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1 | =head1 NAME |
2 | |
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3 | perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $) |
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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. |
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14 | Have you read the appropriate man pages? Here's a brief index: |
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15 | |
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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 |
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21 | Modules perlmod, perlmodlib, perlsub |
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22 | Regexes perlre, perlfunc, perlop, perllocale |
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23 | Moving to perl5 perltrap, perl |
24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed |
25 | Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html |
26 | (not a man-page but still useful) |
27 | |
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28 | A crude table of contents for the Perl man page set is found in L<perltoc>. |
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29 | |
30 | =head2 How can I use Perl interactively? |
31 | |
32 | The typical approach uses the Perl debugger, described in the |
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33 | perldebug(1) man page, on an ``empty'' program, like this: |
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34 | |
35 | perl -de 42 |
36 | |
37 | Now just type in any legal Perl code, and it will be immediately |
38 | evaluated. You can also examine the symbol table, get stack |
39 | backtraces, check variable values, set breakpoints, and other |
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40 | operations typically found in symbolic debuggers. |
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41 | |
42 | =head2 Is there a Perl shell? |
43 | |
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44 | In general, no. The Shell.pm module (distributed with Perl) makes |
45 | Perl try commands which aren't part of the Perl language as shell |
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46 | commands. perlsh from the source distribution is simplistic and |
47 | uninteresting, but may still be what you want. |
48 | |
49 | =head2 How do I debug my Perl programs? |
50 | |
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51 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
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52 | to detect dubious practices. |
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53 | |
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54 | Have you tried C<use strict>? It prevents you from using symbolic |
55 | references, makes you predeclare any subroutines that you call as bare |
56 | words, and (probably most importantly) forces you to predeclare your |
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57 | variables with C<my>, C<our>, or C<use vars>. |
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58 | |
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59 | Did you check the return values of each and every system call? The operating |
60 | system (and thus Perl) tells you whether they worked, and if not |
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61 | why. |
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62 | |
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63 | open(FH, "> /etc/cantwrite") |
64 | or die "Couldn't write to /etc/cantwrite: $!\n"; |
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65 | |
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66 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
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67 | programmers and even has sections for those of you who are upgrading |
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68 | from languages like I<awk> and I<C>. |
69 | |
70 | Have you tried the Perl debugger, described in L<perldebug>? You can |
71 | step through your program and see what it's doing and thus work out |
72 | why what it's doing isn't what it should be doing. |
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73 | |
74 | =head2 How do I profile my Perl programs? |
75 | |
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76 | You should get the Devel::DProf module from CPAN and also use |
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77 | Benchmark.pm from the standard distribution. Benchmark lets you time |
78 | specific portions of your code, while Devel::DProf gives detailed |
79 | breakdowns of where your code spends its time. |
80 | |
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81 | Here's a sample use of Benchmark: |
82 | |
83 | use Benchmark; |
84 | |
85 | @junk = `cat /etc/motd`; |
86 | $count = 10_000; |
87 | |
88 | timethese($count, { |
89 | 'map' => sub { my @a = @junk; |
90 | map { s/a/b/ } @a; |
91 | return @a |
92 | }, |
93 | 'for' => sub { my @a = @junk; |
94 | local $_; |
95 | for (@a) { s/a/b/ }; |
96 | return @a }, |
97 | }); |
98 | |
99 | This is what it prints (on one machine--your results will be dependent |
100 | on your hardware, operating system, and the load on your machine): |
101 | |
102 | Benchmark: timing 10000 iterations of for, map... |
103 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
104 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
105 | |
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106 | Be aware that a good benchmark is very hard to write. It only tests the |
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107 | data you give it and proves little about the differing complexities |
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108 | of contrasting algorithms. |
109 | |
