Commit | Line | Data |
97a1d740 |
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 | |
5bbd0522 |
12 | =head2 A |
97a1d740 |
13 | |
14 | =over 4 |
15 | |
16 | =item accessor methods |
17 | |
27ed30b8 |
18 | A L</method> used to indirectly inspect or update an L</object>'s |
19 | state (its L<instance variables|/instance variable>). |
97a1d740 |
20 | |
21 | =item actual arguments |
22 | |
27ed30b8 |
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 |
97a1d740 |
25 | C<power("puff")>, the string C<"puff"> is the actual argument. See |
27ed30b8 |
26 | also L</argument> and L</formal arguments>. |
97a1d740 |
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 |
27ed30b8 |
33 | operator in Perl is the backslash operator, but it gives you a L</hard |
97a1d740 |
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 |
27ed30b8 |
48 | comparison function, and in each element of C<@_> for the L</actual |
97a1d740 |
49 | arguments> of a subroutine call. Permanent aliases are explicitly |
27ed30b8 |
50 | created in L<packages|/package> by L<importing|/import> symbols or by |
51 | assignment to L<typeglobs|/typeglob>. Lexically scoped aliases for |
97a1d740 |
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: |
27ed30b8 |
61 | C<||>. Logical alternatives in L</Boolean> expressions are separated |
97a1d740 |
62 | with either C<||> or C<or>. |
63 | |
64 | =item anonymous |
65 | |
27ed30b8 |
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 |
97a1d740 |
69 | hard reference goes away, the anonymous referent is destroyed without |
70 | pity. |
71 | |
72 | =item architecture |
73 | |
d7f8936a |
74 | The kind of computer you're working on, where one "kind" of computer |
97a1d740 |
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 |
27ed30b8 |
79 | compiled into machine code. See also L</platform> and L</operating |
97a1d740 |
80 | system>. |
81 | |
82 | =item argument |
83 | |
84 | A piece of data supplied to a L<program|/executable file>, |
27ed30b8 |
85 | L</subroutine>, L</function>, or L</method> to tell it what it's |
97a1d740 |
86 | supposed to do. Also called a "parameter". |
87 | |
88 | =item ARGV |
89 | |
27ed30b8 |
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. |
97a1d740 |
94 | |
95 | =item arithmetical operator |
96 | |
27ed30b8 |
97 | A L</symbol> such as C<+> or C</> that tells Perl to do the arithmetic |
97a1d740 |
98 | you were supposed to learn in grade school. |
99 | |
100 | =item array |
101 | |
27ed30b8 |
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. |
97a1d740 |
105 | |
106 | =item array context |
107 | |
108 | An archaic expression for what is more correctly referred to as |
27ed30b8 |
109 | L</list context>. |
97a1d740 |
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 |
27ed30b8 |
117 | codes best described as half ASCII. See also L</Unicode>. |
97a1d740 |
118 | |
119 | =item assertion |
120 | |
27ed30b8 |
121 | A component of a L</regular expression> that must be true for the |
97a1d740 |
122 | pattern to match but does not necessarily match any characters itself. |
27ed30b8 |
123 | Often used specifically to mean a L</zero width> assertion. |
97a1d740 |
124 | |
125 | =item assignment |
126 | |
27ed30b8 |
127 | An L</operator> whose assigned mission in life is to change the value |
128 | of a L</variable>. |
97a1d740 |
129 | |
130 | =item assignment operator |
131 | |
27ed30b8 |
132 | Either a regular L</assignment>, or a compound L</operator> composed |
97a1d740 |
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 | |
27ed30b8 |
139 | See L</hash>. Please. |
97a1d740 |
140 | |
141 | =item associativity |
142 | |
27ed30b8 |
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 |
97a1d740 |
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 | |
27ed30b8 |
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 |
97a1d740 |
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 | |
27ed30b8 |
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>. |
97a1d740 |
176 | |
177 | =item autogeneration |
178 | |
27ed30b8 |
179 | A feature of L</operator overloading> of L<objects|/object>, whereby |
180 | the behavior of certain L<operators|/operator> can be reasonably |
97a1d740 |
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 | |
cf525c36 |
187 | To add one to something automatically, hence the name of the C<++> |
97a1d740 |
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 |
27ed30b8 |
194 | call an L<AUTOLOAD|perlsub/Autoloading> subroutine on behalf of an |
195 | undefined subroutine. |
97a1d740 |
196 | |
197 | =item autosplit |
198 | |
27ed30b8 |
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> |
97a1d740 |
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, |
27ed30b8 |
207 | storage locations (L<lvalues|/lvalue>) spontaneously generate |
208 | themselves as needed, including the creation of any L</hard reference> |
97a1d740 |
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 |
27ed30b8 |
219 | types that holds an L</array>. The L</AV> type is a subclass of |
220 | L</SV>. |
97a1d740 |
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 | |
5bbd0522 |
230 | =head2 B |
231 | |
97a1d740 |
232 | =over 4 |
233 | |
234 | =item backreference |
235 | |
236 | A substring L<captured|/capturing> by a subpattern within |
27ed30b8 |
237 | unadorned parentheses in a L</regex>. Backslashed decimal numbers |
97a1d740 |
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 |
27ed30b8 |
250 | when it attempts to match patterns with a L</regular expression>, and |
97a1d740 |
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 | |
27ed30b8 |
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. |
97a1d740 |
263 | |
264 | =item base class |
265 | |
27ed30b8 |
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 |
97a1d740 |
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 |
27ed30b8 |
273 | computers that store the most significant L</byte> of a word at a |
97a1d740 |
274 | lower byte address than the least significant byte. Often considered |
27ed30b8 |
275 | superior to little-endian machines. See also L</little-endian>. |
97a1d740 |
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 |
27ed30b8 |
282 | bits in its bytes. With the advent of L</Unicode>, this distinction, |
97a1d740 |
283 | already suspect, loses even more of its meaning. |
284 | |
285 | =item binary operator |
286 | |
27ed30b8 |
287 | An L</operator> that takes two L<operands|/operand>. |
97a1d740 |
288 | |
289 | =item bind |
290 | |
27ed30b8 |
291 | To assign a specific L</network address> to a L</socket>. |
97a1d740 |
292 | |
293 | =item bit |
294 | |
295 | An integer in the range from 0 to 1, inclusive. The smallest possible |
27ed30b8 |
296 | unit of information storage. An eighth of a L</byte> or of a dollar. |
97a1d740 |
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 | |
27ed30b8 |
308 | A sequence of L<bits|/bit> that is actually being thought of as a |
97a1d740 |
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 |
27ed30b8 |
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 |
97a1d740 |
317 | L<perlfunc/"bless">. |
318 | |
319 | =item block |
320 | |
27ed30b8 |
321 | What a L</process> does when it has to wait for something: "My process |
97a1d740 |
322 | blocked waiting for the disk." As an unrelated noun, it refers to a |
27ed30b8 |
323 | large chunk of data, of a size that the L</operating system> likes to |
97a1d740 |
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 |
27ed30b8 |
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. |
97a1d740 |
332 | Sometimes we also say "block" to mean a lexical scope; that is, a |
27ed30b8 |
333 | sequence of statements that act like a L</BLOCK>, such as within an |
97a1d740 |
334 | L<eval|perlfunc/eval> or a file, even though the statements aren't |
335 | delimited by braces. |
336 | |
337 | =item block buffering |
338 | |
27ed30b8 |
339 | A method of making input and output efficient by passing one L</block> |
97a1d740 |
340 | at a time. By default, Perl does block buffering to disk files. See |
27ed30b8 |
341 | L</buffer> and L</command buffering>. |
97a1d740 |
342 | |
343 | =item Boolean |
344 | |
27ed30b8 |
345 | A value that is either L</true> or L</false>. |
97a1d740 |
346 | |
347 | =item Boolean context |
348 | |
27ed30b8 |
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>. |
97a1d740 |
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 | |
27ed30b8 |
362 | To send a L</datagram> to multiple destinations simultaneously. |
97a1d740 |
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 | |
27ed30b8 |
374 | A location in a L</hash table> containing (potentially) multiple |
97a1d740 |
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 | |
27ed30b8 |
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 |
97a1d740 |
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 | |
27ed30b8 |
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 |
97a1d740 |
394 | L<qualifying|/qualified> its name with the C<CORE::> pseudo-package. |
395 | |
396 | =item bundle |
397 | |
27ed30b8 |
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>.) |
97a1d740 |
400 | |
401 | =item byte |
402 | |
27ed30b8 |
403 | A piece of data worth eight L<bits|/bit> in most places. |
97a1d740 |
404 | |
405 | =item bytecode |
406 | |
407 | A pidgin-like language spoken among 'droids when they don't wish to |
27ed30b8 |
408 | reveal their orientation (see L</endian>). Named after some similar |
97a1d740 |
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 | |
5bbd0522 |
416 | =head2 C |
417 | |
97a1d740 |
418 | =over 4 |
419 | |
420 | =item C |
421 | |
27ed30b8 |
422 | A language beloved by many for its inside-out L</type> definitions, |
423 | inscrutable L</precedence> rules, and heavy L</overloading> of the |
97a1d740 |
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 | |
27ed30b8 |
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 |
97a1d740 |
440 | change the actual arguments by changing the formal arguments. That |
27ed30b8 |
441 | is, the formal argument is an L</alias> for the actual argument. See |
442 | also L</call by value>. |
97a1d740 |
443 | |
444 | =item call by value |
445 | |
27ed30b8 |
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> |
97a1d740 |
448 | cannot change the actual arguments by changing the formal arguments. |
27ed30b8 |
449 | See also L</call by reference>. |
97a1d740 |
450 | |
451 | =item callback |
452 | |
27ed30b8 |
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 |
97a1d740 |
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 | |
27ed30b8 |
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>.) |
97a1d740 |
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 | |
27ed30b8 |
479 | A square-bracketed list of characters used in a L</regular expression> |
97a1d740 |
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 | |
27ed30b8 |
485 | A predefined L</character class> matchable by the C<\p> |
486 | L</metasymbol>. Many standard properties are defined for L</Unicode>. |
97a1d740 |
487 | |
488 | =item circumfix operator |
489 | |
27ed30b8 |
490 | An L</operator> that surrounds its L</operand>, like the angle |
97a1d740 |
491 | operator, or parentheses, or a hug. |
492 | |
493 | =item class |
494 | |
27ed30b8 |
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>. |
97a1d740 |
499 | |
500 | =item class method |
501 | |
27ed30b8 |
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. |
97a1d740 |
504 | |
505 | =item client |
506 | |
27ed30b8 |
507 | In networking, a L</process> that initiates contact with a L</server> |
97a1d740 |
508 | process in order to exchange data and perhaps receive a service. |
509 | |
510 | =item cloister |
511 | |
27ed30b8 |
512 | A L</cluster> used to restrict the scope of a L</regular expression |
97a1d740 |
513 | modifier>. |
514 | |
515 | =item closure |
516 | |
27ed30b8 |
517 | An L</anonymous> subroutine that, when a reference to it is generated |
97a1d740 |
518 | at run time, keeps track of the identities of externally visible |
27ed30b8 |
519 | L<lexical variables|/lexical variable> even after those lexical |
520 | variables have supposedly gone out of L</scope>. They're called |
97a1d740 |
521 | "closures" because this sort of behavior gives mathematicians a sense |
522 | of closure. |
523 | |
524 | =item cluster |
525 | |
27ed30b8 |
526 | A parenthesized L</subpattern> used to group parts of a L</regular |
527 | expression> into a single L</atom>. |
97a1d740 |
528 | |
529 | =item CODE |
530 | |
531 | The word returned by the L<ref|perlfunc/ref> function when you apply |
27ed30b8 |
532 | it to a reference to a subroutine. See also L</CV>. |
97a1d740 |
533 | |
534 | =item code generator |
535 | |
536 | A system that writes code for you in a low-level language, such as |
27ed30b8 |
537 | code to implement the backend of a compiler. See L</program |
97a1d740 |
538 | generator>. |
539 | |
540 | =item code subpattern |
541 | |
27ed30b8 |
542 | A L</regular expression> subpattern whose real purpose is to execute |
97a1d740 |
543 | some Perl code, for example, the C<(?{...})> and C<(??{...})> |
544 | subpatterns. |
545 | |
546 | =item collating sequence |
547 | |
27ed30b8 |
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 |
97a1d740 |
550 | glossary to put "collating sequence". |
551 | |
552 | =item command |
553 | |
27ed30b8 |
554 | In L</shell> programming, the syntactic combination of a program name |
97a1d740 |
555 | and its arguments. More loosely, anything you type to a shell (a |
556 | command interpreter) that starts it doing something. Even more |
27ed30b8 |
557 | loosely, a Perl L</statement>, which might start with a L</label> and |
97a1d740 |
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 |
27ed30b8 |
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<$|> |
97a1d740 |
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 |
27ed30b8 |
567 | happen because the default on a L</file> or L</pipe> is to use |
568 | L</block buffering>. |
97a1d740 |
569 | |
570 | =item command name |
571 | |
572 | The name of the program currently executing, as typed on the command |
27ed30b8 |
573 | line. In C, the L</command> name is passed to the program as the |
97a1d740 |
574 | first command-line argument. In Perl, it comes in separately as |
575 | C<$0>. |
576 | |
577 | =item command-line arguments |
578 | |
27ed30b8 |
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 |
97a1d740 |
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 | |
27ed30b8 |
591 | The L</file> (or L</string>, in the case of L<eval|perlfunc/eval>) |
97a1d740 |
592 | that is currently being compiled. |
593 | |
594 | =item compile phase |
595 | |
596 | Any time before Perl starts running your main program. See also |
27ed30b8 |
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, |
97a1d740 |
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 |
27ed30b8 |
607 | do what it thinks your code says to do, which is L</run time>. |
97a1d740 |
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 |
27ed30b8 |
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 |
97a1d740 |
619 | "real" compiler. See L<O>. |
620 | |
621 | =item composer |
622 | |
27ed30b8 |
623 | A "constructor" for a L</referent> that isn't really an L</object>, |
97a1d740 |
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 |
27ed30b8 |
632 | similar operation on two L<strings|/string>. |
97a1d740 |
633 | |
634 | =item conditional |
635 | |
27ed30b8 |
636 | Something "iffy". See L</Boolean context>. |
97a1d740 |
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 |
27ed30b8 |
642 | circuit between a L</client> and a L</server>. |
97a1d740 |
643 | |
644 | =item construct |
645 | |
646 | As a noun, a piece of syntax made up of smaller pieces. As a |
27ed30b8 |
647 | transitive verb, to create an L</object> using a L</constructor>. |
97a1d740 |
648 | |
649 | =item constructor |
650 | |
27ed30b8 |
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>. |
97a1d740 |
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 |
27ed30b8 |
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 |
97a1d740 |
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 | |
27ed30b8 |
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 |
97a1d740 |
671 | putting a space or tab I<after> the newline. In general, lines in |
27ed30b8 |
672 | Perl do not need any form of continuation mark, because L</whitespace> |
97a1d740 |
673 | (including newlines) is gleefully ignored. Usually. |
674 | |
675 | =item core dump |
676 | |
27ed30b8 |
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 |
97a1d740 |
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 |
27ed30b8 |
688 | true L</hacker> or only a L</script kiddie>. |
