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1 | =head1 NAME |
2 | ||
3 | perlglossary - Perl Glossary | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | A glossary of terms (technical and otherwise) used in the Perl documentation. | |
8 | Other useful sources include the Free On-Line Dictionary of Computing | |
9 | L<http://foldoc.doc.ic.ac.uk/foldoc/index.html>, the Jargon File | |
10 | L<http://catb.org/~esr/jargon/>, and Wikipedia L<http://www.wikipedia.org/>. | |
11 | ||
12 | =head2 A | |
13 | ||
14 | =over 4 | |
15 | ||
16 | =item accessor methods | |
17 | ||
18 | A L</method> used to indirectly inspect or update an L</object>'s | |
19 | state (its L<instance variables|/instance variable>). | |
20 | ||
21 | =item actual arguments | |
22 | ||
23 | The L<scalar values|/scalar value> that you supply to a L</function> | |
24 | or L</subroutine> when you call it. For instance, when you call | |
25 | C<power("puff")>, the string C<"puff"> is the actual argument. See | |
26 | also L</argument> and L</formal arguments>. | |
27 | ||
28 | =item address operator | |
29 | ||
30 | Some languages work directly with the memory addresses of values, but | |
31 | this can be like playing with fire. Perl provides a set of asbestos | |
32 | gloves for handling all memory management. The closest to an address | |
33 | operator in Perl is the backslash operator, but it gives you a L</hard | |
34 | reference>, which is much safer than a memory address. | |
35 | ||
36 | =item algorithm | |
37 | ||
38 | A well-defined sequence of steps, clearly enough explained that even a | |
39 | computer could do them. | |
40 | ||
41 | =item alias | |
42 | ||
43 | A nickname for something, which behaves in all ways as though you'd | |
44 | used the original name instead of the nickname. Temporary aliases are | |
45 | implicitly created in the loop variable for C<foreach> loops, in the | |
46 | C<$_> variable for L<map|perlfunc/map> or L<grep|perlfunc/grep> | |
47 | operators, in C<$a> and C<$b> during L<sort|perlfunc/sort>'s | |
48 | comparison function, and in each element of C<@_> for the L</actual | |
49 | arguments> of a subroutine call. Permanent aliases are explicitly | |
50 | created in L<packages|/package> by L<importing|/import> symbols or by | |
51 | assignment to L<typeglobs|/typeglob>. Lexically scoped aliases for | |
52 | package variables are explicitly created by the L<our|perlfunc/our> | |
53 | declaration. | |
54 | ||
55 | =item alternatives | |
56 | ||
57 | A 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 | |
59 | are separated with a single vertical bar: C<|>. Alternatives in | |
60 | normal Perl expressions are separated with a double vertical bar: | |
61 | C<||>. Logical alternatives in L</Boolean> expressions are separated | |
62 | with either C<||> or C<or>. | |
63 | ||
64 | =item anonymous | |
65 | ||
66 | Used to describe a L</referent> that is not directly accessible | |
67 | through a named L</variable>. Such a referent must be indirectly | |
68 | accessible through at least one L</hard reference>. When the last | |
69 | hard reference goes away, the anonymous referent is destroyed without | |
70 | pity. | |
71 | ||
72 | =item architecture | |
73 | ||
74 | The kind of computer you're working on, where one "kind" of computer | |
75 | means all those computers sharing a compatible machine language. | |
76 | Since Perl programs are (typically) simple text files, not executable | |
77 | images, a Perl program is much less sensitive to the architecture it's | |
78 | running on than programs in other languages, such as C, that are | |
79 | compiled into machine code. See also L</platform> and L</operating | |
80 | system>. | |
81 | ||
82 | =item argument | |
83 | ||
84 | A piece of data supplied to a L<program|/executable file>, | |
85 | L</subroutine>, L</function>, or L</method> to tell it what it's | |
86 | supposed to do. Also called a "parameter". | |
87 | ||
88 | =item ARGV | |
89 | ||
90 | The name of the array containing the L</argument> L</vector> from the | |
91 | command line. If you use the empty C<< E<lt>E<gt> >> operator, L</ARGV> is | |
92 | the name of both the L</filehandle> used to traverse the arguments and | |
93 | the L</scalar> containing the name of the current input file. | |
94 | ||
95 | =item arithmetical operator | |
96 | ||
97 | A L</symbol> such as C<+> or C</> that tells Perl to do the arithmetic | |
98 | you were supposed to learn in grade school. | |
99 | ||
100 | =item array | |
101 | ||
102 | An ordered sequence of L<values|/value>, stored such that you can | |
103 | easily access any of the values using an integer L</subscript> | |
104 | that specifies the value's L</offset> in the sequence. | |
105 | ||
106 | =item array context | |
107 | ||
108 | An archaic expression for what is more correctly referred to as | |
109 | L</list context>. | |
110 | ||
111 | =item ASCII | |
112 | ||
113 | The American Standard Code for Information Interchange (a 7-bit | |
114 | character set adequate only for poorly representing English text). | |
115 | Often used loosely to describe the lowest 128 values of the various | |
116 | ISO-8859-X character sets, a bunch of mutually incompatible 8-bit | |
117 | codes best described as half ASCII. See also L</Unicode>. | |
118 | ||
119 | =item assertion | |
120 | ||
121 | A component of a L</regular expression> that must be true for the | |
122 | pattern to match but does not necessarily match any characters itself. | |
123 | Often used specifically to mean a L</zero width> assertion. | |
124 | ||
125 | =item assignment | |
126 | ||
127 | An L</operator> whose assigned mission in life is to change the value | |
128 | of a L</variable>. | |
129 | ||
130 | =item assignment operator | |
131 | ||
132 | Either a regular L</assignment>, or a compound L</operator> composed | |
133 | of an ordinary assignment and some other operator, that changes the | |
134 | value of a variable in place, that is, relative to its old value. For | |
135 | example, C<$a += 2> adds C<2> to C<$a>. | |
136 | ||
137 | =item associative array | |
138 | ||
139 | See L</hash>. Please. | |
140 | ||
141 | =item associativity | |
142 | ||
143 | Determines whether you do the left L</operator> first or the right | |
144 | L</operator> first when you have "A L</operator> B L</operator> C" and | |
145 | the two operators are of the same precedence. Operators like C<+> are | |
146 | left associative, while operators like C<**> are right associative. | |
147 | See L<perlop> for a list of operators and their associativity. | |
148 | ||
149 | =item asynchronous | |
150 | ||
151 | Said of events or activities whose relative temporal ordering is | |
152 | indeterminate because too many things are going on at once. Hence, an | |
153 | asynchronous event is one you didn't know when to expect. | |
154 | ||
155 | =item atom | |
156 | ||
157 | A L</regular expression> component potentially matching a | |
158 | L</substring> containing one or more characters and treated as an | |
159 | indivisible syntactic unit by any following L</quantifier>. (Contrast | |
160 | with an L</assertion> that matches something of L</zero width> and may | |
161 | not be quantified.) | |
162 | ||
163 | =item atomic operation | |
164 | ||
165 | When Democritus gave the word "atom" to the indivisible bits of | |
166 | matter, he meant literally something that could not be cut: I<a-> | |
167 | (not) + I<tomos> (cuttable). An atomic operation is an action that | |
168 | can't be interrupted, not one forbidden in a nuclear-free zone. | |
169 | ||
170 | =item attribute | |
171 | ||
172 | A new feature that allows the declaration of L<variables|/variable> | |
173 | and L<subroutines|/subroutine> with modifiers as in C<sub foo : locked | |
174 | method>. Also, another name for an L</instance variable> of an | |
175 | L</object>. | |
176 | ||
177 | =item autogeneration | |
178 | ||
179 | A feature of L</operator overloading> of L<objects|/object>, whereby | |
180 | the behavior of certain L<operators|/operator> can be reasonably | |
181 | deduced using more fundamental operators. This assumes that the | |
182 | overloaded operators will often have the same relationships as the | |
183 | regular operators. See L<perlop>. | |
184 | ||
185 | =item autoincrement | |
186 | ||
187 | To add one to something automatically, hence the name of the C<++> | |
188 | operator. To instead subtract one from something automatically is | |
189 | known as an "autodecrement". | |
190 | ||
191 | =item autoload | |
192 | ||
193 | To load on demand. (Also called "lazy" loading.) Specifically, to | |
194 | call an L<AUTOLOAD|perlsub/Autoloading> subroutine on behalf of an | |
195 | undefined subroutine. | |
196 | ||
197 | =item autosplit | |
198 | ||
199 | To split a string automatically, as the B<-a> L</switch> does when | |
200 | running under B<-p> or B<-n> in order to emulate L</awk>. (See also | |
201 | the L<AutoSplit> module, which has nothing to do with the B<-a> | |
202 | switch, but a lot to do with autoloading.) | |
203 | ||
204 | =item autovivification | |
205 | ||
206 | A Greco-Roman word meaning "to bring oneself to life". In Perl, | |
207 | storage locations (L<lvalues|/lvalue>) spontaneously generate | |
208 | themselves as needed, including the creation of any L</hard reference> | |
209 | values to point to the next level of storage. The assignment | |
210 | C<$a[5][5][5][5][5] = "quintet"> potentially creates five scalar | |
211 | storage locations, plus four references (in the first four scalar | |
212 | locations) pointing to four new anonymous arrays (to hold the last | |
213 | four scalar locations). But the point of autovivification is that you | |
214 | don't have to worry about it. | |
215 | ||
216 | =item AV | |
217 | ||
218 | Short for "array value", which refers to one of Perl's internal data | |
219 | types that holds an L</array>. The L</AV> type is a subclass of | |
220 | L</SV>. | |
221 | ||
222 | =item awk | |
223 | ||
224 | Descriptive editing term--short for "awkward". Also coincidentally | |
225 | refers to a venerable text-processing language from which Perl derived | |
226 | some of its high-level ideas. | |
227 | ||
228 | =back | |
229 | ||
230 | =head2 B | |
231 | ||
232 | =over 4 | |
233 | ||
234 | =item backreference | |
235 | ||
236 | A substring L<captured|/capturing> by a subpattern within | |
237 | unadorned parentheses in a L</regex>. Backslashed decimal numbers | |
238 | (C<\1>, C<\2>, etc.) later in the same pattern refer back to the | |
239 | corresponding subpattern in the current match. Outside the pattern, | |
240 | the numbered variables (C<$1>, C<$2>, etc.) continue to refer to these | |
241 | same values, as long as the pattern was the last successful match of | |
242 | the current dynamic scope. | |
243 | ||
244 | =item backtracking | |
245 | ||
246 | The practice of saying, "If I had to do it all over, I'd do it | |
247 | differently," and then actually going back and doing it all over | |
248 | differently. Mathematically speaking, it's returning from an | |
249 | unsuccessful recursion on a tree of possibilities. Perl backtracks | |
250 | when it attempts to match patterns with a L</regular expression>, and | |
251 | its earlier attempts don't pan out. See L<perlre/Backtracking>. | |
252 | ||
253 | =item backward compatibility | |
254 | ||
255 | Means you can still run your old program because we didn't break any | |
256 | of the features or bugs it was relying on. | |
257 | ||
258 | =item bareword | |
259 | ||
260 | A word sufficiently ambiguous to be deemed illegal under L<use strict | |
261 | 'subs'|strict/strict subs>. In the absence of that stricture, a | |
262 | bareword is treated as if quotes were around it. | |
263 | ||
264 | =item base class | |
265 | ||
266 | A generic L</object> type; that is, a L</class> from which other, more | |
267 | specific classes are derived genetically by L</inheritance>. Also | |
268 | called a "superclass" by people who respect their ancestors. | |
269 | ||
270 | =item big-endian | |
271 | ||
272 | From Swift: someone who eats eggs big end first. Also used of | |
273 | computers that store the most significant L</byte> of a word at a | |
274 | lower byte address than the least significant byte. Often considered | |
275 | superior to little-endian machines. See also L</little-endian>. | |
276 | ||
277 | =item binary | |
278 | ||
279 | Having to do with numbers represented in base 2. That means there's | |
280 | basically two numbers, 0 and 1. Also used to describe a "non-text | |
281 | file", presumably because such a file makes full use of all the binary | |
282 | bits in its bytes. With the advent of L</Unicode>, this distinction, | |
283 | already suspect, loses even more of its meaning. | |
284 | ||
285 | =item binary operator | |
286 | ||
287 | An L</operator> that takes two L<operands|/operand>. | |
288 | ||
289 | =item bind | |
290 | ||
291 | To assign a specific L</network address> to a L</socket>. | |
292 | ||
293 | =item bit | |
294 | ||
295 | An integer in the range from 0 to 1, inclusive. The smallest possible | |
296 | unit of information storage. An eighth of a L</byte> or of a dollar. | |
297 | (The term "Pieces of Eight" comes from being able to split the old | |
298 | Spanish dollar into 8 bits, each of which still counted for money. | |
299 | That's why a 25-cent piece today is still "two bits".) | |
300 | ||
301 | =item bit shift | |
302 | ||
303 | The movement of bits left or right in a computer word, which has the | |
304 | effect of multiplying or dividing by a power of 2. | |
305 | ||
306 | =item bit string | |
307 | ||
308 | A sequence of L<bits|/bit> that is actually being thought of as a | |
309 | sequence of bits, for once. | |
310 | ||
311 | =item bless | |
312 | ||
313 | In corporate life, to grant official approval to a thing, as in, "The | |
314 | VP of Engineering has blessed our WebCruncher project." Similarly in | |
315 | Perl, to grant official approval to a L</referent> so that it can | |
316 | function as an L</object>, such as a WebCruncher object. See | |
317 | L<perlfunc/"bless">. | |
318 | ||
319 | =item block | |
320 | ||
321 | What a L</process> does when it has to wait for something: "My process | |
322 | blocked waiting for the disk." As an unrelated noun, it refers to a | |
323 | large chunk of data, of a size that the L</operating system> likes to | |
324 | deal with (normally a power of two such as 512 or 8192). Typically | |
325 | refers to a chunk of data that's coming from or going to a disk file. | |
326 | ||
327 | =item BLOCK | |
328 | ||
329 | A syntactic construct consisting of a sequence of Perl | |
330 | L<statements|/statement> that is delimited by braces. The C<if> and | |
331 | C<while> statements are defined in terms of L<BLOCKs|/BLOCK>, for instance. | |
332 | Sometimes we also say "block" to mean a lexical scope; that is, a | |
333 | sequence of statements that act like a L</BLOCK>, such as within an | |
334 | L<eval|perlfunc/eval> or a file, even though the statements aren't | |
335 | delimited by braces. | |
336 | ||
337 | =item block buffering | |
338 | ||
339 | A method of making input and output efficient by passing one L</block> | |
340 | at a time. By default, Perl does block buffering to disk files. See | |
341 | L</buffer> and L</command buffering>. | |
342 | ||
343 | =item Boolean | |
344 | ||
345 | A value that is either L</true> or L</false>. | |
346 | ||
347 | =item Boolean context | |
348 | ||
349 | A special kind of L</scalar context> used in conditionals to decide | |
350 | whether the L</scalar value> returned by an expression is L</true> or | |
351 | L</false>. Does not evaluate as either a string or a number. See | |
352 | L</context>. | |
353 | ||
354 | =item breakpoint | |
355 | ||
356 | A spot in your program where you've told the debugger to stop | |
357 | L<execution|/execute> so you can poke around and see whether anything | |
358 | is wrong yet. | |
359 | ||
360 | =item broadcast | |
361 | ||
362 | To send a L</datagram> to multiple destinations simultaneously. | |
363 | ||
364 | =item BSD | |
365 | ||
366 | A psychoactive drug, popular in the 80s, probably developed at | |
367 | U. C. Berkeley or thereabouts. Similar in many ways to the | |
368 | prescription-only medication called "System V", but infinitely more | |
369 | useful. (Or, at least, more fun.) The full chemical name is | |
370 | "Berkeley Standard Distribution". | |
371 | ||
372 | =item bucket | |
373 | ||
374 | A location in a L</hash table> containing (potentially) multiple | |
375 | entries whose keys "hash" to the same hash value according to its hash | |
376 | function. (As internal policy, you don't have to worry about it, | |
377 | unless you're into internals, or policy.) | |
378 | ||
379 | =item buffer | |
380 | ||
381 | A temporary holding location for data. L<Block buffering|/block | |
382 | buffering> means that the data is passed on to its destination | |
383 | whenever the buffer is full. L<Line buffering|/line buffering> means | |
384 | that it's passed on whenever a complete line is received. L<Command | |
385 | buffering|/command buffering> means that it's passed every time you do | |
386 | a L<print|perlfunc/print> command (or equivalent). If your output is | |
387 | unbuffered, the system processes it one byte at a time without the use | |
388 | of a holding area. This can be rather inefficient. | |
389 | ||
390 | =item built-in | |
391 | ||
392 | A L</function> that is predefined in the language. Even when hidden | |
393 | by L</overriding>, you can always get at a built-in function by | |
394 | L<qualifying|/qualified> its name with the C<CORE::> pseudo-package. | |
395 | ||
396 | =item bundle | |
397 | ||
398 | A group of related modules on L</CPAN>. (Also, sometimes refers to a | |
399 | group of command-line switches grouped into one L</switch cluster>.) | |
400 | ||
401 | =item byte | |
402 | ||
403 | A piece of data worth eight L<bits|/bit> in most places. | |
