289Once upon a time, C code compilable under both BSD and SysV. In
2290general, code that can be easily converted to run on another
27ed30b8 2291L</platform>, where "easily" can be defined however you like, and
97a1d740
YST
2292usually is. Anything may be considered portable if you try hard
2293enough. See I<mobile home> or I<London Bridge>.
2294
2295=item porter
2296
27ed30b8 2297Someone who "carries" software from one L</platform> to another.
97a1d740
YST
2298Porting programs written in platform-dependent languages such as C can
2299be difficult work, but porting programs like Perl is very much worth
2300the agony.
2301
2302=item POSIX
2303
2304The Portable Operating System Interface specification.
2305
2306=item postfix
2307
27ed30b8 2308An L</operator> that follows its L</operand>, as in C<$x++>.
97a1d740
YST
2309
2310=item pp
2311
2312An internal shorthand for a "push-pop" code, that is, C code
2313implementing Perl's stack machine.
2314
2315=item pragma
2316
2317A standard module whose practical hints and suggestions are received
2318(and possibly ignored) at compile time. Pragmas are named in all
2319lowercase.
2320
2321=item precedence
2322
2323The rules of conduct that, in the absence of other guidance, determine
2324what should happen first. For example, in the absence of parentheses,
2325you always do multiplication before addition.
2326
2327=item prefix
2328
27ed30b8 2329An L</operator> that precedes its L</operand>, as in C<++$x>.
97a1d740
YST
2330
2331=item preprocessing
2332
27ed30b8 2333What some helper L</process> did to transform the incoming data into a
97a1d740 2334form more suitable for the current process. Often done with an
27ed30b8 2335incoming L</pipe>. See also L</C preprocessor>.
97a1d740
YST
2336
2337=item procedure
2338
27ed30b8 2339A L</subroutine>.
97a1d740
YST
2340
2341=item process
2342
2343An instance of a running program. Under multitasking systems like
2344Unix, two or more separate processes could be running the same program
2345independently at the same time--in fact, the L<fork|perlfunc/fork>
2346function is designed to bring about this happy state of affairs.
2347Under other operating systems, processes are sometimes called
2348"threads", "tasks", or "jobs", often with slight nuances in meaning.
2349
2350=item program generator
2351
2352A system that algorithmically writes code for you in a high-level
27ed30b8 2353language. See also L</code generator>.
97a1d740
YST
2354
2355=item progressive matching
2356
27ed30b8 2357L<Pattern matching|/pattern matching> that picks up where it left off before.
97a1d740
YST
2358
2359=item property
2360
27ed30b8 2361See either L</instance variable> or L</character property>.
97a1d740
YST
2362
2363=item protocol
2364
2365In networking, an agreed-upon way of sending messages back and forth
2366so that neither correspondent will get too confused.
2367
2368=item prototype
2369
27ed30b8 2370An optional part of a L</subroutine> declaration telling the Perl
97a1d740 2371compiler how many and what flavor of arguments may be passed as
27ed30b8 2372L</actual arguments>, so that you can write subroutine calls that
97a1d740
YST
2373parse much like built-in functions. (Or don't parse, as the case may
2374be.)
2375
2376=item pseudofunction
2377
2378A construct that sometimes looks like a function but really isn't.
27ed30b8
YST
2379Usually reserved for L</lvalue> modifiers like L<my|perlfunc/my>, for
2380L</context> modifiers like L<scalar|perlfunc/scalar>, and for the
97a1d740
YST
2381pick-your-own-quotes constructs, C<q//>, C<qq//>, C<qx//>, C<qw//>,
2382C<qr//>, C<m//>, C<s///>, C<y///>, and C<tr///>.
2383
2384=item pseudohash
2385
2386A reference to an array whose initial element happens to hold a
2387reference to a hash. You can treat a pseudohash reference as either
2388an array reference or a hash reference.
2389
2390=item pseudoliteral
2391
27ed30b8
YST
2392An L</operator> that looks something like a L</literal>, such as the
2393output-grabbing operator, C<`>I<C<command>>C<`>.
97a1d740
YST
2394
2395=item public domain
2396
2397Something not owned by anybody. Perl is copyrighted and is thus
27ed30b8
YST
2398I<not> in the public domain--it's just L</freely available> and
2399L</freely redistributable>.
97a1d740
YST
2400
2401=item pumpkin
2402
2403A notional "baton" handed around the Perl community indicating who is
2404the lead integrator in some arena of development.
2405
2406=item pumpking
2407
27ed30b8 2408A L</pumpkin> holder, the person in charge of pumping the pump, or at
97a1d740
YST
2409least priming it. Must be willing to play the part of the Great
2410Pumpkin now and then.
2411
2412=item PV
2413
2414A "pointer value", which is Perl Internals Talk for a C<char*>.
2415
2416=back
2417
5bbd0522
YST
2418=head2 Q
2419
97a1d740
YST
2420=over 4
2421
2422=item qualified
2423
2424Possessing a complete name. The symbol C<$Ent::moot> is qualified;
2425C<$moot> is unqualified. A fully qualified filename is specified from
2426the top-level directory.
2427
2428=item quantifier
2429
27ed30b8
YST
2430A component of a L</regular expression> specifying how many times the
2431foregoing L</atom> may occur.
97a1d740
YST
2432
2433=back
2434
5bbd0522
YST
2435=head2 R
2436
97a1d740
YST
2437=over 4
2438
2439=item readable
2440
2441With respect to files, one that has the proper permission bit set to
2442let you access the file. With respect to computer programs, one
2443that's written well enough that someone has a chance of figuring out
2444what it's trying to do.
