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68dc0745 | 1 | =head1 NAME |
2 | ||
c195e131 | 3 | perlfaq7 - General Perl Language Issues ($Revision: 10100 $) |
68dc0745 | 4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | This section deals with general Perl language issues that don't | |
8 | clearly fit into any of the other sections. | |
9 | ||
10 | =head2 Can I get a BNF/yacc/RE for the Perl language? | |
11 | ||
c8db1d39 TC |
12 | There is no BNF, but you can paw your way through the yacc grammar in |
13 | perly.y in the source distribution if you're particularly brave. The | |
14 | grammar relies on very smart tokenizing code, so be prepared to | |
15 | venture into toke.c as well. | |
16 | ||
17 | In the words of Chaim Frenkel: "Perl's grammar can not be reduced to BNF. | |
18 | The work of parsing perl is distributed between yacc, the lexer, smoke | |
19 | and mirrors." | |
68dc0745 | 20 | |
d92eb7b0 | 21 | =head2 What are all these $@%&* punctuation signs, and how do I know when to use them? |
68dc0745 | 22 | |
23 | They are type specifiers, as detailed in L<perldata>: | |
24 | ||
ac003c96 RGS |
25 | $ for scalar values (number, string or reference) |
26 | @ for arrays | |
27 | % for hashes (associative arrays) | |
28 | & for subroutines (aka functions, procedures, methods) | |
29 | * for all types of that symbol name. In version 4 you used them like | |
30 | pointers, but in modern perls you can just use references. | |
68dc0745 | 31 | |
a6dd486b JB |
32 | There are couple of other symbols that you're likely to encounter that aren't |
33 | really type specifiers: | |
68dc0745 | 34 | |
ac003c96 RGS |
35 | <> are used for inputting a record from a filehandle. |
36 | \ takes a reference to something. | |
68dc0745 | 37 | |
c47ff5f1 GS |
38 | Note that <FILE> is I<neither> the type specifier for files |
39 | nor the name of the handle. It is the C<< <> >> operator applied | |
a6dd486b | 40 | to the handle FILE. It reads one line (well, record--see |
197aec24 | 41 | L<perlvar/$E<sol>>) from the handle FILE in scalar context, or I<all> lines |
68dc0745 | 42 | in list context. When performing open, close, or any other operation |
a6dd486b | 43 | besides C<< <> >> on files, or even when talking about the handle, do |
68dc0745 | 44 | I<not> use the brackets. These are correct: C<eof(FH)>, C<seek(FH, 0, |
45 | 2)> and "copying from STDIN to FILE". | |
46 | ||
47 | =head2 Do I always/never have to quote my strings or use semicolons and commas? | |
48 | ||
49 | Normally, a bareword doesn't need to be quoted, but in most cases | |
50 | probably should be (and must be under C<use strict>). But a hash key | |
51 | consisting of a simple word (that isn't the name of a defined | |
c47ff5f1 | 52 | subroutine) and the left-hand operand to the C<< => >> operator both |
68dc0745 | 53 | count as though they were quoted: |
54 | ||
ac003c96 RGS |
55 | This is like this |
56 | ------------ --------------- | |
57 | $foo{line} $foo{'line'} | |
58 | bar => stuff 'bar' => stuff | |
68dc0745 | 59 | |
60 | The final semicolon in a block is optional, as is the final comma in a | |
61 | list. Good style (see L<perlstyle>) says to put them in except for | |
62 | one-liners: | |
63 | ||
ac003c96 RGS |
64 | if ($whoops) { exit 1 } |
65 | @nums = (1, 2, 3); | |
66 | ||
67 | if ($whoops) { | |
68 | exit 1; | |
69 | } | |
68dc0745 | 70 | |
ac003c96 | 71 | @lines = ( |
68dc0745 | 72 | "There Beren came from mountains cold", |
73 | "And lost he wandered under leaves", | |
ac003c96 | 74 | ); |
68dc0745 | 75 | |
76 | =head2 How do I skip some return values? | |
77 | ||
78 | One way is to treat the return values as a list and index into it: | |
79 | ||
ac003c96 | 80 | $dir = (getpwnam($user))[7]; |
68dc0745 | 81 | |
82 | Another way is to use undef as an element on the left-hand-side: | |
83 | ||
ac003c96 | 84 | ($dev, $ino, undef, undef, $uid, $gid) = stat($file); |
197aec24 | 85 | |
49d635f9 RGS |
86 | You can also use a list slice to select only the elements that |
87 | you need: | |
88 | ||
89 | ($dev, $ino, $uid, $gid) = ( stat($file) )[0,1,4,5]; | |
68dc0745 | 90 | |
91 | =head2 How do I temporarily block warnings? | |
92 | ||
9f1b1f2d GS |
93 | If you are running Perl 5.6.0 or better, the C<use warnings> pragma |
94 | allows fine control of what warning are produced. | |
95 | See L<perllexwarn> for more details. | |
96 | ||
ac003c96 | 97 | { |
9f1b1f2d GS |
98 | no warnings; # temporarily turn off warnings |
99 | $a = $b + $c; # I know these might be undef | |
ac003c96 | 100 | } |
6670e5e7 | 101 | |
28b41a80 RGS |
102 | Additionally, you can enable and disable categories of warnings. |
103 | You turn off the categories you want to ignore and you can still | |
104 | get other categories of warnings. See L<perllexwarn> for the | |
105 | complete details, including the category names and hierarchy. | |
106 | ||
107 | { | |
108 | no warnings 'uninitialized'; | |
109 | $a = $b + $c; | |
110 | } | |
9f1b1f2d GS |
111 | |
112 | If you have an older version of Perl, the C<$^W> variable (documented | |
113 | in L<perlvar>) controls runtime warnings for a block: | |
68dc0745 | 114 | |
ac003c96 | 115 | { |
68dc0745 | 116 | local $^W = 0; # temporarily turn off warnings |
117 | $a = $b + $c; # I know these might be undef | |
ac003c96 | 118 | } |
68dc0745 | 119 | |
120 | Note that like all the punctuation variables, you cannot currently | |
121 | use my() on C<$^W>, only local(). | |
122 | ||
68dc0745 | 123 | =head2 What's an extension? |
124 | ||
a6dd486b JB |
125 | An extension is a way of calling compiled C code from Perl. Reading |
126 | L<perlxstut> is a good place to learn more about extensions. | |
68dc0745 | 127 | |
128 | =head2 Why do Perl operators have different precedence than C operators? | |
129 | ||
130 | Actually, they don't. All C operators that Perl copies have the same | |
131 | precedence in Perl as they do in C. The problem is with operators that C | |