404 | ||
405 | =item bytecode | |
406 | ||
407 | A pidgin-like language spoken among 'droids when they don't wish to | |
408 | reveal their orientation (see L</endian>). Named after some similar | |
409 | languages spoken (for similar reasons) between compilers and | |
410 | interpreters in the late 20th century. These languages are | |
411 | characterized by representing everything as a | |
412 | non-architecture-dependent sequence of bytes. | |
413 | ||
414 | =back | |
415 | ||
416 | =head2 C | |
417 | ||
418 | =over 4 | |
419 | ||
420 | =item C | |
421 | ||
422 | A language beloved by many for its inside-out L</type> definitions, | |
423 | inscrutable L</precedence> rules, and heavy L</overloading> of the | |
424 | function-call mechanism. (Well, actually, people first switched to C | |
425 | because they found lowercase identifiers easier to read than upper.) | |
426 | Perl is written in C, so it's not surprising that Perl borrowed a few | |
427 | ideas from it. | |
428 | ||
429 | =item C preprocessor | |
430 | ||
431 | The typical C compiler's first pass, which processes lines beginning | |
432 | with C<#> for conditional compilation and macro definition and does | |
433 | various manipulations of the program text based on the current | |
434 | definitions. Also known as I<cpp>(1). | |
435 | ||
436 | =item call by reference | |
437 | ||
438 | An L</argument>-passing mechanism in which the L</formal arguments> | |
439 | refer directly to the L</actual arguments>, and the L</subroutine> can | |
440 | change the actual arguments by changing the formal arguments. That | |
441 | is, the formal argument is an L</alias> for the actual argument. See | |
442 | also L</call by value>. | |
443 | ||
444 | =item call by value | |
445 | ||
446 | An L</argument>-passing mechanism in which the L</formal arguments> | |
447 | refer to a copy of the L</actual arguments>, and the L</subroutine> | |
448 | cannot change the actual arguments by changing the formal arguments. | |
449 | See also L</call by reference>. | |
450 | ||
451 | =item callback | |
452 | ||
453 | A L</handler> that you register with some other part of your program | |
454 | in the hope that the other part of your program will L</trigger> your | |
455 | handler when some event of interest transpires. | |
456 | ||
457 | =item canonical | |
458 | ||
459 | Reduced to a standard form to facilitate comparison. | |
460 | ||
461 | =item capturing | |
462 | ||
463 | The use of parentheses around a L</subpattern> in a L</regular | |
464 | expression> to store the matched L</substring> as a L</backreference>. | |
465 | (Captured strings are also returned as a list in L</list context>.) | |
466 | ||
467 | =item character | |
468 | ||
469 | A small integer representative of a unit of orthography. | |
470 | Historically, characters were usually stored as fixed-width integers | |
471 | (typically in a byte, or maybe two, depending on the character set), | |
472 | but with the advent of UTF-8, characters are often stored in a | |
473 | variable number of bytes depending on the size of the integer that | |
474 | represents the character. Perl manages this transparently for you, | |
475 | for the most part. | |
476 | ||
477 | =item character class | |
478 | ||
479 | A square-bracketed list of characters used in a L</regular expression> | |
480 | to indicate that any character of the set may occur at a given point. | |
481 | Loosely, any predefined set of characters so used. | |
482 | ||
483 | =item character property | |
484 | ||
485 | A predefined L</character class> matchable by the C<\p> | |
486 | L</metasymbol>. Many standard properties are defined for L</Unicode>. | |
487 | ||
488 | =item circumfix operator | |
489 | ||
490 | An L</operator> that surrounds its L</operand>, like the angle | |
491 | operator, or parentheses, or a hug. | |
492 | ||
493 | =item class | |
494 | ||
495 | A user-defined L</type>, implemented in Perl via a L</package> that | |
496 | provides (either directly or by inheritance) L<methods|/method> (that | |
497 | is, L<subroutines|/subroutine>) to handle L<instances|/instance> of | |
498 | the class (its L<objects|/object>). See also L</inheritance>. | |
499 | ||
500 | =item class method | |
501 | ||
502 | A L</method> whose L</invocant> is a L</package> name, not an | |
503 | L</object> reference. A method associated with the class as a whole. | |
504 | ||
505 | =item client | |
506 | ||
507 | In networking, a L</process> that initiates contact with a L</server> | |
508 | process in order to exchange data and perhaps receive a service. | |
509 | ||
510 | =item cloister | |
511 | ||
512 | A L</cluster> used to restrict the scope of a L</regular expression | |
513 | modifier>. | |
514 | ||
515 | =item closure | |
516 | ||
517 | An L</anonymous> subroutine that, when a reference to it is generated | |
518 | at run time, keeps track of the identities of externally visible | |
519 | L<lexical variables|/lexical variable> even after those lexical | |
520 | variables have supposedly gone out of L</scope>. They're called | |
521 | "closures" because this sort of behavior gives mathematicians a sense | |
522 | of closure. | |
523 | ||
524 | =item cluster | |
525 | ||
526 | A parenthesized L</subpattern> used to group parts of a L</regular | |
527 | expression> into a single L</atom>. | |
528 | ||
529 | =item CODE | |
530 | ||
531 | The word returned by the L<ref|perlfunc/ref> function when you apply | |
532 | it to a reference to a subroutine. See also L</CV>. | |
533 | ||
534 | =item code generator | |
535 | ||
536 | A system that writes code for you in a low-level language, such as | |
537 | code to implement the backend of a compiler. See L</program | |
538 | generator>. | |
539 | ||
540 | =item code subpattern | |
541 | ||
542 | A L</regular expression> subpattern whose real purpose is to execute | |
543 | some Perl code, for example, the C<(?{...})> and C<(??{...})> | |
544 | subpatterns. | |
545 | ||
546 | =item collating sequence | |
547 | ||
548 | The order into which L<characters|/character> sort. This is used by | |
549 | L</string> comparison routines to decide, for example, where in this | |
550 | glossary to put "collating sequence". | |
551 | ||
552 | =item command | |
553 | ||
554 | In L</shell> programming, the syntactic combination of a program name | |
555 | and its arguments. More loosely, anything you type to a shell (a | |
556 | command interpreter) that starts it doing something. Even more | |
557 | loosely, a Perl L</statement>, which might start with a L</label> and | |
558 | typically ends with a semicolon. | |
559 | ||
560 | =item command buffering | |
561 | ||
562 | A mechanism in Perl that lets you store up the output of each Perl | |
563 | L</command> and then flush it out as a single request to the | |
564 | L</operating system>. It's enabled by setting the C<$|> | |
565 | (C<$AUTOFLUSH>) variable to a true value. It's used when you don't | |
566 | want data sitting around not going where it's supposed to, which may | |
567 | happen because the default on a L</file> or L</pipe> is to use | |
568 | L</block buffering>. | |
569 | ||
570 | =item command name | |
571 | ||
572 | The name of the program currently executing, as typed on the command | |
573 | line. In C, the L</command> name is passed to the program as the | |
574 | first command-line argument. In Perl, it comes in separately as | |
575 | C<$0>. | |
576 | ||
577 | =item command-line arguments | |
578 | ||
579 | The L<values|/value> you supply along with a program name when you | |
580 | tell a L</shell> to execute a L</command>. These values are passed to | |
581 | a Perl program through C<@ARGV>. | |
582 | ||
583 | =item comment | |
584 | ||
585 | A remark that doesn't affect the meaning of the program. In Perl, a | |
586 | comment is introduced by a C<#> character and continues to the end of | |
587 | the line. | |
588 | ||
589 | =item compilation unit | |
590 | ||
591 | The L</file> (or L</string>, in the case of L<eval|perlfunc/eval>) | |
592 | that is currently being compiled. | |
593 | ||
594 | =item compile phase | |
595 | ||
596 | Any time before Perl starts running your main program. See also | |
597 | L</run phase>. Compile phase is mostly spent in L</compile time>, but | |
598 | may also be spent in L</run time> when C<BEGIN> blocks, | |
599 | L<use|perlfunc/use> declarations, or constant subexpressions are being | |
600 | evaluated. The startup and import code of any L<use|perlfunc/use> | |
601 | declaration is also run during compile phase. | |
602 | ||
603 | =item compile time | |
604 | ||
605 | The time when Perl is trying to make sense of your code, as opposed to | |
606 | when it thinks it knows what your code means and is merely trying to | |
607 | do what it thinks your code says to do, which is L</run time>. | |
608 | ||
609 | =item compiler | |
610 | ||
611 | Strictly speaking, a program that munches up another program and spits | |
612 | out yet another file containing the program in a "more executable" | |
613 | form, typically containing native machine instructions. The I<perl> | |
614 | program is not a compiler by this definition, but it does contain a | |
615 | kind of compiler that takes a program and turns it into a more | |
616 | executable form (L<syntax trees|/syntax tree>) within the I<perl> | |
617 | process itself, which the L</interpreter> then interprets. There are, | |
618 | however, extension L<modules|/module> to get Perl to act more like a | |
619 | "real" compiler. See L<O>. | |
620 | ||
621 | =item composer | |
622 | ||
623 | A "constructor" for a L</referent> that isn't really an L</object>, | |
624 | like an anonymous array or a hash (or a sonata, for that matter). For | |
625 | example, a pair of braces acts as a composer for a hash, and a pair of | |
626 | brackets acts as a composer for an array. See L<perlref/Making | |
627 | References>. | |
628 | ||
629 | =item concatenation | |
630 | ||
631 | The process of gluing one cat's nose to another cat's tail. Also, a | |
632 | similar operation on two L<strings|/string>. | |
633 | ||
634 | =item conditional | |
635 | ||
636 | Something "iffy". See L</Boolean context>. | |
637 | ||
638 | =item connection | |
639 | ||
640 | In telephony, the temporary electrical circuit between the caller's | |
641 | and the callee's phone. In networking, the same kind of temporary | |
642 | circuit between a L</client> and a L</server>. | |
643 | ||
644 | =item construct | |
645 | ||
646 | As a noun, a piece of syntax made up of smaller pieces. As a | |
647 | transitive verb, to create an L</object> using a L</constructor>. | |
648 | ||
649 | =item constructor | |
650 | ||
651 | Any L</class method>, instance L</method>, or L</subroutine> | |
652 | that composes, initializes, blesses, and returns an L</object>. | |
653 | Sometimes we use the term loosely to mean a L</composer>. | |
654 | ||
655 | =item context | |
656 | ||
657 | The surroundings, or environment. The context given by the | |
658 | surrounding code determines what kind of data a particular | |
659 | L</expression> is expected to return. The three primary contexts are | |
660 | L</list context>, L</scalar context>, and L</void context>. Scalar | |
661 | context is sometimes subdivided into L</Boolean context>, L</numeric | |
662 | context>, L</string context>, and L</void context>. There's also a | |
663 | "don't care" scalar context (which is dealt with in Programming Perl, | |
664 | Third Edition, Chapter 2, "Bits and Pieces" if you care). | |
665 | ||
666 | =item continuation | |
667 | ||
668 | The treatment of more than one physical L</line> as a single logical | |
669 | line. L</Makefile> lines are continued by putting a backslash before | |
670 | the L</newline>. Mail headers as defined by RFC 822 are continued by | |
671 | putting a space or tab I<after> the newline. In general, lines in | |
672 | Perl do not need any form of continuation mark, because L</whitespace> | |
673 | (including newlines) is gleefully ignored. Usually. | |
674 | ||
675 | =item core dump | |
676 | ||
677 | The corpse of a L</process>, in the form of a file left in the | |
678 | L</working directory> of the process, usually as a result of certain | |
679 | kinds of fatal error. | |
680 | ||
681 | =item CPAN | |
682 | ||
683 | The 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?>). | |
684 | ||
685 | =item cracker | |
686 | ||
687 | Someone who breaks security on computer systems. A cracker may be a | |
688 | true L</hacker> or only a L</script kiddie>. | |
689 | ||
690 | =item current package | |
691 | ||
692 | The L</package> in which the current statement is compiled. Scan | |
693 | backwards in the text of your program through the current L<lexical | |
694 | scope|/lexical scoping> or any enclosing lexical scopes till you find | |
695 | a package declaration. That's your current package name. | |
696 | ||
697 | =item current working directory | |
698 | ||
699 | See L</working directory>. | |
700 | ||
701 | =item currently selected output channel | |
702 | ||
703 | The last L</filehandle> that was designated with | |
704 | L<select|perlfunc/select>(C<FILEHANDLE>); L</STDOUT>, if no filehandle | |
705 | has been selected. | |
706 | ||
707 | =item CV | |
708 | ||
709 | An internal "code value" typedef, holding a L</subroutine>. The L</CV> | |
710 | type is a subclass of L</SV>. | |
711 | ||
712 | =back | |
713 | ||
714 | =head2 D | |
715 | ||
716 | =over 4 | |
717 | ||
718 | =item dangling statement | |
719 | ||
720 | A bare, single L</statement>, without any braces, hanging off an C<if> | |
721 | or C<while> conditional. C allows them. Perl doesn't. | |
722 | ||
723 | =item data structure | |
724 | ||
725 | How your various pieces of data relate to each other and what shape | |
726 | they make when you put them all together, as in a rectangular table or | |
727 | a triangular-shaped tree. | |
728 | ||
729 | =item data type | |
730 | ||
731 | A set of possible values, together with all the operations that know | |
732 | how to deal with those values. For example, a numeric data type has a | |
733 | certain set of numbers that you can work with and various mathematical | |
734 | operations that you can do on the numbers but would make little sense | |
735 | on, say, a string such as C<"Kilroy">. Strings have their own | |
736 | operations, such as L</concatenation>. Compound types made of a | |
737 | number of smaller pieces generally have operations to compose and | |
738 | decompose them, and perhaps to rearrange them. L<Objects|/object> | |
739 | that model things in the real world often have operations that | |
740 | correspond to real activities. For instance, if you model an | |
741 | elevator, your elevator object might have an C<open_door()> | |
742 | L</method>. | |
743 | ||
744 | =item datagram | |
745 | ||
746 | A packet of data, such as a L</UDP> message, that (from the viewpoint | |
747 | of the programs involved) can be sent independently over the network. | |
748 | (In fact, all packets are sent independently at the L</IP> level, but | |
749 | L</stream> protocols such as L</TCP> hide this from your program.) | |
750 | ||
751 | =item DBM | |
752 | ||
753 | Stands for "Data Base Management" routines, a set of routines that | |
754 | emulate an L</associative array> using disk files. The routines use a | |
755 | dynamic hashing scheme to locate any entry with only two disk | |
756 | accesses. DBM files allow a Perl program to keep a persistent | |
757 | L</hash> across multiple invocations. You can L<tie|perlfunc/tie> | |
758 | your hash variables to various DBM implementations--see L<AnyDBM_File> | |
759 | and L<DB_File>. | |
760 | ||
761 | =item declaration | |
762 | ||
763 | An L</assertion> that states something exists and perhaps describes | |
764 | what it's like, without giving any commitment as to how or where | |
765 | you'll use it. A declaration is like the part of your recipe that | |
766 | says, "two cups flour, one large egg, four or five tadpoles..." See | |
767 | L</statement> for its opposite. Note that some declarations also | |
768 | function as statements. Subroutine declarations also act as | |
769 | definitions if a body is supplied. | |
770 | ||
771 | =item decrement | |
772 | ||
773 | To subtract a value from a variable, as in "decrement C<$x>" (meaning | |
774 | to remove 1 from its value) or "decrement C<$x> by 3". | |
775 | ||
776 | =item default | |
777 | ||
778 | A L</value> chosen for you if you don't supply a value of your own. | |
779 | ||
780 | =item defined | |
781 | ||
782 | Having a meaning. Perl thinks that some of the things people try to | |
783 | do are devoid of meaning, in particular, making use of variables that | |
784 | have never been given a L</value> and performing certain operations on | |
785 | data that isn't there. For example, if you try to read data past the | |
786 | end of a file, Perl will hand you back an undefined value. See also | |
787 | L</false> and L<perlfunc/defined>. | |
788 | ||
789 | =item delimiter | |
790 | ||
791 | A L</character> or L</string> that sets bounds to an arbitrarily-sized | |
792 | textual object, not to be confused with a L</separator> or | |
793 | L</terminator>. "To delimit" really just means "to surround" or "to | |
794 | enclose" (like these parentheses are doing). | |
795 | ||
796 | =item dereference | |
797 | ||
798 | A fancy computer science term meaning "to follow a L</reference> to | |
799 | what it points to". The "de" part of it refers to the fact that | |
800 | you're taking away one level of L</indirection>. | |
801 | ||
802 | =item derived class | |
803 | ||
804 | A L</class> that defines some of its L<methods|/method> in terms of a | |
805 | more generic class, called a L</base class>. Note that classes aren't | |
806 | classified exclusively into base classes or derived classes: a class | |
807 | can function as both a derived class and a base class simultaneously, | |
