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1 | =head1 NAME |
2 | |
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3 | perlfaq3 - Programming Tools ($Revision: 3606 $) |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This section of the FAQ answers questions related to programmer tools |
8 | and programming support. |
9 | |
10 | =head2 How do I do (anything)? |
11 | |
12 | Have you looked at CPAN (see L<perlfaq2>)? The chances are that |
13 | someone has already written a module that can solve your problem. |
3958b146 |
14 | Have you read the appropriate manpages? Here's a brief index: |
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15 | |
5a964f20 |
16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
17 | Execution perlrun, perldebug |
18 | Functions perlfunc |
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19 | Objects perlref, perlmod, perlobj, perltie |
20 | Data Structures perlref, perllol, perldsc |
f102b883 |
21 | Modules perlmod, perlmodlib, perlsub |
d92eb7b0 |
22 | Regexes perlre, perlfunc, perlop, perllocale |
68dc0745 |
23 | Moving to perl5 perltrap, perl |
24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed |
06a5f41f |
25 | Various http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz |
26 | (not a man-page but still useful, a collection |
27 | of various essays on Perl techniques) |
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28 | |
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29 | A crude table of contents for the Perl manpage set is found in L<perltoc>. |
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30 | |
31 | =head2 How can I use Perl interactively? |
32 | |
33 | The typical approach uses the Perl debugger, described in the |
b432a672 |
34 | perldebug(1) manpage, on an "empty" program, like this: |
68dc0745 |
35 | |
36 | perl -de 42 |
37 | |
38 | Now just type in any legal Perl code, and it will be immediately |
39 | evaluated. You can also examine the symbol table, get stack |
40 | backtraces, check variable values, set breakpoints, and other |
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41 | operations typically found in symbolic debuggers. |
68dc0745 |
42 | |
43 | =head2 Is there a Perl shell? |
44 | |
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45 | The psh (Perl sh) is currently at version 1.8. The Perl Shell is a shell |
46 | that combines the interactive nature of a Unix shell with the power of |
47 | Perl. The goal is a full featured shell that behaves as expected for |
48 | normal shell activity and uses Perl syntax and functionality for |
49 | control-flow statements and other things. You can get psh at |
50 | http://sourceforge.net/projects/psh/ . |
55e174a4 |
51 | |
f3b9614f |
52 | Zoidberg is a similar project and provides a shell written in perl, |
53 | configured in perl and operated in perl. It is intended as a login shell |
54 | and development environment. It can be found at http://zoidberg.sf.net/ |
55 | or your local CPAN mirror. |
56 | |
55e174a4 |
57 | The Shell.pm module (distributed with Perl) makes Perl try commands |
a05e4845 |
58 | which aren't part of the Perl language as shell commands. perlsh from |
59 | the source distribution is simplistic and uninteresting, but may still |
60 | be what you want. |
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61 | |
49d635f9 |
62 | =head2 How do I find which modules are installed on my system? |
63 | |
a05e4845 |
64 | You can use the ExtUtils::Installed module to show all installed |
65 | distributions, although it can take awhile to do its magic. The |
66 | standard library which comes with Perl just shows up as "Perl" (although |
67 | you can get those with Module::CoreList). |
49d635f9 |
68 | |
69 | use ExtUtils::Installed; |
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70 | |
49d635f9 |
71 | my $inst = ExtUtils::Installed->new(); |
72 | my @modules = $inst->modules(); |
73 | |
74 | If you want a list of all of the Perl module filenames, you |
75 | can use File::Find::Rule. |
76 | |
77 | use File::Find::Rule; |
197aec24 |
78 | |
49d635f9 |
79 | my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC ); |
80 | |
81 | If you do not have that module, you can do the same thing |
197aec24 |
82 | with File::Find which is part of the standard library. |
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83 | |
84 | use File::Find; |
85 | my @files; |
86 | |
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87 | find( |
58103a2e |
88 | sub { |
89 | push @files, $File::Find::name |
90 | if -f $File::Find::name && /\.pm$/ |
a05e4845 |
91 | }, |
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92 | |
54bd407c |
93 | @INC |
a05e4845 |
94 | ); |
49d635f9 |
95 | |
a05e4845 |
96 | print join "\n", @files; |
197aec24 |
97 | |
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98 | If you simply need to quickly check to see if a module is |
99 | available, you can check for its documentation. If you can |
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100 | read the documentation the module is most likely installed. |
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101 | If you cannot read the documentation, the module might not |
102 | have any (in rare cases). |
103 | |
104 | prompt% perldoc Module::Name |
105 | |
106 | You can also try to include the module in a one-liner to see if |
107 | perl finds it. |
108 | |
109 | perl -MModule::Name -e1 |
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110 | |
68dc0745 |
111 | =head2 How do I debug my Perl programs? |
112 | |
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113 | (contributed by brian d foy) |
114 | |
115 | Before you do anything else, you can help yourself by ensuring that |
116 | you let Perl tell you about problem areas in your code. By turning |
117 | on warnings and strictures, you can head off many problems before |
118 | they get too big. You can find out more about these in L<strict> |
119 | and L<warnings>. |
120 | |
121 | #!/usr/bin/perl |
122 | use strict; |
123 | use warnings; |
124 | |
125 | Beyond that, the simplest debugger is the C<print> function. Use it |