132 | doesn't have, especially functions that give a list context to everything | |
a6dd486b | 133 | on their right, eg. print, chmod, exec, and so on. Such functions are |
68dc0745 | 134 | called "list operators" and appear as such in the precedence table in |
135 | L<perlop>. | |
136 | ||
137 | A common mistake is to write: | |
138 | ||
ac003c96 | 139 | unlink $file || die "snafu"; |
68dc0745 | 140 | |
141 | This gets interpreted as: | |
142 | ||
ac003c96 | 143 | unlink ($file || die "snafu"); |
68dc0745 | 144 | |
145 | To avoid this problem, either put in extra parentheses or use the | |
146 | super low precedence C<or> operator: | |
147 | ||
ac003c96 RGS |
148 | (unlink $file) || die "snafu"; |
149 | unlink $file or die "snafu"; | |
68dc0745 | 150 | |
151 | The "English" operators (C<and>, C<or>, C<xor>, and C<not>) | |
152 | deliberately have precedence lower than that of list operators for | |
153 | just such situations as the one above. | |
154 | ||
155 | Another operator with surprising precedence is exponentiation. It | |
156 | binds more tightly even than unary minus, making C<-2**2> product a | |
157 | negative not a positive four. It is also right-associating, meaning | |
158 | that C<2**3**2> is two raised to the ninth power, not eight squared. | |
159 | ||
c8db1d39 TC |
160 | Although it has the same precedence as in C, Perl's C<?:> operator |
161 | produces an lvalue. This assigns $x to either $a or $b, depending | |
162 | on the trueness of $maybe: | |
163 | ||
ac003c96 | 164 | ($maybe ? $a : $b) = $x; |
c8db1d39 | 165 | |
68dc0745 | 166 | =head2 How do I declare/create a structure? |
167 | ||
168 | In general, you don't "declare" a structure. Just use a (probably | |
169 | anonymous) hash reference. See L<perlref> and L<perldsc> for details. | |
170 | Here's an example: | |
171 | ||
ac003c96 RGS |
172 | $person = {}; # new anonymous hash |
173 | $person->{AGE} = 24; # set field AGE to 24 | |
174 | $person->{NAME} = "Nat"; # set field NAME to "Nat" | |
175 | ||
68dc0745 | 176 | If you're looking for something a bit more rigorous, try L<perltoot>. |
177 | ||
178 | =head2 How do I create a module? | |
179 | ||
7678cced | 180 | (contributed by brian d foy) |
68dc0745 | 181 | |
7678cced | 182 | L<perlmod>, L<perlmodlib>, L<perlmodstyle> explain modules |
cf525c36 | 183 | in all the gory details. L<perlnewmod> gives a brief |
7678cced RGS |
184 | overview of the process along with a couple of suggestions |
185 | about style. | |
65acb1b1 | 186 | |
7678cced RGS |
187 | If you need to include C code or C library interfaces in |
188 | your module, you'll need h2xs. h2xs will create the module | |
189 | distribution structure and the initial interface files | |
190 | you'll need. L<perlxs> and L<perlxstut> explain the details. | |
7207e29d | 191 | |
7678cced RGS |
192 | If you don't need to use C code, other tools such as |
193 | ExtUtils::ModuleMaker and Module::Starter, can help you | |
194 | create a skeleton module distribution. | |
195 | ||
196 | You may also want to see Sam Tregar's "Writing Perl Modules | |
197 | for CPAN" ( http://apress.com/book/bookDisplay.html?bID=14 ) | |
198 | which is the best hands-on guide to creating module | |
199 | distributions. | |
65acb1b1 | 200 | |
c195e131 RGS |
201 | =head2 How do I adopt or take over a module already on CPAN? |
202 | ||
203 | (contributed by brian d foy) | |
204 | ||
205 | The easiest way to take over a module is to have the current | |
206 | module maintainer either make you a co-maintainer or transfer | |
207 | the module to you. | |
208 | ||
209 | If you can't reach the author for some reason (e.g. email bounces), | |
210 | the PAUSE admins at modules@perl.org can help. The PAUSE admins | |
211 | treat each case individually. | |
212 | ||
213 | =over 4 | |
214 | ||
215 | =item | |
216 | ||
217 | Get a login for the Perl Authors Upload Server (PAUSE) if you don't | |
218 | already have one: http://pause.perl.org | |
219 | ||
220 | =item | |
221 | ||
222 | Write to modules@perl.org explaining what you did to contact the | |
223 | current maintainer. The PAUSE admins will also try to reach the | |
224 | maintainer. | |
225 | ||
226 | =item | |
227 | ||
228 | Post a public message in a heavily trafficked site announcing your | |
229 | intention to take over the module. | |
230 | ||
231 | =item | |
232 | ||
233 | Wait a bit. The PAUSE admins don't want to act too quickly in case | |
234 | the current maintainer is on holiday. If there's no response to | |
235 | private communication or the public post, a PAUSE admin can transfer | |
236 | it to you. | |
237 | ||
238 | =back | |
239 | ||
68dc0745 | 240 | =head2 How do I create a class? |
241 | ||
242 | See L<perltoot> for an introduction to classes and objects, as well as | |
243 | L<perlobj> and L<perlbot>. | |
244 | ||
245 | =head2 How can I tell if a variable is tainted? | |
246 | ||
213329dd JH |
247 | You can use the tainted() function of the Scalar::Util module, available |
248 | from CPAN (or included with Perl since release 5.8.0). | |
249 | See also L<perlsec/"Laundering and Detecting Tainted Data">. | |
68dc0745 | 250 | |
251 | =head2 What's a closure? | |
252 | ||
253 | Closures are documented in L<perlref>. | |
254 | ||
255 | I<Closure> is a computer science term with a precise but | |
322be77c RGS |
256 | hard-to-explain meaning. Usually, closures are implemented in Perl as |
257 | anonymous subroutines with lasting references to lexical variables | |
258 | outside their own scopes. These lexicals magically refer to the | |
259 | variables that were around when the subroutine was defined (deep | |
260 | binding). | |
261 | ||
262 | Closures are most often used in programming languages where you can | |
263 | have the return value of a function be itself a function, as you can | |
264 | in Perl. Note that some languages provide anonymous functions but are | |
265 | not capable of providing proper closures: the Python language, for | |