808 | which is kind of classy. | |
809 | ||
810 | =item descriptor | |
811 | ||
812 | See L</file descriptor>. | |
813 | ||
814 | =item destroy | |
815 | ||
816 | To deallocate the memory of a L</referent> (first triggering its | |
817 | C<DESTROY> method, if it has one). | |
818 | ||
819 | =item destructor | |
820 | ||
821 | A special L</method> that is called when an L</object> is thinking | |
822 | about L<destroying|/destroy> itself. A Perl program's C<DESTROY> | |
823 | method doesn't do the actual destruction; Perl just | |
824 | L<triggers|/trigger> the method in case the L</class> wants to do any | |
825 | associated cleanup. | |
826 | ||
827 | =item device | |
828 | ||
829 | A whiz-bang hardware gizmo (like a disk or tape drive or a modem or a | |
830 | joystick or a mouse) attached to your computer, that the L</operating | |
831 | system> tries to make look like a L</file> (or a bunch of files). | |
832 | Under Unix, these fake files tend to live in the I</dev> directory. | |
833 | ||
834 | =item directive | |
835 | ||
836 | A L</pod> directive. See L<perlpod>. | |
837 | ||
838 | =item directory | |
839 | ||
840 | A special file that contains other files. Some L<operating | |
841 | systems|/operating system> call these "folders", "drawers", or | |
842 | "catalogs". | |
843 | ||
844 | =item directory handle | |
845 | ||
846 | A name that represents a particular instance of opening a directory to | |
847 | read it, until you close it. See the L<opendir|perlfunc/opendir> | |
848 | function. | |
849 | ||
850 | =item dispatch | |
851 | ||
852 | To send something to its correct destination. Often used | |
853 | metaphorically to indicate a transfer of programmatic control to a | |
854 | destination selected algorithmically, often by lookup in a table of | |
855 | function L<references|/reference> or, in the case of object | |
856 | L<methods|/method>, by traversing the inheritance tree looking for the | |
857 | most specific definition for the method. | |
858 | ||
859 | =item distribution | |
860 | ||
861 | A standard, bundled release of a system of software. The default | |
862 | usage implies source code is included. If that is not the case, it | |
863 | will be called a "binary-only" distribution. | |
864 | ||
865 | =item dweomer | |
866 | ||
867 | An enchantment, illusion, phantasm, or jugglery. Said when Perl's | |
868 | magical L</dwimmer> effects don't do what you expect, but rather seem | |
869 | to be the product of arcane dweomercraft, sorcery, or wonder working. | |
870 | [From Old English] | |
871 | ||
872 | =item dwimmer | |
873 | ||
874 | DWIM is an acronym for "Do What I Mean", the principle that something | |
875 | should just do what you want it to do without an undue amount of fuss. | |
876 | A bit of code that does "dwimming" is a "dwimmer". Dwimming can | |
877 | require a great deal of behind-the-scenes magic, which (if it doesn't | |
878 | stay properly behind the scenes) is called a L</dweomer> instead. | |
879 | ||
880 | =item dynamic scoping | |
881 | ||
882 | Dynamic scoping works over a dynamic scope, making variables visible | |
883 | throughout the rest of the L</block> in which they are first used and | |
884 | in any L<subroutines|/subroutine> that are called by the rest of the | |
885 | block. Dynamically scoped variables can have their values temporarily | |
886 | changed (and implicitly restored later) by a L<local|perlfunc/local> | |
887 | operator. (Compare L</lexical scoping>.) Used more loosely to mean | |
888 | how a subroutine that is in the middle of calling another subroutine | |
889 | "contains" that subroutine at L</run time>. | |
890 | ||
891 | =back | |
892 | ||
893 | =head2 E | |
894 | ||
895 | =over 4 | |
896 | ||
897 | =item eclectic | |
898 | ||
899 | Derived from many sources. Some would say I<too> many. | |
900 | ||
901 | =item element | |
902 | ||
903 | A basic building block. When you're talking about an L</array>, it's | |
904 | one of the items that make up the array. | |
905 | ||
906 | =item embedding | |
907 | ||
908 | When something is contained in something else, particularly when that | |
909 | might be considered surprising: "I've embedded a complete Perl | |
910 | interpreter in my editor!" | |
911 | ||
912 | =item empty subclass test | |
913 | ||
914 | The notion that an empty L</derived class> should behave exactly like | |
915 | its L</base class>. | |
916 | ||
917 | =item en passant | |
918 | ||
919 | When you change a L</value> as it is being copied. [From French, "in | |
920 | passing", as in the exotic pawn-capturing maneuver in chess.] | |
921 | ||
922 | =item encapsulation | |
923 | ||
924 | The veil of abstraction separating the L</interface> from the | |
925 | L</implementation> (whether enforced or not), which mandates that all | |
926 | access to an L</object>'s state be through L<methods|/method> alone. | |
927 | ||
928 | =item endian | |
929 | ||
930 | See L</little-endian> and L</big-endian>. | |
931 | ||
932 | =item environment | |
933 | ||
934 | The collective set of L<environment variables|/environment variable> | |
935 | your L</process> inherits from its parent. Accessed via C<%ENV>. | |
936 | ||
937 | =item environment variable | |
938 | ||
939 | A mechanism by which some high-level agent such as a user can pass its | |
940 | preferences down to its future offspring (child L<processes|/process>, | |
941 | grandchild processes, great-grandchild processes, and so on). Each | |
942 | environment variable is a L</key>/L</value> pair, like one entry in a | |
943 | L</hash>. | |
944 | ||
945 | =item EOF | |
946 | ||
947 | End of File. Sometimes used metaphorically as the terminating string | |
948 | of a L</here document>. | |
949 | ||
950 | =item errno | |
951 | ||
952 | The error number returned by a L</syscall> when it fails. Perl refers | |
953 | to the error by the name C<$!> (or C<$OS_ERROR> if you use the English | |
954 | module). | |
955 | ||
956 | =item error | |
957 | ||
958 | See L</exception> or L</fatal error>. | |
959 | ||
960 | =item escape sequence | |
961 | ||
962 | See L</metasymbol>. | |
963 | ||
964 | =item exception | |
965 | ||
966 | A fancy term for an error. See L</fatal error>. | |
967 | ||
968 | =item exception handling | |
969 | ||
970 | The way a program responds to an error. The exception handling | |
971 | mechanism in Perl is the L<eval|perlfunc/eval> operator. | |
972 | ||
973 | =item exec | |
974 | ||
975 | To throw away the current L</process>'s program and replace it with | |
976 | another without exiting the process or relinquishing any resources | |
977 | held (apart from the old memory image). | |
978 | ||
979 | =item executable file | |
980 | ||
981 | A L</file> that is specially marked to tell the L</operating system> | |
982 | that it's okay to run this file as a program. Usually shortened to | |
983 | "executable". | |
984 | ||
985 | =item execute | |
986 | ||
987 | To run a L<program|/executable file> or L</subroutine>. (Has nothing | |
988 | to do with the L<kill|perlfunc/kill> built-in, unless you're trying to | |
989 | run a L</signal handler>.) | |
990 | ||
991 | =item execute bit | |
992 | ||
993 | The special mark that tells the operating system it can run this | |
994 | program. There are actually three execute bits under Unix, and which | |
995 | bit gets used depends on whether you own the file singularly, | |
996 | collectively, or not at all. | |
997 | ||
998 | =item exit status | |
999 | ||
1000 | See L</status>. | |
1001 | ||
1002 | =item export | |
1003 | ||
1004 | To make symbols from a L</module> available for L</import> by other modules. | |
1005 | ||
1006 | =item expression | |
1007 | ||
1008 | Anything you can legally say in a spot where a L</value> is required. | |
1009 | Typically composed of L<literals|/literal>, L<variables|/variable>, | |
1010 | L<operators|/operator>, L<functions|/function>, and L</subroutine> | |
1011 | calls, not necessarily in that order. | |
1012 | ||
1013 | =item extension | |
1014 | ||
1015 | A Perl module that also pulls in compiled C or C++ code. More | |
1016 | generally, any experimental option that can be compiled into Perl, | |
1017 | such as multithreading. | |
1018 | ||
1019 | =back | |
1020 | ||
1021 | =head2 F | |
1022 | ||
1023 | =over 4 | |
1024 | ||
1025 | =item false | |
1026 | ||
1027 | In Perl, any value that would look like C<""> or C<"0"> if evaluated | |
1028 | in a string context. Since undefined values evaluate to C<"">, all | |
1029 | undefined values are false, but not all false values are undefined. | |
1030 | ||
1031 | =item FAQ | |
1032 | ||
1033 | Frequently Asked Question (although not necessarily frequently | |
1034 | answered, especially if the answer appears in the Perl FAQ shipped | |
1035 | standard with Perl). | |
1036 | ||
1037 | =item fatal error | |
1038 | ||
1039 | An uncaught L</exception>, which causes termination of the L</process> | |
1040 | after printing a message on your L</standard error> stream. Errors | |
1041 | that happen inside an L<eval|perlfunc/eval> are not fatal. Instead, | |
1042 | the L<eval|perlfunc/eval> terminates after placing the exception | |
1043 | message in the C<$@> (C<$EVAL_ERROR>) variable. You can try to | |
1044 | provoke a fatal error with the L<die|perlfunc/die> operator (known as | |
1045 | throwing or raising an exception), but this may be caught by a | |
1046 | dynamically enclosing L<eval|perlfunc/eval>. If not caught, the | |
1047 | L<die|perlfunc/die> becomes a fatal error. | |
1048 | ||
1049 | =item field | |
1050 | ||
1051 | A single piece of numeric or string data that is part of a longer | |
1052 | L</string>, L</record>, or L</line>. Variable-width fields are usually | |
1053 | split up by L<separators|/separator> (so use L<split|perlfunc/split> to | |
1054 | extract the fields), while fixed-width fields are usually at fixed | |
1055 | positions (so use L<unpack|perlfunc/unpack>). L<Instance | |
1056 | variables|/instance variable> are also known as fields. | |
1057 | ||
1058 | =item FIFO | |
1059 | ||
1060 | First In, First Out. See also L</LIFO>. Also, a nickname for a | |
1061 | L</named pipe>. | |
1062 | ||
1063 | =item file | |
1064 | ||
1065 | A named collection of data, usually stored on disk in a L</directory> | |
1066 | in a L</filesystem>. Roughly like a document, if you're into office | |
1067 | metaphors. In modern filesystems, you can actually give a file more | |
1068 | than one name. Some files have special properties, like directories | |
1069 | and devices. | |
1070 | ||
1071 | =item file descriptor | |
1072 | ||
1073 | The little number the L</operating system> uses to keep track of which | |
1074 | opened L</file> you're talking about. Perl hides the file descriptor | |
1075 | inside a L</standard IE<sol>O> stream and then attaches the stream to | |
1076 | a L</filehandle>. | |
1077 | ||
1078 | =item file test operator | |
1079 | ||
1080 | A built-in unary operator that you use to determine whether something | |
1081 | is L</true> about a file, such as C<-o $filename> to test whether | |
1082 | you're the owner of the file. | |
1083 | ||
1084 | =item fileglob | |
1085 | ||
1086 | A "wildcard" match on L<filenames|/filename>. See the | |
1087 | L<glob|perlfunc/glob> function. | |
1088 | ||
1089 | =item filehandle | |
1090 | ||
1091 | An identifier (not necessarily related to the real name of a file) | |
1092 | that represents a particular instance of opening a file until you | |
1093 | close it. If you're going to open and close several different files | |
1094 | in succession, it's fine to open each of them with the same | |
1095 | filehandle, so you don't have to write out separate code to process | |
1096 | each file. | |
1097 | ||
1098 | =item filename | |
1099 | ||
1100 | One name for a file. This name is listed in a L</directory>, and you | |
1101 | can use it in an L<open|perlfunc/open> to tell the L</operating | |
1102 | system> exactly which file you want to open, and associate the file | |
1103 | with a L</filehandle> which will carry the subsequent identity of that | |
1104 | file in your program, until you close it. | |
1105 | ||
1106 | =item filesystem | |
1107 | ||
1108 | A set of L<directories|/directory> and L<files|/file> residing on a | |
1109 | partition of the disk. Sometimes known as a "partition". You can | |
1110 | change the file's name or even move a file around from directory to | |
1111 | directory within a filesystem without actually moving the file itself, | |
1112 | at least under Unix. | |
1113 | ||
1114 | =item filter | |
1115 | ||
1116 | A program designed to take a L</stream> of input and transform it into | |
1117 | a stream of output. | |
1118 | ||
1119 | =item flag | |
1120 | ||
1121 | We tend to avoid this term because it means so many things. It may | |
1122 | mean a command-line L</switch> that takes no argument | |
1123 | itself (such as Perl's B<-n> and B<-p> | |
1124 | flags) or, less frequently, a single-bit indicator (such as the | |
1125 | C<O_CREAT> and C<O_EXCL> flags used in | |
1126 | L<sysopen|perlfunc/sysopen>). | |
1127 | ||
1128 | =item floating point | |
1129 | ||
1130 | A method of storing numbers in "scientific notation", such that the | |
1131 | precision of the number is independent of its magnitude (the decimal | |
1132 | point "floats"). Perl does its numeric work with floating-point | |
1133 | numbers (sometimes called "floats"), when it can't get away with | |
1134 | using L<integers|/integer>. Floating-point numbers are mere | |
1135 | approximations of real numbers. | |
1136 | ||
1137 | =item flush | |
1138 | ||
1139 | The act of emptying a L</buffer>, often before it's full. | |
1140 | ||
1141 | =item FMTEYEWTK | |
1142 | ||
1143 | Far More Than Everything You Ever Wanted To Know. An exhaustive | |
1144 | treatise on one narrow topic, something of a super-L</FAQ>. See Tom | |
1145 | for far more. | |
1146 | ||
1147 | =item fork | |
1148 | ||
1149 | To create a child L</process> identical to the parent process at its | |
1150 | moment of conception, at least until it gets ideas of its own. A | |
1151 | thread with protected memory. | |
1152 | ||
1153 | =item formal arguments | |
1154 | ||
1155 | The generic names by which a L</subroutine> knows its | |
1156 | L<arguments|/argument>. In many languages, formal arguments are | |
1157 | always given individual names, but in Perl, the formal arguments are | |
1158 | just the elements of an array. The formal arguments to a Perl program | |
1159 | are C<$ARGV[0]>, C<$ARGV[1]>, and so on. Similarly, the formal | |
1160 | arguments to a Perl subroutine are C<$_[0]>, C<$_[1]>, and so on. You | |
1161 | may give the arguments individual names by assigning the values to a | |
1162 | L<my|perlfunc/my> list. See also L</actual arguments>. | |
1163 | ||
1164 | =item format | |
1165 | ||
1166 | A specification of how many spaces and digits and things to put | |
1167 | somewhere so that whatever you're printing comes out nice and pretty. | |
1168 | ||
1169 | =item freely available | |
1170 | ||
1171 | Means you don't have to pay money to get it, but the copyright on it | |
1172 | may still belong to someone else (like Larry). | |
1173 | ||
1174 | =item freely redistributable | |
1175 | ||
1176 | Means you're not in legal trouble if you give a bootleg copy of it to | |
1177 | your friends and we find out about it. In fact, we'd rather you gave | |
1178 | a copy to all your friends. | |
1179 | ||
1180 | =item freeware | |
1181 | ||
1182 | Historically, any software that you give away, particularly if you | |
1183 | make the source code available as well. Now often called C<open | |
1184 | source software>. Recently there has been a trend to use the term in | |
1185 | contradistinction to L</open source software>, to refer only to free | |
1186 | software released under the Free Software Foundation's GPL (General | |
1187 | Public License), but this is difficult to justify etymologically. | |
1188 | ||
1189 | =item function | |
1190 | ||
1191 | Mathematically, a mapping of each of a set of input values to a | |
1192 | particular output value. In computers, refers to a L</subroutine> or | |
1193 | L</operator> that returns a L</value>. It may or may not have input | |
1194 | values (called L<arguments|/argument>). | |
1195 | ||
1196 | =item funny character | |
1197 | ||
1198 | Someone like Larry, or one of his peculiar friends. Also refers to | |
1199 | the strange prefixes that Perl requires as noun markers on its | |
1200 | variables. | |
1201 | ||
1202 | =item garbage collection | |
1203 | ||
1204 | A misnamed feature--it should be called, "expecting your mother to | |
1205 | pick up after you". Strictly speaking, Perl doesn't do this, but it | |
1206 | relies on a reference-counting mechanism to keep things tidy. | |
1207 | However, we rarely speak strictly and will often refer to the | |
1208 | reference-counting scheme as a form of garbage collection. (If it's | |
1209 | any comfort, when your interpreter exits, a "real" garbage collector | |
1210 | runs to make sure everything is cleaned up if you've been messy with | |
1211 | circular references and such.) | |
1212 | ||
1213 | =back | |
1214 | ||
1215 | =head2 G | |
1216 | ||
1217 | =over 4 | |
1218 | ||
1219 | =item GID | |
1220 | ||
1221 | Group ID--in Unix, the numeric group ID that the L</operating system> | |
1222 | uses to identify you and members of your L</group>. | |
1223 | ||
1224 | =item glob | |
1225 | ||
1226 | Strictly, the shell's C<*> character, which will match a "glob" of | |
1227 | characters when you're trying to generate a list of filenames. | |
1228 | Loosely, the act of using globs and similar symbols to do pattern | |
1229 | matching. See also L</fileglob> and L</typeglob>. | |
1230 | ||
1231 | =item global | |
1232 | ||
1233 | Something you can see from anywhere, usually used of | |
1234 | L<variables|/variable> and L<subroutines|/subroutine> that are visible | |
1235 | everywhere in your program. In Perl, only certain special variables | |
