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68dc0745 | 1 | =head1 NAME |
2 | ||
d92eb7b0 | 3 | perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $) |
68dc0745 | 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. | |
46fc3d4c | 14 | Have you read the appropriate man pages? Here's a brief index: |
68dc0745 | 15 | |
5a964f20 TC |
16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
17 | Execution perlrun, perldebug | |
18 | Functions perlfunc | |
68dc0745 | 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 | |
25 | Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html | |
26 | (not a man-page but still useful) | |
27 | ||
87275199 | 28 | A crude table of contents for the Perl man page set is found in L<perltoc>. |
68dc0745 | 29 | |
30 | =head2 How can I use Perl interactively? | |
31 | ||
32 | The typical approach uses the Perl debugger, described in the | |
92c2ed05 | 33 | perldebug(1) man page, on an ``empty'' program, like this: |
68dc0745 | 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 | |
92c2ed05 | 40 | operations typically found in symbolic debuggers. |
68dc0745 | 41 | |
42 | =head2 Is there a Perl shell? | |
43 | ||
87275199 GS |
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 | |
68dc0745 | 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 | ||
9f1b1f2d | 51 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
a6dd486b | 52 | to detect dubious practices. |
68dc0745 | 53 | |
92c2ed05 GS |
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 | |
a6dd486b | 57 | variables with C<my>, C<our>, or C<use vars>. |
68dc0745 | 58 | |
a6dd486b JB |
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 | |
92c2ed05 | 61 | why. |
68dc0745 | 62 | |
92c2ed05 GS |
63 | open(FH, "> /etc/cantwrite") |
64 | or die "Couldn't write to /etc/cantwrite: $!\n"; | |
68dc0745 | 65 | |
92c2ed05 | 66 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
a6dd486b | 67 | programmers and even has sections for those of you who are upgrading |
92c2ed05 GS |
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. | |
68dc0745 | 73 | |
74 | =head2 How do I profile my Perl programs? | |
75 | ||
e083a89c | 76 | You should get the Devel::DProf module from the standard distribution |
733271b5 PK |
77 | (or separately on CPAN) and also use Benchmark.pm from the standard |
78 | distribution. The Benchmark module lets you time specific portions of | |
79 | your code, while Devel::DProf gives detailed breakdowns of where your | |
e083a89c | 80 | code spends its time. |
68dc0745 | 81 | |
92c2ed05 GS |
82 | Here's a sample use of Benchmark: |
83 | ||
84 | use Benchmark; | |
85 | ||
86 | @junk = `cat /etc/motd`; | |
87 | $count = 10_000; | |
88 | ||
89 | timethese($count, { | |
90 | 'map' => sub { my @a = @junk; | |
91 | map { s/a/b/ } @a; | |
92 | return @a | |
93 | }, | |
94 | 'for' => sub { my @a = @junk; | |
95 | local $_; | |
96 | for (@a) { s/a/b/ }; | |
97 | return @a }, | |
98 | }); | |
99 | ||
100 | This is what it prints (on one machine--your results will be dependent | |
101 | on your hardware, operating system, and the load on your machine): | |
102 | ||
103 | Benchmark: timing 10000 iterations of for, map... | |
104 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) | |
105 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) | |
106 | ||
65acb1b1 | 107 | Be aware that a good benchmark is very hard to write. It only tests the |
a6dd486b | 108 | data you give it and proves little about the differing complexities |
65acb1b1 TC |
109 | of contrasting algorithms. |
110 | ||
68dc0745 | 111 | =head2 How do I cross-reference my Perl programs? |
112 | ||
113 | The B::Xref module, shipped with the new, alpha-release Perl compiler | |
5a964f20 TC |
114 | (not the general distribution prior to the 5.005 release), can be used |
115 | to generate cross-reference reports for Perl programs. | |
68dc0745 | 116 | |
c8db1d39 | 117 | perl -MO=Xref[,OPTIONS] scriptname.plx |
68dc0745 | 118 | |
119 | =head2 Is there a pretty-printer (formatter) for Perl? | |
120 | ||
92c2ed05 GS |
121 | There is no program that will reformat Perl as much as indent(1) does |
122 | for C. The complex feedback between the scanner and the parser (this | |
123 | feedback is what confuses the vgrind and emacs programs) makes it | |
68dc0745 | 124 | challenging at best to write a stand-alone Perl parser. |
125 | ||
126 | Of course, if you simply follow the guidelines in L<perlstyle>, you | |
92c2ed05 GS |
127 | shouldn't need to reformat. The habit of formatting your code as you |
128 | write it will help prevent bugs. Your editor can and should help you | |
a6dd486b JB |
129 | with this. The perl-mode or newer cperl-mode for emacs can provide |
130 | remarkable amounts of help with most (but not all) code, and even less | |
131 | programmable editors can provide significant assistance. Tom swears | |