2445
2446=item reaping
2447
27ed30b8
YST
2448The last rites performed by a parent L</process> on behalf of a
2449deceased child process so that it doesn't remain a L</zombie>. See
97a1d740
YST
2450the L<wait|perlfunc/wait> and L<waitpid|perlfunc/waitpid> function
2451calls.
2452
2453=item record
2454
27ed30b8
YST
2455A set of related data values in a L</file> or L</stream>, often
2456associated with a unique L</key> field. In Unix, often commensurate
2457with a L</line>, or a blank-line-terminated set of lines (a
97a1d740
YST
2458"paragraph"). Each line of the I</etc/passwd> file is a record, keyed
2459on login name, containing information about that user.
2460
2461=item recursion
2462
2463The art of defining something (at least partly) in terms of itself,
2464which is a naughty no-no in dictionaries but often works out okay in
2465computer programs if you're careful not to recurse forever, which is
2466like an infinite loop with more spectacular failure modes.
2467
2468=item reference
2469
2470Where you look to find a pointer to information somewhere else. (See
27ed30b8 2471L</indirection>.) References come in two flavors, L<symbolic
97a1d740
YST
2472references|/symbolic reference> and L<hard references|/hard
2473reference>.
2474
2475=item referent
2476
2477Whatever a reference refers to, which may or may not have a name.
2478Common types of referents include scalars, arrays, hashes, and
2479subroutines.
2480
2481=item regex
2482
27ed30b8 2483See L</regular expression>.
97a1d740
YST
2484
2485=item regular expression
2486
2487A single entity with various interpretations, like an elephant. To a
2488computer scientist, it's a grammar for a little language in which some
2489strings are legal and others aren't. To normal people, it's a pattern
2490you can use to find what you're looking for when it varies from case
2491to case. Perl's regular expressions are far from regular in the
2492theoretical sense, but in regular use they work quite well. Here's a
2493regular expression: C</Oh s.*t./>. This will match strings like "C<Oh
2494say can you see by the dawn's early light>" and "C<Oh sit!>". See
2495L<perlre>.
2496
2497=item regular expression modifier
2498
2499An option on a pattern or substitution, such as C</i> to render the
27ed30b8 2500pattern case insensitive. See also L</cloister>.
97a1d740
YST
2501
2502=item regular file
2503
27ed30b8
YST
2504A L</file> that's not a L</directory>, a L</device>, a named L</pipe>
2505or L</socket>, or a L</symbolic link>. Perl uses the C<-f> file test
97a1d740
YST
2506operator to identify regular files. Sometimes called a "plain" file.
2507
2508=item relational operator
2509
27ed30b8
YST
2510An L</operator> that says whether a particular ordering relationship
2511is L</true> about a pair of L<operands|/operand>. Perl has both
2512numeric and string relational operators. See L</collating sequence>.
97a1d740
YST
2513
2514=item reserved words
2515
27ed30b8 2516A word with a specific, built-in meaning to a L</compiler>, such as
97a1d740
YST
2517C<if> or L<delete|perlfunc/delete>. In many languages (not Perl),
2518it's illegal to use reserved words to name anything else. (Which is
2519why they're reserved, after all.) In Perl, you just can't use them to
27ed30b8 2520name L<labels|/label> or L<filehandles|/filehandle>. Also called
97a1d740
YST
2521"keywords".
2522
2523=item return value
2524
27ed30b8
YST
2525The L</value> produced by a L</subroutine> or L</expression> when
2526evaluated. In Perl, a return value may be either a L</list> or a
2527L</scalar>.
97a1d740
YST
2528
2529=item RFC
2530
2531Request For Comment, which despite the timid connotations is the name
2532of a series of important standards documents.
2533
2534=item right shift
2535
27ed30b8 2536A L</bit shift> that divides a number by some power of 2.
97a1d740
YST
2537
2538=item root
2539
2540The superuser (UID == 0). Also, the top-level directory of the
2541filesystem.
2542
2543=item RTFM
2544
2545What you are told when someone thinks you should Read The Fine Manual.
2546
2547=item run phase
2548
2549Any time after Perl starts running your main program. See also
27ed30b8
YST
2550L</compile phase>. Run phase is mostly spent in L</run time> but may
2551also be spent in L</compile time> when L<require|perlfunc/require>,
97a1d740
YST
2552L<do|perlfunc/do> C<FILE>, or L<eval|perlfunc/eval> C<STRING>
2553operators are executed or when a substitution uses the C</ee>
2554modifier.
2555
2556=item run time
2557
2558The time when Perl is actually doing what your code says to do, as
2559opposed to the earlier period of time when it was trying to figure out
27ed30b8 2560whether what you said made any sense whatsoever, which is L</compile
97a1d740
YST
2561time>.
2562
2563=item run-time pattern
2564
2565A pattern that contains one or more variables to be interpolated
27ed30b8 2566before parsing the pattern as a L</regular expression>, and that
97a1d740
YST
2567therefore cannot be analyzed at compile time, but must be re-analyzed
2568each time the pattern match operator is evaluated. Run-time patterns
2569are useful but expensive.
2570
2571=item RV
2572
2573A recreational vehicle, not to be confused with vehicular recreation.
27ed30b8
YST
2574RV also means an internal Reference Value of the type a L</scalar> can
2575hold. See also L</IV> and L</NV> if you're not confused yet.
97a1d740
YST
2576
2577=item rvalue
2578
27ed30b8
YST
2579A L</value> that you might find on the right side of an
2580L</assignment>. See also L</lvalue>.