97a1d740 |
689 | |
690 | =item current package |
691 | |
27ed30b8 |
692 | The L</package> in which the current statement is compiled. Scan |
97a1d740 |
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 | |
27ed30b8 |
699 | See L</working directory>. |
97a1d740 |
700 | |
701 | =item currently selected output channel |
702 | |
27ed30b8 |
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. |
97a1d740 |
706 | |
707 | =item CV |
708 | |
27ed30b8 |
709 | An internal "code value" typedef, holding a L</subroutine>. The L</CV> |
710 | type is a subclass of L</SV>. |
97a1d740 |
711 | |
712 | =back |
713 | |
5bbd0522 |
714 | =head2 D |
715 | |
97a1d740 |
716 | =over 4 |
717 | |
718 | =item dangling statement |
719 | |
27ed30b8 |
720 | A bare, single L</statement>, without any braces, hanging off an C<if> |
97a1d740 |
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 |
27ed30b8 |
736 | operations, such as L</concatenation>. Compound types made of a |
97a1d740 |
737 | number of smaller pieces generally have operations to compose and |
27ed30b8 |
738 | decompose them, and perhaps to rearrange them. L<Objects|/object> |
739 | that model things in the real world often have operations that |
97a1d740 |
740 | correspond to real activities. For instance, if you model an |
741 | elevator, your elevator object might have an C<open_door()> |
27ed30b8 |
742 | L</method>. |
97a1d740 |
743 | |
744 | =item datagram |
745 | |
27ed30b8 |
746 | A packet of data, such as a L</UDP> message, that (from the viewpoint |
97a1d740 |
747 | of the programs involved) can be sent independently over the network. |
27ed30b8 |
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.) |
97a1d740 |
750 | |
751 | =item DBM |
752 | |
753 | Stands for "Data Base Management" routines, a set of routines that |
27ed30b8 |
754 | emulate an L</associative array> using disk files. The routines use a |
97a1d740 |
755 | dynamic hashing scheme to locate any entry with only two disk |
756 | accesses. DBM files allow a Perl program to keep a persistent |
27ed30b8 |
757 | L</hash> across multiple invocations. You can L<tie|perlfunc/tie> |
97a1d740 |
758 | your hash variables to various DBM implementations--see L<AnyDBM_File> |
759 | and L<DB_File>. |
760 | |
761 | =item declaration |
762 | |
27ed30b8 |
763 | An L</assertion> that states something exists and perhaps describes |
97a1d740 |
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 |
27ed30b8 |
767 | L</statement> for its opposite. Note that some declarations also |
97a1d740 |
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 | |
27ed30b8 |
778 | A L</value> chosen for you if you don't supply a value of your own. |
97a1d740 |
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 |
27ed30b8 |
784 | have never been given a L</value> and performing certain operations on |
97a1d740 |
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 |
27ed30b8 |
787 | L</false> and L<perlfunc/defined>. |
97a1d740 |
788 | |
789 | =item delimiter |
790 | |
27ed30b8 |
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 |
97a1d740 |
794 | enclose" (like these parentheses are doing). |
795 | |
2dd6f5a3 |
796 | =item deprecated modules and features |
797 | |
798 | Deprecated modules and features are those which were part of a stable |
799 | release, but later found to be subtly flawed, and which should be avoided. |
800 | They are subject to removal and/or bug-incompatible reimplementation in |
353c6505 |
801 | the next major release (but they will be preserved through maintenance |
2dd6f5a3 |
802 | releases). Deprecation warnings are issued under B<-w> or C<use |
803 | diagnostics>, and notices are found in L<perldelta>s, as well as various |
804 | other PODs. Coding practices that misuse features, such as C<my $foo if |
805 | 0>, can also be deprecated. |
806 | |
97a1d740 |
807 | =item dereference |
808 | |
27ed30b8 |
809 | A fancy computer science term meaning "to follow a L</reference> to |
97a1d740 |
810 | what it points to". The "de" part of it refers to the fact that |
27ed30b8 |
811 | you're taking away one level of L</indirection>. |
97a1d740 |
812 | |
813 | =item derived class |
814 | |
27ed30b8 |
815 | A L</class> that defines some of its L<methods|/method> in terms of a |
816 | more generic class, called a L</base class>. Note that classes aren't |
97a1d740 |
817 | classified exclusively into base classes or derived classes: a class |
818 | can function as both a derived class and a base class simultaneously, |
819 | which is kind of classy. |
820 | |
821 | =item descriptor |
822 | |
27ed30b8 |
823 | See L</file descriptor>. |
97a1d740 |
824 | |
825 | =item destroy |
826 | |
27ed30b8 |
827 | To deallocate the memory of a L</referent> (first triggering its |
97a1d740 |
828 | C<DESTROY> method, if it has one). |
829 | |
830 | =item destructor |
831 | |
27ed30b8 |
832 | A special L</method> that is called when an L</object> is thinking |
833 | about L<destroying|/destroy> itself. A Perl program's C<DESTROY> |
97a1d740 |
834 | method doesn't do the actual destruction; Perl just |
27ed30b8 |
835 | L<triggers|/trigger> the method in case the L</class> wants to do any |
97a1d740 |
836 | associated cleanup. |
837 | |
838 | =item device |
839 | |
840 | A whiz-bang hardware gizmo (like a disk or tape drive or a modem or a |
27ed30b8 |
841 | joystick or a mouse) attached to your computer, that the L</operating |
842 | system> tries to make look like a L</file> (or a bunch of files). |
97a1d740 |
843 | Under Unix, these fake files tend to live in the I</dev> directory. |
844 | |
845 | =item directive |
846 | |
27ed30b8 |
847 | A L</pod> directive. See L<perlpod>. |
97a1d740 |
848 | |
849 | =item directory |
850 | |
851 | A special file that contains other files. Some L<operating |
852 | systems|/operating system> call these "folders", "drawers", or |
853 | "catalogs". |
854 | |
855 | =item directory handle |
856 | |
857 | A name that represents a particular instance of opening a directory to |
858 | read it, until you close it. See the L<opendir|perlfunc/opendir> |
859 | function. |
860 | |
861 | =item dispatch |
862 | |
863 | To send something to its correct destination. Often used |
864 | metaphorically to indicate a transfer of programmatic control to a |
865 | destination selected algorithmically, often by lookup in a table of |
27ed30b8 |
866 | function L<references|/reference> or, in the case of object |
867 | L<methods|/method>, by traversing the inheritance tree looking for the |
97a1d740 |
868 | most specific definition for the method. |
869 | |
870 | =item distribution |
871 | |
872 | A standard, bundled release of a system of software. The default |
873 | usage implies source code is included. If that is not the case, it |
874 | will be called a "binary-only" distribution. |
875 | |
2dd6f5a3 |
876 | =item (to be) dropped modules |
877 | |
878 | When Perl 5 was first released (see L<perlhistory>), several modules were |
879 | included, which have now fallen out of common use. It has been suggested |
880 | that these modules should be removed, since the distribution became rather |
881 | large, and the common criterion for new module additions is now limited to |
882 | modules that help to build, test, and extend perl itself. Furthermore, |
e6665613 |
883 | the CPAN (which didn't exist at the time of Perl 5.0) can become the new |
884 | home of dropped modules. Dropping modules is currently not an option, but |
2dd6f5a3 |
885 | further developments may clear the last barriers. |
886 | |
97a1d740 |
887 | =item dweomer |
888 | |
889 | An enchantment, illusion, phantasm, or jugglery. Said when Perl's |
27ed30b8 |
890 | magical L</dwimmer> effects don't do what you expect, but rather seem |
97a1d740 |
891 | to be the product of arcane dweomercraft, sorcery, or wonder working. |
892 | [From Old English] |
893 | |
894 | =item dwimmer |
895 | |
896 | DWIM is an acronym for "Do What I Mean", the principle that something |
897 | should just do what you want it to do without an undue amount of fuss. |
898 | A bit of code that does "dwimming" is a "dwimmer". Dwimming can |
899 | require a great deal of behind-the-scenes magic, which (if it doesn't |
27ed30b8 |
900 | stay properly behind the scenes) is called a L</dweomer> instead. |
97a1d740 |
901 | |
902 | =item dynamic scoping |
903 | |
904 | Dynamic scoping works over a dynamic scope, making variables visible |
27ed30b8 |
905 | throughout the rest of the L</block> in which they are first used and |
906 | in any L<subroutines|/subroutine> that are called by the rest of the |
97a1d740 |
907 | block. Dynamically scoped variables can have their values temporarily |
908 | changed (and implicitly restored later) by a L<local|perlfunc/local> |
27ed30b8 |
909 | operator. (Compare L</lexical scoping>.) Used more loosely to mean |
97a1d740 |
910 | how a subroutine that is in the middle of calling another subroutine |
27ed30b8 |
911 | "contains" that subroutine at L</run time>. |
97a1d740 |
912 | |
913 | =back |
914 | |
5bbd0522 |
915 | =head2 E |
916 | |
97a1d740 |
917 | =over 4 |
918 | |
919 | =item eclectic |
920 | |
921 | Derived from many sources. Some would say I<too> many. |
922 | |
923 | =item element |
924 | |
27ed30b8 |
925 | A basic building block. When you're talking about an L</array>, it's |
97a1d740 |
926 | one of the items that make up the array. |
927 | |
928 | =item embedding |
929 | |
930 | When something is contained in something else, particularly when that |
931 | might be considered surprising: "I've embedded a complete Perl |
932 | interpreter in my editor!" |
933 | |
934 | =item empty subclass test |
935 | |
27ed30b8 |
936 | The notion that an empty L</derived class> should behave exactly like |
937 | its L</base class>. |
97a1d740 |
938 | |
939 | =item en passant |
940 | |
27ed30b8 |
941 | When you change a L</value> as it is being copied. [From French, "in |
97a1d740 |
942 | passing", as in the exotic pawn-capturing maneuver in chess.] |
943 | |
944 | =item encapsulation |
945 | |
27ed30b8 |
946 | The veil of abstraction separating the L</interface> from the |
947 | L</implementation> (whether enforced or not), which mandates that all |
948 | access to an L</object>'s state be through L<methods|/method> alone. |
97a1d740 |
949 | |
950 | =item endian |
951 | |
27ed30b8 |
952 | See L</little-endian> and L</big-endian>. |
97a1d740 |
953 | |
954 | =item environment |
955 | |
27ed30b8 |
956 | The collective set of L<environment variables|/environment variable> |
957 | your L</process> inherits from its parent. Accessed via C<%ENV>. |
97a1d740 |
958 | |
959 | =item environment variable |
960 | |
961 | A mechanism by which some high-level agent such as a user can pass its |
27ed30b8 |
962 | preferences down to its future offspring (child L<processes|/process>, |
97a1d740 |
963 | grandchild processes, great-grandchild processes, and so on). Each |
27ed30b8 |
964 | environment variable is a L</key>/L</value> pair, like one entry in a |
965 | L</hash>. |
97a1d740 |
966 | |
967 | =item EOF |
968 | |
969 | End of File. Sometimes used metaphorically as the terminating string |
27ed30b8 |
970 | of a L</here document>. |
97a1d740 |
971 | |
972 | =item errno |
973 | |
27ed30b8 |
974 | The error number returned by a L</syscall> when it fails. Perl refers |
97a1d740 |
975 | to the error by the name C<$!> (or C<$OS_ERROR> if you use the English |
976 | module). |
977 | |
978 | =item error |
979 | |
27ed30b8 |
980 | See L</exception> or L</fatal error>. |
97a1d740 |
981 | |
982 | =item escape sequence |
983 | |
27ed30b8 |
984 | See L</metasymbol>. |
97a1d740 |
985 | |
986 | =item exception |
987 | |
27ed30b8 |
988 | A fancy term for an error. See L</fatal error>. |
97a1d740 |
989 | |
990 | =item exception handling |
991 | |
992 | The way a program responds to an error. The exception handling |
993 | mechanism in Perl is the L<eval|perlfunc/eval> operator. |
994 | |
995 | =item exec |
996 | |
27ed30b8 |
997 | To throw away the current L</process>'s program and replace it with |
97a1d740 |
998 | another without exiting the process or relinquishing any resources |
999 | held (apart from the old memory image). |
1000 | |
1001 | =item executable file |
1002 | |
27ed30b8 |
1003 | A L</file> that is specially marked to tell the L</operating system> |
97a1d740 |
1004 | that it's okay to run this file as a program. Usually shortened to |
1005 | "executable". |
1006 | |
1007 | =item execute |
1008 | |
27ed30b8 |
1009 | To run a L<program|/executable file> or L</subroutine>. (Has nothing |
97a1d740 |
1010 | to do with the L<kill|perlfunc/kill> built-in, unless you're trying to |
27ed30b8 |
1011 | run a L</signal handler>.) |
97a1d740 |
1012 | |
1013 | =item execute bit |
1014 | |
1015 | The special mark that tells the operating system it can run this |
1016 | program. There are actually three execute bits under Unix, and which |
1017 | bit gets used depends on whether you own the file singularly, |
1018 | collectively, or not at all. |
1019 | |
1020 | =item exit status |
1021 | |
27ed30b8 |
1022 | See L</status>. |
97a1d740 |
1023 | |
1024 | =item export |
1025 | |
27ed30b8 |
1026 | To make symbols from a L</module> available for L</import> by other modules. |
97a1d740 |
1027 | |
1028 | =item expression |
1029 | |
27ed30b8 |
1030 | Anything you can legally say in a spot where a L</value> is required. |
1031 | Typically composed of L<literals|/literal>, L<variables|/variable>, |
1032 | L<operators|/operator>, L<functions|/function>, and L</subroutine> |
97a1d740 |
1033 | calls, not necessarily in that order. |
1034 | |
1035 | =item extension |
1036 | |
1037 | A Perl module that also pulls in compiled C or C++ code. More |
1038 | generally, any experimental option that can be compiled into Perl, |
1039 | such as multithreading. |
1040 | |
1041 | =back |
1042 | |
5bbd0522 |
1043 | =head2 F |
1044 | |
97a1d740 |
1045 | =over 4 |
1046 | |
1047 | =item false |
1048 | |
1049 | In Perl, any value that would look like C<""> or C<"0"> if evaluated |
1050 | in a string context. Since undefined values evaluate to C<"">, all |
1051 | undefined values are false, but not all false values are undefined. |
1052 | |
1053 | =item FAQ |
1054 | |
1055 | Frequently Asked Question (although not necessarily frequently |
1056 | answered, especially if the answer appears in the Perl FAQ shipped |
1057 | standard with Perl). |
1058 | |
1059 | =item fatal error |
1060 | |
27ed30b8 |
1061 | An uncaught L</exception>, which causes termination of the L</process> |
1062 | after printing a message on your L</standard error> stream. Errors |
97a1d740 |
1063 | that happen inside an L<eval|perlfunc/eval> are not fatal. Instead, |
1064 | the L<eval|perlfunc/eval> terminates after placing the exception |
1065 | message in the C<$@> (C<$EVAL_ERROR>) variable. You can try to |
1066 | provoke a fatal error with the L<die|perlfunc/die> operator (known as |
1067 | throwing or raising an exception), but this may be caught by a |
1068 | dynamically enclosing L<eval|perlfunc/eval>. If not caught, the |
1069 | L<die|perlfunc/die> becomes a fatal error. |
1070 | |
1071 | =item field |
1072 | |
1073 | A single piece of numeric or string data that is part of a longer |
27ed30b8 |
1074 | L</string>, L</record>, or L</line>. Variable-width fields are usually |
1075 | split up by L<separators|/separator> (so use L<split|perlfunc/split> to |
1076 | extract the fields), while fixed-width fields are usually at fixed |
1077 | positions (so use L<unpack|perlfunc/unpack>). L<Instance |
1078 | variables|/instance variable> are also known as fields. |
97a1d740 |
1079 | |
1080 | =item FIFO |
1081 | |
27ed30b8 |
1082 | First In, First Out. See also L</LIFO>. Also, a nickname for a |
1083 | L</named pipe>. |
97a1d740 |
1084 | |
1085 | =item file |
1086 | |
27ed30b8 |
1087 | A named collection of data, usually stored on disk in a L</directory> |
1088 | in a L</filesystem>. Roughly like a document, if you're into office |
97a1d740 |
1089 | metaphors. In modern filesystems, you can actually give a file more |
1090 | than one name. Some files have special properties, like directories |
1091 | and devices. |
1092 | |
1093 | =item file descriptor |
1094 | |
27ed30b8 |
1095 | The little number the L</operating system> uses to keep track of which |
1096 | opened L</file> you're talking about. Perl hides the file descriptor |
1097 | inside a L</standard IE<sol>O> stream and then attaches the stream to |
1098 | a L</filehandle>. |
97a1d740 |
1099 | |
1100 | =item file test operator |
1101 | |
1102 | A built-in unary operator that you use to determine whether something |
27ed30b8 |
1103 | is L</true> about a file, such as C<-o $filename> to test whether |