126 | to look at values as you run your program: |
127 | |
128 | print STDERR "The value is [$value]\n"; |
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129 | |
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130 | The C<Data::Dumper> module can pretty-print Perl data structures: |
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131 | |
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132 | use Data::Dumper( Dump ); |
133 | print STDERR "The hash is " . Dump( \%hash ) . "\n"; |
134 | |
135 | Perl comes with an interactive debugger, which you can start with the |
136 | C<-d> switch. It's fully explained in L<perldebug>. |
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137 | |
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138 | If you'd like a graphical user interface and you have Tk, you can use |
139 | C<ptkdb>. It's on CPAN and available for free. |
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140 | |
500071f4 |
141 | If you need something much more sophisicated and controllable, Leon |
142 | Brocard's Devel::ebug (which you can call with the -D switch as -Debug) |
143 | gives you the programmatic hooks into everything you need to write your |
144 | own (without too much pain and suffering). |
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145 | |
500071f4 |
146 | You can also use a commercial debugger such as Affrus (Mac OS X), Komodo |
147 | from Activestate (Windows and Mac OS X), or EPIC (most platforms). |
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148 | |
149 | =head2 How do I profile my Perl programs? |
150 | |
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151 | You should get the Devel::DProf module from the standard distribution |
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152 | (or separately on CPAN) and also use Benchmark.pm from the standard |
153 | distribution. The Benchmark module lets you time specific portions of |
154 | your code, while Devel::DProf gives detailed breakdowns of where your |
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155 | code spends its time. |
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156 | |
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157 | Here's a sample use of Benchmark: |
158 | |
159 | use Benchmark; |
160 | |
161 | @junk = `cat /etc/motd`; |
162 | $count = 10_000; |
163 | |
164 | timethese($count, { |
165 | 'map' => sub { my @a = @junk; |
166 | map { s/a/b/ } @a; |
6c43ef16 |
167 | return @a }, |
92c2ed05 |
168 | 'for' => sub { my @a = @junk; |
92c2ed05 |
169 | for (@a) { s/a/b/ }; |
170 | return @a }, |
171 | }); |
172 | |
173 | This is what it prints (on one machine--your results will be dependent |
174 | on your hardware, operating system, and the load on your machine): |
175 | |
176 | Benchmark: timing 10000 iterations of for, map... |
177 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
178 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
179 | |
65acb1b1 |
180 | Be aware that a good benchmark is very hard to write. It only tests the |
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181 | data you give it and proves little about the differing complexities |
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182 | of contrasting algorithms. |
183 | |
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184 | =head2 How do I cross-reference my Perl programs? |
185 | |
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186 | The B::Xref module can be used to generate cross-reference reports |
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187 | for Perl programs. |
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188 | |
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189 | perl -MO=Xref[,OPTIONS] scriptname.plx |
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190 | |
191 | =head2 Is there a pretty-printer (formatter) for Perl? |
192 | |
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193 | Perltidy is a Perl script which indents and reformats Perl scripts |
194 | to make them easier to read by trying to follow the rules of the |
195 | L<perlstyle>. If you write Perl scripts, or spend much time reading |
196 | them, you will probably find it useful. It is available at |
197 | http://perltidy.sourceforge.net |
198 | |
199 | Of course, if you simply follow the guidelines in L<perlstyle>, |
200 | you shouldn't need to reformat. The habit of formatting your code |
201 | as you write it will help prevent bugs. Your editor can and should |
202 | help you with this. The perl-mode or newer cperl-mode for emacs |
203 | can provide remarkable amounts of help with most (but not all) |
204 | code, and even less programmable editors can provide significant |
205 | assistance. Tom Christiansen and many other VI users swear by |
206 | the following settings in vi and its clones: |
65acb1b1 |
207 | |
208 | set ai sw=4 |
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209 | map! ^O {^M}^[O^T |
65acb1b1 |
210 | |
55e174a4 |
211 | Put that in your F<.exrc> file (replacing the caret characters |
65acb1b1 |
212 | with control characters) and away you go. In insert mode, ^T is |
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213 | for indenting, ^D is for undenting, and ^O is for blockdenting-- |
55e174a4 |
214 | as it were. A more complete example, with comments, can be found at |
213329dd |
215 | http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz |
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216 | |
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217 | The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does |
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218 | lots of things related to generating nicely printed output of |
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219 | documents, as does enscript at http://people.ssh.fi/mtr/genscript/ . |
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220 | |
d92eb7b0 |
221 | =head2 Is there a ctags for Perl? |
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222 | |
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223 | (contributed by brian d foy) |