97a1d740
YST
2581
2582=back
2583
5bbd0522
YST
2584=head2 S
2585
97a1d740
YST
2586=over 4
2587
2588=item scalar
2589
27ed30b8 2590A simple, singular value; a number, L</string>, or L</reference>.
97a1d740
YST
2591
2592=item scalar context
2593
27ed30b8
YST
2594The situation in which an L</expression> is expected by its
2595surroundings (the code calling it) to return a single L</value> rather
2596than a L</list> of values. See also L</context> and L</list context>.
97a1d740 2597A scalar context sometimes imposes additional constraints on the
27ed30b8
YST
2598return value--see L</string context> and L</numeric context>.
2599Sometimes we talk about a L</Boolean context> inside conditionals, but
97a1d740 2600this imposes no additional constraints, since any scalar value,
27ed30b8 2601whether numeric or L</string>, is already true or false.
97a1d740
YST
2602
2603=item scalar literal
2604
27ed30b8
YST
2605A number or quoted L</string>--an actual L</value> in the text of your
2606program, as opposed to a L</variable>.
97a1d740
YST
2607
2608=item scalar value
2609
27ed30b8 2610A value that happens to be a L</scalar> as opposed to a L</list>.
97a1d740
YST
2611
2612=item scalar variable
2613
27ed30b8 2614A L</variable> prefixed with C<$> that holds a single value.
97a1d740
YST
2615
2616=item scope
2617
2618How far away you can see a variable from, looking through one. Perl
27ed30b8
YST
2619has two visibility mechanisms: it does L</dynamic scoping> of
2620L<local|perlfunc/local> L<variables|/variable>, meaning that the rest
2621of the L</block>, and any L<subroutines|/subroutine> that are called
97a1d740 2622by the rest of the block, can see the variables that are local to the
27ed30b8 2623block. Perl does L</lexical scoping> of L<my|perlfunc/my> variables,
97a1d740
YST
2624meaning that the rest of the block can see the variable, but other
2625subroutines called by the block I<cannot> see the variable.
2626
2627=item scratchpad
2628
2629The area in which a particular invocation of a particular file or
2630subroutine keeps some of its temporary values, including any lexically
2631scoped variables.
2632
2633=item script
2634
27ed30b8 2635A text L</file> that is a program intended to be L<executed|/execute>
97a1d740 2636directly rather than L<compiled|/compiler> to another form of file
27ed30b8 2637before execution. Also, in the context of L</Unicode>, a writing
97a1d740
YST
2638system for a particular language or group of languages, such as Greek,
2639Bengali, or Klingon.
2640
2641=item script kiddie
2642
27ed30b8 2643A L</cracker> who is not a L</hacker>, but knows just enough to run
97a1d740
YST
2644canned scripts. A cargo-cult programmer.
2645
2646=item sed
2647
2648A venerable Stream EDitor from which Perl derives some of its ideas.
2649
2650=item semaphore
2651
27ed30b8
YST
2652A fancy kind of interlock that prevents multiple L<threads|/thread> or
2653L<processes|/process> from using up the same resources simultaneously.
97a1d740
YST
2654
2655=item separator
2656
27ed30b8 2657A L</character> or L</string> that keeps two surrounding strings from
97a1d740 2658being confused with each other. The L<split|perlfunc/split> function
27ed30b8
YST
2659works on separators. Not to be confused with L<delimiters|/delimiter>
2660or L<terminators|/terminator>. The "or" in the previous sentence
97a1d740
YST
2661separated the two alternatives.
2662
2663=item serialization
2664
27ed30b8
YST
2665Putting a fancy L</data structure> into linear order so that it can be
2666stored as a L</string> in a disk file or database or sent through a
2667L</pipe>. Also called marshalling.
97a1d740
YST
2668
2669=item server
2670
27ed30b8
YST
2671In networking, a L</process> that either advertises a L</service> or
2672just hangs around at a known location and waits for L<clients|/client>
97a1d740
YST
2673who need service to get in touch with it.
2674
2675=item service
2676
2677Something you do for someone else to make them happy, like giving them
2678the time of day (or of their life). On some machines, well-known
2679services are listed by the L<getservent|perlfunc/getservent> function.
2680
2681=item setgid
2682
27ed30b8 2683Same as L</setuid>, only having to do with giving away L</group>
97a1d740
YST
2684privileges.
2685
2686=item setuid
2687
27ed30b8 2688Said of a program that runs with the privileges of its L</owner>
97a1d740 2689rather than (as is usually the case) the privileges of whoever is
27ed30b8 2690running it. Also describes the bit in the mode word (L</permission
97a1d740
YST
2691bits>) that controls the feature. This bit must be explicitly set by
2692the owner to enable this feature, and the program must be carefully
2693written not to give away more privileges than it ought to.
2694
2695=item shared memory
2696
27ed30b8
YST
2697A piece of L</memory> accessible by two different
2698L<processes|/process> who otherwise would not see each other's memory.
97a1d740
YST
2699
2700=item shebang
2701
2702Irish for the whole McGillicuddy. In Perl culture, a portmanteau of
2703"sharp" and "bang", meaning the C<#!> sequence that tells the system
2704where to find the interpreter.
2705
2706=item shell
2707
27ed30b8
YST
2708A L</command>-line L</interpreter>. The program that interactively
2709gives you a prompt, accepts one or more L<lines|/line> of input, and
97a1d740 2710executes the programs you mentioned, feeding each of them their proper
27ed30b8 2711L<arguments|/argument> and input data. Shells can also execute
97a1d740
YST
2712scripts containing such commands. Under Unix, typical shells include
2713the Bourne shell (I</bin/sh>), the C shell (I</bin/csh>), and the Korn
2714shell (I</bin/ksh>). Perl is not strictly a shell because it's not
2715interactive (although Perl programs can be interactive).