97a1d740 |
1104 | you're the owner of the file. |
1105 | |
1106 | =item fileglob |
1107 | |
27ed30b8 |
1108 | A "wildcard" match on L<filenames|/filename>. See the |
97a1d740 |
1109 | L<glob|perlfunc/glob> function. |
1110 | |
1111 | =item filehandle |
1112 | |
1113 | An identifier (not necessarily related to the real name of a file) |
1114 | that represents a particular instance of opening a file until you |
1115 | close it. If you're going to open and close several different files |
1116 | in succession, it's fine to open each of them with the same |
1117 | filehandle, so you don't have to write out separate code to process |
1118 | each file. |
1119 | |
1120 | =item filename |
1121 | |
27ed30b8 |
1122 | One name for a file. This name is listed in a L</directory>, and you |
1123 | can use it in an L<open|perlfunc/open> to tell the L</operating |
97a1d740 |
1124 | system> exactly which file you want to open, and associate the file |
27ed30b8 |
1125 | with a L</filehandle> which will carry the subsequent identity of that |
97a1d740 |
1126 | file in your program, until you close it. |
1127 | |
1128 | =item filesystem |
1129 | |
27ed30b8 |
1130 | A set of L<directories|/directory> and L<files|/file> residing on a |
97a1d740 |
1131 | partition of the disk. Sometimes known as a "partition". You can |
1132 | change the file's name or even move a file around from directory to |
1133 | directory within a filesystem without actually moving the file itself, |
1134 | at least under Unix. |
1135 | |
1136 | =item filter |
1137 | |
27ed30b8 |
1138 | A program designed to take a L</stream> of input and transform it into |
97a1d740 |
1139 | a stream of output. |
1140 | |
1141 | =item flag |
1142 | |
1143 | We tend to avoid this term because it means so many things. It may |
27ed30b8 |
1144 | mean a command-line L</switch> that takes no argument |
97a1d740 |
1145 | itself (such as Perl's B<-n> and B<-p> |
1146 | flags) or, less frequently, a single-bit indicator (such as the |
1147 | C<O_CREAT> and C<O_EXCL> flags used in |
1148 | L<sysopen|perlfunc/sysopen>). |
1149 | |
1150 | =item floating point |
1151 | |
1152 | A method of storing numbers in "scientific notation", such that the |
1153 | precision of the number is independent of its magnitude (the decimal |
1154 | point "floats"). Perl does its numeric work with floating-point |
1155 | numbers (sometimes called "floats"), when it can't get away with |
27ed30b8 |
1156 | using L<integers|/integer>. Floating-point numbers are mere |
97a1d740 |
1157 | approximations of real numbers. |
1158 | |
1159 | =item flush |
1160 | |
27ed30b8 |
1161 | The act of emptying a L</buffer>, often before it's full. |
97a1d740 |
1162 | |
1163 | =item FMTEYEWTK |
1164 | |
1165 | Far More Than Everything You Ever Wanted To Know. An exhaustive |
27ed30b8 |
1166 | treatise on one narrow topic, something of a super-L</FAQ>. See Tom |
97a1d740 |
1167 | for far more. |
1168 | |
1169 | =item fork |
1170 | |
27ed30b8 |
1171 | To create a child L</process> identical to the parent process at its |
97a1d740 |
1172 | moment of conception, at least until it gets ideas of its own. A |
1173 | thread with protected memory. |
1174 | |
1175 | =item formal arguments |
1176 | |
27ed30b8 |
1177 | The generic names by which a L</subroutine> knows its |
1178 | L<arguments|/argument>. In many languages, formal arguments are |
97a1d740 |
1179 | always given individual names, but in Perl, the formal arguments are |
1180 | just the elements of an array. The formal arguments to a Perl program |
1181 | are C<$ARGV[0]>, C<$ARGV[1]>, and so on. Similarly, the formal |
1182 | arguments to a Perl subroutine are C<$_[0]>, C<$_[1]>, and so on. You |
1183 | may give the arguments individual names by assigning the values to a |
27ed30b8 |
1184 | L<my|perlfunc/my> list. See also L</actual arguments>. |
97a1d740 |
1185 | |
1186 | =item format |
1187 | |
1188 | A specification of how many spaces and digits and things to put |
1189 | somewhere so that whatever you're printing comes out nice and pretty. |
1190 | |
1191 | =item freely available |
1192 | |
1193 | Means you don't have to pay money to get it, but the copyright on it |
1194 | may still belong to someone else (like Larry). |
1195 | |
1196 | =item freely redistributable |
1197 | |
1198 | Means you're not in legal trouble if you give a bootleg copy of it to |
1199 | your friends and we find out about it. In fact, we'd rather you gave |
1200 | a copy to all your friends. |
1201 | |
1202 | =item freeware |
1203 | |
1204 | Historically, any software that you give away, particularly if you |
1205 | make the source code available as well. Now often called C<open |
1206 | source software>. Recently there has been a trend to use the term in |
27ed30b8 |
1207 | contradistinction to L</open source software>, to refer only to free |
97a1d740 |
1208 | software released under the Free Software Foundation's GPL (General |
1209 | Public License), but this is difficult to justify etymologically. |
1210 | |
1211 | =item function |
1212 | |
1213 | Mathematically, a mapping of each of a set of input values to a |
27ed30b8 |
1214 | particular output value. In computers, refers to a L</subroutine> or |
1215 | L</operator> that returns a L</value>. It may or may not have input |
1216 | values (called L<arguments|/argument>). |
97a1d740 |
1217 | |
1218 | =item funny character |
1219 | |
1220 | Someone like Larry, or one of his peculiar friends. Also refers to |
1221 | the strange prefixes that Perl requires as noun markers on its |
1222 | variables. |
1223 | |
1224 | =item garbage collection |
1225 | |
1226 | A misnamed feature--it should be called, "expecting your mother to |
1227 | pick up after you". Strictly speaking, Perl doesn't do this, but it |
1228 | relies on a reference-counting mechanism to keep things tidy. |
1229 | However, we rarely speak strictly and will often refer to the |
1230 | reference-counting scheme as a form of garbage collection. (If it's |
1231 | any comfort, when your interpreter exits, a "real" garbage collector |
1232 | runs to make sure everything is cleaned up if you've been messy with |
1233 | circular references and such.) |
1234 | |
1235 | =back |
1236 | |
5bbd0522 |
1237 | =head2 G |
1238 | |
97a1d740 |
1239 | =over 4 |
1240 | |
1241 | =item GID |
1242 | |
27ed30b8 |
1243 | Group ID--in Unix, the numeric group ID that the L</operating system> |
1244 | uses to identify you and members of your L</group>. |
97a1d740 |
1245 | |
1246 | =item glob |
1247 | |
1248 | Strictly, the shell's C<*> character, which will match a "glob" of |
1249 | characters when you're trying to generate a list of filenames. |
1250 | Loosely, the act of using globs and similar symbols to do pattern |
27ed30b8 |
1251 | matching. See also L</fileglob> and L</typeglob>. |
97a1d740 |
1252 | |
1253 | =item global |
1254 | |
1255 | Something you can see from anywhere, usually used of |
27ed30b8 |
1256 | L<variables|/variable> and L<subroutines|/subroutine> that are visible |
97a1d740 |
1257 | everywhere in your program. In Perl, only certain special variables |
1258 | are truly global--most variables (and all subroutines) exist only in |
27ed30b8 |
1259 | the current L</package>. Global variables can be declared with |
97a1d740 |
1260 | L<our|perlfunc/our>. See L<perlfunc/our>. |
1261 | |
1262 | =item global destruction |
1263 | |
27ed30b8 |
1264 | The L</garbage collection> of globals (and the running of any |
97a1d740 |
1265 | associated object destructors) that takes place when a Perl |
27ed30b8 |
1266 | L</interpreter> is being shut down. Global destruction should not be |
97a1d740 |
1267 | confused with the Apocalypse, except perhaps when it should. |
1268 | |
1269 | =item glue language |
1270 | |
1271 | A language such as Perl that is good at hooking things together that |
1272 | weren't intended to be hooked together. |
1273 | |
1274 | =item granularity |
1275 | |
1276 | The size of the pieces you're dealing with, mentally speaking. |
1277 | |
1278 | =item greedy |
1279 | |
27ed30b8 |
1280 | A L</subpattern> whose L</quantifier> wants to match as many things as |
97a1d740 |
1281 | possible. |
1282 | |
1283 | =item grep |
1284 | |
1285 | Originally from the old Unix editor command for "Globally search for a |
1286 | Regular Expression and Print it", now used in the general sense of any |
1287 | kind of search, especially text searches. Perl has a built-in |
1288 | L<grep|perlfunc/grep> function that searches a list for elements |
27ed30b8 |
1289 | matching any given criterion, whereas the I<grep>(1) program searches |
1290 | for lines matching a L</regular expression> in one or more files. |
97a1d740 |
1291 | |
1292 | =item group |
1293 | |
1294 | A set of users of which you are a member. In some operating systems |
1295 | (like Unix), you can give certain file access permissions to other |
1296 | members of your group. |
1297 | |
1298 | =item GV |
1299 | |
27ed30b8 |
1300 | An internal "glob value" typedef, holding a L</typeglob>. The L</GV> |
1301 | type is a subclass of L</SV>. |
97a1d740 |
1302 | |
1303 | =back |
1304 | |
5bbd0522 |
1305 | =head2 H |
1306 | |
97a1d740 |
1307 | =over 4 |
1308 | |
1309 | =item hacker |
1310 | |
1311 | Someone who is brilliantly persistent in solving technical problems, |
1312 | whether these involve golfing, fighting orcs, or programming. Hacker |
1313 | is a neutral term, morally speaking. Good hackers are not to be |
27ed30b8 |
1314 | confused with evil L<crackers|/cracker> or clueless L<script |
97a1d740 |
1315 | kiddies|/script kiddie>. If you confuse them, we will presume that |
1316 | you are either evil or clueless. |
1317 | |
1318 | =item handler |
1319 | |
27ed30b8 |
1320 | A L</subroutine> or L</method> that is called by Perl when your |
1321 | program needs to respond to some internal event, such as a L</signal>, |
1322 | or an encounter with an operator subject to L</operator overloading>. |
1323 | See also L</callback>. |
97a1d740 |
1324 | |
1325 | =item hard reference |
1326 | |
27ed30b8 |
1327 | A L</scalar> L</value> containing the actual address of a |
1328 | L</referent>, such that the referent's L</reference> count accounts |
97a1d740 |
1329 | for it. (Some hard references are held internally, such as the |
27ed30b8 |
1330 | implicit reference from one of a L</typeglob>'s variable slots to its |
97a1d740 |
1331 | corresponding referent.) A hard reference is different from a |
27ed30b8 |
1332 | L</symbolic reference>. |
97a1d740 |
1333 | |
1334 | =item hash |
1335 | |
27ed30b8 |
1336 | An unordered association of L</key>/L</value> pairs, stored such that |
1337 | you can easily use a string L</key> to look up its associated data |
1338 | L</value>. This glossary is like a hash, where the word to be defined |
97a1d740 |
1339 | is the key, and the definition is the value. A hash is also sometimes |
1340 | septisyllabically called an "associative array", which is a pretty |
1341 | good reason for simply calling it a "hash" instead. |
1342 | |
1343 | =item hash table |
1344 | |
1345 | A data structure used internally by Perl for implementing associative |
27ed30b8 |
1346 | arrays (hashes) efficiently. See also L</bucket>. |
97a1d740 |
1347 | |
1348 | =item header file |
1349 | |
1350 | A file containing certain required definitions that you must include |
1351 | "ahead" of the rest of your program to do certain obscure operations. |
1352 | A C header file has a I<.h> extension. Perl doesn't really have |
1353 | header files, though historically Perl has sometimes used translated |
1354 | I<.h> files with a I<.ph> extension. See L<perlfunc/require>. |
27ed30b8 |
1355 | (Header files have been superseded by the L</module> mechanism.) |
97a1d740 |
1356 | |
1357 | =item here document |
1358 | |
27ed30b8 |
1359 | So called because of a similar construct in L<shells|/shell> that |
1360 | pretends that the L<lines|/line> following the L</command> are a |
1361 | separate L</file> to be fed to the command, up to some terminating |
97a1d740 |
1362 | string. In Perl, however, it's just a fancy form of quoting. |
1363 | |
1364 | =item hexadecimal |
1365 | |
1366 | A number in base 16, "hex" for short. The digits for 10 through 16 |
1367 | are customarily represented by the letters C<a> through C<f>. |
1368 | Hexadecimal constants in Perl start with C<0x>. See also |
27ed30b8 |
1369 | L<perlfunc/hex>. |
97a1d740 |
1370 | |
1371 | =item home directory |
1372 | |
1373 | The directory you are put into when you log in. On a Unix system, the |
1374 | name is often placed into C<$ENV{HOME}> or C<$ENV{LOGDIR}> by |
1375 | I<login>, but you can also find it with C<(getpwuid($E<lt>))[7]>. |
1376 | (Some platforms do not have a concept of a home directory.) |
1377 | |
1378 | =item host |
1379 | |
1380 | The computer on which a program or other data resides. |
1381 | |
1382 | =item hubris |
1383 | |
1384 | Excessive pride, the sort of thing Zeus zaps you for. Also the |
1385 | quality that makes you write (and maintain) programs that other people |
1386 | won't want to say bad things about. Hence, the third great virtue of |
27ed30b8 |
1387 | a programmer. See also L</laziness> and L</impatience>. |
97a1d740 |
1388 | |
1389 | =item HV |
1390 | |
1391 | Short for a "hash value" typedef, which holds Perl's internal |
27ed30b8 |
1392 | representation of a hash. The L</HV> type is a subclass of L</SV>. |
97a1d740 |
1393 | |
1394 | =back |
1395 | |
5bbd0522 |
1396 | =head2 I |
1397 | |
97a1d740 |
1398 | =over 4 |
1399 | |
1400 | =item identifier |
1401 | |
1402 | A legally formed name for most anything in which a computer program |
1403 | might be interested. Many languages (including Perl) allow |
1404 | identifiers that start with a letter and contain letters and digits. |
1405 | Perl also counts the underscore character as a valid letter. (Perl |
27ed30b8 |
1406 | also has more complicated names, such as L</qualified> names.) |
97a1d740 |
1407 | |
1408 | =item impatience |
1409 | |
1410 | The anger you feel when the computer is being lazy. This makes you |
1411 | write programs that don't just react to your needs, but actually |
1412 | anticipate them. Or at least that pretend to. Hence, the second |
27ed30b8 |
1413 | great virtue of a programmer. See also L</laziness> and L</hubris>. |
97a1d740 |
1414 | |
1415 | =item implementation |
1416 | |
1417 | How a piece of code actually goes about doing its job. Users of the |
1418 | code should not count on implementation details staying the same |
27ed30b8 |
1419 | unless they are part of the published L</interface>. |
97a1d740 |
1420 | |
1421 | =item import |
1422 | |
1423 | To gain access to symbols that are exported from another module. See |
1424 | L<perlfunc/use>. |
1425 | |
1426 | =item increment |
1427 | |
1428 | To increase the value of something by 1 (or by some other number, if |
1429 | so specified). |
1430 | |
1431 | =item indexing |
1432 | |
27ed30b8 |
1433 | In olden days, the act of looking up a L</key> in an actual index |
97a1d740 |
1434 | (such as a phone book), but now merely the act of using any kind of |
27ed30b8 |
1435 | key or position to find the corresponding L</value>, even if no index |
97a1d740 |
1436 | is involved. Things have degenerated to the point that Perl's |
1437 | L<index|perlfunc/index> function merely locates the position (index) |
1438 | of one string in another. |
1439 | |
1440 | =item indirect filehandle |
1441 | |
27ed30b8 |
1442 | An L</expression> that evaluates to something that can be used as a |
1443 | L</filehandle>: a L</string> (filehandle name), a L</typeglob>, a |
1444 | typeglob L</reference>, or a low-level L</IO> object. |
97a1d740 |
1445 | |
1446 | =item indirect object |
1447 | |
1448 | In English grammar, a short noun phrase between a verb and its direct |
1449 | object indicating the beneficiary or recipient of the action. In |
1450 | Perl, C<print STDOUT "$foo\n";> can be understood as "verb |
27ed30b8 |
1451 | indirect-object object" where L</STDOUT> is the recipient of the |
97a1d740 |
1452 | L<print|perlfunc/print> action, and C<"$foo"> is the object being |
27ed30b8 |
1453 | printed. Similarly, when invoking a L</method>, you might place the |
97a1d740 |
1454 | invocant between the method and its arguments: |
1455 | |
1456 | $gollum = new Pathetic::Creature "Smeagol"; |
1457 | give $gollum "Fisssssh!"; |
1458 | give $gollum "Precious!"; |
1459 | |
797f796a |
1460 | In modern Perl, calling methods this way is often considered bad practice and |
1461 | to be avoided. |
1462 | |
97a1d740 |
1463 | =item indirect object slot |
1464 | |
1465 | The syntactic position falling between a method call and its arguments |
1466 | when using the indirect object invocation syntax. (The slot is |