1236 | are truly global--most variables (and all subroutines) exist only in | |
1237 | the current L</package>. Global variables can be declared with | |
1238 | L<our|perlfunc/our>. See L<perlfunc/our>. | |
1239 | ||
1240 | =item global destruction | |
1241 | ||
1242 | The L</garbage collection> of globals (and the running of any | |
1243 | associated object destructors) that takes place when a Perl | |
1244 | L</interpreter> is being shut down. Global destruction should not be | |
1245 | confused with the Apocalypse, except perhaps when it should. | |
1246 | ||
1247 | =item glue language | |
1248 | ||
1249 | A language such as Perl that is good at hooking things together that | |
1250 | weren't intended to be hooked together. | |
1251 | ||
1252 | =item granularity | |
1253 | ||
1254 | The size of the pieces you're dealing with, mentally speaking. | |
1255 | ||
1256 | =item greedy | |
1257 | ||
1258 | A L</subpattern> whose L</quantifier> wants to match as many things as | |
1259 | possible. | |
1260 | ||
1261 | =item grep | |
1262 | ||
1263 | Originally from the old Unix editor command for "Globally search for a | |
1264 | Regular Expression and Print it", now used in the general sense of any | |
1265 | kind of search, especially text searches. Perl has a built-in | |
1266 | L<grep|perlfunc/grep> function that searches a list for elements | |
1267 | matching any given criterion, whereas the I<grep>(1) program searches | |
1268 | for lines matching a L</regular expression> in one or more files. | |
1269 | ||
1270 | =item group | |
1271 | ||
1272 | A set of users of which you are a member. In some operating systems | |
1273 | (like Unix), you can give certain file access permissions to other | |
1274 | members of your group. | |
1275 | ||
1276 | =item GV | |
1277 | ||
1278 | An internal "glob value" typedef, holding a L</typeglob>. The L</GV> | |
1279 | type is a subclass of L</SV>. | |
1280 | ||
1281 | =back | |
1282 | ||
1283 | =head2 H | |
1284 | ||
1285 | =over 4 | |
1286 | ||
1287 | =item hacker | |
1288 | ||
1289 | Someone who is brilliantly persistent in solving technical problems, | |
1290 | whether these involve golfing, fighting orcs, or programming. Hacker | |
1291 | is a neutral term, morally speaking. Good hackers are not to be | |
1292 | confused with evil L<crackers|/cracker> or clueless L<script | |
1293 | kiddies|/script kiddie>. If you confuse them, we will presume that | |
1294 | you are either evil or clueless. | |
1295 | ||
1296 | =item handler | |
1297 | ||
1298 | A L</subroutine> or L</method> that is called by Perl when your | |
1299 | program needs to respond to some internal event, such as a L</signal>, | |
1300 | or an encounter with an operator subject to L</operator overloading>. | |
1301 | See also L</callback>. | |
1302 | ||
1303 | =item hard reference | |
1304 | ||
1305 | A L</scalar> L</value> containing the actual address of a | |
1306 | L</referent>, such that the referent's L</reference> count accounts | |
1307 | for it. (Some hard references are held internally, such as the | |
1308 | implicit reference from one of a L</typeglob>'s variable slots to its | |
1309 | corresponding referent.) A hard reference is different from a | |
1310 | L</symbolic reference>. | |
1311 | ||
1312 | =item hash | |
1313 | ||
1314 | An unordered association of L</key>/L</value> pairs, stored such that | |
1315 | you can easily use a string L</key> to look up its associated data | |
1316 | L</value>. This glossary is like a hash, where the word to be defined | |
1317 | is the key, and the definition is the value. A hash is also sometimes | |
1318 | septisyllabically called an "associative array", which is a pretty | |
1319 | good reason for simply calling it a "hash" instead. | |
1320 | ||
1321 | =item hash table | |
1322 | ||
1323 | A data structure used internally by Perl for implementing associative | |
1324 | arrays (hashes) efficiently. See also L</bucket>. | |
1325 | ||
1326 | =item header file | |
1327 | ||
1328 | A file containing certain required definitions that you must include | |
1329 | "ahead" of the rest of your program to do certain obscure operations. | |
1330 | A C header file has a I<.h> extension. Perl doesn't really have | |
1331 | header files, though historically Perl has sometimes used translated | |
1332 | I<.h> files with a I<.ph> extension. See L<perlfunc/require>. | |
1333 | (Header files have been superseded by the L</module> mechanism.) | |
1334 | ||
1335 | =item here document | |
1336 | ||
1337 | So called because of a similar construct in L<shells|/shell> that | |
1338 | pretends that the L<lines|/line> following the L</command> are a | |
1339 | separate L</file> to be fed to the command, up to some terminating | |
1340 | string. In Perl, however, it's just a fancy form of quoting. | |
1341 | ||
1342 | =item hexadecimal | |
1343 | ||
1344 | A number in base 16, "hex" for short. The digits for 10 through 16 | |
1345 | are customarily represented by the letters C<a> through C<f>. | |
1346 | Hexadecimal constants in Perl start with C<0x>. See also | |
1347 | L<perlfunc/hex>. | |
1348 | ||
1349 | =item home directory | |
1350 | ||
1351 | The directory you are put into when you log in. On a Unix system, the | |
1352 | name is often placed into C<$ENV{HOME}> or C<$ENV{LOGDIR}> by | |
1353 | I<login>, but you can also find it with C<(getpwuid($E<lt>))[7]>. | |
1354 | (Some platforms do not have a concept of a home directory.) | |
1355 | ||
1356 | =item host | |
1357 | ||
1358 | The computer on which a program or other data resides. | |
1359 | ||
1360 | =item hubris | |
1361 | ||
1362 | Excessive pride, the sort of thing Zeus zaps you for. Also the | |
1363 | quality that makes you write (and maintain) programs that other people | |
1364 | won't want to say bad things about. Hence, the third great virtue of | |
1365 | a programmer. See also L</laziness> and L</impatience>. | |
1366 | ||
1367 | =item HV | |
1368 | ||
1369 | Short for a "hash value" typedef, which holds Perl's internal | |
1370 | representation of a hash. The L</HV> type is a subclass of L</SV>. | |
1371 | ||
1372 | =back | |
1373 | ||
1374 | =head2 I | |
1375 | ||
1376 | =over 4 | |
1377 | ||
1378 | =item identifier | |
1379 | ||
1380 | A legally formed name for most anything in which a computer program | |
1381 | might be interested. Many languages (including Perl) allow | |
1382 | identifiers that start with a letter and contain letters and digits. | |
1383 | Perl also counts the underscore character as a valid letter. (Perl | |
1384 | also has more complicated names, such as L</qualified> names.) | |
1385 | ||
1386 | =item impatience | |
1387 | ||
1388 | The anger you feel when the computer is being lazy. This makes you | |
1389 | write programs that don't just react to your needs, but actually | |
1390 | anticipate them. Or at least that pretend to. Hence, the second | |
1391 | great virtue of a programmer. See also L</laziness> and L</hubris>. | |
1392 | ||
1393 | =item implementation | |
1394 | ||
1395 | How a piece of code actually goes about doing its job. Users of the | |
1396 | code should not count on implementation details staying the same | |
1397 | unless they are part of the published L</interface>. | |
1398 | ||
1399 | =item import | |
1400 | ||
1401 | To gain access to symbols that are exported from another module. See | |
1402 | L<perlfunc/use>. | |
1403 | ||
1404 | =item increment | |
1405 | ||
1406 | To increase the value of something by 1 (or by some other number, if | |
1407 | so specified). | |
1408 | ||
1409 | =item indexing | |
1410 | ||
1411 | In olden days, the act of looking up a L</key> in an actual index | |
1412 | (such as a phone book), but now merely the act of using any kind of | |
1413 | key or position to find the corresponding L</value>, even if no index | |
1414 | is involved. Things have degenerated to the point that Perl's | |
1415 | L<index|perlfunc/index> function merely locates the position (index) | |
1416 | of one string in another. | |
1417 | ||
1418 | =item indirect filehandle | |
1419 | ||
1420 | An L</expression> that evaluates to something that can be used as a | |
1421 | L</filehandle>: a L</string> (filehandle name), a L</typeglob>, a | |
1422 | typeglob L</reference>, or a low-level L</IO> object. | |
1423 | ||
1424 | =item indirect object | |
1425 | ||
1426 | In English grammar, a short noun phrase between a verb and its direct | |
1427 | object indicating the beneficiary or recipient of the action. In | |
1428 | Perl, C<print STDOUT "$foo\n";> can be understood as "verb | |
1429 | indirect-object object" where L</STDOUT> is the recipient of the | |
1430 | L<print|perlfunc/print> action, and C<"$foo"> is the object being | |
1431 | printed. Similarly, when invoking a L</method>, you might place the | |
1432 | invocant between the method and its arguments: | |
1433 | ||
1434 | $gollum = new Pathetic::Creature "Smeagol"; | |
1435 | give $gollum "Fisssssh!"; | |
1436 | give $gollum "Precious!"; | |
1437 | ||
1438 | =item indirect object slot | |
1439 | ||
1440 | The syntactic position falling between a method call and its arguments | |
1441 | when using the indirect object invocation syntax. (The slot is | |
1442 | distinguished by the absence of a comma between it and the next | |
1443 | argument.) L</STDERR> is in the indirect object slot here: | |
1444 | ||
1445 | print STDERR "Awake! Awake! Fear, Fire, | |
1446 | Foes! Awake!\n"; | |
1447 | ||
1448 | =item indirection | |
1449 | ||
1450 | If something in a program isn't the value you're looking for but | |
1451 | indicates where the value is, that's indirection. This can be done | |
1452 | with either L<symbolic references|/symbolic reference> or L<hard | |
1453 | references|/hard reference>. | |
1454 | ||
1455 | =item infix | |
1456 | ||
1457 | An L</operator> that comes in between its L<operands|/operand>, such | |
1458 | as multiplication in C<24 * 7>. | |
1459 | ||
1460 | =item inheritance | |
1461 | ||
1462 | What you get from your ancestors, genetically or otherwise. If you | |
1463 | happen to be a L</class>, your ancestors are called L<base | |
1464 | classes|/base class> and your descendants are called L<derived | |
1465 | classes|/derived class>. See L</single inheritance> and L</multiple | |
1466 | inheritance>. | |
1467 | ||
1468 | =item instance | |
1469 | ||
1470 | Short for "an instance of a class", meaning an L</object> of that L</class>. | |
1471 | ||
1472 | =item instance variable | |
1473 | ||
1474 | An L</attribute> of an L</object>; data stored with the particular | |
1475 | object rather than with the class as a whole. | |
1476 | ||
1477 | =item integer | |
1478 | ||
1479 | A number with no fractional (decimal) part. A counting number, like | |
1480 | 1, 2, 3, and so on, but including 0 and the negatives. | |
1481 | ||
1482 | =item interface | |
1483 | ||
1484 | The services a piece of code promises to provide forever, in contrast to | |
1485 | its L</implementation>, which it should feel free to change whenever it | |
1486 | likes. | |
1487 | ||
1488 | =item interpolation | |
1489 | ||
1490 | The insertion of a scalar or list value somewhere in the middle of | |
1491 | another value, such that it appears to have been there all along. In | |
1492 | Perl, variable interpolation happens in double-quoted strings and | |
1493 | patterns, and list interpolation occurs when constructing the list of | |
1494 | values to pass to a list operator or other such construct that takes a | |
1495 | L</LIST>. | |
1496 | ||
1497 | =item interpreter | |
1498 | ||
1499 | Strictly speaking, a program that reads a second program and does what | |
1500 | the second program says directly without turning the program into a | |
1501 | different form first, which is what L<compilers|/compiler> do. Perl | |
1502 | is not an interpreter by this definition, because it contains a kind | |
1503 | of compiler that takes a program and turns it into a more executable | |
1504 | form (L<syntax trees|/syntax tree>) within the I<perl> process itself, | |
1505 | which the Perl L</run time> system then interprets. | |
1506 | ||
1507 | =item invocant | |
1508 | ||
1509 | The agent on whose behalf a L</method> is invoked. In a L</class> | |
1510 | method, the invocant is a package name. In an L</instance> method, | |
1511 | the invocant is an object reference. | |
1512 | ||
1513 | =item invocation | |
1514 | ||
1515 | The act of calling up a deity, daemon, program, method, subroutine, or | |
1516 | function to get it do what you think it's supposed to do. We usually | |
1517 | "call" subroutines but "invoke" methods, since it sounds cooler. | |
1518 | ||
1519 | =item I/O | |
1520 | ||
1521 | Input from, or output to, a L</file> or L</device>. | |
1522 | ||
1523 | =item IO | |
1524 | ||
1525 | An internal I/O object. Can also mean L</indirect object>. | |
1526 | ||
1527 | =item IP | |
1528 | ||
1529 | Internet Protocol, or Intellectual Property. | |
1530 | ||
1531 | =item IPC | |
1532 | ||
1533 | Interprocess Communication. | |
1534 | ||
1535 | =item is-a | |
1536 | ||
1537 | A relationship between two L<objects|/object> in which one object is | |
1538 | considered to be a more specific version of the other, generic object: | |
1539 | "A camel is a mammal." Since the generic object really only exists in | |
1540 | a Platonic sense, we usually add a little abstraction to the notion of | |
1541 | objects and think of the relationship as being between a generic | |
1542 | L</base class> and a specific L</derived class>. Oddly enough, | |
1543 | Platonic classes don't always have Platonic relationships--see | |
1544 | L</inheritance>. | |
1545 | ||
1546 | =item iteration | |
1547 | ||
1548 | Doing something repeatedly. | |
1549 | ||
1550 | =item iterator | |
1551 | ||
1552 | A special programming gizmo that keeps track of where you are in | |
1553 | something that you're trying to iterate over. The C<foreach> loop in | |
1554 | Perl contains an iterator; so does a hash, allowing you to | |
1555 | L<each|perlfunc/each> through it. | |
1556 | ||
1557 | =item IV | |
1558 | ||
1559 | The integer four, not to be confused with six, Tom's favorite editor. | |
1560 | IV also means an internal Integer Value of the type a L</scalar> can | |
1561 | hold, not to be confused with an L</NV>. | |
1562 | ||
1563 | =back | |
1564 | ||
1565 | =head2 J | |
1566 | ||
1567 | =over 4 | |
1568 | ||
1569 | =item JAPH | |
1570 | ||
1571 | "Just Another Perl Hacker," a clever but cryptic bit of Perl code that | |
1572 | when executed, evaluates to that string. Often used to illustrate a | |
1573 | particular Perl feature, and something of an ungoing Obfuscated Perl | |
1574 | Contest seen in Usenix signatures. | |
1575 | ||
1576 | =back | |
1577 | ||
1578 | =head2 K | |
1579 | ||
1580 | =over 4 | |
1581 | ||
1582 | =item key | |
1583 | ||
1584 | The string index to a L</hash>, used to look up the L</value> | |
1585 | associated with that key. | |
1586 | ||
1587 | =item keyword | |
1588 | ||
1589 | See L</reserved words>. | |
1590 | ||
1591 | =back | |
1592 | ||
1593 | =head2 L | |
1594 | ||
1595 | =over 4 | |
1596 | ||
1597 | =item label | |
1598 | ||
1599 | A name you give to a L</statement> so that you can talk about that | |
1600 | statement elsewhere in the program. | |
1601 | ||
1602 | =item laziness | |
1603 | ||
1604 | The quality that makes you go to great effort to reduce overall energy | |
1605 | expenditure. It makes you write labor-saving programs that other | |
1606 | people will find useful, and document what you wrote so you don't have | |
1607 | to answer so many questions about it. Hence, the first great virtue | |
1608 | of a programmer. Also hence, this book. See also L</impatience> and | |
1609 | L</hubris>. | |
1610 | ||
1611 | =item left shift | |
1612 | ||
1613 | A L</bit shift> that multiplies the number by some power of 2. | |
1614 | ||
1615 | =item leftmost longest | |
1616 | ||
1617 | The preference of the L</regular expression> engine to match the | |
1618 | leftmost occurrence of a L</pattern>, then given a position at which a | |
1619 | match will occur, the preference for the longest match (presuming the | |
1620 | use of a L</greedy> quantifier). See L<perlre> for I<much> more on | |
1621 | this subject. | |
1622 | ||
1623 | =item lexeme | |
1624 | ||
1625 | Fancy term for a L</token>. | |
1626 | ||
1627 | =item lexer | |
1628 | ||
1629 | Fancy term for a L</tokener>. | |
1630 | ||
1631 | =item lexical analysis | |
1632 | ||
1633 | Fancy term for L</tokenizing>. | |
1634 | ||
1635 | =item lexical scoping | |
1636 | ||
1637 | Looking at your I<Oxford English Dictionary> through a microscope. | |
1638 | (Also known as L</static scoping>, because dictionaries don't change | |
1639 | very fast.) Similarly, looking at variables stored in a private | |
1640 | dictionary (namespace) for each scope, which are visible only from | |
1641 | their point of declaration down to the end of the lexical scope in | |
1642 | which they are declared. --Syn. L</static scoping>. | |
1643 | --Ant. L</dynamic scoping>. | |
1644 | ||
1645 | =item lexical variable | |
1646 | ||
1647 | A L</variable> subject to L</lexical scoping>, declared by | |
1648 | L<my|perlfunc/my>. Often just called a "lexical". (The | |
1649 | L<our|perlfunc/our> declaration declares a lexically scoped name for a | |
1650 | global variable, which is not itself a lexical variable.) | |
1651 | ||
1652 | =item library | |
1653 | ||
1654 | Generally, a collection of procedures. In ancient days, referred to a | |
1655 | collection of subroutines in a I<.pl> file. In modern times, refers | |
1656 | more often to the entire collection of Perl L<modules|/module> on your | |
1657 | system. | |
1658 | ||
1659 | =item LIFO | |
1660 | ||
1661 | Last In, First Out. See also L</FIFO>. A LIFO is usually called a | |
1662 | L</stack>. | |
1663 | ||
1664 | =item line | |
1665 | ||
1666 | In Unix, a sequence of zero or more non-newline characters terminated | |