68dc0745 | 266 | example. For more information on closures, check out any textbook on |
267 | functional programming. Scheme is a language that not only supports | |
268 | but encourages closures. | |
269 | ||
322be77c | 270 | Here's a classic non-closure function-generating function: |
68dc0745 | 271 | |
ac003c96 RGS |
272 | sub add_function_generator { |
273 | return sub { shift() + shift() }; | |
274 | } | |
68dc0745 | 275 | |
ac003c96 RGS |
276 | $add_sub = add_function_generator(); |
277 | $sum = $add_sub->(4,5); # $sum is 9 now. | |
68dc0745 | 278 | |
322be77c RGS |
279 | The anonymous subroutine returned by add_function_generator() isn't |
280 | technically a closure because it refers to no lexicals outside its own | |
281 | scope. Using a closure gives you a I<function template> with some | |
282 | customization slots left out to be filled later. | |
68dc0745 | 283 | |
284 | Contrast this with the following make_adder() function, in which the | |
285 | returned anonymous function contains a reference to a lexical variable | |
286 | outside the scope of that function itself. Such a reference requires | |
287 | that Perl return a proper closure, thus locking in for all time the | |
288 | value that the lexical had when the function was created. | |
289 | ||
ac003c96 RGS |
290 | sub make_adder { |
291 | my $addpiece = shift; | |
292 | return sub { shift() + $addpiece }; | |
293 | } | |
294 | ||
295 | $f1 = make_adder(20); | |
296 | $f2 = make_adder(555); | |
68dc0745 | 297 | |
298 | Now C<&$f1($n)> is always 20 plus whatever $n you pass in, whereas | |
299 | C<&$f2($n)> is always 555 plus whatever $n you pass in. The $addpiece | |
300 | in the closure sticks around. | |
301 | ||
302 | Closures are often used for less esoteric purposes. For example, when | |
303 | you want to pass in a bit of code into a function: | |
304 | ||
ac003c96 RGS |
305 | my $line; |
306 | timeout( 30, sub { $line = <STDIN> } ); | |
68dc0745 | 307 | |
c47ff5f1 GS |
308 | If the code to execute had been passed in as a string, |
309 | C<< '$line = <STDIN>' >>, there would have been no way for the | |
310 | hypothetical timeout() function to access the lexical variable | |
311 | $line back in its caller's scope. | |
68dc0745 | 312 | |
322be77c RGS |
313 | Another use for a closure is to make a variable I<private> to a |
314 | named subroutine, e.g. a counter that gets initialized at creation | |
315 | time of the sub and can only be modified from within the sub. | |
316 | This is sometimes used with a BEGIN block in package files to make | |
317 | sure a variable doesn't get meddled with during the lifetime of the | |
318 | package: | |
319 | ||
ac003c96 RGS |
320 | BEGIN { |
321 | my $id = 0; | |
322 | sub next_id { ++$id } | |
323 | } | |
322be77c RGS |
324 | |
325 | This is discussed in more detail in L<perlsub>, see the entry on | |
326 | I<Persistent Private Variables>. | |
327 | ||
46fc3d4c | 328 | =head2 What is variable suicide and how can I prevent it? |
329 | ||
9e72e4c6 RGS |
330 | This problem was fixed in perl 5.004_05, so preventing it means upgrading |
331 | your version of perl. ;) | |
46fc3d4c | 332 | |
9e72e4c6 RGS |
333 | Variable suicide is when you (temporarily or permanently) lose the value |
334 | of a variable. It is caused by scoping through my() and local() | |
335 | interacting with either closures or aliased foreach() iterator variables | |
336 | and subroutine arguments. It used to be easy to inadvertently lose a | |
337 | variable's value this way, but now it's much harder. Take this code: | |
338 | ||
ac003c96 RGS |
339 | my $f = 'foo'; |
340 | sub T { | |
341 | while ($i++ < 3) { my $f = $f; $f .= "bar"; print $f, "\n" } | |
342 | } | |
343 | ||
344 | T; | |
345 | print "Finally $f\n"; | |
46fc3d4c | 346 | |
9e72e4c6 RGS |
347 | If you are experiencing variable suicide, that C<my $f> in the subroutine |
348 | doesn't pick up a fresh copy of the C<$f> whose value is <foo>. The output | |
349 | shows that inside the subroutine the value of C<$f> leaks through when it | |
350 | shouldn't, as in this output: | |
351 | ||
352 | foobar | |
353 | foobarbar | |
354 | foobarbarbar | |
355 | Finally foo | |
356 | ||
46fc3d4c | 357 | The $f that has "bar" added to it three times should be a new C<$f> |
9e72e4c6 RGS |
358 | C<my $f> should create a new lexical variable each time through the loop. |
359 | The expected output is: | |
360 | ||
361 | foobar | |
362 | foobar | |
363 | foobar | |
364 | Finally foo | |
46fc3d4c | 365 | |
d92eb7b0 | 366 | =head2 How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}? |
68dc0745 | 367 | |
d92eb7b0 | 368 | With the exception of regexes, you need to pass references to these |
68dc0745 | 369 | objects. See L<perlsub/"Pass by Reference"> for this particular |
370 | question, and L<perlref> for information on references. | |
371 | ||
ac9dac7f RGS |
372 | See "Passing Regexes", later in L<perlfaq7>, for information on |
373 | passing regular expressions. | |
a6dd486b | 374 | |
68dc0745 | 375 | =over 4 |
376 | ||
377 | =item Passing Variables and Functions | |
378 | ||
a6dd486b | 379 | Regular variables and functions are quite easy to pass: just pass in a |
68dc0745 | 380 | reference to an existing or anonymous variable or function: |
381 | ||
ac003c96 | 382 | func( \$some_scalar ); |
68dc0745 | 383 | |
ac003c96 RGS |
384 | func( \@some_array ); |
385 | func( [ 1 .. 10 ] ); | |
68dc0745 | 386 | |
ac003c96 RGS |
387 | func( \%some_hash ); |
388 | func( { this => 10, that => 20 } ); | |
68dc0745 | 389 | |
ac003c96 RGS |
390 | func( \&some_func ); |
391 | func( sub { $_[0] ** $_[1] } ); | |
68dc0745 | 392 | |
393 | =item Passing Filehandles | |
394 | ||
49d635f9 RGS |
395 | As of Perl 5.6, you can represent filehandles with scalar variables |
396 | which you treat as any other scalar. | |
397 | ||
398 | open my $fh, $filename or die "Cannot open $filename! $!"; | |
399 | func( $fh ); | |
197aec24 | 400 | |
49d635f9 RGS |