2716
2717=item side effects
2718
27ed30b8 2719Something extra that happens when you evaluate an L</expression>.
97a1d740
YST
2720Nowadays it can refer to almost anything. For example, evaluating a
2721simple assignment statement typically has the "side effect" of
2722assigning a value to a variable. (And you thought assigning the value
2723was your primary intent in the first place!) Likewise, assigning a
27ed30b8
YST
2724value to the special variable C<$|> (C<$AUTOFLUSH>) has the side
2725effect of forcing a flush after every L<write|perlfunc/write> or
2726L<print|perlfunc/print> on the currently selected filehandle.
97a1d740
YST
2727
2728=item signal
2729
2730A bolt out of the blue; that is, an event triggered by the
27ed30b8 2731L</operating system>, probably when you're least expecting it.
97a1d740
YST
2732
2733=item signal handler
2734
27ed30b8 2735A L</subroutine> that, instead of being content to be called in the
97a1d740 2736normal fashion, sits around waiting for a bolt out of the blue before
27ed30b8 2737it will deign to L</execute>. Under Perl, bolts out of the blue are
97a1d740
YST
2738called signals, and you send them with the L<kill|perlfunc/kill>
2739built-in. See L<perlvar/%SIG> and L<perlipc/Signals>.
2740
2741=item single inheritance
2742
2743The features you got from your mother, if she told you that you don't
27ed30b8 2744have a father. (See also L</inheritance> and L</multiple
97a1d740 2745inheritance>.) In computer languages, the notion that
27ed30b8
YST
2746L<classes|/class> reproduce asexually so that a given class can only
2747have one direct ancestor or L</base class>. Perl supplies no such
97a1d740
YST
2748restriction, though you may certainly program Perl that way if you
2749like.
2750
2751=item slice
2752
27ed30b8
YST
2753A selection of any number of L<elements|/element> from a L</list>,
2754L</array>, or L</hash>.
97a1d740
YST
2755
2756=item slurp
2757
27ed30b8 2758To read an entire L</file> into a L</string> in one operation.
97a1d740
YST
2759
2760=item socket
2761
2762An endpoint for network communication among multiple
27ed30b8
YST
2763L<processes|/process> that works much like a telephone or a post
2764office box. The most important thing about a socket is its L</network
97a1d740
YST
2765address> (like a phone number). Different kinds of sockets have
2766different kinds of addresses--some look like filenames, and some
2767don't.
2768
2769=item soft reference
2770
27ed30b8 2771See L</symbolic reference>.
97a1d740
YST
2772
2773=item source filter
2774
27ed30b8
YST
2775A special kind of L</module> that does L</preprocessing> on your
2776script just before it gets to the L</tokener>.
97a1d740
YST
2777
2778=item stack
2779
2780A device you can put things on the top of, and later take them back
27ed30b8 2781off in the opposite order in which you put them on. See L</LIFO>.
97a1d740
YST
2782
2783=item standard
2784
2785Included in the official Perl distribution, as in a standard module, a
27ed30b8 2786standard tool, or a standard Perl L</manpage>.
97a1d740
YST
2787
2788=item standard error
2789
27ed30b8
YST
2790The default output L</stream> for nasty remarks that don't belong in
2791L</standard output>. Represented within a Perl program by the
2792L</filehandle> L</STDERR>. You can use this stream explicitly, but the
97a1d740
YST
2793L<die|perlfunc/die> and L<warn|perlfunc/warn> built-ins write to your
2794standard error stream automatically.
2795
2796=item standard I/O
2797
27ed30b8
YST
2798A standard C library for doing L<buffered|/buffer> input and output to
2799the L</operating system>. (The "standard" of standard I/O is only
97a1d740
YST
2800marginally related to the "standard" of standard input and output.)
2801In general, Perl relies on whatever implementation of standard I/O a
2802given operating system supplies, so the buffering characteristics of a
2803Perl program on one machine may not exactly match those on another
2804machine. Normally this only influences efficiency, not semantics. If
2805your standard I/O package is doing block buffering and you want it to
27ed30b8 2806L</flush> the buffer more often, just set the C<$|> variable to a true
97a1d740
YST
2807value.
2808
2809=item standard input
2810
27ed30b8 2811The default input L</stream> for your program, which if possible
97a1d740 2812shouldn't care where its data is coming from. Represented within a
27ed30b8 2813Perl program by the L</filehandle> L</STDIN>.
97a1d740
YST
2814
2815=item standard output
2816
27ed30b8 2817The default output L</stream> for your program, which if possible
97a1d740 2818shouldn't care where its data is going. Represented within a Perl
27ed30b8 2819program by the L</filehandle> L</STDOUT>.
97a1d740
YST
2820
2821=item stat structure
2822
2823A special internal spot in which Perl keeps the information about the
27ed30b8 2824last L</file> on which you requested information.
97a1d740
YST
2825
2826=item statement
2827
27ed30b8 2828A L</command> to the computer about what to do next, like a step in a
97a1d740 2829recipe: "Add marmalade to batter and mix until mixed." A statement is
27ed30b8 2830distinguished from a L</declaration>, which doesn't tell the computer
97a1d740
YST
2831to do anything, but just to learn something.
2832
2833=item statement modifier
2834
27ed30b8 2835A L</conditional> or L</loop> that you put after the L</statement>
97a1d740
YST
2836instead of before, if you know what we mean.