224 | |
225 | Exuberent ctags supports Perl: http://ctags.sourceforge.net/ |
bc06af74 |
226 | |
b68463f7 |
227 | You might also try pltags: http://www.mscha.com/pltags.zip |
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228 | |
229 | =head2 Is there an IDE or Windows Perl Editor? |
230 | |
6641ed39 |
231 | Perl programs are just plain text, so any editor will do. |
232 | |
6641ed39 |
233 | If you're on Unix, you already have an IDE--Unix itself. The UNIX |
234 | philosophy is the philosophy of several small tools that each do one |
235 | thing and do it well. It's like a carpenter's toolbox. |
236 | |
28b41a80 |
237 | If you want an IDE, check the following (in alphabetical order, not |
238 | order of preference): |
68fbfbd7 |
239 | |
240 | =over 4 |
241 | |
28b41a80 |
242 | =item Eclipse |
243 | |
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244 | http://e-p-i-c.sf.net/ |
245 | |
6670e5e7 |
246 | The Eclipse Perl Integration Project integrates Perl |
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247 | editing/debugging with Eclipse. |
248 | |
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249 | =item Enginsite |
250 | |
251 | http://www.enginsite.com/ |
252 | |
253 | Perl Editor by EngInSite is a complete integrated development |
254 | environment (IDE) for creating, testing, and debugging Perl scripts; |
255 | the tool runs on Windows 9x/NT/2000/XP or later. |
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256 | |
68fbfbd7 |
257 | =item Komodo |
258 | |
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259 | http://www.ActiveState.com/Products/Komodo/ |
260 | |
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261 | ActiveState's cross-platform (as of October 2004, that's Windows, Linux, |
262 | and Solaris), multi-language IDE has Perl support, including a regular expression |
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263 | debugger and remote debugging. |
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264 | |
ac1094a1 |
265 | =item Open Perl IDE |
266 | |
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267 | http://open-perl-ide.sourceforge.net/ |
268 | |
ac1094a1 |
269 | Open Perl IDE is an integrated development environment for writing |
270 | and debugging Perl scripts with ActiveState's ActivePerl distribution |
271 | under Windows 95/98/NT/2000. |
272 | |
28b41a80 |
273 | =item OptiPerl |
274 | |
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275 | http://www.optiperl.com/ |
276 | |
277 | OptiPerl is a Windows IDE with simulated CGI environment, including |
278 | debugger and syntax highlighting editor. |
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279 | |
5ca69f12 |
280 | =item PerlBuilder |
281 | |
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282 | http://www.solutionsoft.com/perl.htm |
283 | |
284 | PerlBuidler is an integrated development environment for Windows that |
285 | supports Perl development. |
8782d048 |
286 | |
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287 | =item visiPerl+ |
288 | |
b68463f7 |
289 | http://helpconsulting.net/visiperl/ |
290 | |
ac1094a1 |
291 | From Help Consulting, for Windows. |
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292 | |
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293 | =item Visual Perl |
294 | |
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295 | http://www.activestate.com/Products/Visual_Perl/ |
296 | |
28b41a80 |
297 | Visual Perl is a Visual Studio.NET plug-in from ActiveState. |
29b1171f |
298 | |
b68463f7 |
299 | =item Zeus |
300 | |
301 | http://www.zeusedit.com/lookmain.html |
302 | |
303 | Zeus for Window is another Win32 multi-language editor/IDE |
304 | that comes with support for Perl: |
29b1171f |
305 | |
68fbfbd7 |
306 | =back |
307 | |
b68463f7 |
308 | For editors: if you're on Unix you probably have vi or a vi clone |
309 | already, and possibly an emacs too, so you may not need to download |
310 | anything. In any emacs the cperl-mode (M-x cperl-mode) gives you |
311 | perhaps the best available Perl editing mode in any editor. |
312 | |
313 | If you are using Windows, you can use any editor that lets you work |
314 | with plain text, such as NotePad or WordPad. Word processors, such as |
315 | Microsoft Word or WordPerfect, typically do not work since they insert |
316 | all sorts of behind-the-scenes information, although some allow you to |
317 | save files as "Text Only". You can also download text editors designed |
318 | specifically for programming, such as Textpad ( |
319 | http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ), |
320 | among others. |
321 | |
322 | If you are using MacOS, the same concerns apply. MacPerl (for Classic |
323 | environments) comes with a simple editor. Popular external editors are |
324 | BBEdit ( http://www.bbedit.com/ ) or Alpha ( |
325 | http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use |
326 | Unix editors as well. Neil Bowers (the man behind Geekcruises) has a |
327 | list of Mac editors that can handle Perl ( |
328 | http://www.neilbowers.org/macperleditors.html ). |
68fbfbd7 |
329 | |
330 | =over 4 |
331 | |
332 | =item GNU Emacs |
333 | |
334 | http://www.gnu.org/software/emacs/windows/ntemacs.html |
335 | |
336 | =item MicroEMACS |
337 | |
49d635f9 |
338 | http://www.microemacs.de/ |
68fbfbd7 |
339 | |
340 | =item XEmacs |
341 | |
342 | http://www.xemacs.org/Download/index.html |
343 | |
49d635f9 |
344 | =item Jed |
345 | |
346 | http://space.mit.edu/~davis/jed/ |
347 | |
68fbfbd7 |
348 | =back |
349 | |
350 | or a vi clone such as |
351 | |
352 | =over 4 |
353 | |
354 | =item Elvis |
355 | |
356 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ |
357 | |
358 | =item Vile |
359 | |
49d635f9 |
360 | http://dickey.his.com/vile/vile.html |
68fbfbd7 |
361 | |
362 | =item Vim |
363 | |
364 | http://www.vim.org/ |
365 | |
68fbfbd7 |
366 | =back |
367 | |
5a13f98a |
368 | For vi lovers in general, Windows or elsewhere: |
f05bbc40 |
369 | |
370 | http://www.thomer.com/thomer/vi/vi.html |
6641ed39 |
371 | |
f224927c |