1667 | with a L</newline> character. On non-Unix machines, this is emulated | |
1668 | by the C library even if the underlying L</operating system> has | |
1669 | different ideas. | |
1670 | ||
1671 | =item line buffering | |
1672 | ||
1673 | Used by a L</standard IE<sol>O> output stream that flushes its | |
1674 | L</buffer> after every L</newline>. Many standard I/O libraries | |
1675 | automatically set up line buffering on output that is going to the | |
1676 | terminal. | |
1677 | ||
1678 | =item line number | |
1679 | ||
1680 | The number of lines read previous to this one, plus 1. Perl keeps a | |
1681 | separate line number for each source or input file it opens. The | |
1682 | current source file's line number is represented by C<__LINE__>. The | |
1683 | current input line number (for the file that was most recently read | |
1684 | via C<< E<lt>FHE<gt> >>) is represented by the C<$.> | |
1685 | (C<$INPUT_LINE_NUMBER>) variable. Many error messages report both | |
1686 | values, if available. | |
1687 | ||
1688 | =item link | |
1689 | ||
1690 | Used as a noun, a name in a L</directory>, representing a L</file>. A | |
1691 | given file can have multiple links to it. It's like having the same | |
1692 | phone number listed in the phone directory under different names. As | |
1693 | a verb, to resolve a partially compiled file's unresolved symbols into | |
1694 | a (nearly) executable image. Linking can generally be static or | |
1695 | dynamic, which has nothing to do with static or dynamic scoping. | |
1696 | ||
1697 | =item LIST | |
1698 | ||
1699 | A syntactic construct representing a comma-separated list of | |
1700 | expressions, evaluated to produce a L</list value>. Each | |
1701 | L</expression> in a L</LIST> is evaluated in L</list context> and | |
1702 | interpolated into the list value. | |
1703 | ||
1704 | =item list | |
1705 | ||
1706 | An ordered set of scalar values. | |
1707 | ||
1708 | =item list context | |
1709 | ||
1710 | The situation in which an L</expression> is expected by its | |
1711 | surroundings (the code calling it) to return a list of values rather | |
1712 | than a single value. Functions that want a L</LIST> of arguments tell | |
1713 | those arguments that they should produce a list value. See also | |
1714 | L</context>. | |
1715 | ||
1716 | =item list operator | |
1717 | ||
1718 | An L</operator> that does something with a list of values, such as | |
1719 | L<join|perlfunc/join> or L<grep|perlfunc/grep>. Usually used for | |
1720 | named built-in operators (such as L<print|perlfunc/print>, | |
1721 | L<unlink|perlfunc/unlink>, and L<system|perlfunc/system>) that do not | |
1722 | require parentheses around their L</argument> list. | |
1723 | ||
1724 | =item list value | |
1725 | ||
1726 | An unnamed list of temporary scalar values that may be passed around | |
1727 | within a program from any list-generating function to any function or | |
1728 | construct that provides a L</list context>. | |
1729 | ||
1730 | =item literal | |
1731 | ||
1732 | A token in a programming language such as a number or L</string> that | |
1733 | gives you an actual L</value> instead of merely representing possible | |
1734 | values as a L</variable> does. | |
1735 | ||
1736 | =item little-endian | |
1737 | ||
1738 | From Swift: someone who eats eggs little end first. Also used of | |
1739 | computers that store the least significant L</byte> of a word at a | |
1740 | lower byte address than the most significant byte. Often considered | |
1741 | superior to big-endian machines. See also L</big-endian>. | |
1742 | ||
1743 | =item local | |
1744 | ||
1745 | Not meaning the same thing everywhere. A global variable in Perl can | |
1746 | be localized inside a L<dynamic scope|/dynamic scoping> via the | |
1747 | L<local|perlfunc/local> operator. | |
1748 | ||
1749 | =item logical operator | |
1750 | ||
1751 | Symbols representing the concepts "and", "or", "xor", and "not". | |
1752 | ||
1753 | =item lookahead | |
1754 | ||
1755 | An L</assertion> that peeks at the string to the right of the current | |
1756 | match location. | |
1757 | ||
1758 | =item lookbehind | |
1759 | ||
1760 | An L</assertion> that peeks at the string to the left of the current | |
1761 | match location. | |
1762 | ||
1763 | =item loop | |
1764 | ||
1765 | A construct that performs something repeatedly, like a roller coaster. | |
1766 | ||
1767 | =item loop control statement | |
1768 | ||
1769 | Any statement within the body of a loop that can make a loop | |
1770 | prematurely stop looping or skip an L</iteration>. Generally you | |
1771 | shouldn't try this on roller coasters. | |
1772 | ||
1773 | =item loop label | |
1774 | ||
1775 | A kind of key or name attached to a loop (or roller coaster) so that | |
1776 | loop control statements can talk about which loop they want to | |
1777 | control. | |
1778 | ||
1779 | =item lvaluable | |
1780 | ||
1781 | Able to serve as an L</lvalue>. | |
1782 | ||
1783 | =item lvalue | |
1784 | ||
1785 | Term used by language lawyers for a storage location you can assign a | |
1786 | new L</value> to, such as a L</variable> or an element of an | |
1787 | L</array>. The "l" is short for "left", as in the left side of an | |
1788 | assignment, a typical place for lvalues. An L</lvaluable> function or | |
1789 | expression is one to which a value may be assigned, as in C<pos($x) = | |
1790 | 10>. | |
1791 | ||
1792 | =item lvalue modifier | |
1793 | ||
1794 | An adjectival pseudofunction that warps the meaning of an L</lvalue> | |
1795 | in some declarative fashion. Currently there are three lvalue | |
1796 | modifiers: L<my|perlfunc/my>, L<our|perlfunc/our>, and | |
1797 | L<local|perlfunc/local>. | |
1798 | ||
1799 | =back | |
1800 | ||
1801 | =head2 M | |
1802 | ||
1803 | =over 4 | |
1804 | ||
1805 | =item magic | |
1806 | ||
1807 | Technically speaking, any extra semantics attached to a variable such | |
1808 | as C<$!>, C<$0>, C<%ENV>, or C<%SIG>, or to any tied variable. | |
1809 | Magical things happen when you diddle those variables. | |
1810 | ||
1811 | =item magical increment | |
1812 | ||
1813 | An L</increment> operator that knows how to bump up alphabetics as | |
1814 | well as numbers. | |
1815 | ||
1816 | =item magical variables | |
1817 | ||
1818 | Special variables that have side effects when you access them or | |
1819 | assign to them. For example, in Perl, changing elements of the | |
1820 | C<%ENV> array also changes the corresponding environment variables | |
1821 | that subprocesses will use. Reading the C<$!> variable gives you the | |
1822 | current system error number or message. | |
1823 | ||
1824 | =item Makefile | |
1825 | ||
1826 | A file that controls the compilation of a program. Perl programs | |
1827 | don't usually need a L</Makefile> because the Perl compiler has plenty | |
1828 | of self-control. | |
1829 | ||
1830 | =item man | |
1831 | ||
1832 | The Unix program that displays online documentation (manual pages) for | |
1833 | you. | |
1834 | ||
1835 | =item manpage | |
1836 | ||
1837 | A "page" from the manuals, typically accessed via the I<man>(1) | |
1838 | command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of | |
1839 | BUGS, and so on, and is typically longer than a page. There are | |
1840 | manpages documenting L<commands|/command>, L<syscalls|/syscall>, | |
1841 | L</library> L<functions|/function>, L<devices|/device>, | |
1842 | L<protocols|/protocol>, L<files|/file>, and such. In this book, we | |
1843 | call any piece of standard Perl documentation (like I<perlop> or | |
1844 | I<perldelta>) a manpage, no matter what format it's installed in on | |
1845 | your system. | |
1846 | ||
1847 | =item matching | |
1848 | ||
1849 | See L</pattern matching>. | |
1850 | ||
1851 | =item member data | |
1852 | ||
1853 | See L</instance variable>. | |
1854 | ||
1855 | =item memory | |
1856 | ||
1857 | This always means your main memory, not your disk. Clouding the issue | |
1858 | is the fact that your machine may implement L</virtual> memory; that | |
1859 | is, it will pretend that it has more memory than it really does, and | |
1860 | it'll use disk space to hold inactive bits. This can make it seem | |
1861 | like you have a little more memory than you really do, but it's not a | |
1862 | substitute for real memory. The best thing that can be said about | |
1863 | virtual memory is that it lets your performance degrade gradually | |
1864 | rather than suddenly when you run out of real memory. But your | |
1865 | program can die when you run out of virtual memory too, if you haven't | |
1866 | thrashed your disk to death first. | |
1867 | ||
1868 | =item metacharacter | |
1869 | ||
1870 | A L</character> that is I<not> supposed to be treated normally. Which | |
1871 | characters are to be treated specially as metacharacters varies | |
1872 | greatly from context to context. Your L</shell> will have certain | |
1873 | metacharacters, double-quoted Perl L<strings|/string> have other | |
1874 | metacharacters, and L</regular expression> patterns have all the | |
1875 | double-quote metacharacters plus some extra ones of their own. | |
1876 | ||
1877 | =item metasymbol | |
1878 | ||
1879 | Something we'd call a L</metacharacter> except that it's a sequence of | |
1880 | more than one character. Generally, the first character in the | |
1881 | sequence must be a true metacharacter to get the other characters in | |
1882 | the metasymbol to misbehave along with it. | |
1883 | ||
1884 | =item method | |
1885 | ||
1886 | A kind of action that an L</object> can take if you tell it to. See | |
1887 | L<perlobj>. | |
1888 | ||
1889 | =item minimalism | |
1890 | ||
1891 | The belief that "small is beautiful." Paradoxically, if you say | |
1892 | something in a small language, it turns out big, and if you say it in | |
1893 | a big language, it turns out small. Go figure. | |
1894 | ||
1895 | =item mode | |
1896 | ||
1897 | In the context of the L<stat> syscall, refers to the field holding | |
1898 | the L</permission bits> and the type of the L</file>. | |
1899 | ||
1900 | =item modifier | |
1901 | ||
1902 | See L</statement modifier>, L</regular expression modifier>, and | |
1903 | L</lvalue modifier>, not necessarily in that order. | |
1904 | ||
1905 | =item module | |
1906 | ||
1907 | A L</file> that defines a L</package> of (almost) the same name, which | |
1908 | can either L</export> symbols or function as an L</object> class. (A | |
1909 | module's main I<.pm> file may also load in other files in support of | |
1910 | the module.) See the L<use|perlfunc/use> built-in. | |
1911 | ||
1912 | =item modulus | |
1913 | ||
1914 | An integer divisor when you're interested in the remainder instead of | |
1915 | the quotient. | |
1916 | ||
1917 | =item monger | |
1918 | ||
1919 | Short for Perl Monger, a purveyor of Perl. | |
1920 | ||
1921 | =item mortal | |
1922 | ||
1923 | A temporary value scheduled to die when the current statement | |
1924 | finishes. | |
1925 | ||
1926 | =item multidimensional array | |
1927 | ||
1928 | An array with multiple subscripts for finding a single element. Perl | |
1929 | implements these using L<references|/reference>--see L<perllol> and | |
1930 | L<perldsc>. | |
1931 | ||
1932 | =item multiple inheritance | |
1933 | ||
1934 | The features you got from your mother and father, mixed together | |
1935 | unpredictably. (See also L</inheritance>, and L</single | |
1936 | inheritance>.) In computer languages (including Perl), the notion | |
1937 | that a given class may have multiple direct ancestors or L<base | |
1938 | classes|/base class>. | |
1939 | ||
1940 | =back | |
1941 | ||
1942 | =head2 N | |
1943 | ||
1944 | =over 4 | |
1945 | ||
1946 | =item named pipe | |
1947 | ||
1948 | A L</pipe> with a name embedded in the L</filesystem> so that it can | |
1949 | be accessed by two unrelated L<processes|/process>. | |
1950 | ||
1951 | =item namespace | |
1952 | ||
1953 | A domain of names. You needn't worry about whether the names in one | |
1954 | such domain have been used in another. See L</package>. | |
1955 | ||
1956 | =item network address | |
1957 | ||
1958 | The most important attribute of a socket, like your telephone's | |
1959 | telephone number. Typically an IP address. See also L</port>. | |
1960 | ||
1961 | =item newline | |
1962 | ||
1963 | A single character that represents the end of a line, with the ASCII | |
1964 | value of 012 octal under Unix (but 015 on a Mac), and represented by | |
1965 | C<\n> in Perl strings. For Windows machines writing text files, and | |
1966 | for certain physical devices like terminals, the single newline gets | |
1967 | automatically translated by your C library into a line feed and a | |
1968 | carriage return, but normally, no translation is done. | |
1969 | ||
1970 | =item NFS | |
1971 | ||
1972 | Network File System, which allows you to mount a remote filesystem as | |
1973 | if it were local. | |
1974 | ||
1975 | =item null character | |
1976 | ||
1977 | A character with the ASCII value of zero. It's used by C to terminate | |
1978 | strings, but Perl allows strings to contain a null. | |
1979 | ||
1980 | =item null list | |
1981 | ||
1982 | A L</list value> with zero elements, represented in Perl by C<()>. | |
1983 | ||
1984 | =item null string | |
1985 | ||
1986 | A L</string> containing no characters, not to be confused with a | |
1987 | string containing a L</null character>, which has a positive length | |
1988 | and is L</true>. | |
1989 | ||
1990 | =item numeric context | |
1991 | ||
1992 | The situation in which an expression is expected by its surroundings | |
1993 | (the code calling it) to return a number. See also L</context> and | |
1994 | L</string context>. | |
1995 | ||
1996 | =item NV | |
1997 | ||
1998 | Short for Nevada, no part of which will ever be confused with | |
1999 | civilization. NV also means an internal floating-point Numeric Value | |
2000 | of the type a L</scalar> can hold, not to be confused with an L</IV>. | |
2001 | ||
2002 | =item nybble | |
2003 | ||
2004 | Half a L</byte>, equivalent to one L</hexadecimal> digit, and worth | |
2005 | four L<bits|/bit>. | |
2006 | ||
2007 | =back | |
2008 | ||
2009 | =head2 O | |
2010 | ||
2011 | =over 4 | |
2012 | ||
2013 | =item object | |
2014 | ||
2015 | An L</instance> of a L</class>. Something that "knows" what | |
2016 | user-defined type (class) it is, and what it can do because of what | |
2017 | class it is. Your program can request an object to do things, but the | |
2018 | object gets to decide whether it wants to do them or not. Some | |
2019 | objects are more accommodating than others. | |
2020 | ||
2021 | =item octal | |
2022 | ||
2023 | A number in base 8. Only the digits 0 through 7 are allowed. Octal | |
2024 | constants in Perl start with 0, as in 013. See also the | |
2025 | L<oct|perlfunc/oct> function. | |
2026 | ||
2027 | =item offset | |
2028 | ||
2029 | How many things you have to skip over when moving from the beginning | |
2030 | of a string or array to a specific position within it. Thus, the | |
2031 | minimum offset is zero, not one, because you don't skip anything to | |
2032 | get to the first item. | |
2033 | ||
2034 | =item one-liner | |
2035 | ||
2036 | An entire computer program crammed into one line of text. | |
2037 | ||
2038 | =item open source software | |
2039 | ||
2040 | Programs for which the source code is freely available and freely | |
2041 | redistributable, with no commercial strings attached. For a more | |
2042 | detailed definition, see L<http://www.opensource.org/osd.html>. | |
2043 | ||
2044 | =item operand | |
2045 | ||
2046 | An L</expression> that yields a L</value> that an L</operator> | |
2047 | operates on. See also L</precedence>. | |
2048 | ||
2049 | =item operating system | |
2050 | ||
2051 | A special program that runs on the bare machine and hides the gory | |
2052 | details of managing L<processes|/process> and L<devices|/device>. | |
2053 | Usually used in a looser sense to indicate a particular culture of | |
2054 | programming. The loose sense can be used at varying levels of | |
2055 | specificity. At one extreme, you might say that all versions of Unix | |
2056 | and Unix-lookalikes are the same operating system (upsetting many | |
2057 | people, especially lawyers and other advocates). At the other | |
2058 | extreme, you could say this particular version of this particular | |
2059 | vendor's operating system is different from any other version of this | |
2060 | or any other vendor's operating system. Perl is much more portable | |
2061 | across operating systems than many other languages. See also | |
2062 | L</architecture> and L</platform>. | |
2063 | ||
2064 | =item operator | |
2065 | ||
2066 | A gizmo that transforms some number of input values to some number of | |
2067 | output values, often built into a language with a special syntax or | |
2068 | symbol. A given operator may have specific expectations about what | |
2069 | L<types|/type> of data you give as its arguments | |
2070 | (L<operands|/operand>) and what type of data you want back from it. | |
2071 | ||
2072 | =item operator overloading | |
2073 | ||
2074 | A kind of L</overloading> that you can do on built-in | |
2075 | L<operators|/operator> to make them work on L<objects|/object> as if | |
2076 | the objects were ordinary scalar values, but with the actual semantics | |
2077 | supplied by the object class. This is set up with the L<overload> | |
2078 | L</pragma>. | |
2079 | ||
2080 | =item options | |
2081 | ||
2082 | See either L<switches|/switch> or L</regular expression modifier>. | |
2083 | ||
2084 | =item overloading | |
2085 | ||
2086 | Giving additional meanings to a symbol or construct. Actually, all | |
2087 | languages do overloading to one extent or another, since people are | |
2088 | good at figuring out things from L</context>. | |
2089 | ||
2090 | =item overriding | |