132 | by the following settings in vi and its clones: | |
65acb1b1 TC |
133 | |
134 | set ai sw=4 | |
d92eb7b0 | 135 | map! ^O {^M}^[O^T |
65acb1b1 TC |
136 | |
137 | Now put that in your F<.exrc> file (replacing the caret characters | |
138 | with control characters) and away you go. In insert mode, ^T is | |
a6dd486b | 139 | for indenting, ^D is for undenting, and ^O is for blockdenting-- |
65acb1b1 TC |
140 | as it were. If you haven't used the last one, you're missing |
141 | a lot. A more complete example, with comments, can be found at | |
142 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz | |
92c2ed05 | 143 | |
65acb1b1 | 144 | If you are used to using the I<vgrind> program for printing out nice code |
92c2ed05 | 145 | to a laser printer, you can take a stab at this using |
68dc0745 | 146 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
147 | results are not particularly satisfying for sophisticated code. | |
148 | ||
87275199 | 149 | The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things |
65acb1b1 TC |
150 | related to generating nicely printed output of documents. |
151 | ||
d92eb7b0 | 152 | =head2 Is there a ctags for Perl? |
68dc0745 | 153 | |
d92eb7b0 | 154 | There's a simple one at |
68dc0745 | 155 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
65acb1b1 TC |
156 | the trick. And if not, it's easy to hack into what you want. |
157 | ||
158 | =head2 Is there an IDE or Windows Perl Editor? | |
159 | ||
6641ed39 JH |
160 | Perl programs are just plain text, so any editor will do. |
161 | ||
6641ed39 JH |
162 | If you're on Unix, you already have an IDE--Unix itself. The UNIX |
163 | philosophy is the philosophy of several small tools that each do one | |
164 | thing and do it well. It's like a carpenter's toolbox. | |
165 | ||
5ca69f12 | 166 | If you want an IDE, check the following: |
68fbfbd7 JH |
167 | |
168 | =over 4 | |
169 | ||
170 | =item CodeMagicCD | |
171 | ||
172 | http://www.codemagiccd.com/ | |
173 | ||
5ca69f12 JH |
174 | Collection of various programming tools for Windows: Perl (5.005_03), |
175 | TclTk, Python, GNU programming tools, REBOL, wxWindows toolkit, the | |
176 | MinGW GNU C/C++ compiler, DJGPP GNU C/C++ compiler, Cint C | |
177 | interpreter, YaBasic. | |
178 | ||
68fbfbd7 JH |
179 | =item Komodo |
180 | ||
5ca69f12 JH |
181 | ActiveState's cross-platform (as of April 2001 Windows and Linux), |
182 | multi-language IDE has Perl support, including a regular expression | |
183 | debugger and remote debugging | |
184 | (http://www.ActiveState.com/Products/Komodo/index.html). (Visual | |
185 | Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta | |
186 | (http://www.ActiveState.com/Products/VisualPerl/index.html)). | |
68fbfbd7 JH |
187 | |
188 | =item The Object System | |
189 | ||
8782d048 | 190 | (http://www.castlelink.co.uk/object_system/) is a Perl web |
5ca69f12 JH |
191 | applications development IDE, apparently for any platform |
192 | that runs Perl. | |
193 | ||
194 | =item PerlBuilder | |
195 | ||
196 | (http://www.solutionsoft.com/perl.htm) is an integrated development | |
197 | environment for Windows that supports Perl development. | |
8782d048 | 198 | |
68fbfbd7 JH |
199 | =item Perl code magic |
200 | ||
201 | (http://www.petes-place.com/codemagic.html). | |
202 | ||
203 | =item visiPerl+ | |
204 | ||
5ca69f12 | 205 | http://helpconsulting.net/visiperl/, from Help Consulting, for Windows. |
68fbfbd7 JH |
206 | |
207 | =back | |
208 | ||
5a13f98a | 209 | For editors: if you're on Unix you probably have vi or a vi clone already, |
6641ed39 | 210 | and possibly an emacs too, so you may not need to download anything. |
5a13f98a | 211 | In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the |
6641ed39 JH |
212 | best available Perl editing mode in any editor. |
213 | ||
68fbfbd7 JH |
214 | For Windows editors: you can download an Emacs |
215 | ||
216 | =over 4 | |
217 | ||
218 | =item GNU Emacs | |
219 | ||
220 | http://www.gnu.org/software/emacs/windows/ntemacs.html | |
221 | ||
222 | =item MicroEMACS | |
223 | ||
224 | http://members.nbci.com/uemacs/ | |
225 | ||
226 | =item XEmacs | |
227 | ||
228 | http://www.xemacs.org/Download/index.html | |
229 | ||
230 | =back | |
231 | ||
232 | or a vi clone such as | |
233 | ||
234 | =over 4 | |
235 | ||
236 | =item Elvis | |
237 | ||
238 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ | |
239 | ||
240 | =item Vile | |
241 | ||
242 | http://vile.cx/ | |
243 | ||
244 | =item Vim | |
245 | ||
246 | http://www.vim.org/ | |
247 | ||
248 | win32: http://www.cs.vu.nl/%7Etmgil/vi.html | |
249 | ||
250 | =back | |
251 | ||
5a13f98a JH |
252 | For vi lovers in general, Windows or elsewhere: |
253 | http://www.thomer.com/thomer/vi/vi.html. | |
6641ed39 JH |
254 | |
255 | nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is | |