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110 | =head2 How do I cross-reference my Perl programs? |
111 | |
112 | The B::Xref module, shipped with the new, alpha-release Perl compiler |
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113 | (not the general distribution prior to the 5.005 release), can be used |
114 | to generate cross-reference reports for Perl programs. |
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115 | |
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116 | perl -MO=Xref[,OPTIONS] scriptname.plx |
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117 | |
118 | =head2 Is there a pretty-printer (formatter) for Perl? |
119 | |
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120 | There is no program that will reformat Perl as much as indent(1) does |
121 | for C. The complex feedback between the scanner and the parser (this |
122 | feedback is what confuses the vgrind and emacs programs) makes it |
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123 | challenging at best to write a stand-alone Perl parser. |
124 | |
125 | Of course, if you simply follow the guidelines in L<perlstyle>, you |
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126 | shouldn't need to reformat. The habit of formatting your code as you |
127 | write it will help prevent bugs. Your editor can and should help you |
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128 | with this. The perl-mode or newer cperl-mode for emacs can provide |
129 | remarkable amounts of help with most (but not all) code, and even less |
130 | programmable editors can provide significant assistance. Tom swears |
131 | by the following settings in vi and its clones: |
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132 | |
133 | set ai sw=4 |
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134 | map! ^O {^M}^[O^T |
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135 | |
136 | Now put that in your F<.exrc> file (replacing the caret characters |
137 | with control characters) and away you go. In insert mode, ^T is |
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138 | for indenting, ^D is for undenting, and ^O is for blockdenting-- |
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139 | as it were. If you haven't used the last one, you're missing |
140 | a lot. A more complete example, with comments, can be found at |
141 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz |
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142 | |
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143 | If you are used to using the I<vgrind> program for printing out nice code |
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144 | to a laser printer, you can take a stab at this using |
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145 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
146 | results are not particularly satisfying for sophisticated code. |
147 | |
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148 | The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things |
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149 | related to generating nicely printed output of documents. |
150 | |
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151 | =head2 Is there a ctags for Perl? |
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152 | |
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153 | There's a simple one at |
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154 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
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155 | the trick. And if not, it's easy to hack into what you want. |
156 | |
157 | =head2 Is there an IDE or Windows Perl Editor? |
158 | |
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159 | If you're on Unix, you already have an IDE--Unix itself. This powerful |
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160 | IDE derives from its interoperability, flexibility, and configurability. |
161 | If you really want to get a feel for Unix-qua-IDE, the best thing to do |
162 | is to find some high-powered programmer whose native language is Unix. |
163 | Find someone who has been at this for many years, and just sit back |
164 | and watch them at work. They have created their own IDE, one that |
165 | suits their own tastes and aptitudes. Quietly observe them edit files, |
166 | move them around, compile them, debug them, test them, etc. The entire |
167 | development *is* integrated, like a top-of-the-line German sports car: |
168 | functional, powerful, and elegant. You will be absolutely astonished |
169 | at the speed and ease exhibited by the native speaker of Unix in his |
170 | home territory. The art and skill of a virtuoso can only be seen to be |
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171 | believed. That is the path to mastery--all these cobbled little IDEs |
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172 | are expensive toys designed to sell a flashy demo using cheap tricks, |
173 | and being optimized for immediate but shallow understanding rather than |
174 | enduring use, are but a dim palimpsest of real tools. |
175 | |
176 | In short, you just have to learn the toolbox. However, if you're not |
177 | on Unix, then your vendor probably didn't bother to provide you with |
178 | a proper toolbox on the so-called complete system that you forked out |
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179 | your hard-earned cash for. |
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180 | |
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181 | PerlBuilder (http://www.solutionsoft.com/perl.htm) is an integrated |
182 | development environment for Windows that supports Perl development. |
183 | Perl programs are just plain text, though, so you could download emacs |