401 | sub func { |
402 | my $passed_fh = shift; | |
197aec24 | 403 | |
ac003c96 | 404 | my $line = <$passed_fh>; |
49d635f9 | 405 | } |
197aec24 | 406 | |
49d635f9 | 407 | Before Perl 5.6, you had to use the C<*FH> or C<\*FH> notations. |
a6dd486b | 408 | These are "typeglobs"--see L<perldata/"Typeglobs and Filehandles"> |
c8db1d39 TC |
409 | and especially L<perlsub/"Pass by Reference"> for more information. |
410 | ||
d92eb7b0 GS |
411 | =item Passing Regexes |
412 | ||
413 | To pass regexes around, you'll need to be using a release of Perl | |
414 | sufficiently recent as to support the C<qr//> construct, pass around | |
415 | strings and use an exception-trapping eval, or else be very, very clever. | |
68dc0745 | 416 | |
d92eb7b0 GS |
417 | Here's an example of how to pass in a string to be regex compared |
418 | using C<qr//>: | |
68dc0745 | 419 | |
ac003c96 RGS |
420 | sub compare($$) { |
421 | my ($val1, $regex) = @_; | |
422 | my $retval = $val1 =~ /$regex/; | |
d92eb7b0 | 423 | return $retval; |
ac003c96 RGS |
424 | } |
425 | $match = compare("old McDonald", qr/d.*D/i); | |
d92eb7b0 GS |
426 | |
427 | Notice how C<qr//> allows flags at the end. That pattern was compiled | |
428 | at compile time, although it was executed later. The nifty C<qr//> | |
429 | notation wasn't introduced until the 5.005 release. Before that, you | |
430 | had to approach this problem much less intuitively. For example, here | |
431 | it is again if you don't have C<qr//>: | |
432 | ||
ac003c96 RGS |
433 | sub compare($$) { |
434 | my ($val1, $regex) = @_; | |
435 | my $retval = eval { $val1 =~ /$regex/ }; | |
68dc0745 | 436 | die if $@; |
437 | return $retval; | |
ac003c96 | 438 | } |
68dc0745 | 439 | |
ac003c96 | 440 | $match = compare("old McDonald", q/($?i)d.*D/); |
68dc0745 | 441 | |
442 | Make sure you never say something like this: | |
443 | ||
ac003c96 | 444 | return eval "\$val =~ /$regex/"; # WRONG |
68dc0745 | 445 | |
d92eb7b0 | 446 | or someone can sneak shell escapes into the regex due to the double |
68dc0745 | 447 | interpolation of the eval and the double-quoted string. For example: |
448 | ||
ac003c96 | 449 | $pattern_of_evil = 'danger ${ system("rm -rf * &") } danger'; |
68dc0745 | 450 | |
ac003c96 | 451 | eval "\$string =~ /$pattern_of_evil/"; |
68dc0745 | 452 | |
453 | Those preferring to be very, very clever might see the O'Reilly book, | |
454 | I<Mastering Regular Expressions>, by Jeffrey Friedl. Page 273's | |
455 | Build_MatchMany_Function() is particularly interesting. A complete | |
456 | citation of this book is given in L<perlfaq2>. | |
457 | ||
458 | =item Passing Methods | |
459 | ||
460 | To pass an object method into a subroutine, you can do this: | |
461 | ||
ac003c96 RGS |
462 | call_a_lot(10, $some_obj, "methname") |
463 | sub call_a_lot { | |
464 | my ($count, $widget, $trick) = @_; | |
465 | for (my $i = 0; $i < $count; $i++) { | |
466 | $widget->$trick(); | |
467 | } | |
468 | } | |
68dc0745 | 469 | |
a6dd486b JB |
470 | Or, you can use a closure to bundle up the object, its |
471 | method call, and arguments: | |
68dc0745 | 472 | |
ac003c96 RGS |
473 | my $whatnot = sub { $some_obj->obfuscate(@args) }; |
474 | func($whatnot); | |
475 | sub func { | |
476 | my $code = shift; | |
477 | &$code(); | |
478 | } | |
68dc0745 | 479 | |
480 | You could also investigate the can() method in the UNIVERSAL class | |
481 | (part of the standard perl distribution). | |
482 | ||
483 | =back | |
484 | ||
485 | =head2 How do I create a static variable? | |
486 | ||
6670e5e7 | 487 | (contributed by brian d foy) |
68dc0745 | 488 | |
6670e5e7 RGS |
489 | Perl doesn't have "static" variables, which can only be accessed from |
490 | the function in which they are declared. You can get the same effect | |
491 | with lexical variables, though. | |
492 | ||
493 | You can fake a static variable by using a lexical variable which goes | |
a05e4845 | 494 | out of scope. In this example, you define the subroutine C<counter>, and |
6670e5e7 RGS |
495 | it uses the lexical variable C<$count>. Since you wrap this in a BEGIN |
496 | block, C<$count> is defined at compile-time, but also goes out of | |
497 | scope at the end of the BEGIN block. The BEGIN block also ensures that | |
498 | the subroutine and the value it uses is defined at compile-time so the | |
499 | subroutine is ready to use just like any other subroutine, and you can | |
500 | put this code in the same place as other subroutines in the program | |
501 | text (i.e. at the end of the code, typically). The subroutine | |
502 | C<counter> still has a reference to the data, and is the only way you | |
503 | can access the value (and each time you do, you increment the value). | |
504 | The data in chunk of memory defined by C<$count> is private to | |
505 | C<counter>. | |
506 | ||
ac003c96 RGS |
507 | BEGIN { |
508 | my $count = 1; | |
509 | sub counter { $count++ } | |
510 | } | |
511 | ||
512 | my $start = counter(); | |
513 | ||
514 | .... # code that calls counter(); | |
515 | ||
516 | my $end = counter(); | |
68dc0745 | 517 | |
6670e5e7 RGS |
518 | In the previous example, you created a function-private variable |
519 | because only one function remembered its reference. You could define | |
520 | multiple functions while the variable is in scope, and each function | |
521 | can share the "private" variable. It's not really "static" because you | |
522 | can access it outside the function while the lexical variable is in | |
523 | scope, and even create references to it. In this example, | |
524 | C<increment_count> and C<return_count> share the variable. One | |
525 | function adds to the value and the other simply returns the value. | |
526 | They can both access C<$count>, and since it has gone out of scope, | |
527 | there is no other way to access it. | |
68dc0745 | 528 | |
ac003c96 RGS |
529 | BEGIN { |
530 | my $count = 1; | |
531 | sub increment_count { $count++ } | |