1467 | distinguished by the absence of a comma between it and the next |
27ed30b8 |
1468 | argument.) L</STDERR> is in the indirect object slot here: |
97a1d740 |
1469 | |
1470 | print STDERR "Awake! Awake! Fear, Fire, |
1471 | Foes! Awake!\n"; |
1472 | |
1473 | =item indirection |
1474 | |
1475 | If something in a program isn't the value you're looking for but |
1476 | indicates where the value is, that's indirection. This can be done |
27ed30b8 |
1477 | with either L<symbolic references|/symbolic reference> or L<hard |
97a1d740 |
1478 | references|/hard reference>. |
1479 | |
1480 | =item infix |
1481 | |
27ed30b8 |
1482 | An L</operator> that comes in between its L<operands|/operand>, such |
97a1d740 |
1483 | as multiplication in C<24 * 7>. |
1484 | |
1485 | =item inheritance |
1486 | |
1487 | What you get from your ancestors, genetically or otherwise. If you |
27ed30b8 |
1488 | happen to be a L</class>, your ancestors are called L<base |
97a1d740 |
1489 | classes|/base class> and your descendants are called L<derived |
27ed30b8 |
1490 | classes|/derived class>. See L</single inheritance> and L</multiple |
97a1d740 |
1491 | inheritance>. |
1492 | |
1493 | =item instance |
1494 | |
27ed30b8 |
1495 | Short for "an instance of a class", meaning an L</object> of that L</class>. |
97a1d740 |
1496 | |
1497 | =item instance variable |
1498 | |
27ed30b8 |
1499 | An L</attribute> of an L</object>; data stored with the particular |
97a1d740 |
1500 | object rather than with the class as a whole. |
1501 | |
1502 | =item integer |
1503 | |
1504 | A number with no fractional (decimal) part. A counting number, like |
1505 | 1, 2, 3, and so on, but including 0 and the negatives. |
1506 | |
1507 | =item interface |
1508 | |
1509 | The services a piece of code promises to provide forever, in contrast to |
27ed30b8 |
1510 | its L</implementation>, which it should feel free to change whenever it |
97a1d740 |
1511 | likes. |
1512 | |
1513 | =item interpolation |
1514 | |
1515 | The insertion of a scalar or list value somewhere in the middle of |
1516 | another value, such that it appears to have been there all along. In |
1517 | Perl, variable interpolation happens in double-quoted strings and |
1518 | patterns, and list interpolation occurs when constructing the list of |
1519 | values to pass to a list operator or other such construct that takes a |
27ed30b8 |
1520 | L</LIST>. |
97a1d740 |
1521 | |
1522 | =item interpreter |
1523 | |
1524 | Strictly speaking, a program that reads a second program and does what |
1525 | the second program says directly without turning the program into a |
27ed30b8 |
1526 | different form first, which is what L<compilers|/compiler> do. Perl |
97a1d740 |
1527 | is not an interpreter by this definition, because it contains a kind |
1528 | of compiler that takes a program and turns it into a more executable |
27ed30b8 |
1529 | form (L<syntax trees|/syntax tree>) within the I<perl> process itself, |
1530 | which the Perl L</run time> system then interprets. |
97a1d740 |
1531 | |
1532 | =item invocant |
1533 | |
27ed30b8 |
1534 | The agent on whose behalf a L</method> is invoked. In a L</class> |
1535 | method, the invocant is a package name. In an L</instance> method, |
97a1d740 |
1536 | the invocant is an object reference. |
1537 | |
1538 | =item invocation |
1539 | |
1540 | The act of calling up a deity, daemon, program, method, subroutine, or |
1541 | function to get it do what you think it's supposed to do. We usually |
1542 | "call" subroutines but "invoke" methods, since it sounds cooler. |
1543 | |
1544 | =item I/O |
1545 | |
27ed30b8 |
1546 | Input from, or output to, a L</file> or L</device>. |
97a1d740 |
1547 | |
1548 | =item IO |
1549 | |
27ed30b8 |
1550 | An internal I/O object. Can also mean L</indirect object>. |
97a1d740 |
1551 | |
1552 | =item IP |
1553 | |
1554 | Internet Protocol, or Intellectual Property. |
1555 | |
1556 | =item IPC |
1557 | |
1558 | Interprocess Communication. |
1559 | |
1560 | =item is-a |
1561 | |
27ed30b8 |
1562 | A relationship between two L<objects|/object> in which one object is |
97a1d740 |
1563 | considered to be a more specific version of the other, generic object: |
1564 | "A camel is a mammal." Since the generic object really only exists in |
1565 | a Platonic sense, we usually add a little abstraction to the notion of |
1566 | objects and think of the relationship as being between a generic |
27ed30b8 |
1567 | L</base class> and a specific L</derived class>. Oddly enough, |
97a1d740 |
1568 | Platonic classes don't always have Platonic relationships--see |
27ed30b8 |
1569 | L</inheritance>. |
97a1d740 |
1570 | |
1571 | =item iteration |
1572 | |
1573 | Doing something repeatedly. |
1574 | |
1575 | =item iterator |
1576 | |
1577 | A special programming gizmo that keeps track of where you are in |
1578 | something that you're trying to iterate over. The C<foreach> loop in |
1579 | Perl contains an iterator; so does a hash, allowing you to |
1580 | L<each|perlfunc/each> through it. |
1581 | |
1582 | =item IV |
1583 | |
1584 | The integer four, not to be confused with six, Tom's favorite editor. |
27ed30b8 |
1585 | IV also means an internal Integer Value of the type a L</scalar> can |
1586 | hold, not to be confused with an L</NV>. |
97a1d740 |
1587 | |
1588 | =back |
1589 | |
5bbd0522 |
1590 | =head2 J |
1591 | |
97a1d740 |
1592 | =over 4 |
1593 | |
1594 | =item JAPH |
1595 | |
1596 | "Just Another Perl Hacker," a clever but cryptic bit of Perl code that |
1597 | when executed, evaluates to that string. Often used to illustrate a |
353c6505 |
1598 | particular Perl feature, and something of an ongoing Obfuscated Perl |
97a1d740 |
1599 | Contest seen in Usenix signatures. |
1600 | |
1601 | =back |
1602 | |
5bbd0522 |
1603 | =head2 K |
1604 | |
97a1d740 |
1605 | =over 4 |
1606 | |
1607 | =item key |
1608 | |
27ed30b8 |
1609 | The string index to a L</hash>, used to look up the L</value> |
97a1d740 |
1610 | associated with that key. |
1611 | |
1612 | =item keyword |
1613 | |
27ed30b8 |
1614 | See L</reserved words>. |
97a1d740 |
1615 | |
1616 | =back |
1617 | |
5bbd0522 |
1618 | =head2 L |
1619 | |
97a1d740 |
1620 | =over 4 |
1621 | |
1622 | =item label |
1623 | |
27ed30b8 |
1624 | A name you give to a L</statement> so that you can talk about that |
97a1d740 |
1625 | statement elsewhere in the program. |
1626 | |
1627 | =item laziness |
1628 | |
1629 | The quality that makes you go to great effort to reduce overall energy |
1630 | expenditure. It makes you write labor-saving programs that other |
1631 | people will find useful, and document what you wrote so you don't have |
1632 | to answer so many questions about it. Hence, the first great virtue |
27ed30b8 |
1633 | of a programmer. Also hence, this book. See also L</impatience> and |
1634 | L</hubris>. |
97a1d740 |
1635 | |
1636 | =item left shift |
1637 | |
27ed30b8 |
1638 | A L</bit shift> that multiplies the number by some power of 2. |
97a1d740 |
1639 | |
1640 | =item leftmost longest |
1641 | |
27ed30b8 |
1642 | The preference of the L</regular expression> engine to match the |
1643 | leftmost occurrence of a L</pattern>, then given a position at which a |
97a1d740 |
1644 | match will occur, the preference for the longest match (presuming the |
27ed30b8 |
1645 | use of a L</greedy> quantifier). See L<perlre> for I<much> more on |
97a1d740 |
1646 | this subject. |
1647 | |
1648 | =item lexeme |
1649 | |
27ed30b8 |
1650 | Fancy term for a L</token>. |
97a1d740 |
1651 | |
1652 | =item lexer |
1653 | |
27ed30b8 |
1654 | Fancy term for a L</tokener>. |
97a1d740 |
1655 | |
1656 | =item lexical analysis |
1657 | |
27ed30b8 |
1658 | Fancy term for L</tokenizing>. |
97a1d740 |
1659 | |
1660 | =item lexical scoping |
1661 | |
1662 | Looking at your I<Oxford English Dictionary> through a microscope. |
27ed30b8 |
1663 | (Also known as L</static scoping>, because dictionaries don't change |
97a1d740 |
1664 | very fast.) Similarly, looking at variables stored in a private |
1665 | dictionary (namespace) for each scope, which are visible only from |
1666 | their point of declaration down to the end of the lexical scope in |
27ed30b8 |
1667 | which they are declared. --Syn. L</static scoping>. |
1668 | --Ant. L</dynamic scoping>. |
97a1d740 |
1669 | |
1670 | =item lexical variable |
1671 | |
27ed30b8 |
1672 | A L</variable> subject to L</lexical scoping>, declared by |
97a1d740 |
1673 | L<my|perlfunc/my>. Often just called a "lexical". (The |
1674 | L<our|perlfunc/our> declaration declares a lexically scoped name for a |
1675 | global variable, which is not itself a lexical variable.) |
1676 | |
1677 | =item library |
1678 | |
1679 | Generally, a collection of procedures. In ancient days, referred to a |
1680 | collection of subroutines in a I<.pl> file. In modern times, refers |
27ed30b8 |
1681 | more often to the entire collection of Perl L<modules|/module> on your |
97a1d740 |
1682 | system. |
1683 | |
1684 | =item LIFO |
1685 | |
27ed30b8 |
1686 | Last In, First Out. See also L</FIFO>. A LIFO is usually called a |
1687 | L</stack>. |
97a1d740 |
1688 | |
1689 | =item line |
1690 | |
1691 | In Unix, a sequence of zero or more non-newline characters terminated |
27ed30b8 |
1692 | with a L</newline> character. On non-Unix machines, this is emulated |
1693 | by the C library even if the underlying L</operating system> has |
97a1d740 |
1694 | different ideas. |
1695 | |
1696 | =item line buffering |
1697 | |
27ed30b8 |
1698 | Used by a L</standard IE<sol>O> output stream that flushes its |
1699 | L</buffer> after every L</newline>. Many standard I/O libraries |
97a1d740 |
1700 | automatically set up line buffering on output that is going to the |
1701 | terminal. |
1702 | |
1703 | =item line number |
1704 | |
1705 | The number of lines read previous to this one, plus 1. Perl keeps a |
1706 | separate line number for each source or input file it opens. The |
1707 | current source file's line number is represented by C<__LINE__>. The |
1708 | current input line number (for the file that was most recently read |
27ed30b8 |
1709 | via C<< E<lt>FHE<gt> >>) is represented by the C<$.> |
97a1d740 |
1710 | (C<$INPUT_LINE_NUMBER>) variable. Many error messages report both |
1711 | values, if available. |
1712 | |
1713 | =item link |
1714 | |
27ed30b8 |
1715 | Used as a noun, a name in a L</directory>, representing a L</file>. A |
97a1d740 |
1716 | given file can have multiple links to it. It's like having the same |
1717 | phone number listed in the phone directory under different names. As |
1718 | a verb, to resolve a partially compiled file's unresolved symbols into |
1719 | a (nearly) executable image. Linking can generally be static or |
1720 | dynamic, which has nothing to do with static or dynamic scoping. |
1721 | |
1722 | =item LIST |
1723 | |
1724 | A syntactic construct representing a comma-separated list of |
27ed30b8 |
1725 | expressions, evaluated to produce a L</list value>. Each |
1726 | L</expression> in a L</LIST> is evaluated in L</list context> and |
97a1d740 |
1727 | interpolated into the list value. |
1728 | |
1729 | =item list |
1730 | |
1731 | An ordered set of scalar values. |
1732 | |
1733 | =item list context |
1734 | |
27ed30b8 |
1735 | The situation in which an L</expression> is expected by its |
97a1d740 |
1736 | surroundings (the code calling it) to return a list of values rather |
27ed30b8 |
1737 | than a single value. Functions that want a L</LIST> of arguments tell |
97a1d740 |
1738 | those arguments that they should produce a list value. See also |
27ed30b8 |
1739 | L</context>. |
97a1d740 |
1740 | |
1741 | =item list operator |
1742 | |
27ed30b8 |
1743 | An L</operator> that does something with a list of values, such as |
97a1d740 |
1744 | L<join|perlfunc/join> or L<grep|perlfunc/grep>. Usually used for |
1745 | named built-in operators (such as L<print|perlfunc/print>, |
1746 | L<unlink|perlfunc/unlink>, and L<system|perlfunc/system>) that do not |
27ed30b8 |
1747 | require parentheses around their L</argument> list. |
97a1d740 |
1748 | |
1749 | =item list value |
1750 | |
1751 | An unnamed list of temporary scalar values that may be passed around |
1752 | within a program from any list-generating function to any function or |
27ed30b8 |
1753 | construct that provides a L</list context>. |
97a1d740 |
1754 | |
1755 | =item literal |
1756 | |
27ed30b8 |
1757 | A token in a programming language such as a number or L</string> that |
1758 | gives you an actual L</value> instead of merely representing possible |
1759 | values as a L</variable> does. |
97a1d740 |
1760 | |
1761 | =item little-endian |
1762 | |
1763 | From Swift: someone who eats eggs little end first. Also used of |
27ed30b8 |
1764 | computers that store the least significant L</byte> of a word at a |
97a1d740 |
1765 | lower byte address than the most significant byte. Often considered |
27ed30b8 |
1766 | superior to big-endian machines. See also L</big-endian>. |
97a1d740 |
1767 | |
1768 | =item local |
1769 | |
1770 | Not meaning the same thing everywhere. A global variable in Perl can |
1771 | be localized inside a L<dynamic scope|/dynamic scoping> via the |
1772 | L<local|perlfunc/local> operator. |
1773 | |
1774 | =item logical operator |
1775 | |
1776 | Symbols representing the concepts "and", "or", "xor", and "not". |
1777 | |
1778 | =item lookahead |
1779 | |
27ed30b8 |
1780 | An L</assertion> that peeks at the string to the right of the current |
97a1d740 |
1781 | match location. |
1782 | |
1783 | =item lookbehind |
1784 | |
27ed30b8 |
1785 | An L</assertion> that peeks at the string to the left of the current |
97a1d740 |
1786 | match location. |
1787 | |
1788 | =item loop |
1789 | |
1790 | A construct that performs something repeatedly, like a roller coaster. |
1791 | |
1792 | =item loop control statement |
1793 | |
1794 | Any statement within the body of a loop that can make a loop |
27ed30b8 |
1795 | prematurely stop looping or skip an L</iteration>. Generally you |
97a1d740 |
1796 | shouldn't try this on roller coasters. |
1797 | |
1798 | =item loop label |
1799 | |
1800 | A kind of key or name attached to a loop (or roller coaster) so that |
1801 | loop control statements can talk about which loop they want to |
1802 | control. |
1803 | |
1804 | =item lvaluable |
1805 | |
27ed30b8 |
1806 | Able to serve as an L</lvalue>. |
97a1d740 |
1807 | |
1808 | =item lvalue |
1809 | |
1810 | Term used by language lawyers for a storage location you can assign a |
27ed30b8 |
1811 | new L</value> to, such as a L</variable> or an element of an |
1812 | L</array>. The "l" is short for "left", as in the left side of an |
1813 | assignment, a typical place for lvalues. An L</lvaluable> function or |
97a1d740 |
1814 | expression is one to which a value may be assigned, as in C<pos($x) = |
1815 | 10>. |
1816 | |
1817 | =item lvalue modifier |
1818 | |
27ed30b8 |
1819 | An adjectival pseudofunction that warps the meaning of an L</lvalue> |
97a1d740 |
1820 | in some declarative fashion. Currently there are three lvalue |
1821 | modifiers: L<my|perlfunc/my>, L<our|perlfunc/our>, and |
1822 | L<local|perlfunc/local>. |
1823 | |
1824 | =back |
1825 | |
5bbd0522 |
1826 | =head2 M |
1827 | |
97a1d740 |
1828 | =over 4 |
1829 | |
1830 | =item magic |
1831 | |
1832 | Technically speaking, any extra semantics attached to a variable such |
1833 | as C<$!>, C<$0>, C<%ENV>, or C<%SIG>, or to any tied variable. |
1834 | Magical things happen when you diddle those variables. |
1835 | |
1836 | =item magical increment |
1837 | |
27ed30b8 |
1838 | An L</increment> operator that knows how to bump up alphabetics as |
97a1d740 |
1839 | well as numbers. |
1840 | |
1841 | =item magical variables |
1842 | |
1843 | Special variables that have side effects when you access them or |
1844 | assign to them. For example, in Perl, changing elements of the |
1845 | C<%ENV> array also changes the corresponding environment variables |
1846 | that subprocesses will use. Reading the C<$!> variable gives you the |
1847 | current system error number or message. |
1848 | |
1849 | =item Makefile |
1850 | |
1851 | A file that controls the compilation of a program. Perl programs |
27ed30b8 |
1852 | don't usually need a L</Makefile> because the Perl compiler has plenty |
97a1d740 |
1853 | of self-control. |
1854 | |
1855 | =item man |
1856 | |
1857 | The Unix program that displays online documentation (manual pages) for |
1858 | you. |
1859 | |
1860 | =item manpage |
1861 | |
27ed30b8 |
1862 | A "page" from the manuals, typically accessed via the I<man>(1) |
97a1d740 |
1863 | command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of |