5a13f98a | 256 | yet another vi clone, unfortunately not available for Windows, but in |
6641ed39 JH |
257 | UNIX platforms you might be interested in trying it out, firstly because |
258 | strictly speaking it is not a vi clone, it is the real vi, or the new | |
259 | incarnation of it, and secondly because you can embed Perl inside it | |
260 | to use Perl as the scripting language. nvi is not alone in this, | |
7c82de66 | 261 | though: at least also vim and vile offer an embedded Perl. |
614a1598 | 262 | |
68fbfbd7 JH |
263 | The following are Win32 multilanguage editor/IDESs that support Perl: |
264 | ||
265 | =over 4 | |
266 | ||
267 | =item Codewright | |
268 | ||
269 | http://www.starbase.com/ | |
270 | ||
271 | =item MultiEdit | |
272 | ||
273 | http://www.MultiEdit.com/ | |
274 | ||
275 | =item SlickEdit | |
276 | ||
277 | http://www.slickedit.com/ | |
278 | ||
279 | =back | |
8782d048 | 280 | |
6641ed39 JH |
281 | There is also a toyedit Text widget based editor written in Perl |
282 | that is distributed with the Tk module on CPAN. The ptkdb | |
8782d048 JH |
283 | (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that |
284 | acts as a development environment of sorts. Perl Composer | |
e083a89c JH |
285 | (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk |
286 | GUI creation. | |
287 | ||
8782d048 | 288 | In addition to an editor/IDE you might be interested in a more |
68fbfbd7 JH |
289 | powerful shell environment for Win32. Your options include |
290 | ||
291 | =over 4 | |
292 | ||
293 | =item Bash | |
294 | ||
295 | from the Cygwin package (http://sources.redhat.com/cygwin/) | |
296 | ||
297 | =item Ksh | |
298 | ||
299 | from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of | |
300 | the U/WIN environment (http://www.research.att.com/sw/tools/uwin/) | |
301 | ||
302 | =item Tcsh | |
303 | ||
304 | ftp://ftp.astron.com/pub/tcsh/, see also | |
305 | http://www.primate.wisc.edu/software/csh-tcsh-book/ | |
306 | ||
307 | =item Zsh | |
308 | ||
309 | ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/ | |
310 | ||
311 | =back | |
312 | ||
614a1598 JH |
313 | MKS and U/WIN are commercial (U/WIN is free for educational and |
314 | research purposes), Cygwin is covered by the GNU Public License (but | |
315 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all | |
316 | contain (in addition to the shells) a comprehensive set of standard | |
317 | UNIX toolkit utilities. | |
8782d048 | 318 | |
5a13f98a JH |
319 | If you're transferring text files between Unix and Windows using FTP |
320 | be sure to transfer them in ASCII mode so the ends of lines are | |
321 | appropriately converted. | |
322 | ||
e083a89c JH |
323 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
324 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application | |
733271b5 | 325 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
68fbfbd7 JH |
326 | no 32k limit). |
327 | ||
328 | =over 4 | |
329 | ||
330 | =item BBEdit and BBEdit Lite | |
331 | ||
332 | are text editors for Mac OS that have a Perl sensitivity mode | |
333 | (http://web.barebones.com/). | |
334 | ||
335 | =item Alpha | |
336 | ||
337 | is an editor, written and extensible in Tcl, that nonetheless has | |
733271b5 | 338 | built in support for several popular markup and programming languages |
68fbfbd7 JH |
339 | including Perl and HTML (http://alpha.olm.net/). |
340 | ||
341 | =back | |
342 | ||
343 | Pepper and Pe are programming language sensitive text editors for Mac | |
344 | OS X and BeOS respectively (http://www.hekkelman.com/). | |
68dc0745 | 345 | |
346 | =head2 Where can I get Perl macros for vi? | |
347 | ||
348 | For a complete version of Tom Christiansen's vi configuration file, | |
a6dd486b JB |
349 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
350 | the standard benchmark file for vi emulators. The file runs best with nvi, | |
5a964f20 | 351 | the current version of vi out of Berkeley, which incidentally can be built |
a6dd486b | 352 | with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc. |
68dc0745 | 353 | |
354 | =head2 Where can I get perl-mode for emacs? | |
355 | ||
356 | Since Emacs version 19 patchlevel 22 or so, there have been both a | |
87275199 | 357 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 | 358 | come with the standard Emacs 19 distribution. |
359 | ||
87275199 | 360 | In the Perl source directory, you'll find a directory called "emacs", |
68dc0745 | 361 | which contains a cperl-mode that color-codes keywords, provides |
362 | context-sensitive help, and other nifty things. | |
363 | ||
92c2ed05 | 364 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 | 365 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 | 366 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 | 367 | shouldn't be an issue. |