532 | sub return_count { $count } | |
533 | } | |
68dc0745 | 534 | |
6670e5e7 RGS |
535 | To declare a file-private variable, you still use a lexical variable. |
536 | A file is also a scope, so a lexical variable defined in the file | |
537 | cannot be seen from any other file. | |
68dc0745 | 538 | |
6670e5e7 RGS |
539 | See L<perlsub/"Persistent Private Variables"> for more information. |
540 | The discussion of closures in L<perlref> may help you even though we | |
541 | did not use anonymous subroutines in this answer. See | |
542 | L<perlsub/"Persistent Private Variables"> for details. | |
c8db1d39 | 543 | |
68dc0745 | 544 | =head2 What's the difference between dynamic and lexical (static) scoping? Between local() and my()? |
545 | ||
a6dd486b JB |
546 | C<local($x)> saves away the old value of the global variable C<$x> |
547 | and assigns a new value for the duration of the subroutine I<which is | |
68dc0745 | 548 | visible in other functions called from that subroutine>. This is done |
549 | at run-time, so is called dynamic scoping. local() always affects global | |
550 | variables, also called package variables or dynamic variables. | |
551 | ||
552 | C<my($x)> creates a new variable that is only visible in the current | |
a6dd486b | 553 | subroutine. This is done at compile-time, so it is called lexical or |
68dc0745 | 554 | static scoping. my() always affects private variables, also called |
555 | lexical variables or (improperly) static(ly scoped) variables. | |
556 | ||
557 | For instance: | |
558 | ||
ac003c96 RGS |
559 | sub visible { |
560 | print "var has value $var\n"; | |
561 | } | |
562 | ||
563 | sub dynamic { | |
564 | local $var = 'local'; # new temporary value for the still-global | |
565 | visible(); # variable called $var | |
566 | } | |
567 | ||
568 | sub lexical { | |
569 | my $var = 'private'; # new private variable, $var | |
570 | visible(); # (invisible outside of sub scope) | |
571 | } | |
572 | ||
573 | $var = 'global'; | |
574 | ||
575 | visible(); # prints global | |
576 | dynamic(); # prints local | |
577 | lexical(); # prints global | |
68dc0745 | 578 | |
579 | Notice how at no point does the value "private" get printed. That's | |
580 | because $var only has that value within the block of the lexical() | |
581 | function, and it is hidden from called subroutine. | |
582 | ||
583 | In summary, local() doesn't make what you think of as private, local | |
584 | variables. It gives a global variable a temporary value. my() is | |
585 | what you're looking for if you want private variables. | |
586 | ||
197aec24 | 587 | See L<perlsub/"Private Variables via my()"> and |
13a2d996 | 588 | L<perlsub/"Temporary Values via local()"> for excruciating details. |
68dc0745 | 589 | |
590 | =head2 How can I access a dynamic variable while a similarly named lexical is in scope? | |
591 | ||
49d635f9 RGS |
592 | If you know your package, you can just mention it explicitly, as in |
593 | $Some_Pack::var. Note that the notation $::var is B<not> the dynamic $var | |
594 | in the current package, but rather the one in the "main" package, as | |
595 | though you had written $main::var. | |
596 | ||
597 | use vars '$var'; | |
598 | local $var = "global"; | |
599 | my $var = "lexical"; | |
68dc0745 | 600 | |
49d635f9 RGS |
601 | print "lexical is $var\n"; |
602 | print "global is $main::var\n"; | |
68dc0745 | 603 | |
49d635f9 RGS |
604 | Alternatively you can use the compiler directive our() to bring a |
605 | dynamic variable into the current lexical scope. | |
68dc0745 | 606 | |
49d635f9 RGS |
607 | require 5.006; # our() did not exist before 5.6 |
608 | use vars '$var'; | |
68dc0745 | 609 | |
49d635f9 RGS |
610 | local $var = "global"; |
611 | my $var = "lexical"; | |
612 | ||
613 | print "lexical is $var\n"; | |
614 | ||
615 | { | |
ac003c96 RGS |
616 | our $var; |
617 | print "global is $var\n"; | |
49d635f9 | 618 | } |
68dc0745 | 619 | |
620 | =head2 What's the difference between deep and shallow binding? | |
621 | ||
622 | In deep binding, lexical variables mentioned in anonymous subroutines | |
623 | are the same ones that were in scope when the subroutine was created. | |
624 | In shallow binding, they are whichever variables with the same names | |
625 | happen to be in scope when the subroutine is called. Perl always uses | |
626 | deep binding of lexical variables (i.e., those created with my()). | |
627 | However, dynamic variables (aka global, local, or package variables) | |
628 | are effectively shallowly bound. Consider this just one more reason | |
629 | not to use them. See the answer to L<"What's a closure?">. | |
630 | ||
04d666b1 | 631 | =head2 Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right? |
68dc0745 | 632 | |
c8db1d39 | 633 | C<my()> and C<local()> give list context to the right hand side |
c47ff5f1 | 634 | of C<=>. The <FH> read operation, like so many of Perl's |
c8db1d39 TC |
635 | functions and operators, can tell which context it was called in and |
636 | behaves appropriately. In general, the scalar() function can help. | |
637 | This function does nothing to the data itself (contrary to popular myth) | |
638 | but rather tells its argument to behave in whatever its scalar fashion is. | |
639 | If that function doesn't have a defined scalar behavior, this of course | |
640 | doesn't help you (such as with sort()). | |
68dc0745 | 641 | |
642 | To enforce scalar context in this particular case, however, you need | |
643 | merely omit the parentheses: | |
644 | ||
ac003c96 RGS |
645 | local($foo) = <FILE>; # WRONG |
646 | local($foo) = scalar(<FILE>); # ok | |
647 | local $foo = <FILE>; # right | |
68dc0745 | 648 | |
649 | You should probably be using lexical variables anyway, although the | |
650 | issue is the same here: | |
651 | ||
ac003c96 RGS |
652 | my($foo) = <FILE>; # WRONG |
653 | my $foo = <FILE>; # right | |
68dc0745 | 654 | |
54310121 | 655 | =head2 How do I redefine a builtin function, operator, or method? |