2837
2838=item static
2839
2840Varying slowly compared to something else. (Unfortunately, everything
2841is relatively stable compared to something else, except for certain
2842elementary particles, and we're not so sure about them.) In
2843computers, where things are supposed to vary rapidly, "static" has a
2844derogatory connotation, indicating a slightly dysfunctional
27ed30b8 2845L</variable>, L</subroutine>, or L</method>. In Perl culture, the
97a1d740
YST
2846word is politely avoided.
2847
2848=item static method
2849
27ed30b8 2850No such thing. See L</class method>.
97a1d740
YST
2851
2852=item static scoping
2853
27ed30b8 2854No such thing. See L</lexical scoping>.
97a1d740
YST
2855
2856=item static variable
2857
27ed30b8
YST
2858No such thing. Just use a L</lexical variable> in a scope larger than
2859your L</subroutine>.
97a1d740
YST
2860
2861=item status
2862
27ed30b8 2863The L</value> returned to the parent L</process> when one of its child
97a1d740 2864processes dies. This value is placed in the special variable C<$?>.
27ed30b8 2865Its upper eight L<bits|/bit> are the exit status of the defunct
97a1d740
YST
2866process, and its lower eight bits identify the signal (if any) that
2867the process died from. On Unix systems, this status value is the same
2868as the status word returned by I<wait>(2). See L<perlfunc/system>.
2869
2870=item STDERR
2871
27ed30b8 2872See L</standard error>.
97a1d740
YST
2873
2874=item STDIN
2875
27ed30b8 2876See L</standard input>.
97a1d740
YST
2877
2878=item STDIO
2879
27ed30b8 2880See L</standard IE<sol>O>.
97a1d740
YST
2881
2882=item STDOUT
2883
27ed30b8 2884See L</standard output>.
97a1d740
YST
2885
2886=item stream
2887
2888A flow of data into or out of a process as a steady sequence of bytes
2889or characters, without the appearance of being broken up into packets.
27ed30b8 2890This is a kind of L</interface>--the underlying L</implementation> may
97a1d740
YST
2891well break your data up into separate packets for delivery, but this
2892is hidden from you.
2893
2894=item string
2895
2896A sequence of characters such as "He said !@#*&%@#*?!". A string does
2897not have to be entirely printable.
2898
2899=item string context
2900
2901The situation in which an expression is expected by its surroundings
27ed30b8
YST
2902(the code calling it) to return a L</string>. See also L</context>
2903and L</numeric context>.
97a1d740
YST
2904
2905=item stringification
2906
27ed30b8 2907The process of producing a L</string> representation of an abstract
97a1d740
YST
2908object.
2909
2910=item struct
2911
2912C keyword introducing a structure definition or name.
2913
2914=item structure
2915
27ed30b8 2916See L</data structure>.
97a1d740
YST
2917
2918=item subclass
2919
27ed30b8 2920See L</derived class>.
97a1d740
YST
2921
2922=item subpattern
2923
27ed30b8 2924A component of a L</regular expression> pattern.
97a1d740
YST
2925
2926=item subroutine
2927
2928A named or otherwise accessible piece of program that can be invoked
2929from elsewhere in the program in order to accomplish some sub-goal of
2930the program. A subroutine is often parameterized to accomplish
2931different but related things depending on its input
27ed30b8
YST
2932L<arguments|/argument>. If the subroutine returns a meaningful
2933L</value>, it is also called a L</function>.
97a1d740
YST
2934
2935=item subscript
2936
27ed30b8
YST
2937A L</value> that indicates the position of a particular L</array>
2938L</element> in an array.
97a1d740
YST
2939
2940=item substitution
2941
2942Changing parts of a string via the C<s///> operator. (We avoid use of
27ed30b8 2943this term to mean L</variable interpolation>.)
97a1d740
YST
2944
2945=item substring
2946
27ed30b8
YST
2947A portion of a L</string>, starting at a certain L</character>
2948position (L</offset>) and proceeding for a certain number of
97a1d740
YST
2949characters.
2950
2951=item superclass
2952
27ed30b8 2953See L</base class>.
97a1d740
YST
2954
2955=item superuser
2956
27ed30b8 2957The person whom the L</operating system> will let do almost anything.
97a1d740 2958Typically your system administrator or someone pretending to be your
27ed30b8 2959system administrator. On Unix systems, the L</root> user. On Windows
97a1d740
YST
2960systems, usually the Administrator user.
2961
2962=item SV
2963
2964Short for "scalar value". But within the Perl interpreter every
27ed30b8
YST
2965L</referent> is treated as a member of a class derived from SV, in an
2966object-oriented sort of way. Every L</value> inside Perl is passed
2967around as a C language C<SV*> pointer. The SV L</struct> knows its
97a1d740 2968own "referent type", and the code is smart enough (we hope) not to try
27ed30b8 2969to call a L</hash> function on a L</subroutine>.
97a1d740
YST
2970
2971=item switch
2972
2973An option you give on a command line to influence the way your program
2974works, usually introduced with a minus sign. The word is also used as
27ed30b8 2975a nickname for a L</switch statement>.
97a1d740
YST
2976
2977=item switch cluster
2978
2979The combination of multiple command-line switches (e.g., B<-a -b -c>)
2980into one switch (e.g., B<-abc>). Any switch with an additional
27ed30b8 2981L</argument> must be the last switch in a cluster.