184 | for Windows (http://www.gnu.org/software/emacs/windows/ntemacs.html) |
185 | or a vi clone (vim) which runs on for win32 |
186 | (http://www.cs.vu.nl/%7Etmgil/vi.html). If you're transferring |
187 | Windows files to Unix be sure to transfer them in ASCII mode so the ends |
188 | of lines are appropriately mangled. |
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189 | |
190 | =head2 Where can I get Perl macros for vi? |
191 | |
192 | For a complete version of Tom Christiansen's vi configuration file, |
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193 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
194 | the standard benchmark file for vi emulators. The file runs best with nvi, |
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195 | the current version of vi out of Berkeley, which incidentally can be built |
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196 | with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc. |
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197 | |
198 | =head2 Where can I get perl-mode for emacs? |
199 | |
200 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
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201 | perl-mode.el and support for the Perl debugger built in. These should |
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202 | come with the standard Emacs 19 distribution. |
203 | |
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204 | In the Perl source directory, you'll find a directory called "emacs", |
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205 | which contains a cperl-mode that color-codes keywords, provides |
206 | context-sensitive help, and other nifty things. |
207 | |
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208 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
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209 | (single quote), and mess up the indentation and highlighting. You |
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210 | are probably using C<"main::foo"> in new Perl code anyway, so this |
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211 | shouldn't be an issue. |
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212 | |
213 | =head2 How can I use curses with Perl? |
214 | |
215 | The Curses module from CPAN provides a dynamically loadable object |
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216 | module interface to a curses library. A small demo can be found at the |
217 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; |
218 | this program repeats a command and updates the screen as needed, rendering |
219 | B<rep ps axu> similar to B<top>. |
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220 | |
221 | =head2 How can I use X or Tk with Perl? |
222 | |
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223 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
224 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
225 | to the Athena Widget set. Both are available from CPAN. See the |
226 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ |
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227 | |
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228 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
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229 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
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230 | Guide available at |
231 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the |
232 | online manpages at |
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233 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
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234 | |
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235 | =head2 How can I generate simple menus without using CGI or Tk? |
236 | |
237 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz |
238 | module, which is curses-based, can help with this. |
239 | |
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240 | =head2 What is undump? |
241 | |
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242 | See the next question on ``How can I make my Perl program run faster?'' |
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243 | |
244 | =head2 How can I make my Perl program run faster? |
245 | |
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246 | The best way to do this is to come up with a better algorithm. This |
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247 | can often make a dramatic difference. Jon Bentley's book |
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248 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
249 | on optimization, too. Advice on benchmarking boils down to: benchmark |
250 | and profile to make sure you're optimizing the right part, look for |
251 | better algorithms instead of microtuning your code, and when all else |
252 | fails consider just buying faster hardware. |
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253 | |
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254 | A different approach is to autoload seldom-used Perl code. See the |
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255 | AutoSplit and AutoLoader modules in the standard distribution for |
256 | that. Or you could locate the bottleneck and think about writing just |
257 | that part in C, the way we used to take bottlenecks in C code and |
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258 | write them in assembler. Similar to rewriting in C, |
259 | modules that have critical sections can be written in C (for instance, the |
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260 | PDL module from CPAN). |
261 | |
262 | In some cases, it may be worth it to use the backend compiler to |
263 | produce byte code (saving compilation time) or compile into C, which |
264 | will certainly save compilation time and sometimes a small amount (but |