68dc0745 | 656 | |
657 | Why do you want to do that? :-) | |
658 | ||
659 | If you want to override a predefined function, such as open(), | |
660 | then you'll have to import the new definition from a different | |
4a4eefd0 | 661 | module. See L<perlsub/"Overriding Built-in Functions">. There's |
65acb1b1 | 662 | also an example in L<perltoot/"Class::Template">. |
68dc0745 | 663 | |
664 | If you want to overload a Perl operator, such as C<+> or C<**>, | |
665 | then you'll want to use the C<use overload> pragma, documented | |
666 | in L<overload>. | |
667 | ||
668 | If you're talking about obscuring method calls in parent classes, | |
669 | see L<perltoot/"Overridden Methods">. | |
670 | ||
671 | =head2 What's the difference between calling a function as &foo and foo()? | |
672 | ||
673 | When you call a function as C<&foo>, you allow that function access to | |
a6dd486b JB |
674 | your current @_ values, and you bypass prototypes. |
675 | The function doesn't get an empty @_--it gets yours! While not | |
68dc0745 | 676 | strictly speaking a bug (it's documented that way in L<perlsub>), it |
677 | would be hard to consider this a feature in most cases. | |
678 | ||
c8db1d39 | 679 | When you call your function as C<&foo()>, then you I<do> get a new @_, |
68dc0745 | 680 | but prototyping is still circumvented. |
681 | ||
682 | Normally, you want to call a function using C<foo()>. You may only | |
683 | omit the parentheses if the function is already known to the compiler | |
684 | because it already saw the definition (C<use> but not C<require>), | |
685 | or via a forward reference or C<use subs> declaration. Even in this | |
686 | case, you get a clean @_ without any of the old values leaking through | |
687 | where they don't belong. | |
688 | ||
689 | =head2 How do I create a switch or case statement? | |
690 | ||
f449fe8a RGS |
691 | If one wants to use pure Perl and to be compatible with Perl versions |
692 | prior to 5.10, the general answer is to write a construct like this: | |
c8db1d39 | 693 | |
ac003c96 RGS |
694 | for ($variable_to_test) { |
695 | if (/pat1/) { } # do something | |
696 | elsif (/pat2/) { } # do something else | |
697 | elsif (/pat3/) { } # do something else | |
698 | else { } # default | |
699 | } | |
68dc0745 | 700 | |
f449fe8a RGS |
701 | Here's a simple example of a switch based on pattern matching, |
702 | lined up in a way to make it look more like a switch statement. | |
8305e449 | 703 | We'll do a multiway conditional based on the type of reference stored |
c8db1d39 TC |
704 | in $whatchamacallit: |
705 | ||
706 | SWITCH: for (ref $whatchamacallit) { | |
68dc0745 | 707 | |
708 | /^$/ && die "not a reference"; | |
709 | ||
710 | /SCALAR/ && do { | |
711 | print_scalar($$ref); | |
712 | last SWITCH; | |
713 | }; | |
714 | ||
715 | /ARRAY/ && do { | |
716 | print_array(@$ref); | |
717 | last SWITCH; | |
718 | }; | |
719 | ||
720 | /HASH/ && do { | |
721 | print_hash(%$ref); | |
722 | last SWITCH; | |
723 | }; | |
724 | ||
725 | /CODE/ && do { | |
726 | warn "can't print function ref"; | |
727 | last SWITCH; | |
728 | }; | |
729 | ||
730 | # DEFAULT | |
731 | ||
732 | warn "User defined type skipped"; | |
733 | ||
734 | } | |
735 | ||
f449fe8a | 736 | See L<perlsyn> for other examples in this style. |
c8db1d39 TC |
737 | |
738 | Sometimes you should change the positions of the constant and the variable. | |
739 | For example, let's say you wanted to test which of many answers you were | |
740 | given, but in a case-insensitive way that also allows abbreviations. | |
741 | You can use the following technique if the strings all start with | |
a6dd486b | 742 | different characters or if you want to arrange the matches so that |
c8db1d39 TC |
743 | one takes precedence over another, as C<"SEND"> has precedence over |
744 | C<"STOP"> here: | |
745 | ||
ac003c96 RGS |
746 | chomp($answer = <>); |
747 | if ("SEND" =~ /^\Q$answer/i) { print "Action is send\n" } | |
748 | elsif ("STOP" =~ /^\Q$answer/i) { print "Action is stop\n" } | |
749 | elsif ("ABORT" =~ /^\Q$answer/i) { print "Action is abort\n" } | |
750 | elsif ("LIST" =~ /^\Q$answer/i) { print "Action is list\n" } | |
751 | elsif ("EDIT" =~ /^\Q$answer/i) { print "Action is edit\n" } | |
c8db1d39 | 752 | |
197aec24 | 753 | A totally different approach is to create a hash of function references. |
c8db1d39 | 754 | |
ac003c96 RGS |
755 | my %commands = ( |
756 | "happy" => \&joy, | |
757 | "sad", => \&sullen, | |
758 | "done" => sub { die "See ya!" }, | |
759 | "mad" => \&angry, | |
760 | ); | |
761 | ||
762 | print "How are you? "; | |
763 | chomp($string = <STDIN>); | |
764 | if ($commands{$string}) { | |
765 | $commands{$string}->(); | |
766 | } else { | |
767 | print "No such command: $string\n"; | |
768 | } | |
c8db1d39 | 769 | |
f449fe8a RGS |
770 | Note that starting from version 5.10, Perl has now a native switch |
771 | statement. See L<perlsyn>. | |
772 | ||
773 | Starting from Perl 5.8, a source filter module, C<Switch>, can also be | |
774 | used to get switch and case. Its use is now discouraged, because it's | |
775 | not fully compatible with the native switch of Perl 5.10, and because, | |
776 | as it's implemented as a source filter, it doesn't always work as intended | |
777 | when complex syntax is involved. | |
778 | ||
49d635f9 | 779 | =head2 How can I catch accesses to undefined variables, functions, or methods? |
68dc0745 | 780 | |
781 | The AUTOLOAD method, discussed in L<perlsub/"Autoloading"> and | |
782 | L<perltoot/"AUTOLOAD: Proxy Methods">, lets you capture calls to | |
783 | undefined functions and methods. | |
784 | ||
785 | When it comes to undefined variables that would trigger a warning | |
49d635f9 | 786 | under C<use warnings>, you can promote the warning to an error. |
68dc0745 | 787 | |
49d635f9 | 788 | use warnings FATAL => qw(uninitialized); |
68dc0745 | 789 | |
790 | =head2 Why can't a method included in this same file be found? | |