68dc0745 | 368 | |
369 | =head2 How can I use curses with Perl? | |
370 | ||
371 | The Curses module from CPAN provides a dynamically loadable object | |
5a964f20 TC |
372 | module interface to a curses library. A small demo can be found at the |
373 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; | |
374 | this program repeats a command and updates the screen as needed, rendering | |
375 | B<rep ps axu> similar to B<top>. | |
68dc0745 | 376 | |
377 | =head2 How can I use X or Tk with Perl? | |
378 | ||
5a964f20 TC |
379 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
380 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface | |
381 | to the Athena Widget set. Both are available from CPAN. See the | |
382 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ | |
68dc0745 | 383 | |
a6dd486b | 384 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
87275199 | 385 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
92c2ed05 GS |
386 | Guide available at |
387 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the | |
388 | online manpages at | |
87275199 | 389 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 | 390 | |
68dc0745 | 391 | =head2 How can I generate simple menus without using CGI or Tk? |
392 | ||
393 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz | |
394 | module, which is curses-based, can help with this. | |
395 | ||
68dc0745 | 396 | =head2 What is undump? |
397 | ||
a6dd486b | 398 | See the next question on ``How can I make my Perl program run faster?'' |
68dc0745 | 399 | |
400 | =head2 How can I make my Perl program run faster? | |
401 | ||
92c2ed05 | 402 | The best way to do this is to come up with a better algorithm. This |
b73a15ae | 403 | can often make a dramatic difference. Jon Bentley's book |
92c2ed05 GS |
404 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
405 | on optimization, too. Advice on benchmarking boils down to: benchmark | |
406 | and profile to make sure you're optimizing the right part, look for | |
407 | better algorithms instead of microtuning your code, and when all else | |
408 | fails consider just buying faster hardware. | |
68dc0745 | 409 | |
92c2ed05 | 410 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 | 411 | AutoSplit and AutoLoader modules in the standard distribution for |
412 | that. Or you could locate the bottleneck and think about writing just | |
413 | that part in C, the way we used to take bottlenecks in C code and | |
a6dd486b JB |
414 | write them in assembler. Similar to rewriting in C, |
415 | modules that have critical sections can be written in C (for instance, the | |
68dc0745 | 416 | PDL module from CPAN). |
417 | ||
418 | In some cases, it may be worth it to use the backend compiler to | |
419 | produce byte code (saving compilation time) or compile into C, which | |
420 | will certainly save compilation time and sometimes a small amount (but | |
421 | not much) execution time. See the question about compiling your Perl | |
92c2ed05 GS |
422 | programs for more on the compiler--the wins aren't as obvious as you'd |
423 | hope. | |
68dc0745 | 424 | |
92c2ed05 | 425 | If you're currently linking your perl executable to a shared I<libc.so>, |
68dc0745 | 426 | you can often gain a 10-25% performance benefit by rebuilding it to |
427 | link with a static libc.a instead. This will make a bigger perl | |
428 | executable, but your Perl programs (and programmers) may thank you for | |
429 | it. See the F<INSTALL> file in the source distribution for more | |
430 | information. | |
431 | ||
432 | Unsubstantiated reports allege that Perl interpreters that use sfio | |
87275199 | 433 | outperform those that don't (for I/O intensive applications). To try |
68dc0745 | 434 | this, see the F<INSTALL> file in the source distribution, especially |
87275199 | 435 | the ``Selecting File I/O mechanisms'' section. |
68dc0745 | 436 | |
437 | The undump program was an old attempt to speed up your Perl program | |
438 | by storing the already-compiled form to disk. This is no longer | |
439 | a viable option, as it only worked on a few architectures, and | |
440 | wasn't a good solution anyway. | |
441 | ||
442 | =head2 How can I make my Perl program take less memory? | |
443 | ||
444 | When it comes to time-space tradeoffs, Perl nearly always prefers to | |
445 | throw memory at a problem. Scalars in Perl use more memory than | |
65acb1b1 | 446 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 | 447 | there's still a lot to be done, recent releases have been addressing |
448 | these issues. For example, as of 5.004, duplicate hash keys are | |
449 | shared amongst all hashes using them, so require no reallocation. | |
450 | ||
451 | In some cases, using substr() or vec() to simulate arrays can be | |
452 | highly beneficial. For example, an array of a thousand booleans will | |