265 | not much) execution time. See the question about compiling your Perl |
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266 | programs for more on the compiler--the wins aren't as obvious as you'd |
267 | hope. |
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268 | |
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269 | If you're currently linking your perl executable to a shared I<libc.so>, |
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270 | you can often gain a 10-25% performance benefit by rebuilding it to |
271 | link with a static libc.a instead. This will make a bigger perl |
272 | executable, but your Perl programs (and programmers) may thank you for |
273 | it. See the F<INSTALL> file in the source distribution for more |
274 | information. |
275 | |
276 | Unsubstantiated reports allege that Perl interpreters that use sfio |
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277 | outperform those that don't (for I/O intensive applications). To try |
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278 | this, see the F<INSTALL> file in the source distribution, especially |
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279 | the ``Selecting File I/O mechanisms'' section. |
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280 | |
281 | The undump program was an old attempt to speed up your Perl program |
282 | by storing the already-compiled form to disk. This is no longer |
283 | a viable option, as it only worked on a few architectures, and |
284 | wasn't a good solution anyway. |
285 | |
286 | =head2 How can I make my Perl program take less memory? |
287 | |
288 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
289 | throw memory at a problem. Scalars in Perl use more memory than |
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290 | strings in C, arrays take more than that, and hashes use even more. While |
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291 | there's still a lot to be done, recent releases have been addressing |
292 | these issues. For example, as of 5.004, duplicate hash keys are |
293 | shared amongst all hashes using them, so require no reallocation. |
294 | |
295 | In some cases, using substr() or vec() to simulate arrays can be |
296 | highly beneficial. For example, an array of a thousand booleans will |
297 | take at least 20,000 bytes of space, but it can be turned into one |
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298 | 125-byte bit vector--a considerable memory savings. The standard |
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299 | Tie::SubstrHash module can also help for certain types of data |
300 | structure. If you're working with specialist data structures |
301 | (matrices, for instance) modules that implement these in C may use |
302 | less memory than equivalent Perl modules. |
303 | |
304 | Another thing to try is learning whether your Perl was compiled with |
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305 | the system malloc or with Perl's builtin malloc. Whichever one it |
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306 | is, try using the other one and see whether this makes a difference. |
307 | Information about malloc is in the F<INSTALL> file in the source |
308 | distribution. You can find out whether you are using perl's malloc by |
309 | typing C<perl -V:usemymalloc>. |
310 | |
311 | =head2 Is it unsafe to return a pointer to local data? |
312 | |
313 | No, Perl's garbage collection system takes care of this. |
314 | |
315 | sub makeone { |
316 | my @a = ( 1 .. 10 ); |
317 | return \@a; |
318 | } |
319 | |
320 | for $i ( 1 .. 10 ) { |
321 | push @many, makeone(); |
322 | } |
323 | |
324 | print $many[4][5], "\n"; |
325 | |
326 | print "@many\n"; |
327 | |
328 | =head2 How can I free an array or hash so my program shrinks? |
329 | |
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330 | You can't. On most operating systems, memory allocated to a program |
331 | can never be returned to the system. That's why long-running programs |
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332 | sometimes re-exec themselves. Some operating systems (notably, |
333 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no |
334 | longer used, but it doesn't appear to happen with Perl (yet). The Mac |
335 | appears to be the only platform that will reliably (albeit, slowly) |
336 | return memory to the OS. |
337 | |
338 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef |
339 | $scalar> will return memory to the system, while on Solaris 2.6 it |
340 | won't. In general, try it yourself and see. |
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341 | |
342 | However, judicious use of my() on your variables will help make sure |
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343 | that they go out of scope so that Perl can free up that space for |
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344 | use in other parts of your program. A global variable, of course, never |
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345 | goes out of scope, so you can't get its space automatically reclaimed, |
346 | although undef()ing and/or delete()ing it will achieve the same effect. |
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347 | In general, memory allocation and de-allocation isn't something you can |
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348 | or should be worrying about much in Perl, but even this capability |
349 | (preallocation of data types) is in the works. |
350 | |
351 | =head2 How can I make my CGI script more efficient? |
352 | |
353 | Beyond the normal measures described to make general Perl programs |
354 | faster or smaller, a CGI program has additional issues. It may be run |
355 | several times per second. Given that each time it runs it will need |