372 | nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is |
5a13f98a |
373 | yet another vi clone, unfortunately not available for Windows, but in |
6641ed39 |
374 | UNIX platforms you might be interested in trying it out, firstly because |
375 | strictly speaking it is not a vi clone, it is the real vi, or the new |
376 | incarnation of it, and secondly because you can embed Perl inside it |
377 | to use Perl as the scripting language. nvi is not alone in this, |
7c82de66 |
378 | though: at least also vim and vile offer an embedded Perl. |
614a1598 |
379 | |
68fbfbd7 |
380 | The following are Win32 multilanguage editor/IDESs that support Perl: |
381 | |
382 | =over 4 |
383 | |
384 | =item Codewright |
385 | |
c98c5709 |
386 | http://www.borland.com/codewright/ |
68fbfbd7 |
387 | |
388 | =item MultiEdit |
389 | |
390 | http://www.MultiEdit.com/ |
391 | |
392 | =item SlickEdit |
393 | |
394 | http://www.slickedit.com/ |
395 | |
396 | =back |
8782d048 |
397 | |
6641ed39 |
398 | There is also a toyedit Text widget based editor written in Perl |
399 | that is distributed with the Tk module on CPAN. The ptkdb |
f224927c |
400 | ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that |
8782d048 |
401 | acts as a development environment of sorts. Perl Composer |
49d635f9 |
402 | ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk |
e083a89c |
403 | GUI creation. |
404 | |
8782d048 |
405 | In addition to an editor/IDE you might be interested in a more |
68fbfbd7 |
406 | powerful shell environment for Win32. Your options include |
407 | |
408 | =over 4 |
409 | |
410 | =item Bash |
411 | |
1577cd80 |
412 | from the Cygwin package ( http://sources.redhat.com/cygwin/ ) |
68fbfbd7 |
413 | |
414 | =item Ksh |
415 | |
f224927c |
416 | from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of |
1577cd80 |
417 | the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ ) |
68fbfbd7 |
418 | |
419 | =item Tcsh |
420 | |
f224927c |
421 | ftp://ftp.astron.com/pub/tcsh/ , see also |
68fbfbd7 |
422 | http://www.primate.wisc.edu/software/csh-tcsh-book/ |
423 | |
424 | =item Zsh |
425 | |
f224927c |
426 | ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/ |
68fbfbd7 |
427 | |
428 | =back |
429 | |
614a1598 |
430 | MKS and U/WIN are commercial (U/WIN is free for educational and |
431 | research purposes), Cygwin is covered by the GNU Public License (but |
432 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all |
433 | contain (in addition to the shells) a comprehensive set of standard |
434 | UNIX toolkit utilities. |
8782d048 |
435 | |
5a13f98a |
436 | If you're transferring text files between Unix and Windows using FTP |
437 | be sure to transfer them in ASCII mode so the ends of lines are |
438 | appropriately converted. |
439 | |
e083a89c |
440 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
441 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application |
733271b5 |
442 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
68fbfbd7 |
443 | no 32k limit). |
444 | |
445 | =over 4 |
446 | |
c98c5709 |
447 | =item Affrus |
68fbfbd7 |
448 | |
d7f8936a |
449 | is a full Perl development environment with full debugger support |
7678cced |
450 | ( http://www.latenightsw.com ). |
68fbfbd7 |
451 | |
452 | =item Alpha |
453 | |
454 | is an editor, written and extensible in Tcl, that nonetheless has |
733271b5 |
455 | built in support for several popular markup and programming languages |
c98c5709 |
456 | including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ). |
457 | |
458 | =item BBEdit and BBEdit Lite |
459 | |
460 | are text editors for Mac OS that have a Perl sensitivity mode |
461 | ( http://web.barebones.com/ ). |
462 | |
68fbfbd7 |
463 | |
464 | =back |
465 | |
466 | Pepper and Pe are programming language sensitive text editors for Mac |
1577cd80 |
467 | OS X and BeOS respectively ( http://www.hekkelman.com/ ). |
68dc0745 |
468 | |
469 | =head2 Where can I get Perl macros for vi? |
470 | |
471 | For a complete version of Tom Christiansen's vi configuration file, |
a93751fa |
472 | see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
a6dd486b |
473 | the standard benchmark file for vi emulators. The file runs best with nvi, |
5a964f20 |
474 | the current version of vi out of Berkeley, which incidentally can be built |
bfeeaf1b |
475 | with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ . |
68dc0745 |
476 | |
477 | =head2 Where can I get perl-mode for emacs? |
478 | |
479 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
87275199 |
480 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 |
481 | come with the standard Emacs 19 distribution. |
482 | |
87275199 |
483 | In the Perl source directory, you'll find a directory called "emacs", |
68dc0745 |
484 | which contains a cperl-mode that color-codes keywords, provides |
485 | context-sensitive help, and other nifty things. |
486 | |
92c2ed05 |
487 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 |
488 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 |
489 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 |
490 | shouldn't be an issue. |
68dc0745 |
491 | |
492 | =head2 How can I use curses with Perl? |
493 | |
494 | The Curses module from CPAN provides a dynamically loadable object |
5a964f20 |
495 | module interface to a curses library. A small demo can be found at the |
49d635f9 |
496 | directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ; |
5a964f20 |
497 | this program repeats a command and updates the screen as needed, rendering |
498 | B<rep ps axu> similar to B<top>. |
68dc0745 |
499 | |
500 | =head2 How can I use X or Tk with Perl? |
501 | |
5a964f20 |
502 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
503 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
504 | to the Athena Widget set. Both are available from CPAN. See the |
a93751fa |
505 | directory http://www.cpan.org/modules/by-category/08_User_Interfaces/ |
68dc0745 |
506 | |
a6dd486b |
507 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
c98c5709 |
508 | http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference |
92c2ed05 |
509 | Guide available at |