453 | take at least 20,000 bytes of space, but it can be turned into one | |
a6dd486b | 454 | 125-byte bit vector--a considerable memory savings. The standard |
68dc0745 | 455 | Tie::SubstrHash module can also help for certain types of data |
456 | structure. If you're working with specialist data structures | |
457 | (matrices, for instance) modules that implement these in C may use | |
458 | less memory than equivalent Perl modules. | |
459 | ||
460 | Another thing to try is learning whether your Perl was compiled with | |
54310121 | 461 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 | 462 | is, try using the other one and see whether this makes a difference. |
463 | Information about malloc is in the F<INSTALL> file in the source | |
464 | distribution. You can find out whether you are using perl's malloc by | |
465 | typing C<perl -V:usemymalloc>. | |
466 | ||
467 | =head2 Is it unsafe to return a pointer to local data? | |
468 | ||
469 | No, Perl's garbage collection system takes care of this. | |
470 | ||
471 | sub makeone { | |
472 | my @a = ( 1 .. 10 ); | |
473 | return \@a; | |
474 | } | |
475 | ||
476 | for $i ( 1 .. 10 ) { | |
477 | push @many, makeone(); | |
478 | } | |
479 | ||
480 | print $many[4][5], "\n"; | |
481 | ||
482 | print "@many\n"; | |
483 | ||
484 | =head2 How can I free an array or hash so my program shrinks? | |
485 | ||
c8db1d39 TC |
486 | You can't. On most operating systems, memory allocated to a program |
487 | can never be returned to the system. That's why long-running programs | |
65acb1b1 TC |
488 | sometimes re-exec themselves. Some operating systems (notably, |
489 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no | |
490 | longer used, but it doesn't appear to happen with Perl (yet). The Mac | |
491 | appears to be the only platform that will reliably (albeit, slowly) | |
492 | return memory to the OS. | |
493 | ||
494 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef | |
495 | $scalar> will return memory to the system, while on Solaris 2.6 it | |
496 | won't. In general, try it yourself and see. | |
68dc0745 | 497 | |
498 | However, judicious use of my() on your variables will help make sure | |
a6dd486b | 499 | that they go out of scope so that Perl can free up that space for |
92c2ed05 | 500 | use in other parts of your program. A global variable, of course, never |
68dc0745 | 501 | goes out of scope, so you can't get its space automatically reclaimed, |
502 | although undef()ing and/or delete()ing it will achieve the same effect. | |
46fc3d4c | 503 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 | 504 | or should be worrying about much in Perl, but even this capability |
505 | (preallocation of data types) is in the works. | |
506 | ||
507 | =head2 How can I make my CGI script more efficient? | |
508 | ||
509 | Beyond the normal measures described to make general Perl programs | |
510 | faster or smaller, a CGI program has additional issues. It may be run | |
511 | several times per second. Given that each time it runs it will need | |
46fc3d4c | 512 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 | 513 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c | 514 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 | 515 | |
92c2ed05 GS |
516 | There are two popular ways to avoid this overhead. One solution |
517 | involves running the Apache HTTP server (available from | |
68dc0745 | 518 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
92c2ed05 GS |
519 | plugin modules. |
520 | ||
521 | With mod_perl and the Apache::Registry module (distributed with | |
522 | mod_perl), httpd will run with an embedded Perl interpreter which | |
523 | pre-compiles your script and then executes it within the same address | |
524 | space without forking. The Apache extension also gives Perl access to | |
525 | the internal server API, so modules written in Perl can do just about | |
526 | anything a module written in C can. For more on mod_perl, see | |
527 | http://perl.apache.org/ | |
528 | ||
65acb1b1 | 529 | With the FCGI module (from CPAN) and the mod_fastcgi |
87275199 GS |
530 | module (available from http://www.fastcgi.com/) each of your Perl |
531 | programs becomes a permanent CGI daemon process. | |
68dc0745 | 532 | |
533 | Both of these solutions can have far-reaching effects on your system | |
87275199 | 534 | and on the way you write your CGI programs, so investigate them with |
68dc0745 | 535 | care. |
536 | ||
92c2ed05 | 537 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 | 538 | |
65acb1b1 | 539 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
a6dd486b JB |
540 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ ) |
541 | might also be worth looking at. It will allow you to increase the | |