1864 | BUGS, and so on, and is typically longer than a page. There are |
27ed30b8 |
1865 | manpages documenting L<commands|/command>, L<syscalls|/syscall>, |
1866 | L</library> L<functions|/function>, L<devices|/device>, |
1867 | L<protocols|/protocol>, L<files|/file>, and such. In this book, we |
97a1d740 |
1868 | call any piece of standard Perl documentation (like I<perlop> or |
1869 | I<perldelta>) a manpage, no matter what format it's installed in on |
1870 | your system. |
1871 | |
1872 | =item matching |
1873 | |
27ed30b8 |
1874 | See L</pattern matching>. |
97a1d740 |
1875 | |
1876 | =item member data |
1877 | |
27ed30b8 |
1878 | See L</instance variable>. |
97a1d740 |
1879 | |
1880 | =item memory |
1881 | |
1882 | This always means your main memory, not your disk. Clouding the issue |
27ed30b8 |
1883 | is the fact that your machine may implement L</virtual> memory; that |
97a1d740 |
1884 | is, it will pretend that it has more memory than it really does, and |
1885 | it'll use disk space to hold inactive bits. This can make it seem |
1886 | like you have a little more memory than you really do, but it's not a |
1887 | substitute for real memory. The best thing that can be said about |
1888 | virtual memory is that it lets your performance degrade gradually |
1889 | rather than suddenly when you run out of real memory. But your |
1890 | program can die when you run out of virtual memory too, if you haven't |
1891 | thrashed your disk to death first. |
1892 | |
1893 | =item metacharacter |
1894 | |
27ed30b8 |
1895 | A L</character> that is I<not> supposed to be treated normally. Which |
97a1d740 |
1896 | characters are to be treated specially as metacharacters varies |
27ed30b8 |
1897 | greatly from context to context. Your L</shell> will have certain |
1898 | metacharacters, double-quoted Perl L<strings|/string> have other |
1899 | metacharacters, and L</regular expression> patterns have all the |
97a1d740 |
1900 | double-quote metacharacters plus some extra ones of their own. |
1901 | |
1902 | =item metasymbol |
1903 | |
27ed30b8 |
1904 | Something we'd call a L</metacharacter> except that it's a sequence of |
97a1d740 |
1905 | more than one character. Generally, the first character in the |
1906 | sequence must be a true metacharacter to get the other characters in |
1907 | the metasymbol to misbehave along with it. |
1908 | |
1909 | =item method |
1910 | |
27ed30b8 |
1911 | A kind of action that an L</object> can take if you tell it to. See |
97a1d740 |
1912 | L<perlobj>. |
1913 | |
1914 | =item minimalism |
1915 | |
1916 | The belief that "small is beautiful." Paradoxically, if you say |
1917 | something in a small language, it turns out big, and if you say it in |
1918 | a big language, it turns out small. Go figure. |
1919 | |
1920 | =item mode |
1921 | |
27ed30b8 |
1922 | In the context of the L<stat> syscall, refers to the field holding |
1923 | the L</permission bits> and the type of the L</file>. |
97a1d740 |
1924 | |
1925 | =item modifier |
1926 | |
27ed30b8 |
1927 | See L</statement modifier>, L</regular expression modifier>, and |
1928 | L</lvalue modifier>, not necessarily in that order. |
97a1d740 |
1929 | |
1930 | =item module |
1931 | |
27ed30b8 |
1932 | A L</file> that defines a L</package> of (almost) the same name, which |
1933 | can either L</export> symbols or function as an L</object> class. (A |
97a1d740 |
1934 | module's main I<.pm> file may also load in other files in support of |
1935 | the module.) See the L<use|perlfunc/use> built-in. |
1936 | |
1937 | =item modulus |
1938 | |
1939 | An integer divisor when you're interested in the remainder instead of |
1940 | the quotient. |
1941 | |
1942 | =item monger |
1943 | |
1944 | Short for Perl Monger, a purveyor of Perl. |
1945 | |
1946 | =item mortal |
1947 | |
1948 | A temporary value scheduled to die when the current statement |
1949 | finishes. |
1950 | |
1951 | =item multidimensional array |
1952 | |
1953 | An array with multiple subscripts for finding a single element. Perl |
27ed30b8 |
1954 | implements these using L<references|/reference>--see L<perllol> and |
97a1d740 |
1955 | L<perldsc>. |
1956 | |
1957 | =item multiple inheritance |
1958 | |
1959 | The features you got from your mother and father, mixed together |
27ed30b8 |
1960 | unpredictably. (See also L</inheritance>, and L</single |
97a1d740 |
1961 | inheritance>.) In computer languages (including Perl), the notion |
1962 | that a given class may have multiple direct ancestors or L<base |
1963 | classes|/base class>. |
1964 | |
1965 | =back |
1966 | |
5bbd0522 |
1967 | =head2 N |
1968 | |
97a1d740 |
1969 | =over 4 |
1970 | |
1971 | =item named pipe |
1972 | |
27ed30b8 |
1973 | A L</pipe> with a name embedded in the L</filesystem> so that it can |
1974 | be accessed by two unrelated L<processes|/process>. |
97a1d740 |
1975 | |
1976 | =item namespace |
1977 | |
1978 | A domain of names. You needn't worry about whether the names in one |
27ed30b8 |
1979 | such domain have been used in another. See L</package>. |
97a1d740 |
1980 | |
1981 | =item network address |
1982 | |
1983 | The most important attribute of a socket, like your telephone's |
27ed30b8 |
1984 | telephone number. Typically an IP address. See also L</port>. |
97a1d740 |
1985 | |
1986 | =item newline |
1987 | |
1988 | A single character that represents the end of a line, with the ASCII |
1989 | value of 012 octal under Unix (but 015 on a Mac), and represented by |
1990 | C<\n> in Perl strings. For Windows machines writing text files, and |
1991 | for certain physical devices like terminals, the single newline gets |
1992 | automatically translated by your C library into a line feed and a |
1993 | carriage return, but normally, no translation is done. |
1994 | |
1995 | =item NFS |
1996 | |
1997 | Network File System, which allows you to mount a remote filesystem as |
1998 | if it were local. |
1999 | |
2000 | =item null character |
2001 | |
2002 | A character with the ASCII value of zero. It's used by C to terminate |
2003 | strings, but Perl allows strings to contain a null. |
2004 | |
2005 | =item null list |
2006 | |
27ed30b8 |
2007 | A L</list value> with zero elements, represented in Perl by C<()>. |
97a1d740 |
2008 | |
2009 | =item null string |
2010 | |
27ed30b8 |
2011 | A L</string> containing no characters, not to be confused with a |
2012 | string containing a L</null character>, which has a positive length |
2013 | and is L</true>. |
97a1d740 |
2014 | |
2015 | =item numeric context |
2016 | |
2017 | The situation in which an expression is expected by its surroundings |
27ed30b8 |
2018 | (the code calling it) to return a number. See also L</context> and |
2019 | L</string context>. |
97a1d740 |
2020 | |
2021 | =item NV |
2022 | |
2023 | Short for Nevada, no part of which will ever be confused with |
2024 | civilization. NV also means an internal floating-point Numeric Value |
27ed30b8 |
2025 | of the type a L</scalar> can hold, not to be confused with an L</IV>. |
97a1d740 |
2026 | |
2027 | =item nybble |
2028 | |
27ed30b8 |
2029 | Half a L</byte>, equivalent to one L</hexadecimal> digit, and worth |
2030 | four L<bits|/bit>. |
97a1d740 |
2031 | |
2032 | =back |
2033 | |
5bbd0522 |
2034 | =head2 O |
2035 | |
97a1d740 |
2036 | =over 4 |
2037 | |
2038 | =item object |
2039 | |
27ed30b8 |
2040 | An L</instance> of a L</class>. Something that "knows" what |
97a1d740 |
2041 | user-defined type (class) it is, and what it can do because of what |
2042 | class it is. Your program can request an object to do things, but the |
2043 | object gets to decide whether it wants to do them or not. Some |
2044 | objects are more accommodating than others. |
2045 | |
2046 | =item octal |
2047 | |
2048 | A number in base 8. Only the digits 0 through 7 are allowed. Octal |
2049 | constants in Perl start with 0, as in 013. See also the |
2050 | L<oct|perlfunc/oct> function. |
2051 | |
2052 | =item offset |
2053 | |
2054 | How many things you have to skip over when moving from the beginning |
2055 | of a string or array to a specific position within it. Thus, the |
2056 | minimum offset is zero, not one, because you don't skip anything to |
2057 | get to the first item. |
2058 | |
2059 | =item one-liner |
2060 | |
2061 | An entire computer program crammed into one line of text. |
2062 | |
2063 | =item open source software |
2064 | |
2065 | Programs for which the source code is freely available and freely |
2066 | redistributable, with no commercial strings attached. For a more |
2067 | detailed definition, see L<http://www.opensource.org/osd.html>. |
2068 | |
2069 | =item operand |
2070 | |
27ed30b8 |
2071 | An L</expression> that yields a L</value> that an L</operator> |
2072 | operates on. See also L</precedence>. |
97a1d740 |
2073 | |
2074 | =item operating system |
2075 | |
2076 | A special program that runs on the bare machine and hides the gory |
27ed30b8 |
2077 | details of managing L<processes|/process> and L<devices|/device>. |
97a1d740 |
2078 | Usually used in a looser sense to indicate a particular culture of |
2079 | programming. The loose sense can be used at varying levels of |
2080 | specificity. At one extreme, you might say that all versions of Unix |
2081 | and Unix-lookalikes are the same operating system (upsetting many |
2082 | people, especially lawyers and other advocates). At the other |
2083 | extreme, you could say this particular version of this particular |
2084 | vendor's operating system is different from any other version of this |
2085 | or any other vendor's operating system. Perl is much more portable |
2086 | across operating systems than many other languages. See also |
27ed30b8 |
2087 | L</architecture> and L</platform>. |
97a1d740 |
2088 | |
2089 | =item operator |
2090 | |
2091 | A gizmo that transforms some number of input values to some number of |
2092 | output values, often built into a language with a special syntax or |
2093 | symbol. A given operator may have specific expectations about what |
27ed30b8 |
2094 | L<types|/type> of data you give as its arguments |
2095 | (L<operands|/operand>) and what type of data you want back from it. |
97a1d740 |
2096 | |
2097 | =item operator overloading |
2098 | |
27ed30b8 |
2099 | A kind of L</overloading> that you can do on built-in |
2100 | L<operators|/operator> to make them work on L<objects|/object> as if |
97a1d740 |
2101 | the objects were ordinary scalar values, but with the actual semantics |
2102 | supplied by the object class. This is set up with the L<overload> |
27ed30b8 |
2103 | L</pragma>. |
97a1d740 |
2104 | |
2105 | =item options |
2106 | |
27ed30b8 |
2107 | See either L<switches|/switch> or L</regular expression modifier>. |
97a1d740 |
2108 | |
2109 | =item overloading |
2110 | |
2111 | Giving additional meanings to a symbol or construct. Actually, all |
2112 | languages do overloading to one extent or another, since people are |
27ed30b8 |
2113 | good at figuring out things from L</context>. |
97a1d740 |
2114 | |
2115 | =item overriding |
2116 | |
2117 | Hiding or invalidating some other definition of the same name. (Not |
27ed30b8 |
2118 | to be confused with L</overloading>, which adds definitions that must |
97a1d740 |
2119 | be disambiguated some other way.) To confuse the issue further, we use |
2120 | the word with two overloaded definitions: to describe how you can |
27ed30b8 |
2121 | define your own L</subroutine> to hide a built-in L</function> of the |
97a1d740 |
2122 | same name (see L<perlsub/Overriding Built-in Functions>) and to |
27ed30b8 |
2123 | describe how you can define a replacement L</method> in a L</derived |
2124 | class> to hide a L</base class>'s method of the same name (see |
97a1d740 |
2125 | L<perlobj>). |
2126 | |
2127 | =item owner |
2128 | |
2129 | The one user (apart from the superuser) who has absolute control over |
27ed30b8 |
2130 | a L</file>. A file may also have a L</group> of users who may |
97a1d740 |
2131 | exercise joint ownership if the real owner permits it. See |
27ed30b8 |
2132 | L</permission bits>. |
97a1d740 |
2133 | |
2134 | =back |
2135 | |
5bbd0522 |
2136 | =head2 P |
2137 | |
97a1d740 |
2138 | =over 4 |
2139 | |
2140 | =item package |
2141 | |
27ed30b8 |
2142 | A L</namespace> for global L<variables|/variable>, |
2143 | L<subroutines|/subroutine>, and the like, such that they can be kept |
2144 | separate from like-named L<symbols|/symbol> in other namespaces. In a |
97a1d740 |
2145 | sense, only the package is global, since the symbols in the package's |
2146 | symbol table are only accessible from code compiled outside the |
2147 | package by naming the package. But in another sense, all package |
2148 | symbols are also globals--they're just well-organized globals. |
2149 | |
2150 | =item pad |
2151 | |
27ed30b8 |
2152 | Short for L</scratchpad>. |
97a1d740 |
2153 | |
2154 | =item parameter |
2155 | |
27ed30b8 |
2156 | See L</argument>. |
97a1d740 |
2157 | |
2158 | =item parent class |
2159 | |
27ed30b8 |
2160 | See L</base class>. |
97a1d740 |
2161 | |
2162 | =item parse tree |
2163 | |
27ed30b8 |
2164 | See L</syntax tree>. |
97a1d740 |
2165 | |
2166 | =item parsing |
2167 | |
2168 | The subtle but sometimes brutal art of attempting to turn your |
27ed30b8 |
2169 | possibly malformed program into a valid L</syntax tree>. |
97a1d740 |
2170 | |
2171 | =item patch |
2172 | |
2173 | To fix by applying one, as it were. In the realm of hackerdom, a |
2174 | listing of the differences between two versions of a program as might |
27ed30b8 |
2175 | be applied by the I<patch>(1) program when you want to fix a bug or |
97a1d740 |
2176 | upgrade your old version. |
2177 | |
2178 | =item PATH |
2179 | |
2180 | The list of L<directories|/directory> the system searches to find a |
27ed30b8 |
2181 | program you want to L</execute>. The list is stored as one of your |
2182 | L<environment variables|/environment variable>, accessible in Perl as |
97a1d740 |
2183 | C<$ENV{PATH}>. |
2184 | |
2185 | =item pathname |
2186 | |
2187 | A fully qualified filename such as I</usr/bin/perl>. Sometimes |
27ed30b8 |
2188 | confused with L</PATH>. |
97a1d740 |
2189 | |
2190 | =item pattern |
2191 | |
27ed30b8 |
2192 | A template used in L</pattern matching>. |
97a1d740 |
2193 | |
2194 | =item pattern matching |
2195 | |
27ed30b8 |
2196 | Taking a pattern, usually a L</regular expression>, and trying the |
97a1d740 |
2197 | pattern various ways on a string to see whether there's any way to |
2198 | make it fit. Often used to pick interesting tidbits out of a file. |
2199 | |
2200 | =item permission bits |
2201 | |
27ed30b8 |
2202 | Bits that the L</owner> of a file sets or unsets to allow or disallow |
2203 | access to other people. These flag bits are part of the L</mode> word |
97a1d740 |
2204 | returned by the L<stat|perlfunc/stat> built-in when you ask about a |
2205 | file. On Unix systems, you can check the I<ls>(1) manpage for more |
2206 | information. |
2207 | |
2208 | =item Pern |
2209 | |
2210 | What you get when you do C<Perl++> twice. Doing it only once will |
2211 | curl your hair. You have to increment it eight times to shampoo your |
2212 | hair. Lather, rinse, iterate. |
2213 | |
2214 | =item pipe |
2215 | |
27ed30b8 |
2216 | A direct L</connection> that carries the output of one L</process> to |
97a1d740 |
2217 | the input of another without an intermediate temporary file. Once the |
2218 | pipe is set up, the two processes in question can read and write as if |
2219 | they were talking to a normal file, with some caveats. |
2220 | |
2221 | =item pipeline |
2222 | |
27ed30b8 |
2223 | A series of L<processes|/process> all in a row, linked by |
2224 | L<pipes|/pipe>, where each passes its output stream to the next. |
97a1d740 |
2225 | |
2226 | =item platform |
2227 | |
2228 | The entire hardware and software context in which a program runs. A |
2229 | program written in a platform-dependent language might break if you |
2230 | change any of: machine, operating system, libraries, compiler, or |
2231 | system configuration. The I<perl> interpreter has to be compiled |
2232 | differently for each platform because it is implemented in C, but |
2233 | programs written in the Perl language are largely |
2234 | platform-independent. |
2235 | |
2236 | =item pod |
2237 | |
2238 | The markup used to embed documentation into your Perl code. See |
2239 | L<perlpod>. |
2240 | |
2241 | =item pointer |
2242 | |
27ed30b8 |
2243 | A L</variable> in a language like C that contains the exact memory |
97a1d740 |
2244 | location of some other item. Perl handles pointers internally so you |
2245 | don't have to worry about them. Instead, you just use symbolic |
27ed30b8 |
2246 | pointers in the form of L<keys|/key> and L</variable> names, or L<hard |