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356 | to be re-compiled and will often allocate a megabyte or more of system |
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357 | memory, this can be a killer. Compiling into C B<isn't going to help |
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358 | you> because the process start-up overhead is where the bottleneck is. |
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359 | |
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360 | There are two popular ways to avoid this overhead. One solution |
361 | involves running the Apache HTTP server (available from |
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362 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
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363 | plugin modules. |
364 | |
365 | With mod_perl and the Apache::Registry module (distributed with |
366 | mod_perl), httpd will run with an embedded Perl interpreter which |
367 | pre-compiles your script and then executes it within the same address |
368 | space without forking. The Apache extension also gives Perl access to |
369 | the internal server API, so modules written in Perl can do just about |
370 | anything a module written in C can. For more on mod_perl, see |
371 | http://perl.apache.org/ |
372 | |
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373 | With the FCGI module (from CPAN) and the mod_fastcgi |
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374 | module (available from http://www.fastcgi.com/) each of your Perl |
375 | programs becomes a permanent CGI daemon process. |
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376 | |
377 | Both of these solutions can have far-reaching effects on your system |
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378 | and on the way you write your CGI programs, so investigate them with |
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379 | care. |
380 | |
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381 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
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382 | |
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383 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
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384 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ ) |
385 | might also be worth looking at. It will allow you to increase the |
386 | performance of your Perl programs, running programs up to 25 times |
387 | faster than normal CGI Perl when running in persistent Perl mode or 4 |
388 | to 5 times faster without any modification to your existing CGI |
389 | programs. Fully functional evaluation copies are available from the |
390 | web site. |
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391 | |
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392 | =head2 How can I hide the source for my Perl program? |
393 | |
394 | Delete it. :-) Seriously, there are a number of (mostly |
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395 | unsatisfactory) solutions with varying levels of ``security''. |
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396 | |
397 | First of all, however, you I<can't> take away read permission, because |
398 | the source code has to be readable in order to be compiled and |
399 | interpreted. (That doesn't mean that a CGI script's source is |
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400 | readable by people on the web, though--only by people with access to |
401 | the filesystem.) So you have to leave the permissions at the socially |
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402 | friendly 0755 level. |
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403 | |
404 | Some people regard this as a security problem. If your program does |
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405 | insecure things and relies on people not knowing how to exploit those |
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406 | insecurities, it is not secure. It is often possible for someone to |
407 | determine the insecure things and exploit them without viewing the |
408 | source. Security through obscurity, the name for hiding your bugs |
409 | instead of fixing them, is little security indeed. |
410 | |
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411 | You can try using encryption via source filters (Filter::* from CPAN), |
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412 | but any decent programmer will be able to decrypt it. You can try using |
413 | the byte code compiler and interpreter described below, but the curious |
414 | might still be able to de-compile it. You can try using the native-code |
415 | compiler described below, but crackers might be able to disassemble it. |
416 | These pose varying degrees of difficulty to people wanting to get at |
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417 | your code, but none can definitively conceal it (true of every |
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418 | language, not just Perl). |
419 | |
420 | If you're concerned about people profiting from your code, then the |
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421 | bottom line is that nothing but a restrictive license will give you |
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422 | legal security. License your software and pepper it with threatening |
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423 | statements like ``This is unpublished proprietary software of XYZ Corp. |
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424 | Your access to it does not give you permission to use it blah blah |
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425 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