542 | performance of your Perl programs, running programs up to 25 times | |
543 | faster than normal CGI Perl when running in persistent Perl mode or 4 | |
544 | to 5 times faster without any modification to your existing CGI | |
545 | programs. Fully functional evaluation copies are available from the | |
546 | web site. | |
c8db1d39 | 547 | |
68dc0745 | 548 | =head2 How can I hide the source for my Perl program? |
549 | ||
550 | Delete it. :-) Seriously, there are a number of (mostly | |
92c2ed05 | 551 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 | 552 | |
553 | First of all, however, you I<can't> take away read permission, because | |
554 | the source code has to be readable in order to be compiled and | |
555 | interpreted. (That doesn't mean that a CGI script's source is | |
a6dd486b JB |
556 | readable by people on the web, though--only by people with access to |
557 | the filesystem.) So you have to leave the permissions at the socially | |
92c2ed05 | 558 | friendly 0755 level. |
68dc0745 | 559 | |
560 | Some people regard this as a security problem. If your program does | |
a6dd486b | 561 | insecure things and relies on people not knowing how to exploit those |
68dc0745 | 562 | insecurities, it is not secure. It is often possible for someone to |
563 | determine the insecure things and exploit them without viewing the | |
564 | source. Security through obscurity, the name for hiding your bugs | |
565 | instead of fixing them, is little security indeed. | |
566 | ||
83df6a1d JH |
567 | You can try using encryption via source filters (Starting from Perl |
568 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in | |
569 | the standard distribution), but any decent programmer will be able to | |
570 | decrypt it. You can try using the byte code compiler and interpreter | |
571 | described below, but the curious might still be able to de-compile it. | |
572 | You can try using the native-code compiler described below, but | |
573 | crackers might be able to disassemble it. These pose varying degrees | |
574 | of difficulty to people wanting to get at your code, but none can | |
575 | definitively conceal it (true of every language, not just Perl). | |
68dc0745 | 576 | |
577 | If you're concerned about people profiting from your code, then the | |
d92eb7b0 | 578 | bottom line is that nothing but a restrictive license will give you |
68dc0745 | 579 | legal security. License your software and pepper it with threatening |
92c2ed05 | 580 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 | 581 | Your access to it does not give you permission to use it blah blah |
92c2ed05 | 582 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 | 583 | you want to be sure your license's wording will stand up in court. |
68dc0745 | 584 | |
54310121 | 585 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 | 586 | |
587 | Malcolm Beattie has written a multifunction backend compiler, | |
5e3006a4 GS |
588 | available from CPAN, that can do both these things. It is included |
589 | in the perl5.005 release, but is still considered experimental. | |
590 | This means it's fun to play with if you're a programmer but not | |
591 | really for people looking for turn-key solutions. | |
68dc0745 | 592 | |
92c2ed05 GS |
593 | Merely compiling into C does not in and of itself guarantee that your |
594 | code will run very much faster. That's because except for lucky cases | |
595 | where a lot of native type inferencing is possible, the normal Perl | |
a6dd486b | 596 | run-time system is still present and so your program will take just as |
92c2ed05 GS |
597 | long to run and be just as big. Most programs save little more than |
598 | compilation time, leaving execution no more than 10-30% faster. A few | |
a6dd486b | 599 | rare programs actually benefit significantly (even running several times |
92c2ed05 | 600 | faster), but this takes some tweaking of your code. |
68dc0745 | 601 | |
68dc0745 | 602 | You'll probably be astonished to learn that the current version of the |
603 | compiler generates a compiled form of your script whose executable is | |
604 | just as big as the original perl executable, and then some. That's | |
605 | because as currently written, all programs are prepared for a full | |
606 | eval() statement. You can tremendously reduce this cost by building a | |
92c2ed05 | 607 | shared I<libperl.so> library and linking against that. See the |
87275199 | 608 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 | 609 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 | 610 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 | 611 | size! |
612 | ||
5a964f20 | 613 | In general, the compiler will do nothing to make a Perl program smaller, |
a6dd486b JB |
614 | faster, more portable, or more secure. In fact, it can make your |
615 | situation worse. The executable will be bigger, your VM system may take | |