213329dd |
510 | http://www.cpan.org/authors/Stephen_O_Lidie/ , and the |
92c2ed05 |
511 | online manpages at |
87275199 |
512 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 |
513 | |
68dc0745 |
514 | =head2 How can I make my Perl program run faster? |
515 | |
92c2ed05 |
516 | The best way to do this is to come up with a better algorithm. This |
b73a15ae |
517 | can often make a dramatic difference. Jon Bentley's book |
5cd0b561 |
518 | I<Programming Pearls> (that's not a misspelling!) has some good tips |
92c2ed05 |
519 | on optimization, too. Advice on benchmarking boils down to: benchmark |
520 | and profile to make sure you're optimizing the right part, look for |
521 | better algorithms instead of microtuning your code, and when all else |
57b19278 |
522 | fails consider just buying faster hardware. You will probably want to |
b432a672 |
523 | read the answer to the earlier question "How do I profile my Perl |
524 | programs?" if you haven't done so already. |
68dc0745 |
525 | |
92c2ed05 |
526 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 |
527 | AutoSplit and AutoLoader modules in the standard distribution for |
528 | that. Or you could locate the bottleneck and think about writing just |
529 | that part in C, the way we used to take bottlenecks in C code and |
5cd0b561 |
530 | write them in assembler. Similar to rewriting in C, modules that have |
531 | critical sections can be written in C (for instance, the PDL module |
532 | from CPAN). |
533 | |
534 | If you're currently linking your perl executable to a shared |
535 | I<libc.so>, you can often gain a 10-25% performance benefit by |
536 | rebuilding it to link with a static libc.a instead. This will make a |
537 | bigger perl executable, but your Perl programs (and programmers) may |
538 | thank you for it. See the F<INSTALL> file in the source distribution |
539 | for more information. |
540 | |
541 | The undump program was an ancient attempt to speed up Perl program by |
542 | storing the already-compiled form to disk. This is no longer a viable |
543 | option, as it only worked on a few architectures, and wasn't a good |
544 | solution anyway. |
68dc0745 |
545 | |
546 | =head2 How can I make my Perl program take less memory? |
547 | |
548 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
549 | throw memory at a problem. Scalars in Perl use more memory than |
65acb1b1 |
550 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 |
551 | there's still a lot to be done, recent releases have been addressing |
552 | these issues. For example, as of 5.004, duplicate hash keys are |
553 | shared amongst all hashes using them, so require no reallocation. |
554 | |
555 | In some cases, using substr() or vec() to simulate arrays can be |
556 | highly beneficial. For example, an array of a thousand booleans will |
557 | take at least 20,000 bytes of space, but it can be turned into one |
a6dd486b |
558 | 125-byte bit vector--a considerable memory savings. The standard |
68dc0745 |
559 | Tie::SubstrHash module can also help for certain types of data |
560 | structure. If you're working with specialist data structures |
561 | (matrices, for instance) modules that implement these in C may use |
562 | less memory than equivalent Perl modules. |
563 | |
564 | Another thing to try is learning whether your Perl was compiled with |
54310121 |
565 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 |
566 | is, try using the other one and see whether this makes a difference. |
567 | Information about malloc is in the F<INSTALL> file in the source |
568 | distribution. You can find out whether you are using perl's malloc by |
569 | typing C<perl -V:usemymalloc>. |
570 | |
24f1ba9b |
571 | Of course, the best way to save memory is to not do anything to waste |
572 | it in the first place. Good programming practices can go a long way |
573 | toward this: |
574 | |
575 | =over 4 |
576 | |
577 | =item * Don't slurp! |
578 | |
579 | Don't read an entire file into memory if you can process it line |
580 | by line. Or more concretely, use a loop like this: |
581 | |
582 | # |
583 | # Good Idea |
584 | # |
585 | while (<FILE>) { |
586 | # ... |
587 | } |
588 | |
589 | instead of this: |
590 | |
591 | # |
592 | # Bad Idea |
593 | # |
594 | @data = <FILE>; |
595 | foreach (@data) { |
596 | # ... |
597 | } |
598 | |
599 | When the files you're processing are small, it doesn't much matter which |
600 | way you do it, but it makes a huge difference when they start getting |
197aec24 |
601 | larger. |
24f1ba9b |
602 | |
bc06af74 |
603 | =item * Use map and grep selectively |
604 | |
605 | Remember that both map and grep expect a LIST argument, so doing this: |
606 | |
607 | @wanted = grep {/pattern/} <FILE>; |
608 | |
609 | will cause the entire file to be slurped. For large files, it's better |
610 | to loop: |
611 | |
612 | while (<FILE>) { |
613 | push(@wanted, $_) if /pattern/; |
614 | } |
615 | |
616 | =item * Avoid unnecessary quotes and stringification |
617 | |
618 | Don't quote large strings unless absolutely necessary: |
619 | |
620 | my $copy = "$large_string"; |
621 | |
622 | makes 2 copies of $large_string (one for $copy and another for the |
623 | quotes), whereas |
624 | |
625 | my $copy = $large_string; |
626 | |
627 | only makes one copy. |
628 | |
629 | Ditto for stringifying large arrays: |
630 | |
631 | { |
632 | local $, = "\n"; |
633 | print @big_array; |
634 | } |
635 | |
636 | is much more memory-efficient than either |
637 | |
638 | print join "\n", @big_array; |
639 | |
640 | or |
641 | |
642 | { |
643 | local $" = "\n"; |
644 | print "@big_array"; |
645 | } |
646 | |
647 | |
24f1ba9b |
648 | =item * Pass by reference |
649 | |
650 | Pass arrays and hashes by reference, not by value. For one thing, it's |
651 | the only way to pass multiple lists or hashes (or both) in a single |
652 | call/return. It also avoids creating a copy of all the contents. This |
653 | requires some judgment, however, because any changes will be propagated |
654 | back to the original data. If you really want to mangle (er, modify) a |
655 | copy, you'll have to sacrifice the memory needed to make one. |