97a1d740
YST
2982
2983=item switch statement
2984
27ed30b8 2985A program technique that lets you evaluate an L</expression> and then,
97a1d740
YST
2986based on the value of the expression, do a multiway branch to the
2987appropriate piece of code for that value. Also called a "case
96090e4f 2988structure", named after the similar Pascal construct. See
dfcceb59 2989See L<perlsyn/Basic BLOCKs>.
97a1d740
YST
2990
2991=item symbol
2992
27ed30b8
YST
2993Generally, any L</token> or L</metasymbol>. Often used more
2994specifically to mean the sort of name you might find in a L</symbol
97a1d740
YST
2995table>.
2996
2997=item symbol table
2998
27ed30b8
YST
2999Where a L</compiler> remembers symbols. A program like Perl must
3000somehow remember all the names of all the L<variables|/variable>,
3001L<filehandles|/filehandle>, and L<subroutines|/subroutine> you've
97a1d740 3002used. It does this by placing the names in a symbol table, which is
27ed30b8
YST
3003implemented in Perl using a L</hash table>. There is a separate
3004symbol table for each L</package> to give each package its own
3005L</namespace>.
97a1d740
YST
3006
3007=item symbolic debugger
3008
3009A program that lets you step through the L<execution|/execute> of your
3010program, stopping or printing things out here and there to see whether
3011anything has gone wrong, and if so, what. The "symbolic" part just
3012means that you can talk to the debugger using the same symbols with
3013which your program is written.
3014
3015=item symbolic link
3016
27ed30b8
YST
3017An alternate filename that points to the real L</filename>, which in
3018turn points to the real L</file>. Whenever the L</operating system>
3019is trying to parse a L</pathname> containing a symbolic link, it
97a1d740
YST
3020merely substitutes the new name and continues parsing.
3021
3022=item symbolic reference
3023
3024A variable whose value is the name of another variable or subroutine.
3025By L<dereferencing|/dereference> the first variable, you can get at
27ed30b8
YST
3026the second one. Symbolic references are illegal under L<use strict
3027'refs'|strict/strict refs>.
97a1d740
YST
3028
3029=item synchronous
3030
3031Programming in which the orderly sequence of events can be determined;
3032that is, when things happen one after the other, not at the same time.
3033
3034=item syntactic sugar
3035
3036An alternative way of writing something more easily; a shortcut.
3037
3038=item syntax
3039
3040From Greek, "with-arrangement". How things (particularly symbols) are
3041put together with each other.
3042
3043=item syntax tree
3044
3045An internal representation of your program wherein lower-level
27ed30b8 3046L<constructs|/construct> dangle off the higher-level constructs
97a1d740
YST
3047enclosing them.
3048
3049=item syscall
3050
27ed30b8 3051A L</function> call directly to the L</operating system>. Many of the
97a1d740
YST
3052important subroutines and functions you use aren't direct system
3053calls, but are built up in one or more layers above the system call
3054level. In general, Perl programmers don't need to worry about the
3055distinction. However, if you do happen to know which Perl functions
3056are really syscalls, you can predict which of these will set the C<$!>
3057(C<$ERRNO>) variable on failure. Unfortunately, beginning programmers
3058often confusingly employ the term "system call" to mean what happens
3059when you call the Perl L<system|perlfunc/system> function, which
3060actually involves many syscalls. To avoid any confusion, we nearly
3061always use say "syscall" for something you could call indirectly via
3062Perl's L<syscall|perlfunc/syscall> function, and never for something
3063you would call with Perl's L<system|perlfunc/system> function.
3064
3065=back
3066
5bbd0522
YST
3067=head2 T
3068
97a1d740
YST
3069=over 4
3070
3071=item tainted
3072
3073Said of data derived from the grubby hands of a user and thus unsafe
3074for a secure program to rely on. Perl does taint checks if you run a
27ed30b8 3075L</setuid> (or L</setgid>) program, or if you use the B<-T> switch.
97a1d740
YST
3076
3077=item TCP
3078
3079Short for Transmission Control Protocol. A protocol wrapped around
3080the Internet Protocol to make an unreliable packet transmission
3081mechanism appear to the application program to be a reliable
27ed30b8 3082L</stream> of bytes. (Usually.)
97a1d740
YST
3083
3084=item term
3085
27ed30b8
YST
3086Short for a "terminal", that is, a leaf node of a L</syntax tree>. A
3087thing that functions grammatically as an L</operand> for the operators
97a1d740
YST
3088in an expression.
3089
3090=item terminator
3091
27ed30b8 3092A L</character> or L</string> that marks the end of another string.
97a1d740
YST
3093The C<$/> variable contains the string that terminates a
3094L<readline|perlfunc/readline> operation, which L<chomp|perlfunc/chomp>
3095deletes from the end. Not to be confused with
27ed30b8 3096L<delimiters|/delimiter> or L<separators|/separator>. The period at
97a1d740
YST
3097the end of this sentence is a terminator.
3098
3099=item ternary
3100
27ed30b8
YST
3101An L</operator> taking three L<operands|/operand>. Sometimes
3102pronounced L</trinary>.
97a1d740
YST
3103
3104=item text
3105
27ed30b8 3106A L</string> or L</file> containing primarily printable characters.
97a1d740
YST
3107
3108=item thread
3109
27ed30b8 3110Like a forked process, but without L</fork>'s inherent memory
97a1d740
YST
3111protection. A thread is lighter weight than a full process, in that a
3112process could have multiple threads running around in it, all fighting
3113over the same process's memory space unless steps are taken to protect
3114threads from each other. See L<threads>.
3115
3116=item tie
3117
3118The bond between a magical variable and its implementation class. See
3119L<perlfunc/tie> and L<perltie>.