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426 | you want to be sure your license's wording will stand up in court. |
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427 | |
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428 | =head2 How can I compile my Perl program into byte code or C? |
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429 | |
430 | Malcolm Beattie has written a multifunction backend compiler, |
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431 | available from CPAN, that can do both these things. It is included |
432 | in the perl5.005 release, but is still considered experimental. |
433 | This means it's fun to play with if you're a programmer but not |
434 | really for people looking for turn-key solutions. |
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435 | |
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436 | Merely compiling into C does not in and of itself guarantee that your |
437 | code will run very much faster. That's because except for lucky cases |
438 | where a lot of native type inferencing is possible, the normal Perl |
a6dd486b |
439 | run-time system is still present and so your program will take just as |
92c2ed05 |
440 | long to run and be just as big. Most programs save little more than |
441 | compilation time, leaving execution no more than 10-30% faster. A few |
a6dd486b |
442 | rare programs actually benefit significantly (even running several times |
92c2ed05 |
443 | faster), but this takes some tweaking of your code. |
68dc0745 |
444 | |
68dc0745 |
445 | You'll probably be astonished to learn that the current version of the |
446 | compiler generates a compiled form of your script whose executable is |
447 | just as big as the original perl executable, and then some. That's |
448 | because as currently written, all programs are prepared for a full |
449 | eval() statement. You can tremendously reduce this cost by building a |
92c2ed05 |
450 | shared I<libperl.so> library and linking against that. See the |
87275199 |
451 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 |
452 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 |
453 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 |
454 | size! |
455 | |
5a964f20 |
456 | In general, the compiler will do nothing to make a Perl program smaller, |
a6dd486b |
457 | faster, more portable, or more secure. In fact, it can make your |
458 | situation worse. The executable will be bigger, your VM system may take |
5a964f20 |
459 | longer to load the whole thing, the binary is fragile and hard to fix, |
460 | and compilation never stopped software piracy in the form of crackers, |
461 | viruses, or bootleggers. The real advantage of the compiler is merely |
462 | packaging, and once you see the size of what it makes (well, unless |
463 | you use a shared I<libperl.so>), you'll probably want a complete |
5e3006a4 |
464 | Perl install anyway. |
5a964f20 |
465 | |
65acb1b1 |
466 | =head2 How can I compile Perl into Java? |
467 | |
a6dd486b |
468 | You can also integrate Java and Perl with the |
65acb1b1 |
469 | Perl Resource Kit from O'Reilly and Associates. See |
a6dd486b |
470 | http://www.oreilly.com/catalog/prkunix/ . |
471 | |
472 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in |
473 | development, allows Perl code to be called from Java. See jpl/README |
474 | in the Perl source tree. |
65acb1b1 |
475 | |
92c2ed05 |
476 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 |
477 | |
478 | For OS/2 just use |
479 | |
480 | extproc perl -S -your_switches |
481 | |
482 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
46fc3d4c |
483 | `extproc' handling). For DOS one should first invent a corresponding |
a6dd486b |
484 | batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the |
68dc0745 |
485 | F<INSTALL> file in the source distribution for more information). |
486 | |
92c2ed05 |
487 | The Win95/NT installation, when using the ActiveState port of Perl, |
488 | will modify the Registry to associate the C<.pl> extension with the |
d92eb7b0 |
489 | perl interpreter. If you install another port, perhaps even building |
490 | your own Win95/NT Perl from the standard sources by using a Windows port |
d702ae42 |
491 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 |
492 | the Registry yourself. In addition to associating C<.pl> with the |
493 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them |
494 | run the program C<install-linux.pl> merely by typing C<install-linux>. |
68dc0745 |
495 | |
87275199 |
496 | Macintosh Perl programs will have the appropriate Creator and |
497 | Type, so that double-clicking them will invoke the Perl application. |
68dc0745 |
498 | |
499 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
500 | throw the perl interpreter into your cgi-bin directory, in order to |
87275199 |
501 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 |
502 | security risk. Take the time to figure out how to do it correctly. |
503 | |
87275199 |
504 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 |
505 | |
506 | Yes. Read L<perlrun> for more information. Some examples follow. |
507 | (These assume standard Unix shell quoting rules.) |
508 | |
509 | # sum first and last fields |
5a964f20 |
510 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 |
511 | |
512 | # identify text files |
513 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
514 | |
5a964f20 |
515 | # remove (most) comments from C program |
68dc0745 |
516 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
517 | |
518 | # make file a month younger than today, defeating reaper daemons |
519 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
520 | |
521 | # find first unused uid |
522 | perl -le '$i++ while getpwuid($i); print $i' |
523 | |
524 | # display reasonable manpath |
525 | echo $PATH | perl -nl -072 -e ' |
526 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
527 | |
87275199 |