2091 | ||
2092 | Hiding or invalidating some other definition of the same name. (Not | |
2093 | to be confused with L</overloading>, which adds definitions that must | |
2094 | be disambiguated some other way.) To confuse the issue further, we use | |
2095 | the word with two overloaded definitions: to describe how you can | |
2096 | define your own L</subroutine> to hide a built-in L</function> of the | |
2097 | same name (see L<perlsub/Overriding Built-in Functions>) and to | |
2098 | describe how you can define a replacement L</method> in a L</derived | |
2099 | class> to hide a L</base class>'s method of the same name (see | |
2100 | L<perlobj>). | |
2101 | ||
2102 | =item owner | |
2103 | ||
2104 | The one user (apart from the superuser) who has absolute control over | |
2105 | a L</file>. A file may also have a L</group> of users who may | |
2106 | exercise joint ownership if the real owner permits it. See | |
2107 | L</permission bits>. | |
2108 | ||
2109 | =back | |
2110 | ||
2111 | =head2 P | |
2112 | ||
2113 | =over 4 | |
2114 | ||
2115 | =item package | |
2116 | ||
2117 | A L</namespace> for global L<variables|/variable>, | |
2118 | L<subroutines|/subroutine>, and the like, such that they can be kept | |
2119 | separate from like-named L<symbols|/symbol> in other namespaces. In a | |
2120 | sense, only the package is global, since the symbols in the package's | |
2121 | symbol table are only accessible from code compiled outside the | |
2122 | package by naming the package. But in another sense, all package | |
2123 | symbols are also globals--they're just well-organized globals. | |
2124 | ||
2125 | =item pad | |
2126 | ||
2127 | Short for L</scratchpad>. | |
2128 | ||
2129 | =item parameter | |
2130 | ||
2131 | See L</argument>. | |
2132 | ||
2133 | =item parent class | |
2134 | ||
2135 | See L</base class>. | |
2136 | ||
2137 | =item parse tree | |
2138 | ||
2139 | See L</syntax tree>. | |
2140 | ||
2141 | =item parsing | |
2142 | ||
2143 | The subtle but sometimes brutal art of attempting to turn your | |
2144 | possibly malformed program into a valid L</syntax tree>. | |
2145 | ||
2146 | =item patch | |
2147 | ||
2148 | To fix by applying one, as it were. In the realm of hackerdom, a | |
2149 | listing of the differences between two versions of a program as might | |
2150 | be applied by the I<patch>(1) program when you want to fix a bug or | |
2151 | upgrade your old version. | |
2152 | ||
2153 | =item PATH | |
2154 | ||
2155 | The list of L<directories|/directory> the system searches to find a | |
2156 | program you want to L</execute>. The list is stored as one of your | |
2157 | L<environment variables|/environment variable>, accessible in Perl as | |
2158 | C<$ENV{PATH}>. | |
2159 | ||
2160 | =item pathname | |
2161 | ||
2162 | A fully qualified filename such as I</usr/bin/perl>. Sometimes | |
2163 | confused with L</PATH>. | |
2164 | ||
2165 | =item pattern | |
2166 | ||
2167 | A template used in L</pattern matching>. | |
2168 | ||
2169 | =item pattern matching | |
2170 | ||
2171 | Taking a pattern, usually a L</regular expression>, and trying the | |
2172 | pattern various ways on a string to see whether there's any way to | |
2173 | make it fit. Often used to pick interesting tidbits out of a file. | |
2174 | ||
2175 | =item permission bits | |
2176 | ||
2177 | Bits that the L</owner> of a file sets or unsets to allow or disallow | |
2178 | access to other people. These flag bits are part of the L</mode> word | |
2179 | returned by the L<stat|perlfunc/stat> built-in when you ask about a | |
2180 | file. On Unix systems, you can check the I<ls>(1) manpage for more | |
2181 | information. | |
2182 | ||
2183 | =item Pern | |
2184 | ||
2185 | What you get when you do C<Perl++> twice. Doing it only once will | |
2186 | curl your hair. You have to increment it eight times to shampoo your | |
2187 | hair. Lather, rinse, iterate. | |
2188 | ||
2189 | =item pipe | |
2190 | ||
2191 | A direct L</connection> that carries the output of one L</process> to | |
2192 | the input of another without an intermediate temporary file. Once the | |
2193 | pipe is set up, the two processes in question can read and write as if | |
2194 | they were talking to a normal file, with some caveats. | |
2195 | ||
2196 | =item pipeline | |
2197 | ||
2198 | A series of L<processes|/process> all in a row, linked by | |
2199 | L<pipes|/pipe>, where each passes its output stream to the next. | |
2200 | ||
2201 | =item platform | |
2202 | ||
2203 | The entire hardware and software context in which a program runs. A | |
2204 | program written in a platform-dependent language might break if you | |
2205 | change any of: machine, operating system, libraries, compiler, or | |
2206 | system configuration. The I<perl> interpreter has to be compiled | |
2207 | differently for each platform because it is implemented in C, but | |
2208 | programs written in the Perl language are largely | |
2209 | platform-independent. | |
2210 | ||
2211 | =item pod | |
2212 | ||
2213 | The markup used to embed documentation into your Perl code. See | |
2214 | L<perlpod>. | |
2215 | ||
2216 | =item pointer | |
2217 | ||
2218 | A L</variable> in a language like C that contains the exact memory | |
2219 | location of some other item. Perl handles pointers internally so you | |
2220 | don't have to worry about them. Instead, you just use symbolic | |
2221 | pointers in the form of L<keys|/key> and L</variable> names, or L<hard | |
2222 | references|/hard reference>, which aren't pointers (but act like | |
2223 | pointers and do in fact contain pointers). | |
2224 | ||
2225 | =item polymorphism | |
2226 | ||
2227 | The notion that you can tell an L</object> to do something generic, | |
2228 | and the object will interpret the command in different ways depending | |
2229 | on its type. [E<lt>Gk many shapes] | |
2230 | ||
2231 | =item port | |
2232 | ||
2233 | The part of the address of a TCP or UDP socket that directs packets to | |
2234 | the correct process after finding the right machine, something like | |
2235 | the phone extension you give when you reach the company operator. | |
2236 | Also, the result of converting code to run on a different platform | |
2237 | than originally intended, or the verb denoting this conversion. | |
2238 | ||
2239 | =item portable | |
2240 | ||
2241 | Once upon a time, C code compilable under both BSD and SysV. In | |
2242 | general, code that can be easily converted to run on another | |
2243 | L</platform>, where "easily" can be defined however you like, and | |
2244 | usually is. Anything may be considered portable if you try hard | |
2245 | enough. See I<mobile home> or I<London Bridge>. | |
2246 | ||
2247 | =item porter | |
2248 | ||
2249 | Someone who "carries" software from one L</platform> to another. | |
2250 | Porting programs written in platform-dependent languages such as C can | |
2251 | be difficult work, but porting programs like Perl is very much worth | |
2252 | the agony. | |
2253 | ||
2254 | =item POSIX | |
2255 | ||
2256 | The Portable Operating System Interface specification. | |
2257 | ||
2258 | =item postfix | |
2259 | ||
2260 | An L</operator> that follows its L</operand>, as in C<$x++>. | |
2261 | ||
2262 | =item pp | |
2263 | ||
2264 | An internal shorthand for a "push-pop" code, that is, C code | |
2265 | implementing Perl's stack machine. | |
2266 | ||
2267 | =item pragma | |
2268 | ||
2269 | A standard module whose practical hints and suggestions are received | |
2270 | (and possibly ignored) at compile time. Pragmas are named in all | |
2271 | lowercase. | |
2272 | ||
2273 | =item precedence | |
2274 | ||
2275 | The rules of conduct that, in the absence of other guidance, determine | |
2276 | what should happen first. For example, in the absence of parentheses, | |
2277 | you always do multiplication before addition. | |
2278 | ||
2279 | =item prefix | |
2280 | ||
2281 | An L</operator> that precedes its L</operand>, as in C<++$x>. | |
2282 | ||
2283 | =item preprocessing | |
2284 | ||
2285 | What some helper L</process> did to transform the incoming data into a | |
2286 | form more suitable for the current process. Often done with an | |
2287 | incoming L</pipe>. See also L</C preprocessor>. | |
2288 | ||
2289 | =item procedure | |
2290 | ||
2291 | A L</subroutine>. | |
2292 | ||
2293 | =item process | |
2294 | ||
2295 | An instance of a running program. Under multitasking systems like | |
2296 | Unix, two or more separate processes could be running the same program | |
2297 | independently at the same time--in fact, the L<fork|perlfunc/fork> | |
2298 | function is designed to bring about this happy state of affairs. | |
2299 | Under other operating systems, processes are sometimes called | |
2300 | "threads", "tasks", or "jobs", often with slight nuances in meaning. | |
2301 | ||
2302 | =item program generator | |
2303 | ||
2304 | A system that algorithmically writes code for you in a high-level | |
2305 | language. See also L</code generator>. | |
2306 | ||
2307 | =item progressive matching | |
2308 | ||
2309 | L<Pattern matching|/pattern matching> that picks up where it left off before. | |
2310 | ||
2311 | =item property | |
2312 | ||
2313 | See either L</instance variable> or L</character property>. | |
2314 | ||
2315 | =item protocol | |
2316 | ||
2317 | In networking, an agreed-upon way of sending messages back and forth | |
2318 | so that neither correspondent will get too confused. | |
2319 | ||
2320 | =item prototype | |
2321 | ||
2322 | An optional part of a L</subroutine> declaration telling the Perl | |
2323 | compiler how many and what flavor of arguments may be passed as | |
2324 | L</actual arguments>, so that you can write subroutine calls that | |
2325 | parse much like built-in functions. (Or don't parse, as the case may | |
2326 | be.) | |
2327 | ||
2328 | =item pseudofunction | |
2329 | ||
2330 | A construct that sometimes looks like a function but really isn't. | |
2331 | Usually reserved for L</lvalue> modifiers like L<my|perlfunc/my>, for | |
2332 | L</context> modifiers like L<scalar|perlfunc/scalar>, and for the | |
2333 | pick-your-own-quotes constructs, C<q//>, C<qq//>, C<qx//>, C<qw//>, | |
2334 | C<qr//>, C<m//>, C<s///>, C<y///>, and C<tr///>. | |
2335 | ||
2336 | =item pseudohash | |
2337 | ||
2338 | A reference to an array whose initial element happens to hold a | |
2339 | reference to a hash. You can treat a pseudohash reference as either | |
2340 | an array reference or a hash reference. | |
2341 | ||
2342 | =item pseudoliteral | |
2343 | ||
2344 | An L</operator> that looks something like a L</literal>, such as the | |
2345 | output-grabbing operator, C<`>I<C<command>>C<`>. | |
2346 | ||
2347 | =item public domain | |
2348 | ||
2349 | Something not owned by anybody. Perl is copyrighted and is thus | |
2350 | I<not> in the public domain--it's just L</freely available> and | |
2351 | L</freely redistributable>. | |
2352 | ||
2353 | =item pumpkin | |
2354 | ||
2355 | A notional "baton" handed around the Perl community indicating who is | |
2356 | the lead integrator in some arena of development. | |
2357 | ||
2358 | =item pumpking | |
2359 | ||
2360 | A L</pumpkin> holder, the person in charge of pumping the pump, or at | |
2361 | least priming it. Must be willing to play the part of the Great | |
2362 | Pumpkin now and then. | |
2363 | ||
2364 | =item PV | |
2365 | ||
2366 | A "pointer value", which is Perl Internals Talk for a C<char*>. | |
2367 | ||
2368 | =back | |
2369 | ||
2370 | =head2 Q | |
2371 | ||
2372 | =over 4 | |
2373 | ||
2374 | =item qualified | |
2375 | ||
2376 | Possessing a complete name. The symbol C<$Ent::moot> is qualified; | |
2377 | C<$moot> is unqualified. A fully qualified filename is specified from | |
2378 | the top-level directory. | |
2379 | ||
2380 | =item quantifier | |
2381 | ||
2382 | A component of a L</regular expression> specifying how many times the | |
2383 | foregoing L</atom> may occur. | |
2384 | ||
2385 | =back | |
2386 | ||
2387 | =head2 R | |
2388 | ||
2389 | =over 4 | |
2390 | ||
2391 | =item readable | |
2392 | ||
2393 | With respect to files, one that has the proper permission bit set to | |
2394 | let you access the file. With respect to computer programs, one | |
2395 | that's written well enough that someone has a chance of figuring out | |
2396 | what it's trying to do. | |
2397 | ||
2398 | =item reaping | |
2399 | ||
2400 | The last rites performed by a parent L</process> on behalf of a | |
2401 | deceased child process so that it doesn't remain a L</zombie>. See | |
2402 | the L<wait|perlfunc/wait> and L<waitpid|perlfunc/waitpid> function | |
2403 | calls. | |
2404 | ||
2405 | =item record | |
2406 | ||
2407 | A set of related data values in a L</file> or L</stream>, often | |
2408 | associated with a unique L</key> field. In Unix, often commensurate | |
2409 | with a L</line>, or a blank-line-terminated set of lines (a | |
2410 | "paragraph"). Each line of the I</etc/passwd> file is a record, keyed | |
2411 | on login name, containing information about that user. | |
2412 | ||
2413 | =item recursion | |
2414 | ||
2415 | The art of defining something (at least partly) in terms of itself, | |
2416 | which is a naughty no-no in dictionaries but often works out okay in | |
2417 | computer programs if you're careful not to recurse forever, which is | |
2418 | like an infinite loop with more spectacular failure modes. | |
2419 | ||
2420 | =item reference | |
2421 | ||
2422 | Where you look to find a pointer to information somewhere else. (See | |
2423 | L</indirection>.) References come in two flavors, L<symbolic | |
2424 | references|/symbolic reference> and L<hard references|/hard | |
2425 | reference>. | |
2426 | ||
2427 | =item referent | |
2428 | ||
2429 | Whatever a reference refers to, which may or may not have a name. | |
2430 | Common types of referents include scalars, arrays, hashes, and | |
2431 | subroutines. | |
2432 | ||
2433 | =item regex | |
2434 | ||
2435 | See L</regular expression>. | |
2436 | ||
2437 | =item regular expression | |
2438 | ||
2439 | A single entity with various interpretations, like an elephant. To a | |
2440 | computer scientist, it's a grammar for a little language in which some | |
2441 | strings are legal and others aren't. To normal people, it's a pattern | |
2442 | you can use to find what you're looking for when it varies from case | |
2443 | to case. Perl's regular expressions are far from regular in the | |
2444 | theoretical sense, but in regular use they work quite well. Here's a | |
2445 | regular expression: C</Oh s.*t./>. This will match strings like "C<Oh | |
2446 | say can you see by the dawn's early light>" and "C<Oh sit!>". See | |
2447 | L<perlre>. | |
2448 | ||
2449 | =item regular expression modifier | |
2450 | ||
2451 | An option on a pattern or substitution, such as C</i> to render the | |
2452 | pattern case insensitive. See also L</cloister>. | |
2453 | ||
2454 | =item regular file | |
2455 | ||
2456 | A L</file> that's not a L</directory>, a L</device>, a named L</pipe> | |
2457 | or L</socket>, or a L</symbolic link>. Perl uses the C<-f> file test | |
2458 | operator to identify regular files. Sometimes called a "plain" file. | |
2459 | ||
2460 | =item relational operator | |
2461 | ||
2462 | An L</operator> that says whether a particular ordering relationship | |
2463 | is L</true> about a pair of L<operands|/operand>. Perl has both | |
2464 | numeric and string relational operators. See L</collating sequence>. | |
2465 | ||
2466 | =item reserved words | |
2467 | ||
2468 | A word with a specific, built-in meaning to a L</compiler>, such as | |
2469 | C<if> or L<delete|perlfunc/delete>. In many languages (not Perl), | |
2470 | it's illegal to use reserved words to name anything else. (Which is | |
2471 | why they're reserved, after all.) In Perl, you just can't use them to | |
2472 | name L<labels|/label> or L<filehandles|/filehandle>. Also called | |
2473 | "keywords". | |
2474 | ||
2475 | =item return value | |
2476 | ||
2477 | The L</value> produced by a L</subroutine> or L</expression> when | |
2478 | evaluated. In Perl, a return value may be either a L</list> or a | |
2479 | L</scalar>. | |
2480 | ||
2481 | =item RFC | |
2482 | ||
2483 | Request For Comment, which despite the timid connotations is the name | |
2484 | of a series of important standards documents. | |
2485 | ||
2486 | =item right shift | |
2487 | ||
2488 | A L</bit shift> that divides a number by some power of 2. | |
2489 | ||
2490 | =item root | |
2491 | ||
2492 | The superuser (UID == 0). Also, the top-level directory of the | |
2493 | filesystem. | |
2494 | ||
2495 | =item RTFM | |
2496 | ||
2497 | What you are told when someone thinks you should Read The Fine Manual. | |
2498 | ||
2499 | =item run phase | |
2500 | ||
2501 | Any time after Perl starts running your main program. See also | |
2502 | L</compile phase>. Run phase is mostly spent in L</run time> but may | |
2503 | also be spent in L</compile time> when L<require|perlfunc/require>, | |
2504 | L<do|perlfunc/do> C<FILE>, or L<eval|perlfunc/eval> C<STRING> | |
2505 | operators are executed or when a substitution uses the C</ee> | |
2506 | modifier. | |
2507 | ||
2508 | =item run time | |
2509 | ||
2510 | The time when Perl is actually doing what your code says to do, as | |
2511 | opposed to the earlier period of time when it was trying to figure out | |
2512 | whether what you said made any sense whatsoever, which is L</compile | |
2513 | time>. | |
2514 | ||
2515 | =item run-time pattern | |
2516 | ||
2517 | A pattern that contains one or more variables to be interpolated | |
2518 | before parsing the pattern as a L</regular expression>, and that | |
2519 | therefore cannot be analyzed at compile time, but must be re-analyzed | |
2520 | each time the pattern match operator is evaluated. Run-time patterns | |
2521 | are useful but expensive. | |
2522 | ||
2523 | =item RV | |