656 | |
657 | =item * Tie large variables to disk. |
658 | |
659 | For "big" data stores (i.e. ones that exceed available memory) consider |
660 | using one of the DB modules to store it on disk instead of in RAM. This |
ed8cf1fe |
661 | will incur a penalty in access time, but that's probably better than |
24f1ba9b |
662 | causing your hard disk to thrash due to massive swapping. |
663 | |
664 | =back |
665 | |
49d635f9 |
666 | =head2 Is it safe to return a reference to local or lexical data? |
68dc0745 |
667 | |
49d635f9 |
668 | Yes. Perl's garbage collection system takes care of this so |
669 | everything works out right. |
68dc0745 |
670 | |
671 | sub makeone { |
672 | my @a = ( 1 .. 10 ); |
673 | return \@a; |
674 | } |
675 | |
197aec24 |
676 | for ( 1 .. 10 ) { |
68dc0745 |
677 | push @many, makeone(); |
678 | } |
679 | |
680 | print $many[4][5], "\n"; |
681 | |
682 | print "@many\n"; |
683 | |
684 | =head2 How can I free an array or hash so my program shrinks? |
685 | |
7678cced |
686 | (contributed by Michael Carman) |
687 | |
688 | You usually can't. Memory allocated to lexicals (i.e. my() variables) |
689 | cannot be reclaimed or reused even if they go out of scope. It is |
690 | reserved in case the variables come back into scope. Memory allocated |
691 | to global variables can be reused (within your program) by using |
692 | undef()ing and/or delete(). |
693 | |
694 | On most operating systems, memory allocated to a program can never be |
695 | returned to the system. That's why long-running programs sometimes re- |
696 | exec themselves. Some operating systems (notably, systems that use |
697 | mmap(2) for allocating large chunks of memory) can reclaim memory that |
698 | is no longer used, but on such systems, perl must be configured and |
699 | compiled to use the OS's malloc, not perl's. |
700 | |
46fc3d4c |
701 | In general, memory allocation and de-allocation isn't something you can |
7678cced |
702 | or should be worrying about much in Perl. |
703 | |
704 | See also "How can I make my Perl program take less memory?" |
68dc0745 |
705 | |
706 | =head2 How can I make my CGI script more efficient? |
707 | |
708 | Beyond the normal measures described to make general Perl programs |
709 | faster or smaller, a CGI program has additional issues. It may be run |
710 | several times per second. Given that each time it runs it will need |
46fc3d4c |
711 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 |
712 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c |
713 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 |
714 | |
92c2ed05 |
715 | There are two popular ways to avoid this overhead. One solution |
716 | involves running the Apache HTTP server (available from |
f224927c |
717 | http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi |
92c2ed05 |
718 | plugin modules. |
719 | |
720 | With mod_perl and the Apache::Registry module (distributed with |
721 | mod_perl), httpd will run with an embedded Perl interpreter which |
722 | pre-compiles your script and then executes it within the same address |
723 | space without forking. The Apache extension also gives Perl access to |
724 | the internal server API, so modules written in Perl can do just about |
725 | anything a module written in C can. For more on mod_perl, see |
726 | http://perl.apache.org/ |
727 | |
65acb1b1 |
728 | With the FCGI module (from CPAN) and the mod_fastcgi |
bfeeaf1b |
729 | module (available from http://www.fastcgi.com/ ) each of your Perl |
87275199 |
730 | programs becomes a permanent CGI daemon process. |
68dc0745 |
731 | |
732 | Both of these solutions can have far-reaching effects on your system |
87275199 |
733 | and on the way you write your CGI programs, so investigate them with |
68dc0745 |
734 | care. |
735 | |
a93751fa |
736 | See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 |
737 | |
68dc0745 |
738 | =head2 How can I hide the source for my Perl program? |
739 | |
740 | Delete it. :-) Seriously, there are a number of (mostly |
b432a672 |
741 | unsatisfactory) solutions with varying levels of "security". |
68dc0745 |
742 | |
743 | First of all, however, you I<can't> take away read permission, because |
744 | the source code has to be readable in order to be compiled and |
745 | interpreted. (That doesn't mean that a CGI script's source is |
a6dd486b |
746 | readable by people on the web, though--only by people with access to |
747 | the filesystem.) So you have to leave the permissions at the socially |
92c2ed05 |
748 | friendly 0755 level. |
68dc0745 |
749 | |
750 | Some people regard this as a security problem. If your program does |
a6dd486b |
751 | insecure things and relies on people not knowing how to exploit those |
68dc0745 |
752 | insecurities, it is not secure. It is often possible for someone to |
753 | determine the insecure things and exploit them without viewing the |
754 | source. Security through obscurity, the name for hiding your bugs |
755 | instead of fixing them, is little security indeed. |
756 | |
83df6a1d |
757 | You can try using encryption via source filters (Starting from Perl |
758 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in |
759 | the standard distribution), but any decent programmer will be able to |
760 | decrypt it. You can try using the byte code compiler and interpreter |
761 | described below, but the curious might still be able to de-compile it. |
762 | You can try using the native-code compiler described below, but |
763 | crackers might be able to disassemble it. These pose varying degrees |
764 | of difficulty to people wanting to get at your code, but none can |
765 | definitively conceal it (true of every language, not just Perl). |
68dc0745 |
766 | |
49d635f9 |
767 | It is very easy to recover the source of Perl programs. You simply |
768 | feed the program to the perl interpreter and use the modules in |
769 | the B:: hierarchy. The B::Deparse module should be able to |
770 | defeat most attempts to hide source. Again, this is not |
771 | unique to Perl. |
772 | |
68dc0745 |
773 | If you're concerned about people profiting from your code, then the |