97a1d740 |
2247 | references|/hard reference>, which aren't pointers (but act like |
2248 | pointers and do in fact contain pointers). |
2249 | |
2250 | =item polymorphism |
2251 | |
27ed30b8 |
2252 | The notion that you can tell an L</object> to do something generic, |
97a1d740 |
2253 | and the object will interpret the command in different ways depending |
2254 | on its type. [E<lt>Gk many shapes] |
2255 | |
2256 | =item port |
2257 | |
2258 | The part of the address of a TCP or UDP socket that directs packets to |
2259 | the correct process after finding the right machine, something like |
2260 | the phone extension you give when you reach the company operator. |
2261 | Also, the result of converting code to run on a different platform |
2262 | than originally intended, or the verb denoting this conversion. |
2263 | |
2264 | =item portable |
2265 | |
2266 | Once upon a time, C code compilable under both BSD and SysV. In |
2267 | general, code that can be easily converted to run on another |
27ed30b8 |
2268 | L</platform>, where "easily" can be defined however you like, and |
97a1d740 |
2269 | usually is. Anything may be considered portable if you try hard |
2270 | enough. See I<mobile home> or I<London Bridge>. |
2271 | |
2272 | =item porter |
2273 | |
27ed30b8 |
2274 | Someone who "carries" software from one L</platform> to another. |
97a1d740 |
2275 | Porting programs written in platform-dependent languages such as C can |
2276 | be difficult work, but porting programs like Perl is very much worth |
2277 | the agony. |
2278 | |
2279 | =item POSIX |
2280 | |
2281 | The Portable Operating System Interface specification. |
2282 | |
2283 | =item postfix |
2284 | |
27ed30b8 |
2285 | An L</operator> that follows its L</operand>, as in C<$x++>. |
97a1d740 |
2286 | |
2287 | =item pp |
2288 | |
2289 | An internal shorthand for a "push-pop" code, that is, C code |
2290 | implementing Perl's stack machine. |
2291 | |
2292 | =item pragma |
2293 | |
2294 | A standard module whose practical hints and suggestions are received |
2295 | (and possibly ignored) at compile time. Pragmas are named in all |
2296 | lowercase. |
2297 | |
2298 | =item precedence |
2299 | |
2300 | The rules of conduct that, in the absence of other guidance, determine |
2301 | what should happen first. For example, in the absence of parentheses, |
2302 | you always do multiplication before addition. |
2303 | |
2304 | =item prefix |
2305 | |
27ed30b8 |
2306 | An L</operator> that precedes its L</operand>, as in C<++$x>. |
97a1d740 |
2307 | |
2308 | =item preprocessing |
2309 | |
27ed30b8 |
2310 | What some helper L</process> did to transform the incoming data into a |
97a1d740 |
2311 | form more suitable for the current process. Often done with an |
27ed30b8 |
2312 | incoming L</pipe>. See also L</C preprocessor>. |
97a1d740 |
2313 | |
2314 | =item procedure |
2315 | |
27ed30b8 |
2316 | A L</subroutine>. |
97a1d740 |
2317 | |
2318 | =item process |
2319 | |
2320 | An instance of a running program. Under multitasking systems like |
2321 | Unix, two or more separate processes could be running the same program |
2322 | independently at the same time--in fact, the L<fork|perlfunc/fork> |
2323 | function is designed to bring about this happy state of affairs. |
2324 | Under other operating systems, processes are sometimes called |
2325 | "threads", "tasks", or "jobs", often with slight nuances in meaning. |
2326 | |
2327 | =item program generator |
2328 | |
2329 | A system that algorithmically writes code for you in a high-level |
27ed30b8 |
2330 | language. See also L</code generator>. |
97a1d740 |
2331 | |
2332 | =item progressive matching |
2333 | |
27ed30b8 |
2334 | L<Pattern matching|/pattern matching> that picks up where it left off before. |
97a1d740 |
2335 | |
2336 | =item property |
2337 | |
27ed30b8 |
2338 | See either L</instance variable> or L</character property>. |
97a1d740 |
2339 | |
2340 | =item protocol |
2341 | |
2342 | In networking, an agreed-upon way of sending messages back and forth |
2343 | so that neither correspondent will get too confused. |
2344 | |
2345 | =item prototype |
2346 | |
27ed30b8 |
2347 | An optional part of a L</subroutine> declaration telling the Perl |
97a1d740 |
2348 | compiler how many and what flavor of arguments may be passed as |
27ed30b8 |
2349 | L</actual arguments>, so that you can write subroutine calls that |
97a1d740 |
2350 | parse much like built-in functions. (Or don't parse, as the case may |
2351 | be.) |
2352 | |
2353 | =item pseudofunction |
2354 | |
2355 | A construct that sometimes looks like a function but really isn't. |
27ed30b8 |
2356 | Usually reserved for L</lvalue> modifiers like L<my|perlfunc/my>, for |
2357 | L</context> modifiers like L<scalar|perlfunc/scalar>, and for the |
97a1d740 |
2358 | pick-your-own-quotes constructs, C<q//>, C<qq//>, C<qx//>, C<qw//>, |
2359 | C<qr//>, C<m//>, C<s///>, C<y///>, and C<tr///>. |
2360 | |
2361 | =item pseudohash |
2362 | |
2363 | A reference to an array whose initial element happens to hold a |
2364 | reference to a hash. You can treat a pseudohash reference as either |
2365 | an array reference or a hash reference. |
2366 | |
2367 | =item pseudoliteral |
2368 | |
27ed30b8 |
2369 | An L</operator> that looks something like a L</literal>, such as the |
2370 | output-grabbing operator, C<`>I<C<command>>C<`>. |
97a1d740 |
2371 | |
2372 | =item public domain |
2373 | |
2374 | Something not owned by anybody. Perl is copyrighted and is thus |
27ed30b8 |
2375 | I<not> in the public domain--it's just L</freely available> and |
2376 | L</freely redistributable>. |
97a1d740 |
2377 | |
2378 | =item pumpkin |
2379 | |
2380 | A notional "baton" handed around the Perl community indicating who is |
2381 | the lead integrator in some arena of development. |
2382 | |
2383 | =item pumpking |
2384 | |
27ed30b8 |
2385 | A L</pumpkin> holder, the person in charge of pumping the pump, or at |
97a1d740 |
2386 | least priming it. Must be willing to play the part of the Great |
2387 | Pumpkin now and then. |
2388 | |
2389 | =item PV |
2390 | |
2391 | A "pointer value", which is Perl Internals Talk for a C<char*>. |
2392 | |
2393 | =back |
2394 | |
5bbd0522 |
2395 | =head2 Q |
2396 | |
97a1d740 |
2397 | =over 4 |
2398 | |
2399 | =item qualified |
2400 | |
2401 | Possessing a complete name. The symbol C<$Ent::moot> is qualified; |
2402 | C<$moot> is unqualified. A fully qualified filename is specified from |
2403 | the top-level directory. |
2404 | |
2405 | =item quantifier |
2406 | |
27ed30b8 |
2407 | A component of a L</regular expression> specifying how many times the |
2408 | foregoing L</atom> may occur. |
97a1d740 |
2409 | |
2410 | =back |
2411 | |
5bbd0522 |
2412 | =head2 R |
2413 | |
97a1d740 |
2414 | =over 4 |
2415 | |
2416 | =item readable |
2417 | |
2418 | With respect to files, one that has the proper permission bit set to |
2419 | let you access the file. With respect to computer programs, one |
2420 | that's written well enough that someone has a chance of figuring out |
2421 | what it's trying to do. |
2422 | |
2423 | =item reaping |
2424 | |
27ed30b8 |
2425 | The last rites performed by a parent L</process> on behalf of a |
2426 | deceased child process so that it doesn't remain a L</zombie>. See |
97a1d740 |
2427 | the L<wait|perlfunc/wait> and L<waitpid|perlfunc/waitpid> function |
2428 | calls. |
2429 | |
2430 | =item record |
2431 | |
27ed30b8 |
2432 | A set of related data values in a L</file> or L</stream>, often |
2433 | associated with a unique L</key> field. In Unix, often commensurate |
2434 | with a L</line>, or a blank-line-terminated set of lines (a |
97a1d740 |
2435 | "paragraph"). Each line of the I</etc/passwd> file is a record, keyed |
2436 | on login name, containing information about that user. |
2437 | |
2438 | =item recursion |
2439 | |
2440 | The art of defining something (at least partly) in terms of itself, |
2441 | which is a naughty no-no in dictionaries but often works out okay in |
2442 | computer programs if you're careful not to recurse forever, which is |
2443 | like an infinite loop with more spectacular failure modes. |
2444 | |
2445 | =item reference |
2446 | |
2447 | Where you look to find a pointer to information somewhere else. (See |
27ed30b8 |
2448 | L</indirection>.) References come in two flavors, L<symbolic |
97a1d740 |
2449 | references|/symbolic reference> and L<hard references|/hard |
2450 | reference>. |
2451 | |
2452 | =item referent |
2453 | |
2454 | Whatever a reference refers to, which may or may not have a name. |
2455 | Common types of referents include scalars, arrays, hashes, and |
2456 | subroutines. |
2457 | |
2458 | =item regex |
2459 | |
27ed30b8 |
2460 | See L</regular expression>. |
97a1d740 |
2461 | |
2462 | =item regular expression |
2463 | |
2464 | A single entity with various interpretations, like an elephant. To a |
2465 | computer scientist, it's a grammar for a little language in which some |
2466 | strings are legal and others aren't. To normal people, it's a pattern |
2467 | you can use to find what you're looking for when it varies from case |
2468 | to case. Perl's regular expressions are far from regular in the |
2469 | theoretical sense, but in regular use they work quite well. Here's a |
2470 | regular expression: C</Oh s.*t./>. This will match strings like "C<Oh |
2471 | say can you see by the dawn's early light>" and "C<Oh sit!>". See |
2472 | L<perlre>. |
2473 | |
2474 | =item regular expression modifier |
2475 | |
2476 | An option on a pattern or substitution, such as C</i> to render the |
27ed30b8 |
2477 | pattern case insensitive. See also L</cloister>. |
97a1d740 |
2478 | |
2479 | =item regular file |
2480 | |
27ed30b8 |
2481 | A L</file> that's not a L</directory>, a L</device>, a named L</pipe> |
2482 | or L</socket>, or a L</symbolic link>. Perl uses the C<-f> file test |
97a1d740 |
2483 | operator to identify regular files. Sometimes called a "plain" file. |
2484 | |
2485 | =item relational operator |
2486 | |
27ed30b8 |
2487 | An L</operator> that says whether a particular ordering relationship |
2488 | is L</true> about a pair of L<operands|/operand>. Perl has both |
2489 | numeric and string relational operators. See L</collating sequence>. |
97a1d740 |
2490 | |
2491 | =item reserved words |
2492 | |
27ed30b8 |
2493 | A word with a specific, built-in meaning to a L</compiler>, such as |
97a1d740 |
2494 | C<if> or L<delete|perlfunc/delete>. In many languages (not Perl), |
2495 | it's illegal to use reserved words to name anything else. (Which is |
2496 | why they're reserved, after all.) In Perl, you just can't use them to |
27ed30b8 |
2497 | name L<labels|/label> or L<filehandles|/filehandle>. Also called |
97a1d740 |
2498 | "keywords". |
2499 | |
2500 | =item return value |
2501 | |
27ed30b8 |
2502 | The L</value> produced by a L</subroutine> or L</expression> when |
2503 | evaluated. In Perl, a return value may be either a L</list> or a |
2504 | L</scalar>. |
97a1d740 |
2505 | |
2506 | =item RFC |
2507 | |
2508 | Request For Comment, which despite the timid connotations is the name |
2509 | of a series of important standards documents. |
2510 | |
2511 | =item right shift |
2512 | |
27ed30b8 |
2513 | A L</bit shift> that divides a number by some power of 2. |
97a1d740 |
2514 | |
2515 | =item root |
2516 | |
2517 | The superuser (UID == 0). Also, the top-level directory of the |
2518 | filesystem. |
2519 | |
2520 | =item RTFM |
2521 | |
2522 | What you are told when someone thinks you should Read The Fine Manual. |
2523 | |
2524 | =item run phase |
2525 | |
2526 | Any time after Perl starts running your main program. See also |
27ed30b8 |
2527 | L</compile phase>. Run phase is mostly spent in L</run time> but may |
2528 | also be spent in L</compile time> when L<require|perlfunc/require>, |
97a1d740 |
2529 | L<do|perlfunc/do> C<FILE>, or L<eval|perlfunc/eval> C<STRING> |
2530 | operators are executed or when a substitution uses the C</ee> |
2531 | modifier. |
2532 | |
2533 | =item run time |
2534 | |
2535 | The time when Perl is actually doing what your code says to do, as |
2536 | opposed to the earlier period of time when it was trying to figure out |
27ed30b8 |
2537 | whether what you said made any sense whatsoever, which is L</compile |
97a1d740 |
2538 | time>. |
2539 | |
2540 | =item run-time pattern |
2541 | |
2542 | A pattern that contains one or more variables to be interpolated |
27ed30b8 |
2543 | before parsing the pattern as a L</regular expression>, and that |
97a1d740 |
2544 | therefore cannot be analyzed at compile time, but must be re-analyzed |
2545 | each time the pattern match operator is evaluated. Run-time patterns |
2546 | are useful but expensive. |
2547 | |
2548 | =item RV |
2549 | |
2550 | A recreational vehicle, not to be confused with vehicular recreation. |
27ed30b8 |
2551 | RV also means an internal Reference Value of the type a L</scalar> can |
2552 | hold. See also L</IV> and L</NV> if you're not confused yet. |
97a1d740 |
2553 | |
2554 | =item rvalue |
2555 | |
27ed30b8 |
2556 | A L</value> that you might find on the right side of an |
2557 | L</assignment>. See also L</lvalue>. |
97a1d740 |
2558 | |
2559 | =back |
2560 | |
5bbd0522 |
2561 | =head2 S |
2562 | |
97a1d740 |
2563 | =over 4 |
2564 | |
2565 | =item scalar |
2566 | |
27ed30b8 |
2567 | A simple, singular value; a number, L</string>, or L</reference>. |
97a1d740 |
2568 | |
2569 | =item scalar context |
2570 | |
27ed30b8 |
2571 | The situation in which an L</expression> is expected by its |
2572 | surroundings (the code calling it) to return a single L</value> rather |
2573 | than a L</list> of values. See also L</context> and L</list context>. |
97a1d740 |
2574 | A scalar context sometimes imposes additional constraints on the |
27ed30b8 |
2575 | return value--see L</string context> and L</numeric context>. |
2576 | Sometimes we talk about a L</Boolean context> inside conditionals, but |
97a1d740 |
2577 | this imposes no additional constraints, since any scalar value, |
27ed30b8 |
2578 | whether numeric or L</string>, is already true or false. |
97a1d740 |
2579 | |
2580 | =item scalar literal |
2581 | |
27ed30b8 |
2582 | A number or quoted L</string>--an actual L</value> in the text of your |
2583 | program, as opposed to a L</variable>. |
97a1d740 |
2584 | |
2585 | =item scalar value |
2586 | |
27ed30b8 |
2587 | A value that happens to be a L</scalar> as opposed to a L</list>. |
97a1d740 |
2588 | |
2589 | =item scalar variable |
2590 | |
27ed30b8 |
2591 | A L</variable> prefixed with C<$> that holds a single value. |
97a1d740 |
2592 | |
2593 | =item scope |
2594 | |
2595 | How far away you can see a variable from, looking through one. Perl |
27ed30b8 |
2596 | has two visibility mechanisms: it does L</dynamic scoping> of |
2597 | L<local|perlfunc/local> L<variables|/variable>, meaning that the rest |
2598 | of the L</block>, and any L<subroutines|/subroutine> that are called |
97a1d740 |
2599 | by the rest of the block, can see the variables that are local to the |
27ed30b8 |
2600 | block. Perl does L</lexical scoping> of L<my|perlfunc/my> variables, |
97a1d740 |
2601 | meaning that the rest of the block can see the variable, but other |
2602 | subroutines called by the block I<cannot> see the variable. |
2603 | |
2604 | =item scratchpad |
2605 | |
2606 | The area in which a particular invocation of a particular file or |
2607 | subroutine keeps some of its temporary values, including any lexically |
2608 | scoped variables. |
2609 | |
2610 | =item script |
2611 | |
27ed30b8 |
2612 | A text L</file> that is a program intended to be L<executed|/execute> |
97a1d740 |
2613 | directly rather than L<compiled|/compiler> to another form of file |
27ed30b8 |
2614 | before execution. Also, in the context of L</Unicode>, a writing |
97a1d740 |
2615 | system for a particular language or group of languages, such as Greek, |
2616 | Bengali, or Klingon. |
2617 | |
2618 | =item script kiddie |
2619 | |
27ed30b8 |
2620 | A L</cracker> who is not a L</hacker>, but knows just enough to run |
97a1d740 |
2621 | canned scripts. A cargo-cult programmer. |
2622 | |
2623 | =item sed |
2624 | |
2625 | A venerable Stream EDitor from which Perl derives some of its ideas. |
2626 | |
2627 | =item semaphore |
2628 | |
27ed30b8 |
2629 | A fancy kind of interlock that prevents multiple L<threads|/thread> or |
2630 | L<processes|/process> from using up the same resources simultaneously. |
97a1d740 |
2631 | |
2632 | =item separator |
2633 | |
27ed30b8 |
2634 | A L</character> or L</string> that keeps two surrounding strings from |
97a1d740 |
2635 | being confused with each other. The L<split|perlfunc/split> function |