2524 | ||
2525 | A recreational vehicle, not to be confused with vehicular recreation. | |
2526 | RV also means an internal Reference Value of the type a L</scalar> can | |
2527 | hold. See also L</IV> and L</NV> if you're not confused yet. | |
2528 | ||
2529 | =item rvalue | |
2530 | ||
2531 | A L</value> that you might find on the right side of an | |
2532 | L</assignment>. See also L</lvalue>. | |
2533 | ||
2534 | =back | |
2535 | ||
2536 | =head2 S | |
2537 | ||
2538 | =over 4 | |
2539 | ||
2540 | =item scalar | |
2541 | ||
2542 | A simple, singular value; a number, L</string>, or L</reference>. | |
2543 | ||
2544 | =item scalar context | |
2545 | ||
2546 | The situation in which an L</expression> is expected by its | |
2547 | surroundings (the code calling it) to return a single L</value> rather | |
2548 | than a L</list> of values. See also L</context> and L</list context>. | |
2549 | A scalar context sometimes imposes additional constraints on the | |
2550 | return value--see L</string context> and L</numeric context>. | |
2551 | Sometimes we talk about a L</Boolean context> inside conditionals, but | |
2552 | this imposes no additional constraints, since any scalar value, | |
2553 | whether numeric or L</string>, is already true or false. | |
2554 | ||
2555 | =item scalar literal | |
2556 | ||
2557 | A number or quoted L</string>--an actual L</value> in the text of your | |
2558 | program, as opposed to a L</variable>. | |
2559 | ||
2560 | =item scalar value | |
2561 | ||
2562 | A value that happens to be a L</scalar> as opposed to a L</list>. | |
2563 | ||
2564 | =item scalar variable | |
2565 | ||
2566 | A L</variable> prefixed with C<$> that holds a single value. | |
2567 | ||
2568 | =item scope | |
2569 | ||
2570 | How far away you can see a variable from, looking through one. Perl | |
2571 | has two visibility mechanisms: it does L</dynamic scoping> of | |
2572 | L<local|perlfunc/local> L<variables|/variable>, meaning that the rest | |
2573 | of the L</block>, and any L<subroutines|/subroutine> that are called | |
2574 | by the rest of the block, can see the variables that are local to the | |
2575 | block. Perl does L</lexical scoping> of L<my|perlfunc/my> variables, | |
2576 | meaning that the rest of the block can see the variable, but other | |
2577 | subroutines called by the block I<cannot> see the variable. | |
2578 | ||
2579 | =item scratchpad | |
2580 | ||
2581 | The area in which a particular invocation of a particular file or | |
2582 | subroutine keeps some of its temporary values, including any lexically | |
2583 | scoped variables. | |
2584 | ||
2585 | =item script | |
2586 | ||
2587 | A text L</file> that is a program intended to be L<executed|/execute> | |
2588 | directly rather than L<compiled|/compiler> to another form of file | |
2589 | before execution. Also, in the context of L</Unicode>, a writing | |
2590 | system for a particular language or group of languages, such as Greek, | |
2591 | Bengali, or Klingon. | |
2592 | ||
2593 | =item script kiddie | |
2594 | ||
2595 | A L</cracker> who is not a L</hacker>, but knows just enough to run | |
2596 | canned scripts. A cargo-cult programmer. | |
2597 | ||
2598 | =item sed | |
2599 | ||
2600 | A venerable Stream EDitor from which Perl derives some of its ideas. | |
2601 | ||
2602 | =item semaphore | |
2603 | ||
2604 | A fancy kind of interlock that prevents multiple L<threads|/thread> or | |
2605 | L<processes|/process> from using up the same resources simultaneously. | |
2606 | ||
2607 | =item separator | |
2608 | ||
2609 | A L</character> or L</string> that keeps two surrounding strings from | |
2610 | being confused with each other. The L<split|perlfunc/split> function | |
2611 | works on separators. Not to be confused with L<delimiters|/delimiter> | |
2612 | or L<terminators|/terminator>. The "or" in the previous sentence | |
2613 | separated the two alternatives. | |
2614 | ||
2615 | =item serialization | |
2616 | ||
2617 | Putting a fancy L</data structure> into linear order so that it can be | |
2618 | stored as a L</string> in a disk file or database or sent through a | |
2619 | L</pipe>. Also called marshalling. | |
2620 | ||
2621 | =item server | |
2622 | ||
2623 | In networking, a L</process> that either advertises a L</service> or | |
2624 | just hangs around at a known location and waits for L<clients|/client> | |
2625 | who need service to get in touch with it. | |
2626 | ||
2627 | =item service | |
2628 | ||
2629 | Something you do for someone else to make them happy, like giving them | |
2630 | the time of day (or of their life). On some machines, well-known | |
2631 | services are listed by the L<getservent|perlfunc/getservent> function. | |
2632 | ||
2633 | =item setgid | |
2634 | ||
2635 | Same as L</setuid>, only having to do with giving away L</group> | |
2636 | privileges. | |
2637 | ||
2638 | =item setuid | |
2639 | ||
2640 | Said of a program that runs with the privileges of its L</owner> | |
2641 | rather than (as is usually the case) the privileges of whoever is | |
2642 | running it. Also describes the bit in the mode word (L</permission | |
2643 | bits>) that controls the feature. This bit must be explicitly set by | |
2644 | the owner to enable this feature, and the program must be carefully | |
2645 | written not to give away more privileges than it ought to. | |
2646 | ||
2647 | =item shared memory | |
2648 | ||
2649 | A piece of L</memory> accessible by two different | |
2650 | L<processes|/process> who otherwise would not see each other's memory. | |
2651 | ||
2652 | =item shebang | |
2653 | ||
2654 | Irish for the whole McGillicuddy. In Perl culture, a portmanteau of | |
2655 | "sharp" and "bang", meaning the C<#!> sequence that tells the system | |
2656 | where to find the interpreter. | |
2657 | ||
2658 | =item shell | |
2659 | ||
2660 | A L</command>-line L</interpreter>. The program that interactively | |
2661 | gives you a prompt, accepts one or more L<lines|/line> of input, and | |
2662 | executes the programs you mentioned, feeding each of them their proper | |
2663 | L<arguments|/argument> and input data. Shells can also execute | |
2664 | scripts containing such commands. Under Unix, typical shells include | |
2665 | the Bourne shell (I</bin/sh>), the C shell (I</bin/csh>), and the Korn | |
2666 | shell (I</bin/ksh>). Perl is not strictly a shell because it's not | |
2667 | interactive (although Perl programs can be interactive). | |
2668 | ||
2669 | =item side effects | |
2670 | ||
2671 | Something extra that happens when you evaluate an L</expression>. | |
2672 | Nowadays it can refer to almost anything. For example, evaluating a | |
2673 | simple assignment statement typically has the "side effect" of | |
2674 | assigning a value to a variable. (And you thought assigning the value | |
2675 | was your primary intent in the first place!) Likewise, assigning a | |
2676 | value to the special variable C<$|> (C<$AUTOFLUSH>) has the side | |
2677 | effect of forcing a flush after every L<write|perlfunc/write> or | |
2678 | L<print|perlfunc/print> on the currently selected filehandle. | |
2679 | ||
2680 | =item signal | |
2681 | ||
2682 | A bolt out of the blue; that is, an event triggered by the | |
2683 | L</operating system>, probably when you're least expecting it. | |
2684 | ||
2685 | =item signal handler | |
2686 | ||
2687 | A L</subroutine> that, instead of being content to be called in the | |
2688 | normal fashion, sits around waiting for a bolt out of the blue before | |
2689 | it will deign to L</execute>. Under Perl, bolts out of the blue are | |
2690 | called signals, and you send them with the L<kill|perlfunc/kill> | |
2691 | built-in. See L<perlvar/%SIG> and L<perlipc/Signals>. | |
2692 | ||
2693 | =item single inheritance | |
2694 | ||
2695 | The features you got from your mother, if she told you that you don't | |
2696 | have a father. (See also L</inheritance> and L</multiple | |
2697 | inheritance>.) In computer languages, the notion that | |
2698 | L<classes|/class> reproduce asexually so that a given class can only | |
2699 | have one direct ancestor or L</base class>. Perl supplies no such | |
2700 | restriction, though you may certainly program Perl that way if you | |
2701 | like. | |
2702 | ||
2703 | =item slice | |
2704 | ||
2705 | A selection of any number of L<elements|/element> from a L</list>, | |
2706 | L</array>, or L</hash>. | |
2707 | ||
2708 | =item slurp | |
2709 | ||
2710 | To read an entire L</file> into a L</string> in one operation. | |
2711 | ||
2712 | =item socket | |
2713 | ||
2714 | An endpoint for network communication among multiple | |
2715 | L<processes|/process> that works much like a telephone or a post | |
2716 | office box. The most important thing about a socket is its L</network | |
2717 | address> (like a phone number). Different kinds of sockets have | |
2718 | different kinds of addresses--some look like filenames, and some | |
2719 | don't. | |
2720 | ||
2721 | =item soft reference | |
2722 | ||
2723 | See L</symbolic reference>. | |
2724 | ||
2725 | =item source filter | |
2726 | ||
2727 | A special kind of L</module> that does L</preprocessing> on your | |
2728 | script just before it gets to the L</tokener>. | |
2729 | ||
2730 | =item stack | |
2731 | ||
2732 | A device you can put things on the top of, and later take them back | |
2733 | off in the opposite order in which you put them on. See L</LIFO>. | |
2734 | ||
2735 | =item standard | |
2736 | ||
2737 | Included in the official Perl distribution, as in a standard module, a | |
2738 | standard tool, or a standard Perl L</manpage>. | |
2739 | ||
2740 | =item standard error | |
2741 | ||
2742 | The default output L</stream> for nasty remarks that don't belong in | |
2743 | L</standard output>. Represented within a Perl program by the | |
2744 | L</filehandle> L</STDERR>. You can use this stream explicitly, but the | |
2745 | L<die|perlfunc/die> and L<warn|perlfunc/warn> built-ins write to your | |
2746 | standard error stream automatically. | |
2747 | ||
2748 | =item standard I/O | |
2749 | ||
2750 | A standard C library for doing L<buffered|/buffer> input and output to | |
2751 | the L</operating system>. (The "standard" of standard I/O is only | |
2752 | marginally related to the "standard" of standard input and output.) | |
2753 | In general, Perl relies on whatever implementation of standard I/O a | |
2754 | given operating system supplies, so the buffering characteristics of a | |
2755 | Perl program on one machine may not exactly match those on another | |
2756 | machine. Normally this only influences efficiency, not semantics. If | |
2757 | your standard I/O package is doing block buffering and you want it to | |
2758 | L</flush> the buffer more often, just set the C<$|> variable to a true | |
2759 | value. | |
2760 | ||
2761 | =item standard input | |
2762 | ||
2763 | The default input L</stream> for your program, which if possible | |
2764 | shouldn't care where its data is coming from. Represented within a | |
2765 | Perl program by the L</filehandle> L</STDIN>. | |
2766 | ||
2767 | =item standard output | |
2768 | ||
2769 | The default output L</stream> for your program, which if possible | |
2770 | shouldn't care where its data is going. Represented within a Perl | |
2771 | program by the L</filehandle> L</STDOUT>. | |
2772 | ||
2773 | =item stat structure | |
2774 | ||
2775 | A special internal spot in which Perl keeps the information about the | |
2776 | last L</file> on which you requested information. | |
2777 | ||
2778 | =item statement | |
2779 | ||
2780 | A L</command> to the computer about what to do next, like a step in a | |
2781 | recipe: "Add marmalade to batter and mix until mixed." A statement is | |
2782 | distinguished from a L</declaration>, which doesn't tell the computer | |
2783 | to do anything, but just to learn something. | |
2784 | ||
2785 | =item statement modifier | |
2786 | ||
2787 | A L</conditional> or L</loop> that you put after the L</statement> | |
2788 | instead of before, if you know what we mean. | |
2789 | ||
2790 | =item static | |
2791 | ||
2792 | Varying slowly compared to something else. (Unfortunately, everything | |
2793 | is relatively stable compared to something else, except for certain | |
2794 | elementary particles, and we're not so sure about them.) In | |
2795 | computers, where things are supposed to vary rapidly, "static" has a | |
2796 | derogatory connotation, indicating a slightly dysfunctional | |
2797 | L</variable>, L</subroutine>, or L</method>. In Perl culture, the | |
2798 | word is politely avoided. | |
2799 | ||
2800 | =item static method | |
2801 | ||
2802 | No such thing. See L</class method>. | |
2803 | ||
2804 | =item static scoping | |
2805 | ||
2806 | No such thing. See L</lexical scoping>. | |
2807 | ||
2808 | =item static variable | |
2809 | ||
2810 | No such thing. Just use a L</lexical variable> in a scope larger than | |
2811 | your L</subroutine>. | |
2812 | ||
2813 | =item status | |
2814 | ||
2815 | The L</value> returned to the parent L</process> when one of its child | |
2816 | processes dies. This value is placed in the special variable C<$?>. | |
2817 | Its upper eight L<bits|/bit> are the exit status of the defunct | |
2818 | process, and its lower eight bits identify the signal (if any) that | |
2819 | the process died from. On Unix systems, this status value is the same | |
2820 | as the status word returned by I<wait>(2). See L<perlfunc/system>. | |
2821 | ||
2822 | =item STDERR | |
2823 | ||
2824 | See L</standard error>. | |
2825 | ||
2826 | =item STDIN | |
2827 | ||
2828 | See L</standard input>. | |
2829 | ||
2830 | =item STDIO | |
2831 | ||
2832 | See L</standard IE<sol>O>. | |
2833 | ||
2834 | =item STDOUT | |
2835 | ||
2836 | See L</standard output>. | |
2837 | ||
2838 | =item stream | |
2839 | ||
2840 | A flow of data into or out of a process as a steady sequence of bytes | |
2841 | or characters, without the appearance of being broken up into packets. | |
2842 | This is a kind of L</interface>--the underlying L</implementation> may | |
2843 | well break your data up into separate packets for delivery, but this | |
2844 | is hidden from you. | |
2845 | ||
2846 | =item string | |
2847 | ||
2848 | A sequence of characters such as "He said !@#*&%@#*?!". A string does | |
2849 | not have to be entirely printable. | |
2850 | ||
2851 | =item string context | |
2852 | ||
2853 | The situation in which an expression is expected by its surroundings | |
2854 | (the code calling it) to return a L</string>. See also L</context> | |
2855 | and L</numeric context>. | |
2856 | ||
2857 | =item stringification | |
2858 | ||
2859 | The process of producing a L</string> representation of an abstract | |
2860 | object. | |
2861 | ||
2862 | =item struct | |
2863 | ||
2864 | C keyword introducing a structure definition or name. | |
2865 | ||
2866 | =item structure | |
2867 | ||
2868 | See L</data structure>. | |
2869 | ||
2870 | =item subclass | |
2871 | ||
2872 | See L</derived class>. | |
2873 | ||
2874 | =item subpattern | |
2875 | ||
2876 | A component of a L</regular expression> pattern. | |
2877 | ||
2878 | =item subroutine | |
2879 | ||
2880 | A named or otherwise accessible piece of program that can be invoked | |
2881 | from elsewhere in the program in order to accomplish some sub-goal of | |
2882 | the program. A subroutine is often parameterized to accomplish | |
2883 | different but related things depending on its input | |
2884 | L<arguments|/argument>. If the subroutine returns a meaningful | |
2885 | L</value>, it is also called a L</function>. | |
2886 | ||
2887 | =item subscript | |
2888 | ||
2889 | A L</value> that indicates the position of a particular L</array> | |
2890 | L</element> in an array. | |
2891 | ||
2892 | =item substitution | |
2893 | ||
2894 | Changing parts of a string via the C<s///> operator. (We avoid use of | |
2895 | this term to mean L</variable interpolation>.) | |
2896 | ||
2897 | =item substring | |
2898 | ||
2899 | A portion of a L</string>, starting at a certain L</character> | |
2900 | position (L</offset>) and proceeding for a certain number of | |
2901 | characters. | |
2902 | ||
2903 | =item superclass | |
2904 | ||
2905 | See L</base class>. | |
2906 | ||
2907 | =item superuser | |
2908 | ||
2909 | The person whom the L</operating system> will let do almost anything. | |
2910 | Typically your system administrator or someone pretending to be your | |
2911 | system administrator. On Unix systems, the L</root> user. On Windows | |
2912 | systems, usually the Administrator user. | |
2913 | ||
2914 | =item SV | |
2915 | ||
2916 | Short for "scalar value". But within the Perl interpreter every | |
2917 | L</referent> is treated as a member of a class derived from SV, in an | |
2918 | object-oriented sort of way. Every L</value> inside Perl is passed | |
2919 | around as a C language C<SV*> pointer. The SV L</struct> knows its | |
2920 | own "referent type", and the code is smart enough (we hope) not to try | |
2921 | to call a L</hash> function on a L</subroutine>. | |
2922 | ||
2923 | =item switch | |
2924 | ||
2925 | An option you give on a command line to influence the way your program | |
2926 | works, usually introduced with a minus sign. The word is also used as | |
2927 | a nickname for a L</switch statement>. | |
2928 | ||
2929 | =item switch cluster | |
2930 | ||
2931 | The combination of multiple command-line switches (e.g., B<-a -b -c>) | |
2932 | into one switch (e.g., B<-abc>). Any switch with an additional | |
2933 | L</argument> must be the last switch in a cluster. | |
2934 | ||
2935 | =item switch statement | |
2936 | ||
2937 | A program technique that lets you evaluate an L</expression> and then, | |
2938 | based on the value of the expression, do a multiway branch to the | |
2939 | appropriate piece of code for that value. Also called a "case | |
2940 | structure", named after the similar Pascal construct. Most switch | |