5a964f20 TC |
616 | longer to load the whole thing, the binary is fragile and hard to fix, |
617 | and compilation never stopped software piracy in the form of crackers, | |
618 | viruses, or bootleggers. The real advantage of the compiler is merely | |
619 | packaging, and once you see the size of what it makes (well, unless | |
620 | you use a shared I<libperl.so>), you'll probably want a complete | |
5e3006a4 | 621 | Perl install anyway. |
5a964f20 | 622 | |
65acb1b1 TC |
623 | =head2 How can I compile Perl into Java? |
624 | ||
a6dd486b | 625 | You can also integrate Java and Perl with the |
65acb1b1 | 626 | Perl Resource Kit from O'Reilly and Associates. See |
a6dd486b JB |
627 | http://www.oreilly.com/catalog/prkunix/ . |
628 | ||
629 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in | |
630 | development, allows Perl code to be called from Java. See jpl/README | |
631 | in the Perl source tree. | |
65acb1b1 | 632 | |
92c2ed05 | 633 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 | 634 | |
635 | For OS/2 just use | |
636 | ||
637 | extproc perl -S -your_switches | |
638 | ||
639 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's | |
46fc3d4c | 640 | `extproc' handling). For DOS one should first invent a corresponding |
a6dd486b | 641 | batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the |
68dc0745 | 642 | F<INSTALL> file in the source distribution for more information). |
643 | ||
92c2ed05 GS |
644 | The Win95/NT installation, when using the ActiveState port of Perl, |
645 | will modify the Registry to associate the C<.pl> extension with the | |
d92eb7b0 GS |
646 | perl interpreter. If you install another port, perhaps even building |
647 | your own Win95/NT Perl from the standard sources by using a Windows port | |
d702ae42 | 648 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 GS |
649 | the Registry yourself. In addition to associating C<.pl> with the |
650 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them | |
651 | run the program C<install-linux.pl> merely by typing C<install-linux>. | |
68dc0745 | 652 | |
87275199 GS |
653 | Macintosh Perl programs will have the appropriate Creator and |
654 | Type, so that double-clicking them will invoke the Perl application. | |
68dc0745 | 655 | |
656 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just | |
657 | throw the perl interpreter into your cgi-bin directory, in order to | |
87275199 | 658 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 | 659 | security risk. Take the time to figure out how to do it correctly. |
660 | ||
87275199 | 661 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 | 662 | |
663 | Yes. Read L<perlrun> for more information. Some examples follow. | |
664 | (These assume standard Unix shell quoting rules.) | |
665 | ||
666 | # sum first and last fields | |
5a964f20 | 667 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 | 668 | |
669 | # identify text files | |
670 | perl -le 'for(@ARGV) {print if -f && -T _}' * | |
671 | ||
5a964f20 | 672 | # remove (most) comments from C program |
68dc0745 | 673 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
674 | ||
675 | # make file a month younger than today, defeating reaper daemons | |
676 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * | |
677 | ||
678 | # find first unused uid | |
679 | perl -le '$i++ while getpwuid($i); print $i' | |
680 | ||
681 | # display reasonable manpath | |
682 | echo $PATH | perl -nl -072 -e ' | |
683 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' | |
684 | ||
87275199 | 685 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 | 686 | |
87275199 | 687 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 | 688 | |
689 | The problem is usually that the command interpreters on those systems | |
690 | have rather different ideas about quoting than the Unix shells under | |
691 | which the one-liners were created. On some systems, you may have to | |
692 | change single-quotes to double ones, which you must I<NOT> do on Unix | |
693 | or Plan9 systems. You might also have to change a single % to a %%. | |
694 | ||
695 | For example: | |
696 | ||
697 | # Unix | |
698 | perl -e 'print "Hello world\n"' | |
699 | ||
46fc3d4c | 700 | # DOS, etc. |
68dc0745 | 701 | perl -e "print \"Hello world\n\"" |
702 | ||
46fc3d4c | 703 | # Mac |
68dc0745 | 704 | print "Hello world\n" |
705 | (then Run "Myscript" or Shift-Command-R) | |
706 | ||
707 | # VMS | |
708 | perl -e "print ""Hello world\n""" | |
709 | ||
a6dd486b | 710 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 | 711 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b | 712 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 | 713 | you'd probably have better luck like this: |
68dc0745 | 714 | |
715 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