528 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 |
529 | |
87275199 |
530 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 |
531 | |
532 | The problem is usually that the command interpreters on those systems |
533 | have rather different ideas about quoting than the Unix shells under |
534 | which the one-liners were created. On some systems, you may have to |
535 | change single-quotes to double ones, which you must I<NOT> do on Unix |
536 | or Plan9 systems. You might also have to change a single % to a %%. |
537 | |
538 | For example: |
539 | |
540 | # Unix |
541 | perl -e 'print "Hello world\n"' |
542 | |
46fc3d4c |
543 | # DOS, etc. |
68dc0745 |
544 | perl -e "print \"Hello world\n\"" |
545 | |
46fc3d4c |
546 | # Mac |
68dc0745 |
547 | print "Hello world\n" |
548 | (then Run "Myscript" or Shift-Command-R) |
549 | |
550 | # VMS |
551 | perl -e "print ""Hello world\n""" |
552 | |
a6dd486b |
553 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 |
554 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b |
555 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 |
556 | you'd probably have better luck like this: |
68dc0745 |
557 | |
558 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
559 | |
46fc3d4c |
560 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 |
561 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c |
562 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 |
563 | characters as control characters. |
564 | |
65acb1b1 |
565 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
566 | quotes', and `backticks`, may make one-liners easier to write. |
567 | |
92c2ed05 |
568 | There is no general solution to all of this. It is a mess, pure and |
569 | simple. Sucks to be away from Unix, huh? :-) |
68dc0745 |
570 | |
571 | [Some of this answer was contributed by Kenneth Albanowski.] |
572 | |
573 | =head2 Where can I learn about CGI or Web programming in Perl? |
574 | |
575 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
576 | see the two especially dedicated to web stuff in the question on |
92c2ed05 |
577 | books. For problems and questions related to the web, like ``Why |
578 | do I get 500 Errors'' or ``Why doesn't it run from the browser right |
579 | when it runs fine on the command line'', see these sources: |
68dc0745 |
580 | |
5a964f20 |
581 | WWW Security FAQ |
582 | http://www.w3.org/Security/Faq/ |
68dc0745 |
583 | |
5a964f20 |
584 | Web FAQ |
585 | http://www.boutell.com/faq/ |
68dc0745 |
586 | |
5a964f20 |
587 | CGI FAQ |
6cecdcac |
588 | http://www.webthing.com/tutorials/cgifaq.html |
68dc0745 |
589 | |
5a964f20 |
590 | HTTP Spec |
591 | http://www.w3.org/pub/WWW/Protocols/HTTP/ |
592 | |
593 | HTML Spec |
594 | http://www.w3.org/TR/REC-html40/ |
595 | http://www.w3.org/pub/WWW/MarkUp/ |
596 | |
597 | CGI Spec |
598 | http://www.w3.org/CGI/ |
599 | |
600 | CGI Security FAQ |
601 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt |
68dc0745 |
602 | |
68dc0745 |
603 | =head2 Where can I learn about object-oriented Perl programming? |
604 | |
a6dd486b |
605 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
606 | L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out |
607 | until the 5.004 release; you can get a copy (in pod, html, or |
608 | postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ . |
68dc0745 |
609 | |
610 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] |
611 | |
612 | If you want to call C from Perl, start with L<perlxstut>, |
613 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
614 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
615 | L<perlguts>. Don't forget that you can learn a lot from looking at |
616 | how the authors of existing extension modules wrote their code and |
617 | solved their problems. |
618 | |
619 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in |
a6dd486b |
620 | my C program; what am I doing wrong? |
68dc0745 |
621 | |
622 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
623 | the tests pass, read the pods again and again and again. If they |
87275199 |
624 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 |
625 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
626 | |
627 | =head2 When I tried to run my script, I got this message. What does it |
628 | mean? |
629 | |
87275199 |
630 | A complete list of Perl's error messages and warnings with explanatory |
631 | text can be found in L<perldiag>. You can also use the splain program |
632 | (distributed with Perl) to explain the error messages: |
68dc0745 |
633 | |
634 | perl program 2>diag.out |
635 | splain [-v] [-p] diag.out |
636 | |
637 | or change your program to explain the messages for you: |
638 | |
639 | use diagnostics; |
640 | |
641 | or |
642 | |
643 | use diagnostics -verbose; |
644 | |
645 | =head2 What's MakeMaker? |
646 | |
87275199 |
647 | This module (part of the standard Perl distribution) is designed to |
68dc0745 |
648 | write a Makefile for an extension module from a Makefile.PL. For more |
649 | information, see L<ExtUtils::MakeMaker>. |
650 | |
651 | =head1 AUTHOR AND COPYRIGHT |
652 | |
65acb1b1 |
653 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 |
654 | All rights reserved. |
655 | |
c8db1d39 |
656 | When included as an integrated part of the Standard Distribution |
d92eb7b0 |
657 | of Perl or of its documentation (printed or otherwise), this works is |
658 | covered under Perl's Artistic License. For separate distributions of |
c8db1d39 |
659 | all or part of this FAQ outside of that, see L<perlfaq>. |
660 | |
87275199 |
661 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 |
662 | domain. You are permitted and encouraged to use this code and any |
663 | derivatives thereof in your own programs for fun or for profit as you |
664 | see fit. A simple comment in the code giving credit to the FAQ would |
665 | be courteous but is not required. |