27ed30b8 |
2636 | works on separators. Not to be confused with L<delimiters|/delimiter> |
2637 | or L<terminators|/terminator>. The "or" in the previous sentence |
97a1d740 |
2638 | separated the two alternatives. |
2639 | |
2640 | =item serialization |
2641 | |
27ed30b8 |
2642 | Putting a fancy L</data structure> into linear order so that it can be |
2643 | stored as a L</string> in a disk file or database or sent through a |
2644 | L</pipe>. Also called marshalling. |
97a1d740 |
2645 | |
2646 | =item server |
2647 | |
27ed30b8 |
2648 | In networking, a L</process> that either advertises a L</service> or |
2649 | just hangs around at a known location and waits for L<clients|/client> |
97a1d740 |
2650 | who need service to get in touch with it. |
2651 | |
2652 | =item service |
2653 | |
2654 | Something you do for someone else to make them happy, like giving them |
2655 | the time of day (or of their life). On some machines, well-known |
2656 | services are listed by the L<getservent|perlfunc/getservent> function. |
2657 | |
2658 | =item setgid |
2659 | |
27ed30b8 |
2660 | Same as L</setuid>, only having to do with giving away L</group> |
97a1d740 |
2661 | privileges. |
2662 | |
2663 | =item setuid |
2664 | |
27ed30b8 |
2665 | Said of a program that runs with the privileges of its L</owner> |
97a1d740 |
2666 | rather than (as is usually the case) the privileges of whoever is |
27ed30b8 |
2667 | running it. Also describes the bit in the mode word (L</permission |
97a1d740 |
2668 | bits>) that controls the feature. This bit must be explicitly set by |
2669 | the owner to enable this feature, and the program must be carefully |
2670 | written not to give away more privileges than it ought to. |
2671 | |
2672 | =item shared memory |
2673 | |
27ed30b8 |
2674 | A piece of L</memory> accessible by two different |
2675 | L<processes|/process> who otherwise would not see each other's memory. |
97a1d740 |
2676 | |
2677 | =item shebang |
2678 | |
2679 | Irish for the whole McGillicuddy. In Perl culture, a portmanteau of |
2680 | "sharp" and "bang", meaning the C<#!> sequence that tells the system |
2681 | where to find the interpreter. |
2682 | |
2683 | =item shell |
2684 | |
27ed30b8 |
2685 | A L</command>-line L</interpreter>. The program that interactively |
2686 | gives you a prompt, accepts one or more L<lines|/line> of input, and |
97a1d740 |
2687 | executes the programs you mentioned, feeding each of them their proper |
27ed30b8 |
2688 | L<arguments|/argument> and input data. Shells can also execute |
97a1d740 |
2689 | scripts containing such commands. Under Unix, typical shells include |
2690 | the Bourne shell (I</bin/sh>), the C shell (I</bin/csh>), and the Korn |
2691 | shell (I</bin/ksh>). Perl is not strictly a shell because it's not |
2692 | interactive (although Perl programs can be interactive). |
2693 | |
2694 | =item side effects |
2695 | |
27ed30b8 |
2696 | Something extra that happens when you evaluate an L</expression>. |
97a1d740 |
2697 | Nowadays it can refer to almost anything. For example, evaluating a |
2698 | simple assignment statement typically has the "side effect" of |
2699 | assigning a value to a variable. (And you thought assigning the value |
2700 | was your primary intent in the first place!) Likewise, assigning a |
27ed30b8 |
2701 | value to the special variable C<$|> (C<$AUTOFLUSH>) has the side |
2702 | effect of forcing a flush after every L<write|perlfunc/write> or |
2703 | L<print|perlfunc/print> on the currently selected filehandle. |
97a1d740 |
2704 | |
2705 | =item signal |
2706 | |
2707 | A bolt out of the blue; that is, an event triggered by the |
27ed30b8 |
2708 | L</operating system>, probably when you're least expecting it. |
97a1d740 |
2709 | |
2710 | =item signal handler |
2711 | |
27ed30b8 |
2712 | A L</subroutine> that, instead of being content to be called in the |
97a1d740 |
2713 | normal fashion, sits around waiting for a bolt out of the blue before |
27ed30b8 |
2714 | it will deign to L</execute>. Under Perl, bolts out of the blue are |
97a1d740 |
2715 | called signals, and you send them with the L<kill|perlfunc/kill> |
2716 | built-in. See L<perlvar/%SIG> and L<perlipc/Signals>. |
2717 | |
2718 | =item single inheritance |
2719 | |
2720 | The features you got from your mother, if she told you that you don't |
27ed30b8 |
2721 | have a father. (See also L</inheritance> and L</multiple |
97a1d740 |
2722 | inheritance>.) In computer languages, the notion that |
27ed30b8 |
2723 | L<classes|/class> reproduce asexually so that a given class can only |
2724 | have one direct ancestor or L</base class>. Perl supplies no such |
97a1d740 |
2725 | restriction, though you may certainly program Perl that way if you |
2726 | like. |
2727 | |
2728 | =item slice |
2729 | |
27ed30b8 |
2730 | A selection of any number of L<elements|/element> from a L</list>, |
2731 | L</array>, or L</hash>. |
97a1d740 |
2732 | |
2733 | =item slurp |
2734 | |
27ed30b8 |
2735 | To read an entire L</file> into a L</string> in one operation. |
97a1d740 |
2736 | |
2737 | =item socket |
2738 | |
2739 | An endpoint for network communication among multiple |
27ed30b8 |
2740 | L<processes|/process> that works much like a telephone or a post |
2741 | office box. The most important thing about a socket is its L</network |
97a1d740 |
2742 | address> (like a phone number). Different kinds of sockets have |
2743 | different kinds of addresses--some look like filenames, and some |
2744 | don't. |
2745 | |
2746 | =item soft reference |
2747 | |
27ed30b8 |
2748 | See L</symbolic reference>. |
97a1d740 |
2749 | |
2750 | =item source filter |
2751 | |
27ed30b8 |
2752 | A special kind of L</module> that does L</preprocessing> on your |
2753 | script just before it gets to the L</tokener>. |
97a1d740 |
2754 | |
2755 | =item stack |
2756 | |
2757 | A device you can put things on the top of, and later take them back |
27ed30b8 |
2758 | off in the opposite order in which you put them on. See L</LIFO>. |
97a1d740 |
2759 | |
2760 | =item standard |
2761 | |
2762 | Included in the official Perl distribution, as in a standard module, a |
27ed30b8 |
2763 | standard tool, or a standard Perl L</manpage>. |
97a1d740 |
2764 | |
2765 | =item standard error |
2766 | |
27ed30b8 |
2767 | The default output L</stream> for nasty remarks that don't belong in |
2768 | L</standard output>. Represented within a Perl program by the |
2769 | L</filehandle> L</STDERR>. You can use this stream explicitly, but the |
97a1d740 |
2770 | L<die|perlfunc/die> and L<warn|perlfunc/warn> built-ins write to your |
2771 | standard error stream automatically. |
2772 | |
2773 | =item standard I/O |
2774 | |
27ed30b8 |
2775 | A standard C library for doing L<buffered|/buffer> input and output to |
2776 | the L</operating system>. (The "standard" of standard I/O is only |
97a1d740 |
2777 | marginally related to the "standard" of standard input and output.) |
2778 | In general, Perl relies on whatever implementation of standard I/O a |
2779 | given operating system supplies, so the buffering characteristics of a |
2780 | Perl program on one machine may not exactly match those on another |
2781 | machine. Normally this only influences efficiency, not semantics. If |
2782 | your standard I/O package is doing block buffering and you want it to |
27ed30b8 |
2783 | L</flush> the buffer more often, just set the C<$|> variable to a true |
97a1d740 |
2784 | value. |
2785 | |
2786 | =item standard input |
2787 | |
27ed30b8 |
2788 | The default input L</stream> for your program, which if possible |
97a1d740 |
2789 | shouldn't care where its data is coming from. Represented within a |
27ed30b8 |
2790 | Perl program by the L</filehandle> L</STDIN>. |
97a1d740 |
2791 | |
2792 | =item standard output |
2793 | |
27ed30b8 |
2794 | The default output L</stream> for your program, which if possible |
97a1d740 |
2795 | shouldn't care where its data is going. Represented within a Perl |
27ed30b8 |
2796 | program by the L</filehandle> L</STDOUT>. |
97a1d740 |
2797 | |
2798 | =item stat structure |
2799 | |
2800 | A special internal spot in which Perl keeps the information about the |
27ed30b8 |
2801 | last L</file> on which you requested information. |
97a1d740 |
2802 | |
2803 | =item statement |
2804 | |
27ed30b8 |
2805 | A L</command> to the computer about what to do next, like a step in a |
97a1d740 |
2806 | recipe: "Add marmalade to batter and mix until mixed." A statement is |
27ed30b8 |
2807 | distinguished from a L</declaration>, which doesn't tell the computer |
97a1d740 |
2808 | to do anything, but just to learn something. |
2809 | |
2810 | =item statement modifier |
2811 | |
27ed30b8 |
2812 | A L</conditional> or L</loop> that you put after the L</statement> |
97a1d740 |
2813 | instead of before, if you know what we mean. |
2814 | |
2815 | =item static |
2816 | |
2817 | Varying slowly compared to something else. (Unfortunately, everything |
2818 | is relatively stable compared to something else, except for certain |
2819 | elementary particles, and we're not so sure about them.) In |
2820 | computers, where things are supposed to vary rapidly, "static" has a |
2821 | derogatory connotation, indicating a slightly dysfunctional |
27ed30b8 |
2822 | L</variable>, L</subroutine>, or L</method>. In Perl culture, the |
97a1d740 |
2823 | word is politely avoided. |
2824 | |
2825 | =item static method |
2826 | |
27ed30b8 |
2827 | No such thing. See L</class method>. |
97a1d740 |
2828 | |
2829 | =item static scoping |
2830 | |
27ed30b8 |
2831 | No such thing. See L</lexical scoping>. |
97a1d740 |
2832 | |
2833 | =item static variable |
2834 | |
27ed30b8 |
2835 | No such thing. Just use a L</lexical variable> in a scope larger than |
2836 | your L</subroutine>. |
97a1d740 |
2837 | |
2838 | =item status |
2839 | |
27ed30b8 |
2840 | The L</value> returned to the parent L</process> when one of its child |
97a1d740 |
2841 | processes dies. This value is placed in the special variable C<$?>. |
27ed30b8 |
2842 | Its upper eight L<bits|/bit> are the exit status of the defunct |
97a1d740 |
2843 | process, and its lower eight bits identify the signal (if any) that |
2844 | the process died from. On Unix systems, this status value is the same |
2845 | as the status word returned by I<wait>(2). See L<perlfunc/system>. |
2846 | |
2847 | =item STDERR |
2848 | |
27ed30b8 |
2849 | See L</standard error>. |
97a1d740 |
2850 | |
2851 | =item STDIN |
2852 | |
27ed30b8 |
2853 | See L</standard input>. |
97a1d740 |
2854 | |
2855 | =item STDIO |
2856 | |
27ed30b8 |
2857 | See L</standard IE<sol>O>. |
97a1d740 |
2858 | |
2859 | =item STDOUT |
2860 | |
27ed30b8 |
2861 | See L</standard output>. |
97a1d740 |
2862 | |
2863 | =item stream |
2864 | |
2865 | A flow of data into or out of a process as a steady sequence of bytes |
2866 | or characters, without the appearance of being broken up into packets. |
27ed30b8 |
2867 | This is a kind of L</interface>--the underlying L</implementation> may |
97a1d740 |
2868 | well break your data up into separate packets for delivery, but this |
2869 | is hidden from you. |
2870 | |
2871 | =item string |
2872 | |
2873 | A sequence of characters such as "He said !@#*&%@#*?!". A string does |
2874 | not have to be entirely printable. |
2875 | |
2876 | =item string context |
2877 | |
2878 | The situation in which an expression is expected by its surroundings |
27ed30b8 |
2879 | (the code calling it) to return a L</string>. See also L</context> |
2880 | and L</numeric context>. |
97a1d740 |
2881 | |
2882 | =item stringification |
2883 | |
27ed30b8 |
2884 | The process of producing a L</string> representation of an abstract |
97a1d740 |
2885 | object. |
2886 | |
2887 | =item struct |
2888 | |
2889 | C keyword introducing a structure definition or name. |
2890 | |
2891 | =item structure |
2892 | |
27ed30b8 |
2893 | See L</data structure>. |
97a1d740 |
2894 | |
2895 | =item subclass |
2896 | |
27ed30b8 |
2897 | See L</derived class>. |
97a1d740 |
2898 | |
2899 | =item subpattern |
2900 | |
27ed30b8 |
2901 | A component of a L</regular expression> pattern. |
97a1d740 |
2902 | |
2903 | =item subroutine |
2904 | |
2905 | A named or otherwise accessible piece of program that can be invoked |
2906 | from elsewhere in the program in order to accomplish some sub-goal of |
2907 | the program. A subroutine is often parameterized to accomplish |
2908 | different but related things depending on its input |
27ed30b8 |
2909 | L<arguments|/argument>. If the subroutine returns a meaningful |
2910 | L</value>, it is also called a L</function>. |
97a1d740 |
2911 | |
2912 | =item subscript |
2913 | |
27ed30b8 |
2914 | A L</value> that indicates the position of a particular L</array> |
2915 | L</element> in an array. |
97a1d740 |
2916 | |
2917 | =item substitution |
2918 | |
2919 | Changing parts of a string via the C<s///> operator. (We avoid use of |
27ed30b8 |
2920 | this term to mean L</variable interpolation>.) |
97a1d740 |
2921 | |
2922 | =item substring |
2923 | |
27ed30b8 |
2924 | A portion of a L</string>, starting at a certain L</character> |
2925 | position (L</offset>) and proceeding for a certain number of |
97a1d740 |
2926 | characters. |
2927 | |
2928 | =item superclass |
2929 | |
27ed30b8 |
2930 | See L</base class>. |
97a1d740 |
2931 | |
2932 | =item superuser |
2933 | |
27ed30b8 |
2934 | The person whom the L</operating system> will let do almost anything. |
97a1d740 |
2935 | Typically your system administrator or someone pretending to be your |
27ed30b8 |
2936 | system administrator. On Unix systems, the L</root> user. On Windows |
97a1d740 |
2937 | systems, usually the Administrator user. |
2938 | |
2939 | =item SV |
2940 | |
2941 | Short for "scalar value". But within the Perl interpreter every |
27ed30b8 |
2942 | L</referent> is treated as a member of a class derived from SV, in an |
2943 | object-oriented sort of way. Every L</value> inside Perl is passed |
2944 | around as a C language C<SV*> pointer. The SV L</struct> knows its |
97a1d740 |
2945 | own "referent type", and the code is smart enough (we hope) not to try |
27ed30b8 |
2946 | to call a L</hash> function on a L</subroutine>. |
97a1d740 |
2947 | |
2948 | =item switch |
2949 | |
2950 | An option you give on a command line to influence the way your program |
2951 | works, usually introduced with a minus sign. The word is also used as |
27ed30b8 |
2952 | a nickname for a L</switch statement>. |
97a1d740 |
2953 | |
2954 | =item switch cluster |
2955 | |
2956 | The combination of multiple command-line switches (e.g., B<-a -b -c>) |
2957 | into one switch (e.g., B<-abc>). Any switch with an additional |
27ed30b8 |
2958 | L</argument> must be the last switch in a cluster. |
97a1d740 |
2959 | |
2960 | =item switch statement |
2961 | |
27ed30b8 |
2962 | A program technique that lets you evaluate an L</expression> and then, |
97a1d740 |
2963 | based on the value of the expression, do a multiway branch to the |
2964 | appropriate piece of code for that value. Also called a "case |
2965 | structure", named after the similar Pascal construct. Most switch |
2966 | statements in Perl are spelled C<for>. See L<perlsyn/Basic BLOCKs and |
2967 | Switch Statements>. |
2968 | |
2969 | =item symbol |
2970 | |
27ed30b8 |
2971 | Generally, any L</token> or L</metasymbol>. Often used more |
2972 | specifically to mean the sort of name you might find in a L</symbol |
97a1d740 |
2973 | table>. |
2974 | |
2975 | =item symbol table |
2976 | |
27ed30b8 |
2977 | Where a L</compiler> remembers symbols. A program like Perl must |
2978 | somehow remember all the names of all the L<variables|/variable>, |
2979 | L<filehandles|/filehandle>, and L<subroutines|/subroutine> you've |
97a1d740 |
2980 | used. It does this by placing the names in a symbol table, which is |
27ed30b8 |
2981 | implemented in Perl using a L</hash table>. There is a separate |
2982 | symbol table for each L</package> to give each package its own |
2983 | L</namespace>. |
97a1d740 |
2984 | |
2985 | =item symbolic debugger |
2986 | |
2987 | A program that lets you step through the L<execution|/execute> of your |
2988 | program, stopping or printing things out here and there to see whether |
2989 | anything has gone wrong, and if so, what. The "symbolic" part just |
2990 | means that you can talk to the debugger using the same symbols with |
2991 | which your program is written. |
2992 | |
2993 | =item symbolic link |
2994 | |
27ed30b8 |
2995 | An alternate filename that points to the real L</filename>, which in |
2996 | turn points to the real L</file>. Whenever the L</operating system> |
2997 | is trying to parse a L</pathname> containing a symbolic link, it |