716 | ||
46fc3d4c | 717 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 | 718 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c | 719 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 | 720 | characters as control characters. |
721 | ||
65acb1b1 TC |
722 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
723 | quotes', and `backticks`, may make one-liners easier to write. | |
724 | ||
92c2ed05 GS |
725 | There is no general solution to all of this. It is a mess, pure and |
726 | simple. Sucks to be away from Unix, huh? :-) | |
68dc0745 | 727 | |
728 | [Some of this answer was contributed by Kenneth Albanowski.] | |
729 | ||
730 | =head2 Where can I learn about CGI or Web programming in Perl? | |
731 | ||
732 | For modules, get the CGI or LWP modules from CPAN. For textbooks, | |
733 | see the two especially dedicated to web stuff in the question on | |
92c2ed05 GS |
734 | books. For problems and questions related to the web, like ``Why |
735 | do I get 500 Errors'' or ``Why doesn't it run from the browser right | |
736 | when it runs fine on the command line'', see these sources: | |
68dc0745 | 737 | |
5a964f20 TC |
738 | WWW Security FAQ |
739 | http://www.w3.org/Security/Faq/ | |
68dc0745 | 740 | |
5a964f20 TC |
741 | Web FAQ |
742 | http://www.boutell.com/faq/ | |
68dc0745 | 743 | |
5a964f20 | 744 | CGI FAQ |
6cecdcac | 745 | http://www.webthing.com/tutorials/cgifaq.html |
68dc0745 | 746 | |
5a964f20 TC |
747 | HTTP Spec |
748 | http://www.w3.org/pub/WWW/Protocols/HTTP/ | |
749 | ||
750 | HTML Spec | |
751 | http://www.w3.org/TR/REC-html40/ | |
752 | http://www.w3.org/pub/WWW/MarkUp/ | |
753 | ||
754 | CGI Spec | |
755 | http://www.w3.org/CGI/ | |
756 | ||
757 | CGI Security FAQ | |
758 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt | |
68dc0745 | 759 | |
68dc0745 | 760 | =head2 Where can I learn about object-oriented Perl programming? |
761 | ||
a6dd486b JB |
762 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
763 | L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out | |
764 | until the 5.004 release; you can get a copy (in pod, html, or | |
765 | postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ . | |
68dc0745 | 766 | |
767 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
768 | ||
769 | If you want to call C from Perl, start with L<perlxstut>, | |
770 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to | |
771 | call Perl from C, then read L<perlembed>, L<perlcall>, and | |
772 | L<perlguts>. Don't forget that you can learn a lot from looking at | |
773 | how the authors of existing extension modules wrote their code and | |
774 | solved their problems. | |
775 | ||
776 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in | |
a6dd486b | 777 | my C program; what am I doing wrong? |
68dc0745 | 778 | |
779 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If | |
780 | the tests pass, read the pods again and again and again. If they | |
87275199 | 781 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 | 782 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
783 | ||
784 | =head2 When I tried to run my script, I got this message. What does it | |
785 | mean? | |
786 | ||
87275199 GS |
787 | A complete list of Perl's error messages and warnings with explanatory |
788 | text can be found in L<perldiag>. You can also use the splain program | |
789 | (distributed with Perl) to explain the error messages: | |
68dc0745 | 790 | |
791 | perl program 2>diag.out | |
792 | splain [-v] [-p] diag.out | |
793 | ||
794 | or change your program to explain the messages for you: | |
795 | ||
796 | use diagnostics; | |
797 | ||
798 | or | |
799 | ||
800 | use diagnostics -verbose; | |
801 | ||
802 | =head2 What's MakeMaker? | |
803 | ||
87275199 | 804 | This module (part of the standard Perl distribution) is designed to |
68dc0745 | 805 | write a Makefile for an extension module from a Makefile.PL. For more |
806 | information, see L<ExtUtils::MakeMaker>. | |
807 | ||
808 | =head1 AUTHOR AND COPYRIGHT | |
809 | ||
65acb1b1 | 810 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 TC |
811 | All rights reserved. |
812 | ||
c8db1d39 | 813 | When included as an integrated part of the Standard Distribution |
d92eb7b0 GS |
814 | of Perl or of its documentation (printed or otherwise), this works is |
815 | covered under Perl's Artistic License. For separate distributions of | |
c8db1d39 TC |
816 | all or part of this FAQ outside of that, see L<perlfaq>. |
817 | ||
87275199 | 818 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
819 | domain. You are permitted and encouraged to use this code and any |
820 | derivatives thereof in your own programs for fun or for profit as you | |
821 | see fit. A simple comment in the code giving credit to the FAQ would | |
822 | be courteous but is not required. |