791 | ||
792 | Some possible reasons: your inheritance is getting confused, you've | |
793 | misspelled the method name, or the object is of the wrong type. Check | |
a6dd486b JB |
794 | out L<perltoot> for details about any of the above cases. You may |
795 | also use C<print ref($object)> to find out the class C<$object> was | |
796 | blessed into. | |
68dc0745 | 797 | |
798 | Another possible reason for problems is because you've used the | |
799 | indirect object syntax (eg, C<find Guru "Samy">) on a class name | |
800 | before Perl has seen that such a package exists. It's wisest to make | |
801 | sure your packages are all defined before you start using them, which | |
802 | will be taken care of if you use the C<use> statement instead of | |
a6dd486b | 803 | C<require>. If not, make sure to use arrow notation (eg., |
c47ff5f1 | 804 | C<< Guru->find("Samy") >>) instead. Object notation is explained in |
68dc0745 | 805 | L<perlobj>. |
806 | ||
c8db1d39 | 807 | Make sure to read about creating modules in L<perlmod> and |
ae93639c | 808 | the perils of indirect objects in L<perlobj/"Method Invocation">. |
c8db1d39 | 809 | |
68dc0745 | 810 | =head2 How can I find out my current package? |
811 | ||
812 | If you're just a random program, you can do this to find | |
813 | out what the currently compiled package is: | |
814 | ||
ac003c96 | 815 | my $packname = __PACKAGE__; |
68dc0745 | 816 | |
a6dd486b | 817 | But, if you're a method and you want to print an error message |
68dc0745 | 818 | that includes the kind of object you were called on (which is |
819 | not necessarily the same as the one in which you were compiled): | |
820 | ||
ac003c96 RGS |
821 | sub amethod { |
822 | my $self = shift; | |
823 | my $class = ref($self) || $self; | |
824 | warn "called me from a $class object"; | |
825 | } | |
68dc0745 | 826 | |
46fc3d4c | 827 | =head2 How can I comment out a large block of perl code? |
828 | ||
659cfd94 | 829 | You can use embedded POD to discard it. Enclose the blocks you want |
7678cced RGS |
830 | to comment out in POD markers. The <=begin> directive marks a section |
831 | for a specific formatter. Use the C<comment> format, which no formatter | |
832 | should claim to understand (by policy). Mark the end of the block | |
833 | with <=end>. | |
46fc3d4c | 834 | |
ac003c96 RGS |
835 | # program is here |
836 | ||
837 | =begin comment | |
838 | ||
839 | all of this stuff | |
840 | ||
841 | here will be ignored | |
842 | by everyone | |
843 | ||
7678cced | 844 | =end comment |
ac003c96 RGS |
845 | |
846 | =cut | |
847 | ||
848 | # program continues | |
46fc3d4c | 849 | |
f05bbc40 JH |
850 | The pod directives cannot go just anywhere. You must put a |
851 | pod directive where the parser is expecting a new statement, | |
852 | not just in the middle of an expression or some other | |
659cfd94 | 853 | arbitrary grammar production. |
fc36a67e | 854 | |
f05bbc40 | 855 | See L<perlpod> for more details. |
c8db1d39 | 856 | |
65acb1b1 TC |
857 | =head2 How do I clear a package? |
858 | ||
859 | Use this code, provided by Mark-Jason Dominus: | |
860 | ||
ac003c96 RGS |
861 | sub scrub_package { |
862 | no strict 'refs'; | |
863 | my $pack = shift; | |
864 | die "Shouldn't delete main package" | |
865 | if $pack eq "" || $pack eq "main"; | |
866 | my $stash = *{$pack . '::'}{HASH}; | |
867 | my $name; | |
868 | foreach $name (keys %$stash) { | |
869 | my $fullname = $pack . '::' . $name; | |
870 | # Get rid of everything with that name. | |
871 | undef $$fullname; | |
872 | undef @$fullname; | |
873 | undef %$fullname; | |
874 | undef &$fullname; | |
875 | undef *$fullname; | |
876 | } | |
65acb1b1 | 877 | } |
65acb1b1 | 878 | |
197aec24 | 879 | Or, if you're using a recent release of Perl, you can |
65acb1b1 TC |
880 | just use the Symbol::delete_package() function instead. |
881 | ||
d92eb7b0 GS |
882 | =head2 How can I use a variable as a variable name? |
883 | ||
884 | Beginners often think they want to have a variable contain the name | |
885 | of a variable. | |
886 | ||
ac003c96 RGS |
887 | $fred = 23; |
888 | $varname = "fred"; | |
889 | ++$$varname; # $fred now 24 | |
d92eb7b0 GS |
890 | |
891 | This works I<sometimes>, but it is a very bad idea for two reasons. | |
892 | ||
a6dd486b JB |
893 | The first reason is that this technique I<only works on global |
894 | variables>. That means that if $fred is a lexical variable created | |
895 | with my() in the above example, the code wouldn't work at all: you'd | |
896 | accidentally access the global and skip right over the private lexical | |
897 | altogether. Global variables are bad because they can easily collide | |
898 | accidentally and in general make for non-scalable and confusing code. | |
d92eb7b0 GS |
899 | |
900 | Symbolic references are forbidden under the C<use strict> pragma. | |
901 | They are not true references and consequently are not reference counted | |
902 | or garbage collected. | |
903 | ||
904 | The other reason why using a variable to hold the name of another | |
a6dd486b | 905 | variable is a bad idea is that the question often stems from a lack of |
d92eb7b0 GS |
906 | understanding of Perl data structures, particularly hashes. By using |
907 | symbolic references, you are just using the package's symbol-table hash | |
908 | (like C<%main::>) instead of a user-defined hash. The solution is to | |
909 | use your own hash or a real reference instead. | |
910 | ||
ac003c96 RGS |
911 | $USER_VARS{"fred"} = 23; |
912 | $varname = "fred"; | |
913 | $USER_VARS{$varname}++; # not $$varname++ | |
d92eb7b0 GS |
914 | |
915 | There we're using the %USER_VARS hash instead of symbolic references. | |
916 | Sometimes this comes up in reading strings from the user with variable | |
917 | references and wanting to expand them to the values of your perl | |
918 | program's variables. This is also a bad idea because it conflates the | |
