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