3120
3121=item TMTOWTDI
3122
3123There's More Than One Way To Do It, the Perl Motto. The notion that
3124there can be more than one valid path to solving a programming problem
3125in context. (This doesn't mean that more ways are always better or
3126that all possible paths are equally desirable--just that there need
3127not be One True Way.) Pronounced TimToady.
3128
3129=item token
3130
3131A morpheme in a programming language, the smallest unit of text with
3132semantic significance.
3133
3134=item tokener
3135
3136A module that breaks a program text into a sequence of
27ed30b8 3137L<tokens|/token> for later analysis by a parser.
97a1d740
YST
3138
3139=item tokenizing
3140
27ed30b8 3141Splitting up a program text into L<tokens|/token>. Also known as
97a1d740
YST
3142"lexing", in which case you get "lexemes" instead of tokens.
3143
3144=item toolbox approach
3145
3146The notion that, with a complete set of simple tools that work well
3147together, you can build almost anything you want. Which is fine if
3148you're assembling a tricycle, but if you're building a defranishizing
3149comboflux regurgalator, you really want your own machine shop in which
3150to build special tools. Perl is sort of a machine shop.
3151
3152=item transliterate
3153
3154To turn one string representation into another by mapping each
3155character of the source string to its corresponding character in the
3156result string. See
96090e4f 3157L<perlop/trE<sol>SEARCHLISTE<sol>REPLACEMENTLISTE<sol>cdsr>.
97a1d740
YST
3158
3159=item trigger
3160
27ed30b8 3161An event that causes a L</handler> to be run.
97a1d740
YST
3162
3163=item trinary
3164
27ed30b8
YST
3165Not a stellar system with three stars, but an L</operator> taking
3166three L<operands|/operand>. Sometimes pronounced L</ternary>.
97a1d740
YST
3167
3168=item troff
3169
3170A venerable typesetting language from which Perl derives the name of
3171its C<$%> variable and which is secretly used in the production of
3172Camel books.
3173
3174=item true
3175
3176Any scalar value that doesn't evaluate to 0 or C<"">.
3177
3178=item truncating
3179
3180Emptying a file of existing contents, either automatically when
3181opening a file for writing or explicitly via the
3182L<truncate|perlfunc/truncate> function.
3183
3184=item type
3185
27ed30b8 3186See L</data type> and L</class>.
97a1d740
YST
3187
3188=item type casting
3189
3190Converting data from one type to another. C permits this. Perl does
3191not need it. Nor want it.
3192
3193=item typed lexical
3194
27ed30b8 3195A L</lexical variable> that is declared with a L</class> type: C<my
97a1d740
YST
3196Pony $bill>.
3197
3198=item typedef
3199
3200A type definition in the C language.
3201
3202=item typeglob
3203
3204Use of a single identifier, prefixed with C<*>. For example, C<*name>
3205stands for any or all of C<$name>, C<@name>, C<%name>, C<&name>, or
3206just C<name>. How you use it determines whether it is interpreted as
3207all or only one of them. See L<perldata/Typeglobs and Filehandles>.
3208
3209=item typemap
3210
3211A description of how C types may be transformed to and from Perl types
27ed30b8 3212within an L</extension> module written in L</XS>.
97a1d740
YST
3213
3214=back
3215
5bbd0522
YST
3216=head2 U
3217
97a1d740
YST
3218=over 4
3219
3220=item UDP
3221
27ed30b8 3222User Datagram Protocol, the typical way to send L<datagrams|/datagram>
97a1d740
YST
3223over the Internet.
3224
3225=item UID
3226
27ed30b8 3227A user ID. Often used in the context of L</file> or L</process>
97a1d740
YST
3228ownership.
3229
3230=item umask
3231
27ed30b8 3232A mask of those L</permission bits> that should be forced off when
97a1d740
YST
3233creating files or directories, in order to establish a policy of whom
3234you'll ordinarily deny access to. See the L<umask|perlfunc/umask>
3235function.
3236
3237=item unary operator
3238
27ed30b8 3239An operator with only one L</operand>, like C<!> or
97a1d740
YST
3240L<chdir|perlfunc/chdir>. Unary operators are usually prefix
3241operators; that is, they precede their operand. The C<++> and C<-->
3242operators can be either prefix or postfix. (Their position I<does>
3243change their meanings.)
3244
3245=item Unicode
3246
3247A character set comprising all the major character sets of the world,
e1b711da 3248more or less. See L<perlunicode> and L<http://www.unicode.org>.
97a1d740
YST
3249
3250=item Unix
3251
3252A very large and constantly evolving language with several alternative
3253and largely incompatible syntaxes, in which anyone can define anything
3254any way they choose, and usually do. Speakers of this language think
3255it's easy to learn because it's so easily twisted to one's own ends,
3256but dialectical differences make tribal intercommunication nearly
3257impossible, and travelers are often reduced to a pidgin-like subset of
3258the language. To be universally understood, a Unix shell programmer
3259must spend years of study in the art. Many have abandoned this
3260discipline and now communicate via an Esperanto-like language called
3261Perl.
3262
3263In ancient times, Unix was also used to refer to some code that a
3264couple of people at Bell Labs wrote to make use of a PDP-7 computer
3265that wasn't doing much of anything else at the time.
3266
3267=back
3268
5bbd0522
YST
3269=head2 V
3270
97a1d740
YST
3271=over 4
3272
3273=item value
3274
3275An actual piece of data, in contrast to all the variables, references,
3276keys, indexes, operators, and whatnot that you need to access the
3277value.