2941 | statements in Perl are spelled C<for>. See L<perlsyn/Basic BLOCKs and | |
2942 | Switch Statements>. | |
2943 | ||
2944 | =item symbol | |
2945 | ||
2946 | Generally, any L</token> or L</metasymbol>. Often used more | |
2947 | specifically to mean the sort of name you might find in a L</symbol | |
2948 | table>. | |
2949 | ||
2950 | =item symbol table | |
2951 | ||
2952 | Where a L</compiler> remembers symbols. A program like Perl must | |
2953 | somehow remember all the names of all the L<variables|/variable>, | |
2954 | L<filehandles|/filehandle>, and L<subroutines|/subroutine> you've | |
2955 | used. It does this by placing the names in a symbol table, which is | |
2956 | implemented in Perl using a L</hash table>. There is a separate | |
2957 | symbol table for each L</package> to give each package its own | |
2958 | L</namespace>. | |
2959 | ||
2960 | =item symbolic debugger | |
2961 | ||
2962 | A program that lets you step through the L<execution|/execute> of your | |
2963 | program, stopping or printing things out here and there to see whether | |
2964 | anything has gone wrong, and if so, what. The "symbolic" part just | |
2965 | means that you can talk to the debugger using the same symbols with | |
2966 | which your program is written. | |
2967 | ||
2968 | =item symbolic link | |
2969 | ||
2970 | An alternate filename that points to the real L</filename>, which in | |
2971 | turn points to the real L</file>. Whenever the L</operating system> | |
2972 | is trying to parse a L</pathname> containing a symbolic link, it | |
2973 | merely substitutes the new name and continues parsing. | |
2974 | ||
2975 | =item symbolic reference | |
2976 | ||
2977 | A variable whose value is the name of another variable or subroutine. | |
2978 | By L<dereferencing|/dereference> the first variable, you can get at | |
2979 | the second one. Symbolic references are illegal under L<use strict | |
2980 | 'refs'|strict/strict refs>. | |
2981 | ||
2982 | =item synchronous | |
2983 | ||
2984 | Programming in which the orderly sequence of events can be determined; | |
2985 | that is, when things happen one after the other, not at the same time. | |
2986 | ||
2987 | =item syntactic sugar | |
2988 | ||
2989 | An alternative way of writing something more easily; a shortcut. | |
2990 | ||
2991 | =item syntax | |
2992 | ||
2993 | From Greek, "with-arrangement". How things (particularly symbols) are | |
2994 | put together with each other. | |
2995 | ||
2996 | =item syntax tree | |
2997 | ||
2998 | An internal representation of your program wherein lower-level | |
2999 | L<constructs|/construct> dangle off the higher-level constructs | |
3000 | enclosing them. | |
3001 | ||
3002 | =item syscall | |
3003 | ||
3004 | A L</function> call directly to the L</operating system>. Many of the | |
3005 | important subroutines and functions you use aren't direct system | |
3006 | calls, but are built up in one or more layers above the system call | |
3007 | level. In general, Perl programmers don't need to worry about the | |
3008 | distinction. However, if you do happen to know which Perl functions | |
3009 | are really syscalls, you can predict which of these will set the C<$!> | |
3010 | (C<$ERRNO>) variable on failure. Unfortunately, beginning programmers | |
3011 | often confusingly employ the term "system call" to mean what happens | |
3012 | when you call the Perl L<system|perlfunc/system> function, which | |
3013 | actually involves many syscalls. To avoid any confusion, we nearly | |
3014 | always use say "syscall" for something you could call indirectly via | |
3015 | Perl's L<syscall|perlfunc/syscall> function, and never for something | |
3016 | you would call with Perl's L<system|perlfunc/system> function. | |
3017 | ||
3018 | =back | |
3019 | ||
3020 | =head2 T | |
3021 | ||
3022 | =over 4 | |
3023 | ||
3024 | =item tainted | |
3025 | ||
3026 | Said of data derived from the grubby hands of a user and thus unsafe | |
3027 | for a secure program to rely on. Perl does taint checks if you run a | |
3028 | L</setuid> (or L</setgid>) program, or if you use the B<-T> switch. | |
3029 | ||
3030 | =item TCP | |
3031 | ||
3032 | Short for Transmission Control Protocol. A protocol wrapped around | |
3033 | the Internet Protocol to make an unreliable packet transmission | |
3034 | mechanism appear to the application program to be a reliable | |
3035 | L</stream> of bytes. (Usually.) | |
3036 | ||
3037 | =item term | |
3038 | ||
3039 | Short for a "terminal", that is, a leaf node of a L</syntax tree>. A | |
3040 | thing that functions grammatically as an L</operand> for the operators | |
3041 | in an expression. | |
3042 | ||
3043 | =item terminator | |
3044 | ||
3045 | A L</character> or L</string> that marks the end of another string. | |
3046 | The C<$/> variable contains the string that terminates a | |
3047 | L<readline|perlfunc/readline> operation, which L<chomp|perlfunc/chomp> | |
3048 | deletes from the end. Not to be confused with | |
3049 | L<delimiters|/delimiter> or L<separators|/separator>. The period at | |
3050 | the end of this sentence is a terminator. | |
3051 | ||
3052 | =item ternary | |
3053 | ||
3054 | An L</operator> taking three L<operands|/operand>. Sometimes | |
3055 | pronounced L</trinary>. | |
3056 | ||
3057 | =item text | |
3058 | ||
3059 | A L</string> or L</file> containing primarily printable characters. | |
3060 | ||
3061 | =item thread | |
3062 | ||
3063 | Like a forked process, but without L</fork>'s inherent memory | |
3064 | protection. A thread is lighter weight than a full process, in that a | |
3065 | process could have multiple threads running around in it, all fighting | |
3066 | over the same process's memory space unless steps are taken to protect | |
3067 | threads from each other. See L<threads>. | |
3068 | ||
3069 | =item tie | |
3070 | ||
3071 | The bond between a magical variable and its implementation class. See | |
3072 | L<perlfunc/tie> and L<perltie>. | |
3073 | ||
3074 | =item TMTOWTDI | |
3075 | ||
3076 | There's More Than One Way To Do It, the Perl Motto. The notion that | |
3077 | there can be more than one valid path to solving a programming problem | |
3078 | in context. (This doesn't mean that more ways are always better or | |
3079 | that all possible paths are equally desirable--just that there need | |
3080 | not be One True Way.) Pronounced TimToady. | |
3081 | ||
3082 | =item token | |
3083 | ||
3084 | A morpheme in a programming language, the smallest unit of text with | |
3085 | semantic significance. | |
3086 | ||
3087 | =item tokener | |
3088 | ||
3089 | A module that breaks a program text into a sequence of | |
3090 | L<tokens|/token> for later analysis by a parser. | |
3091 | ||
3092 | =item tokenizing | |
3093 | ||
3094 | Splitting up a program text into L<tokens|/token>. Also known as | |
3095 | "lexing", in which case you get "lexemes" instead of tokens. | |
3096 | ||
3097 | =item toolbox approach | |
3098 | ||
3099 | The notion that, with a complete set of simple tools that work well | |
3100 | together, you can build almost anything you want. Which is fine if | |
3101 | you're assembling a tricycle, but if you're building a defranishizing | |
3102 | comboflux regurgalator, you really want your own machine shop in which | |
3103 | to build special tools. Perl is sort of a machine shop. | |
3104 | ||
3105 | =item transliterate | |
3106 | ||
3107 | To turn one string representation into another by mapping each | |
3108 | character of the source string to its corresponding character in the | |
3109 | result string. See | |
3110 | L<perlop/trE<sol>SEARCHLISTE<sol>REPLACEMENTLISTE<sol>cds>. | |
3111 | ||
3112 | =item trigger | |
3113 | ||
3114 | An event that causes a L</handler> to be run. | |
3115 | ||
3116 | =item trinary | |
3117 | ||
3118 | Not a stellar system with three stars, but an L</operator> taking | |
3119 | three L<operands|/operand>. Sometimes pronounced L</ternary>. | |
3120 | ||
3121 | =item troff | |
3122 | ||
3123 | A venerable typesetting language from which Perl derives the name of | |
3124 | its C<$%> variable and which is secretly used in the production of | |
3125 | Camel books. | |
3126 | ||
3127 | =item true | |
3128 | ||
3129 | Any scalar value that doesn't evaluate to 0 or C<"">. | |
3130 | ||
3131 | =item truncating | |
3132 | ||
3133 | Emptying a file of existing contents, either automatically when | |
3134 | opening a file for writing or explicitly via the | |
3135 | L<truncate|perlfunc/truncate> function. | |
3136 | ||
3137 | =item type | |
3138 | ||
3139 | See L</data type> and L</class>. | |
3140 | ||
3141 | =item type casting | |
3142 | ||
3143 | Converting data from one type to another. C permits this. Perl does | |
3144 | not need it. Nor want it. | |
3145 | ||
3146 | =item typed lexical | |
3147 | ||
3148 | A L</lexical variable> that is declared with a L</class> type: C<my | |
3149 | Pony $bill>. | |
3150 | ||
3151 | =item typedef | |
3152 | ||
3153 | A type definition in the C language. | |
3154 | ||
3155 | =item typeglob | |
3156 | ||
3157 | Use of a single identifier, prefixed with C<*>. For example, C<*name> | |
3158 | stands for any or all of C<$name>, C<@name>, C<%name>, C<&name>, or | |
3159 | just C<name>. How you use it determines whether it is interpreted as | |
3160 | all or only one of them. See L<perldata/Typeglobs and Filehandles>. | |
3161 | ||
3162 | =item typemap | |
3163 | ||
3164 | A description of how C types may be transformed to and from Perl types | |
3165 | within an L</extension> module written in L</XS>. | |
3166 | ||
3167 | =back | |
3168 | ||
3169 | =head2 U | |
3170 | ||
3171 | =over 4 | |
3172 | ||
3173 | =item UDP | |
3174 | ||
3175 | User Datagram Protocol, the typical way to send L<datagrams|/datagram> | |
3176 | over the Internet. | |
3177 | ||
3178 | =item UID | |
3179 | ||
3180 | A user ID. Often used in the context of L</file> or L</process> | |
3181 | ownership. | |
3182 | ||
3183 | =item umask | |
3184 | ||
3185 | A mask of those L</permission bits> that should be forced off when | |
3186 | creating files or directories, in order to establish a policy of whom | |
3187 | you'll ordinarily deny access to. See the L<umask|perlfunc/umask> | |
3188 | function. | |
3189 | ||
3190 | =item unary operator | |
3191 | ||
3192 | An operator with only one L</operand>, like C<!> or | |
3193 | L<chdir|perlfunc/chdir>. Unary operators are usually prefix | |
3194 | operators; that is, they precede their operand. The C<++> and C<--> | |
3195 | operators can be either prefix or postfix. (Their position I<does> | |
3196 | change their meanings.) | |
3197 | ||
3198 | =item Unicode | |
3199 | ||
3200 | A character set comprising all the major character sets of the world, | |
3201 | more or less. See L<http://www.unicode.org>. | |
3202 | ||
3203 | =item Unix | |
3204 | ||
3205 | A very large and constantly evolving language with several alternative | |
3206 | and largely incompatible syntaxes, in which anyone can define anything | |
3207 | any way they choose, and usually do. Speakers of this language think | |
3208 | it's easy to learn because it's so easily twisted to one's own ends, | |
3209 | but dialectical differences make tribal intercommunication nearly | |
3210 | impossible, and travelers are often reduced to a pidgin-like subset of | |
3211 | the language. To be universally understood, a Unix shell programmer | |
3212 | must spend years of study in the art. Many have abandoned this | |
3213 | discipline and now communicate via an Esperanto-like language called | |
3214 | Perl. | |
3215 | ||
3216 | In ancient times, Unix was also used to refer to some code that a | |
3217 | couple of people at Bell Labs wrote to make use of a PDP-7 computer | |
3218 | that wasn't doing much of anything else at the time. | |
3219 | ||
3220 | =back | |
3221 | ||
3222 | =head2 V | |
3223 | ||
3224 | =over 4 | |
3225 | ||
3226 | =item value | |
3227 | ||
3228 | An actual piece of data, in contrast to all the variables, references, | |
3229 | keys, indexes, operators, and whatnot that you need to access the | |
3230 | value. | |
3231 | ||
3232 | =item variable | |
3233 | ||
3234 | A named storage location that can hold any of various kinds of | |
3235 | L</value>, as your program sees fit. | |
3236 | ||
3237 | =item variable interpolation | |
3238 | ||
3239 | The L</interpolation> of a scalar or array variable into a string. | |
3240 | ||
3241 | =item variadic | |
3242 | ||
3243 | Said of a L</function> that happily receives an indeterminate number | |
3244 | of L</actual arguments>. | |
3245 | ||
3246 | =item vector | |
3247 | ||
3248 | Mathematical jargon for a list of L<scalar values|/scalar value>. | |
3249 | ||
3250 | =item virtual | |
3251 | ||
3252 | Providing the appearance of something without the reality, as in: | |
3253 | virtual memory is not real memory. (See also L</memory>.) The | |
3254 | opposite of "virtual" is "transparent", which means providing the | |
3255 | reality of something without the appearance, as in: Perl handles the | |
3256 | variable-length UTF-8 character encoding transparently. | |
3257 | ||
3258 | =item void context | |
3259 | ||
3260 | A form of L</scalar context> in which an L</expression> is not | |
3261 | expected to return any L</value> at all and is evaluated for its | |
3262 | L</side effects> alone. | |
3263 | ||
3264 | =item v-string | |
3265 | ||
3266 | A "version" or "vector" L</string> specified with a C<v> followed by a | |
3267 | series of decimal integers in dot notation, for instance, | |
3268 | C<v1.20.300.4000>. Each number turns into a L</character> with the | |
3269 | specified ordinal value. (The C<v> is optional when there are at | |
3270 | least three integers.) | |
3271 | ||
3272 | =back | |
3273 | ||
3274 | =head2 W | |
3275 | ||
3276 | =over 4 | |
3277 | ||
3278 | =item warning | |
3279 | ||
3280 | A message printed to the L</STDERR> stream to the effect that something | |
3281 | might be wrong but isn't worth blowing up over. See L<perlfunc/warn> | |
3282 | and the L<warnings> pragma. | |
3283 | ||
3284 | =item watch expression | |
3285 | ||
3286 | An expression which, when its value changes, causes a breakpoint in | |
3287 | the Perl debugger. | |
3288 | ||
3289 | =item whitespace | |
3290 | ||
3291 | A L</character> that moves your cursor but doesn't otherwise put | |
3292 | anything on your screen. Typically refers to any of: space, tab, line | |
3293 | feed, carriage return, or form feed. | |
3294 | ||
3295 | =item word | |
3296 | ||
3297 | In normal "computerese", the piece of data of the size most | |
3298 | efficiently handled by your computer, typically 32 bits or so, give or | |
3299 | take a few powers of 2. In Perl culture, it more often refers to an | |
3300 | alphanumeric L</identifier> (including underscores), or to a string of | |
3301 | nonwhitespace L<characters|/character> bounded by whitespace or string | |
3302 | boundaries. | |
3303 | ||
3304 | =item working directory | |
3305 | ||
3306 | Your current L</directory>, from which relative pathnames are | |
3307 | interpreted by the L</operating system>. The operating system knows | |
3308 | your current directory because you told it with a | |
3309 | L<chdir|perlfunc/chdir> or because you started out in the place where | |
3310 | your parent L</process> was when you were born. | |
3311 | ||
3312 | =item wrapper | |
3313 | ||
3314 | A program or subroutine that runs some other program or subroutine for | |
3315 | you, modifying some of its input or output to better suit your | |
3316 | purposes. | |
3317 | ||
3318 | =item WYSIWYG | |
3319 | ||
3320 | What You See Is What You Get. Usually used when something that | |
3321 | appears on the screen matches how it will eventually look, like Perl's | |
3322 | L<format|perlfunc/format> declarations. Also used to mean the | |
3323 | opposite of magic because everything works exactly as it appears, as | |
3324 | in the three-argument form of L<open|perlfunc/open>. | |
3325 | ||
3326 | =back | |
3327 | ||
3328 | =head2 X | |
3329 | ||
3330 | =over 4 | |
3331 | ||
3332 | =item XS | |
3333 | ||
3334 | An extraordinarily exported, expeditiously excellent, expressly | |
3335 | eXternal Subroutine, executed in existing C or C++ or in an exciting | |
3336 | new extension language called (exasperatingly) XS. Examine L<perlxs> | |
3337 | for the exact explanation or L<perlxstut> for an exemplary unexacting | |
3338 | one. | |
3339 | ||
3340 | =item XSUB | |
3341 | ||
3342 | An external L</subroutine> defined in L</XS>. | |
3343 | ||
3344 | =back | |
3345 | ||
3346 | =head2 Y | |
3347 | ||
3348 | =over 4 | |
3349 | ||
3350 | =item yacc | |
3351 | ||
3352 | Yet Another Compiler Compiler. A parser generator without which Perl | |
3353 | probably would not have existed. See the file I<perly.y> in the Perl | |
3354 | source distribution. | |
3355 | ||
3356 | =back | |
3357 | ||
3358 | =head2 Z | |
3359 | ||
3360 | =over 4 | |
3361 | ||
3362 | =item zero width | |
3363 | ||
3364 | A subpattern L</assertion> matching the L</null string> between | |
3365 | L<characters|/character>. | |
3366 | ||
3367 | =item zombie | |
3368 | ||
3369 | A process that has died (exited) but whose parent has not yet received | |
3370 | proper notification of its demise by virtue of having called | |
3371 | L<wait|perlfunc/wait> or L<waitpid|perlfunc/waitpid>. If you | |
3372 | L<fork|perlfunc/fork>, you must clean up after your child processes | |
3373 | when they exit, or else the process table will fill up and your system | |
3374 | administrator will Not Be Happy with you. | |
3375 | ||
3376 | =back | |
3377 | ||
3378 | =head1 AUTHOR AND COPYRIGHT | |
3379 | ||
3380 | Based on the Glossary of Programming Perl, Third Edition, | |
3381 | by Larry Wall, Tom Christiansen & Jon Orwant. | |
3382 | Copyright (c) 2000, 1996, 1991 O'Reilly Media, Inc. | |
3383 | This document may be distributed under the same terms as Perl itself. |