d92eb7b0 |
774 | bottom line is that nothing but a restrictive license will give you |
68dc0745 |
775 | legal security. License your software and pepper it with threatening |
b432a672 |
776 | statements like "This is unpublished proprietary software of XYZ Corp. |
68dc0745 |
777 | Your access to it does not give you permission to use it blah blah |
b432a672 |
778 | blah." We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 |
779 | you want to be sure your license's wording will stand up in court. |
68dc0745 |
780 | |
54310121 |
781 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 |
782 | |
7678cced |
783 | (contributed by brian d foy) |
784 | |
785 | In general, you can't do this. There are some things that may work |
786 | for your situation though. People usually ask this question |
6670e5e7 |
787 | because they want to distribute their works without giving away |
7678cced |
788 | the source code, and most solutions trade disk space for convenience. |
789 | You probably won't see much of a speed increase either, since most |
6670e5e7 |
790 | solutions simply bundle a Perl interpreter in the final product |
7678cced |
791 | (but see L<How can I make my Perl program run faster?>). |
792 | |
9e72e4c6 |
793 | The Perl Archive Toolkit ( http://par.perl.org/index.cgi ) is Perl's |
794 | analog to Java's JAR. It's freely available and on CPAN ( |
795 | http://search.cpan.org/dist/PAR/ ). |
7678cced |
796 | |
9e72e4c6 |
797 | The B::* namespace, often called "the Perl compiler", but is really a way |
798 | for Perl programs to peek at its innards rather than create pre-compiled |
799 | versions of your program. However. the B::Bytecode module can turn your |
800 | script into a bytecode format that could be loaded later by the |
801 | ByteLoader module and executed as a regular Perl script. |
7678cced |
802 | |
9e72e4c6 |
803 | There are also some commercial products that may work for you, although |
804 | you have to buy a license for them. |
7678cced |
805 | |
9e72e4c6 |
806 | The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ ) |
807 | from ActiveState can "Turn your Perl programs into ready-to-run |
7678cced |
808 | executables for HP-UX, Linux, Solaris and Windows." |
809 | |
9e72e4c6 |
810 | Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line |
811 | program for converting perl scripts to executable files. It targets both |
812 | Windows and unix platforms. |
5a964f20 |
813 | |
65acb1b1 |
814 | =head2 How can I compile Perl into Java? |
815 | |
a6dd486b |
816 | You can also integrate Java and Perl with the |
c98c5709 |
817 | Perl Resource Kit from O'Reilly Media. See |
a6dd486b |
818 | http://www.oreilly.com/catalog/prkunix/ . |
819 | |
820 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in |
821 | development, allows Perl code to be called from Java. See jpl/README |
822 | in the Perl source tree. |
65acb1b1 |
823 | |
92c2ed05 |
824 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 |
825 | |
826 | For OS/2 just use |
827 | |
828 | extproc perl -S -your_switches |
829 | |
830 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
b432a672 |
831 | "extproc" handling). For DOS one should first invent a corresponding |
fd1adc71 |
832 | batch file and codify it in C<ALTERNATE_SHEBANG> (see the |
833 | F<dosish.h> file in the source distribution for more information). |
68dc0745 |
834 | |
92c2ed05 |
835 | The Win95/NT installation, when using the ActiveState port of Perl, |
836 | will modify the Registry to associate the C<.pl> extension with the |
d92eb7b0 |
837 | perl interpreter. If you install another port, perhaps even building |
838 | your own Win95/NT Perl from the standard sources by using a Windows port |
d702ae42 |
839 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 |
840 | the Registry yourself. In addition to associating C<.pl> with the |
841 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them |
842 | run the program C<install-linux.pl> merely by typing C<install-linux>. |
68dc0745 |
843 | |
8e30f651 |
844 | Under "Classic" MacOS, a perl program will have the appropriate Creator and |
845 | Type, so that double-clicking them will invoke the MacPerl application. |
846 | Under Mac OS X, clickable apps can be made from any C<#!> script using Wil |
847 | Sanchez' DropScript utility: http://www.wsanchez.net/software/ . |
68dc0745 |
848 | |
849 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
850 | throw the perl interpreter into your cgi-bin directory, in order to |
87275199 |
851 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 |
852 | security risk. Take the time to figure out how to do it correctly. |
853 | |
87275199 |
854 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 |
855 | |
856 | Yes. Read L<perlrun> for more information. Some examples follow. |
857 | (These assume standard Unix shell quoting rules.) |
858 | |
859 | # sum first and last fields |
5a964f20 |
860 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 |
861 | |
862 | # identify text files |
863 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
864 | |
5a964f20 |
865 | # remove (most) comments from C program |
68dc0745 |
866 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
867 | |
868 | # make file a month younger than today, defeating reaper daemons |
869 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
870 | |
871 | # find first unused uid |
872 | perl -le '$i++ while getpwuid($i); print $i' |
873 | |
874 | # display reasonable manpath |
875 | echo $PATH | perl -nl -072 -e ' |
876 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
877 | |
87275199 |
878 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 |
879 | |
87275199 |
880 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 |
881 | |
882 | The problem is usually that the command interpreters on those systems |
883 | have rather different ideas about quoting than the Unix shells under |
884 | which the one-liners were created. On some systems, you may have to |
885 | change single-quotes to double ones, which you must I<NOT> do on Unix |
886 | or Plan9 systems. You might also have to change a single % to a %%. |