97a1d740 |
2998 | merely substitutes the new name and continues parsing. |
2999 | |
3000 | =item symbolic reference |
3001 | |
3002 | A variable whose value is the name of another variable or subroutine. |
3003 | By L<dereferencing|/dereference> the first variable, you can get at |
27ed30b8 |
3004 | the second one. Symbolic references are illegal under L<use strict |
3005 | 'refs'|strict/strict refs>. |
97a1d740 |
3006 | |
3007 | =item synchronous |
3008 | |
3009 | Programming in which the orderly sequence of events can be determined; |
3010 | that is, when things happen one after the other, not at the same time. |
3011 | |
3012 | =item syntactic sugar |
3013 | |
3014 | An alternative way of writing something more easily; a shortcut. |
3015 | |
3016 | =item syntax |
3017 | |
3018 | From Greek, "with-arrangement". How things (particularly symbols) are |
3019 | put together with each other. |
3020 | |
3021 | =item syntax tree |
3022 | |
3023 | An internal representation of your program wherein lower-level |
27ed30b8 |
3024 | L<constructs|/construct> dangle off the higher-level constructs |
97a1d740 |
3025 | enclosing them. |
3026 | |
3027 | =item syscall |
3028 | |
27ed30b8 |
3029 | A L</function> call directly to the L</operating system>. Many of the |
97a1d740 |
3030 | important subroutines and functions you use aren't direct system |
3031 | calls, but are built up in one or more layers above the system call |
3032 | level. In general, Perl programmers don't need to worry about the |
3033 | distinction. However, if you do happen to know which Perl functions |
3034 | are really syscalls, you can predict which of these will set the C<$!> |
3035 | (C<$ERRNO>) variable on failure. Unfortunately, beginning programmers |
3036 | often confusingly employ the term "system call" to mean what happens |
3037 | when you call the Perl L<system|perlfunc/system> function, which |
3038 | actually involves many syscalls. To avoid any confusion, we nearly |
3039 | always use say "syscall" for something you could call indirectly via |
3040 | Perl's L<syscall|perlfunc/syscall> function, and never for something |
3041 | you would call with Perl's L<system|perlfunc/system> function. |
3042 | |
3043 | =back |
3044 | |
5bbd0522 |
3045 | =head2 T |
3046 | |
97a1d740 |
3047 | =over 4 |
3048 | |
3049 | =item tainted |
3050 | |
3051 | Said of data derived from the grubby hands of a user and thus unsafe |
3052 | for a secure program to rely on. Perl does taint checks if you run a |
27ed30b8 |
3053 | L</setuid> (or L</setgid>) program, or if you use the B<-T> switch. |
97a1d740 |
3054 | |
3055 | =item TCP |
3056 | |
3057 | Short for Transmission Control Protocol. A protocol wrapped around |
3058 | the Internet Protocol to make an unreliable packet transmission |
3059 | mechanism appear to the application program to be a reliable |
27ed30b8 |
3060 | L</stream> of bytes. (Usually.) |
97a1d740 |
3061 | |
3062 | =item term |
3063 | |
27ed30b8 |
3064 | Short for a "terminal", that is, a leaf node of a L</syntax tree>. A |
3065 | thing that functions grammatically as an L</operand> for the operators |
97a1d740 |
3066 | in an expression. |
3067 | |
3068 | =item terminator |
3069 | |
27ed30b8 |
3070 | A L</character> or L</string> that marks the end of another string. |
97a1d740 |
3071 | The C<$/> variable contains the string that terminates a |
3072 | L<readline|perlfunc/readline> operation, which L<chomp|perlfunc/chomp> |
3073 | deletes from the end. Not to be confused with |
27ed30b8 |
3074 | L<delimiters|/delimiter> or L<separators|/separator>. The period at |
97a1d740 |
3075 | the end of this sentence is a terminator. |
3076 | |
3077 | =item ternary |
3078 | |
27ed30b8 |
3079 | An L</operator> taking three L<operands|/operand>. Sometimes |
3080 | pronounced L</trinary>. |
97a1d740 |
3081 | |
3082 | =item text |
3083 | |
27ed30b8 |
3084 | A L</string> or L</file> containing primarily printable characters. |
97a1d740 |
3085 | |
3086 | =item thread |
3087 | |
27ed30b8 |
3088 | Like a forked process, but without L</fork>'s inherent memory |
97a1d740 |
3089 | protection. A thread is lighter weight than a full process, in that a |
3090 | process could have multiple threads running around in it, all fighting |
3091 | over the same process's memory space unless steps are taken to protect |
3092 | threads from each other. See L<threads>. |
3093 | |
3094 | =item tie |
3095 | |
3096 | The bond between a magical variable and its implementation class. See |
3097 | L<perlfunc/tie> and L<perltie>. |
3098 | |
3099 | =item TMTOWTDI |
3100 | |
3101 | There's More Than One Way To Do It, the Perl Motto. The notion that |
3102 | there can be more than one valid path to solving a programming problem |
3103 | in context. (This doesn't mean that more ways are always better or |
3104 | that all possible paths are equally desirable--just that there need |
3105 | not be One True Way.) Pronounced TimToady. |
3106 | |
3107 | =item token |
3108 | |
3109 | A morpheme in a programming language, the smallest unit of text with |
3110 | semantic significance. |
3111 | |
3112 | =item tokener |
3113 | |
3114 | A module that breaks a program text into a sequence of |
27ed30b8 |
3115 | L<tokens|/token> for later analysis by a parser. |
97a1d740 |
3116 | |
3117 | =item tokenizing |
3118 | |
27ed30b8 |
3119 | Splitting up a program text into L<tokens|/token>. Also known as |
97a1d740 |
3120 | "lexing", in which case you get "lexemes" instead of tokens. |
3121 | |
3122 | =item toolbox approach |
3123 | |
3124 | The notion that, with a complete set of simple tools that work well |
3125 | together, you can build almost anything you want. Which is fine if |
3126 | you're assembling a tricycle, but if you're building a defranishizing |
3127 | comboflux regurgalator, you really want your own machine shop in which |
3128 | to build special tools. Perl is sort of a machine shop. |
3129 | |
3130 | =item transliterate |
3131 | |
3132 | To turn one string representation into another by mapping each |
3133 | character of the source string to its corresponding character in the |
3134 | result string. See |
3135 | L<perlop/trE<sol>SEARCHLISTE<sol>REPLACEMENTLISTE<sol>cds>. |
3136 | |
3137 | =item trigger |
3138 | |
27ed30b8 |
3139 | An event that causes a L</handler> to be run. |
97a1d740 |
3140 | |
3141 | =item trinary |
3142 | |
27ed30b8 |
3143 | Not a stellar system with three stars, but an L</operator> taking |
3144 | three L<operands|/operand>. Sometimes pronounced L</ternary>. |
97a1d740 |
3145 | |
3146 | =item troff |
3147 | |
3148 | A venerable typesetting language from which Perl derives the name of |
3149 | its C<$%> variable and which is secretly used in the production of |
3150 | Camel books. |
3151 | |
3152 | =item true |
3153 | |
3154 | Any scalar value that doesn't evaluate to 0 or C<"">. |
3155 | |
3156 | =item truncating |
3157 | |
3158 | Emptying a file of existing contents, either automatically when |
3159 | opening a file for writing or explicitly via the |
3160 | L<truncate|perlfunc/truncate> function. |
3161 | |
3162 | =item type |
3163 | |
27ed30b8 |
3164 | See L</data type> and L</class>. |
97a1d740 |
3165 | |
3166 | =item type casting |
3167 | |
3168 | Converting data from one type to another. C permits this. Perl does |
3169 | not need it. Nor want it. |
3170 | |
3171 | =item typed lexical |
3172 | |
27ed30b8 |
3173 | A L</lexical variable> that is declared with a L</class> type: C<my |
97a1d740 |
3174 | Pony $bill>. |
3175 | |
3176 | =item typedef |
3177 | |
3178 | A type definition in the C language. |
3179 | |
3180 | =item typeglob |
3181 | |
3182 | Use of a single identifier, prefixed with C<*>. For example, C<*name> |
3183 | stands for any or all of C<$name>, C<@name>, C<%name>, C<&name>, or |
3184 | just C<name>. How you use it determines whether it is interpreted as |
3185 | all or only one of them. See L<perldata/Typeglobs and Filehandles>. |
3186 | |
3187 | =item typemap |
3188 | |
3189 | A description of how C types may be transformed to and from Perl types |
27ed30b8 |
3190 | within an L</extension> module written in L</XS>. |
97a1d740 |
3191 | |
3192 | =back |
3193 | |
5bbd0522 |
3194 | =head2 U |
3195 | |
97a1d740 |
3196 | =over 4 |
3197 | |
3198 | =item UDP |
3199 | |
27ed30b8 |
3200 | User Datagram Protocol, the typical way to send L<datagrams|/datagram> |
97a1d740 |
3201 | over the Internet. |
3202 | |
3203 | =item UID |
3204 | |
27ed30b8 |
3205 | A user ID. Often used in the context of L</file> or L</process> |
97a1d740 |
3206 | ownership. |
3207 | |
3208 | =item umask |
3209 | |
27ed30b8 |
3210 | A mask of those L</permission bits> that should be forced off when |
97a1d740 |
3211 | creating files or directories, in order to establish a policy of whom |
3212 | you'll ordinarily deny access to. See the L<umask|perlfunc/umask> |
3213 | function. |
3214 | |
3215 | =item unary operator |
3216 | |
27ed30b8 |
3217 | An operator with only one L</operand>, like C<!> or |
97a1d740 |
3218 | L<chdir|perlfunc/chdir>. Unary operators are usually prefix |
3219 | operators; that is, they precede their operand. The C<++> and C<--> |
3220 | operators can be either prefix or postfix. (Their position I<does> |
3221 | change their meanings.) |
3222 | |
3223 | =item Unicode |
3224 | |
3225 | A character set comprising all the major character sets of the world, |
3226 | more or less. See L<http://www.unicode.org>. |
3227 | |
3228 | =item Unix |
3229 | |
3230 | A very large and constantly evolving language with several alternative |
3231 | and largely incompatible syntaxes, in which anyone can define anything |
3232 | any way they choose, and usually do. Speakers of this language think |
3233 | it's easy to learn because it's so easily twisted to one's own ends, |
3234 | but dialectical differences make tribal intercommunication nearly |
3235 | impossible, and travelers are often reduced to a pidgin-like subset of |
3236 | the language. To be universally understood, a Unix shell programmer |
3237 | must spend years of study in the art. Many have abandoned this |
3238 | discipline and now communicate via an Esperanto-like language called |
3239 | Perl. |
3240 | |
3241 | In ancient times, Unix was also used to refer to some code that a |
3242 | couple of people at Bell Labs wrote to make use of a PDP-7 computer |
3243 | that wasn't doing much of anything else at the time. |
3244 | |
3245 | =back |
3246 | |
5bbd0522 |
3247 | =head2 V |
3248 | |
97a1d740 |
3249 | =over 4 |
3250 | |
3251 | =item value |
3252 | |
3253 | An actual piece of data, in contrast to all the variables, references, |
3254 | keys, indexes, operators, and whatnot that you need to access the |
3255 | value. |
3256 | |
3257 | =item variable |
3258 | |
3259 | A named storage location that can hold any of various kinds of |
27ed30b8 |
3260 | L</value>, as your program sees fit. |
97a1d740 |
3261 | |
3262 | =item variable interpolation |
3263 | |
27ed30b8 |
3264 | The L</interpolation> of a scalar or array variable into a string. |
97a1d740 |
3265 | |
3266 | =item variadic |
3267 | |
27ed30b8 |
3268 | Said of a L</function> that happily receives an indeterminate number |
3269 | of L</actual arguments>. |
97a1d740 |
3270 | |
3271 | =item vector |
3272 | |
27ed30b8 |
3273 | Mathematical jargon for a list of L<scalar values|/scalar value>. |
97a1d740 |
3274 | |
3275 | =item virtual |
3276 | |
3277 | Providing the appearance of something without the reality, as in: |
27ed30b8 |
3278 | virtual memory is not real memory. (See also L</memory>.) The |
97a1d740 |
3279 | opposite of "virtual" is "transparent", which means providing the |
3280 | reality of something without the appearance, as in: Perl handles the |
3281 | variable-length UTF-8 character encoding transparently. |
3282 | |
3283 | =item void context |
3284 | |
27ed30b8 |
3285 | A form of L</scalar context> in which an L</expression> is not |
3286 | expected to return any L</value> at all and is evaluated for its |
3287 | L</side effects> alone. |
97a1d740 |
3288 | |
3289 | =item v-string |
3290 | |
27ed30b8 |
3291 | A "version" or "vector" L</string> specified with a C<v> followed by a |
97a1d740 |
3292 | series of decimal integers in dot notation, for instance, |
27ed30b8 |
3293 | C<v1.20.300.4000>. Each number turns into a L</character> with the |
97a1d740 |
3294 | specified ordinal value. (The C<v> is optional when there are at |
3295 | least three integers.) |
3296 | |
3297 | =back |
3298 | |
5bbd0522 |
3299 | =head2 W |
3300 | |
97a1d740 |
3301 | =over 4 |
3302 | |
3303 | =item warning |
3304 | |
27ed30b8 |
3305 | A message printed to the L</STDERR> stream to the effect that something |
97a1d740 |
3306 | might be wrong but isn't worth blowing up over. See L<perlfunc/warn> |
3307 | and the L<warnings> pragma. |
3308 | |
3309 | =item watch expression |
3310 | |
3311 | An expression which, when its value changes, causes a breakpoint in |
3312 | the Perl debugger. |
3313 | |
3314 | =item whitespace |
3315 | |
27ed30b8 |
3316 | A L</character> that moves your cursor but doesn't otherwise put |
97a1d740 |
3317 | anything on your screen. Typically refers to any of: space, tab, line |
3318 | feed, carriage return, or form feed. |
3319 | |
3320 | =item word |
3321 | |
3322 | In normal "computerese", the piece of data of the size most |
3323 | efficiently handled by your computer, typically 32 bits or so, give or |
3324 | take a few powers of 2. In Perl culture, it more often refers to an |
27ed30b8 |
3325 | alphanumeric L</identifier> (including underscores), or to a string of |
3326 | nonwhitespace L<characters|/character> bounded by whitespace or string |
97a1d740 |
3327 | boundaries. |
3328 | |
3329 | =item working directory |
3330 | |
27ed30b8 |
3331 | Your current L</directory>, from which relative pathnames are |
3332 | interpreted by the L</operating system>. The operating system knows |
97a1d740 |
3333 | your current directory because you told it with a |
3334 | L<chdir|perlfunc/chdir> or because you started out in the place where |
27ed30b8 |
3335 | your parent L</process> was when you were born. |
97a1d740 |
3336 | |
3337 | =item wrapper |
3338 | |
3339 | A program or subroutine that runs some other program or subroutine for |
3340 | you, modifying some of its input or output to better suit your |
3341 | purposes. |
3342 | |
3343 | =item WYSIWYG |
3344 | |
3345 | What You See Is What You Get. Usually used when something that |
3346 | appears on the screen matches how it will eventually look, like Perl's |
3347 | L<format|perlfunc/format> declarations. Also used to mean the |
3348 | opposite of magic because everything works exactly as it appears, as |
3349 | in the three-argument form of L<open|perlfunc/open>. |
3350 | |
3351 | =back |
3352 | |
5bbd0522 |
3353 | =head2 X |
3354 | |
97a1d740 |
3355 | =over 4 |
3356 | |
3357 | =item XS |
3358 | |
3359 | An extraordinarily exported, expeditiously excellent, expressly |
3360 | eXternal Subroutine, executed in existing C or C++ or in an exciting |
3361 | new extension language called (exasperatingly) XS. Examine L<perlxs> |
3362 | for the exact explanation or L<perlxstut> for an exemplary unexacting |
3363 | one. |
3364 | |
3365 | =item XSUB |
3366 | |
27ed30b8 |
3367 | An external L</subroutine> defined in L</XS>. |
97a1d740 |
3368 | |
3369 | =back |
3370 | |
5bbd0522 |
3371 | =head2 Y |
3372 | |
97a1d740 |
3373 | =over 4 |
3374 | |
3375 | =item yacc |
3376 | |
3377 | Yet Another Compiler Compiler. A parser generator without which Perl |
3378 | probably would not have existed. See the file I<perly.y> in the Perl |
3379 | source distribution. |
3380 | |
3381 | =back |
3382 | |
5bbd0522 |
3383 | =head2 Z |
3384 | |
97a1d740 |
3385 | =over 4 |
3386 | |
3387 | =item zero width |
3388 | |
27ed30b8 |
3389 | A subpattern L</assertion> matching the L</null string> between |
3390 | L<characters|/character>. |
97a1d740 |
3391 | |
3392 | =item zombie |
3393 | |
3394 | A process that has died (exited) but whose parent has not yet received |
3395 | proper notification of its demise by virtue of having called |
3396 | L<wait|perlfunc/wait> or L<waitpid|perlfunc/waitpid>. If you |
3397 | L<fork|perlfunc/fork>, you must clean up after your child processes |
3398 | when they exit, or else the process table will fill up and your system |
3399 | administrator will Not Be Happy with you. |
3400 | |
3401 | =back |
3402 | |
3403 | =head1 AUTHOR AND COPYRIGHT |
3404 | |
3405 | Based on the Glossary of Programming Perl, Third Edition, |
3406 | by Larry Wall, Tom Christiansen & Jon Orwant. |
3407 | Copyright (c) 2000, 1996, 1991 O'Reilly Media, Inc. |
20fd23ef |
3408 | This document may be distributed under the same terms as Perl itself. |