919 | program-addressable namespace and the user-addressable one. Instead of | |
920 | reading a string and expanding it to the actual contents of your program's | |
921 | own variables: | |
922 | ||
ac003c96 RGS |
923 | $str = 'this has a $fred and $barney in it'; |
924 | $str =~ s/(\$\w+)/$1/eeg; # need double eval | |
d92eb7b0 | 925 | |
a6dd486b | 926 | it would be better to keep a hash around like %USER_VARS and have |
d92eb7b0 GS |
927 | variable references actually refer to entries in that hash: |
928 | ||
ac003c96 | 929 | $str =~ s/\$(\w+)/$USER_VARS{$1}/g; # no /e here at all |
d92eb7b0 GS |
930 | |
931 | That's faster, cleaner, and safer than the previous approach. Of course, | |
932 | you don't need to use a dollar sign. You could use your own scheme to | |
933 | make it less confusing, like bracketed percent symbols, etc. | |
934 | ||
ac003c96 RGS |
935 | $str = 'this has a %fred% and %barney% in it'; |
936 | $str =~ s/%(\w+)%/$USER_VARS{$1}/g; # no /e here at all | |
d92eb7b0 | 937 | |
a6dd486b JB |
938 | Another reason that folks sometimes think they want a variable to |
939 | contain the name of a variable is because they don't know how to build | |
940 | proper data structures using hashes. For example, let's say they | |
941 | wanted two hashes in their program: %fred and %barney, and that they | |
942 | wanted to use another scalar variable to refer to those by name. | |
d92eb7b0 | 943 | |
ac003c96 RGS |
944 | $name = "fred"; |
945 | $$name{WIFE} = "wilma"; # set %fred | |
d92eb7b0 | 946 | |
ac003c96 RGS |
947 | $name = "barney"; |
948 | $$name{WIFE} = "betty"; # set %barney | |
d92eb7b0 GS |
949 | |
950 | This is still a symbolic reference, and is still saddled with the | |
951 | problems enumerated above. It would be far better to write: | |
952 | ||
ac003c96 RGS |
953 | $folks{"fred"}{WIFE} = "wilma"; |
954 | $folks{"barney"}{WIFE} = "betty"; | |
d92eb7b0 GS |
955 | |
956 | And just use a multilevel hash to start with. | |
957 | ||
958 | The only times that you absolutely I<must> use symbolic references are | |
959 | when you really must refer to the symbol table. This may be because it's | |
960 | something that can't take a real reference to, such as a format name. | |
961 | Doing so may also be important for method calls, since these always go | |
962 | through the symbol table for resolution. | |
963 | ||
964 | In those cases, you would turn off C<strict 'refs'> temporarily so you | |
965 | can play around with the symbol table. For example: | |
966 | ||
ac003c96 RGS |
967 | @colors = qw(red blue green yellow orange purple violet); |
968 | for my $name (@colors) { | |
969 | no strict 'refs'; # renege for the block | |
970 | *$name = sub { "<FONT COLOR='$name'>@_</FONT>" }; | |
971 | } | |
d92eb7b0 GS |
972 | |
973 | All those functions (red(), blue(), green(), etc.) appear to be separate, | |
974 | but the real code in the closure actually was compiled only once. | |
975 | ||
976 | So, sometimes you might want to use symbolic references to directly | |
977 | manipulate the symbol table. This doesn't matter for formats, handles, and | |
a6dd486b JB |
978 | subroutines, because they are always global--you can't use my() on them. |
979 | For scalars, arrays, and hashes, though--and usually for subroutines-- | |
980 | you probably only want to use hard references. | |
d92eb7b0 | 981 | |
5cd0b561 RGS |
982 | =head2 What does "bad interpreter" mean? |
983 | ||
571e049f RGS |
984 | (contributed by brian d foy) |
985 | ||
5cd0b561 RGS |
986 | The "bad interpreter" message comes from the shell, not perl. The |
987 | actual message may vary depending on your platform, shell, and locale | |
988 | settings. | |
989 | ||
990 | If you see "bad interpreter - no such file or directory", the first | |
991 | line in your perl script (the "shebang" line) does not contain the | |
6670e5e7 | 992 | right path to perl (or any other program capable of running scripts). |
5cd0b561 | 993 | Sometimes this happens when you move the script from one machine to |
ac9dac7f | 994 | another and each machine has a different path to perl--/usr/bin/perl |
571e049f | 995 | versus /usr/local/bin/perl for instance. It may also indicate |
6670e5e7 RGS |
996 | that the source machine has CRLF line terminators and the |
997 | destination machine has LF only: the shell tries to find | |
571e049f | 998 | /usr/bin/perl<CR>, but can't. |
5cd0b561 RGS |
999 | |
1000 | If you see "bad interpreter: Permission denied", you need to make your | |
1001 | script executable. | |
1002 | ||
1003 | In either case, you should still be able to run the scripts with perl | |
1004 | explicitly: | |
1005 | ||
1006 | % perl script.pl | |
1007 | ||
1008 | If you get a message like "perl: command not found", perl is not in | |
1009 | your PATH, which might also mean that the location of perl is not | |
1010 | where you expect it so you need to adjust your shebang line. | |
1011 | ||
500071f4 RGS |
1012 | =head1 REVISION |
1013 | ||
c195e131 | 1014 | Revision: $Revision: 10100 $ |
500071f4 | 1015 | |
c195e131 | 1016 | Date: $Date: 2007-10-21 20:59:30 +0200 (Sun, 21 Oct 2007) $ |
500071f4 RGS |
1017 | |
1018 | See L<perlfaq> for source control details and availability. | |
1019 | ||
68dc0745 | 1020 | =head1 AUTHOR AND COPYRIGHT |
1021 | ||
ee891a00 | 1022 | Copyright (c) 1997-2007 Tom Christiansen, Nathan Torkington, and |
7678cced | 1023 | other authors as noted. All rights reserved. |
5a964f20 | 1024 | |
5a7beb56 JH |
1025 | This documentation is free; you can redistribute it and/or modify it |
1026 | under the same terms as Perl itself. | |
5a964f20 TC |
1027 | |
1028 | Irrespective of its distribution, all code examples in this file | |
1029 | are hereby placed into the public domain. You are permitted and | |
1030 | encouraged to use this code in your own programs for fun | |
1031 | or for profit as you see fit. A simple comment in the code giving | |
1032 | credit would be courteous but is not required. | |
a6dd486b | 1033 |