887 | |
888 | For example: |
889 | |
890 | # Unix |
891 | perl -e 'print "Hello world\n"' |
892 | |
46fc3d4c |
893 | # DOS, etc. |
68dc0745 |
894 | perl -e "print \"Hello world\n\"" |
895 | |
46fc3d4c |
896 | # Mac |
68dc0745 |
897 | print "Hello world\n" |
898 | (then Run "Myscript" or Shift-Command-R) |
899 | |
d2321c93 |
900 | # MPW |
901 | perl -e 'print "Hello world\n"' |
902 | |
68dc0745 |
903 | # VMS |
904 | perl -e "print ""Hello world\n""" |
905 | |
a6dd486b |
906 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 |
907 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b |
908 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 |
909 | you'd probably have better luck like this: |
68dc0745 |
910 | |
911 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
912 | |
46fc3d4c |
913 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 |
914 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c |
915 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 |
916 | characters as control characters. |
917 | |
65acb1b1 |
918 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
919 | quotes', and `backticks`, may make one-liners easier to write. |
920 | |
d2321c93 |
921 | There is no general solution to all of this. It is a mess. |
68dc0745 |
922 | |
923 | [Some of this answer was contributed by Kenneth Albanowski.] |
924 | |
925 | =head2 Where can I learn about CGI or Web programming in Perl? |
926 | |
927 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
928 | see the two especially dedicated to web stuff in the question on |
b432a672 |
929 | books. For problems and questions related to the web, like "Why |
930 | do I get 500 Errors" or "Why doesn't it run from the browser right |
931 | when it runs fine on the command line", see the troubleshooting |
8305e449 |
932 | guides and references in L<perlfaq9> or in the CGI MetaFAQ: |
68dc0745 |
933 | |
8305e449 |
934 | http://www.perl.org/CGI_MetaFAQ.html |
0f542199 |
935 | |
68dc0745 |
936 | =head2 Where can I learn about object-oriented Perl programming? |
937 | |
a6dd486b |
938 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
06a5f41f |
939 | L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference. |
06a5f41f |
940 | |
941 | A good book on OO on Perl is the "Object-Oriented Perl" |
9e72e4c6 |
942 | by Damian Conway from Manning Publications, or "Learning Perl |
943 | References, Objects, & Modules" by Randal Schwartz and Tom |
944 | Phoenix from O'Reilly Media. |
68dc0745 |
945 | |
b68463f7 |
946 | =head2 Where can I learn about linking C with Perl? |
68dc0745 |
947 | |
948 | If you want to call C from Perl, start with L<perlxstut>, |
949 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
950 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
951 | L<perlguts>. Don't forget that you can learn a lot from looking at |
952 | how the authors of existing extension modules wrote their code and |
953 | solved their problems. |
954 | |
b68463f7 |
955 | You might not need all the power of XS. The Inline::C module lets |
956 | you put C code directly in your Perl source. It handles all the |
58103a2e |
957 | magic to make it work. You still have to learn at least some of |
b68463f7 |
958 | the perl API but you won't have to deal with the complexity of the |
959 | XS support files. |
960 | |
7678cced |
961 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong? |
68dc0745 |
962 | |
963 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
964 | the tests pass, read the pods again and again and again. If they |
87275199 |
965 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 |
966 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
967 | |
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968 | =head2 When I tried to run my script, I got this message. What does it mean? |
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969 | |
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970 | A complete list of Perl's error messages and warnings with explanatory |
971 | text can be found in L<perldiag>. You can also use the splain program |
972 | (distributed with Perl) to explain the error messages: |
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973 | |
974 | perl program 2>diag.out |
975 | splain [-v] [-p] diag.out |
976 | |
977 | or change your program to explain the messages for you: |
978 | |
979 | use diagnostics; |
980 | |
981 | or |
982 | |
983 | use diagnostics -verbose; |
984 | |
985 | =head2 What's MakeMaker? |
986 | |
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987 | This module (part of the standard Perl distribution) is designed to |
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988 | write a Makefile for an extension module from a Makefile.PL. For more |
989 | information, see L<ExtUtils::MakeMaker>. |
990 | |
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991 | =head1 REVISION |
992 | |
993 | Revision: $Revision: 3606 $ |
994 | |
995 | Date: $Date: 2006-03-06 12:05:47 +0100 (lun, 06 mar 2006) $ |
996 | |
997 | See L<perlfaq> for source control details and availability. |
998 | |
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999 | =head1 AUTHOR AND COPYRIGHT |
1000 | |
58103a2e |
1001 | Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and |
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1002 | other authors as noted. All rights reserved. |
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1003 | |
5a7beb56 |
1004 | This documentation is free; you can redistribute it and/or modify it |
1005 | under the same terms as Perl itself. |
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1006 | |
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1007 | Irrespective of its distribution, all code examples here are in the public |
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1008 | domain. You are permitted and encouraged to use this code and any |
1009 | derivatives thereof in your own programs for fun or for profit as you |
1010 | see fit. A simple comment in the code giving credit to the FAQ would |
1011 | be courteous but is not required. |