3278
3279=item variable
3280
3281A named storage location that can hold any of various kinds of
27ed30b8 3282L</value>, as your program sees fit.
97a1d740
YST
3283
3284=item variable interpolation
3285
27ed30b8 3286The L</interpolation> of a scalar or array variable into a string.
97a1d740
YST
3287
3288=item variadic
3289
27ed30b8
YST
3290Said of a L</function> that happily receives an indeterminate number
3291of L</actual arguments>.
97a1d740
YST
3292
3293=item vector
3294
27ed30b8 3295Mathematical jargon for a list of L<scalar values|/scalar value>.
97a1d740
YST
3296
3297=item virtual
3298
3299Providing the appearance of something without the reality, as in:
27ed30b8 3300virtual memory is not real memory. (See also L</memory>.) The
97a1d740
YST
3301opposite of "virtual" is "transparent", which means providing the
3302reality of something without the appearance, as in: Perl handles the
3303variable-length UTF-8 character encoding transparently.
3304
3305=item void context
3306
27ed30b8
YST
3307A form of L</scalar context> in which an L</expression> is not
3308expected to return any L</value> at all and is evaluated for its
3309L</side effects> alone.
97a1d740
YST
3310
3311=item v-string
3312
27ed30b8 3313A "version" or "vector" L</string> specified with a C<v> followed by a
97a1d740 3314series of decimal integers in dot notation, for instance,
27ed30b8 3315C<v1.20.300.4000>. Each number turns into a L</character> with the
97a1d740
YST
3316specified ordinal value. (The C<v> is optional when there are at
3317least three integers.)
3318
3319=back
3320
5bbd0522
YST
3321=head2 W
3322
97a1d740
YST
3323=over 4
3324
3325=item warning
3326
27ed30b8 3327A message printed to the L</STDERR> stream to the effect that something
97a1d740
YST
3328might be wrong but isn't worth blowing up over. See L<perlfunc/warn>
3329and the L<warnings> pragma.
3330
3331=item watch expression
3332
3333An expression which, when its value changes, causes a breakpoint in
3334the Perl debugger.
3335
3336=item whitespace
3337
27ed30b8 3338A L</character> that moves your cursor but doesn't otherwise put
97a1d740
YST
3339anything on your screen. Typically refers to any of: space, tab, line
3340feed, carriage return, or form feed.
3341
3342=item word
3343
3344In normal "computerese", the piece of data of the size most
3345efficiently handled by your computer, typically 32 bits or so, give or
3346take a few powers of 2. In Perl culture, it more often refers to an
27ed30b8
YST
3347alphanumeric L</identifier> (including underscores), or to a string of
3348nonwhitespace L<characters|/character> bounded by whitespace or string
97a1d740
YST
3349boundaries.
3350
3351=item working directory
3352
27ed30b8
YST
3353Your current L</directory>, from which relative pathnames are
3354interpreted by the L</operating system>. The operating system knows
97a1d740
YST
3355your current directory because you told it with a
3356L<chdir|perlfunc/chdir> or because you started out in the place where
27ed30b8 3357your parent L</process> was when you were born.
97a1d740
YST
3358
3359=item wrapper
3360
3361A program or subroutine that runs some other program or subroutine for
3362you, modifying some of its input or output to better suit your
3363purposes.
3364
3365=item WYSIWYG
3366
3367What You See Is What You Get. Usually used when something that
3368appears on the screen matches how it will eventually look, like Perl's
3369L<format|perlfunc/format> declarations. Also used to mean the
3370opposite of magic because everything works exactly as it appears, as
3371in the three-argument form of L<open|perlfunc/open>.
3372
3373=back
3374
5bbd0522
YST
3375=head2 X
3376
97a1d740
YST
3377=over 4
3378
3379=item XS
3380
3381An extraordinarily exported, expeditiously excellent, expressly
3382eXternal Subroutine, executed in existing C or C++ or in an exciting
3383new extension language called (exasperatingly) XS. Examine L<perlxs>
3384for the exact explanation or L<perlxstut> for an exemplary unexacting
3385one.
3386
3387=item XSUB
3388
27ed30b8 3389An external L</subroutine> defined in L</XS>.
97a1d740
YST
3390
3391=back
3392
5bbd0522
YST
3393=head2 Y
3394
97a1d740
YST
3395=over 4
3396
3397=item yacc
3398
3399Yet Another Compiler Compiler. A parser generator without which Perl
3400probably would not have existed. See the file I<perly.y> in the Perl
3401source distribution.
3402
3403=back
3404
5bbd0522
YST
3405=head2 Z
3406
97a1d740
YST
3407=over 4
3408
3409=item zero width
3410
27ed30b8
YST
3411A subpattern L</assertion> matching the L</null string> between
3412L<characters|/character>.
97a1d740
YST
3413
3414=item zombie
3415
3416A process that has died (exited) but whose parent has not yet received
3417proper notification of its demise by virtue of having called
3418L<wait|perlfunc/wait> or L<waitpid|perlfunc/waitpid>. If you
3419L<fork|perlfunc/fork>, you must clean up after your child processes
3420when they exit, or else the process table will fill up and your system
3421administrator will Not Be Happy with you.
3422
3423=back
3424
3425=head1 AUTHOR AND COPYRIGHT
3426
3427Based on the Glossary of Programming Perl, Third Edition,
3428by Larry Wall, Tom Christiansen & Jon Orwant.
3429Copyright (c) 2000, 1996, 1991 O'Reilly Media, Inc.
20fd23ef 3430This document may be distributed under the same terms as Perl itself.