Commit | Line | Data |
---|---|---|
86530b38 AT |
1 | =head1 NAME |
2 | ||
3 | perlfaq3 - Programming Tools ($Revision: 1.22 $, $Date: 2002/05/06 13:11:13 $) | |
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. | |
14 | Have you read the appropriate manpages? Here's a brief index: | |
15 | ||
16 | Basics perldata, perlvar, perlsyn, perlop, perlsub | |
17 | Execution perlrun, perldebug | |
18 | Functions perlfunc | |
19 | Objects perlref, perlmod, perlobj, perltie | |
20 | Data Structures perlref, perllol, perldsc | |
21 | Modules perlmod, perlmodlib, perlsub | |
22 | Regexes perlre, perlfunc, perlop, perllocale | |
23 | Moving to perl5 perltrap, perl | |
24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed | |
25 | Various http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz | |
26 | (not a man-page but still useful, a collection | |
27 | of various essays on Perl techniques) | |
28 | ||
29 | A crude table of contents for the Perl manpage set is found in L<perltoc>. | |
30 | ||
31 | =head2 How can I use Perl interactively? | |
32 | ||
33 | The typical approach uses the Perl debugger, described in the | |
34 | perldebug(1) manpage, on an ``empty'' program, like this: | |
35 | ||
36 | perl -de 42 | |
37 | ||
38 | Now just type in any legal Perl code, and it will be immediately | |
39 | evaluated. You can also examine the symbol table, get stack | |
40 | backtraces, check variable values, set breakpoints, and other | |
41 | operations typically found in symbolic debuggers. | |
42 | ||
43 | =head2 Is there a Perl shell? | |
44 | ||
45 | In general, not yet. There is psh available at | |
46 | ||
47 | http://www.focusresearch.com/gregor/psh | |
48 | ||
49 | Which includes the following description: | |
50 | ||
51 | The Perl Shell is a shell that combines the interactive nature | |
52 | of a Unix shell with the power of Perl. The goal is to eventually | |
53 | have a full featured shell that behaves as expected for normal | |
54 | shell activity. But, the Perl Shell will use Perl syntax and | |
55 | functionality for control-flow statements and other things. | |
56 | ||
57 | The Shell.pm module (distributed with Perl) makes Perl try commands | |
58 | which aren't part of the Perl language as shell commands. perlsh | |
59 | from the source distribution is simplistic and uninteresting, but | |
60 | may still be what you want. | |
61 | ||
62 | =head2 How do I debug my Perl programs? | |
63 | ||
64 | Have you tried C<use warnings> or used C<-w>? They enable warnings | |
65 | to detect dubious practices. | |
66 | ||
67 | Have you tried C<use strict>? It prevents you from using symbolic | |
68 | references, makes you predeclare any subroutines that you call as bare | |
69 | words, and (probably most importantly) forces you to predeclare your | |
70 | variables with C<my>, C<our>, or C<use vars>. | |
71 | ||
72 | Did you check the return values of each and every system call? The operating | |
73 | system (and thus Perl) tells you whether they worked, and if not | |
74 | why. | |
75 | ||
76 | open(FH, "> /etc/cantwrite") | |
77 | or die "Couldn't write to /etc/cantwrite: $!\n"; | |
78 | ||
79 | Did you read L<perltrap>? It's full of gotchas for old and new Perl | |
80 | programmers and even has sections for those of you who are upgrading | |
81 | from languages like I<awk> and I<C>. | |
82 | ||
83 | Have you tried the Perl debugger, described in L<perldebug>? You can | |
84 | step through your program and see what it's doing and thus work out | |
85 | why what it's doing isn't what it should be doing. | |
86 | ||
87 | =head2 How do I profile my Perl programs? | |
88 | ||
89 | You should get the Devel::DProf module from the standard distribution | |
90 | (or separately on CPAN) and also use Benchmark.pm from the standard | |
91 | distribution. The Benchmark module lets you time specific portions of | |
92 | your code, while Devel::DProf gives detailed breakdowns of where your | |
93 | code spends its time. | |
94 | ||
95 | Here's a sample use of Benchmark: | |
96 | ||
97 | use Benchmark; | |
98 | ||
99 | @junk = `cat /etc/motd`; | |
100 | $count = 10_000; | |
101 | ||
102 | timethese($count, { | |
103 | 'map' => sub { my @a = @junk; | |
104 | map { s/a/b/ } @a; | |
105 | return @a | |
106 | }, | |
107 | 'for' => sub { my @a = @junk; | |
108 | local $_; | |
109 | for (@a) { s/a/b/ }; | |
110 | return @a }, | |
111 | }); | |
112 | ||
113 | This is what it prints (on one machine--your results will be dependent | |
114 | on your hardware, operating system, and the load on your machine): | |
115 | ||
116 | Benchmark: timing 10000 iterations of for, map... | |
117 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) | |
118 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) | |
119 | ||
120 | Be aware that a good benchmark is very hard to write. It only tests the | |
121 | data you give it and proves little about the differing complexities | |
122 | of contrasting algorithms. | |
123 | ||
124 | =head2 How do I cross-reference my Perl programs? | |
125 | ||
126 | The B::Xref module can be used to generate cross-reference reports | |
127 | for Perl programs. | |
128 | ||
129 | perl -MO=Xref[,OPTIONS] scriptname.plx | |
130 | ||
131 | =head2 Is there a pretty-printer (formatter) for Perl? | |
132 | ||
133 | Perltidy is a Perl script which indents and reformats Perl scripts | |
134 | to make them easier to read by trying to follow the rules of the | |
135 | L<perlstyle>. If you write Perl scripts, or spend much time reading | |
136 | them, you will probably find it useful. It is available at | |
137 | http://perltidy.sourceforge.net | |
138 | ||
139 | Of course, if you simply follow the guidelines in L<perlstyle>, | |
140 | you shouldn't need to reformat. The habit of formatting your code | |
141 | as you write it will help prevent bugs. Your editor can and should | |
142 | help you with this. The perl-mode or newer cperl-mode for emacs | |
143 | can provide remarkable amounts of help with most (but not all) | |
144 | code, and even less programmable editors can provide significant | |
145 | assistance. Tom Christiansen and many other VI users swear by | |
146 | the following settings in vi and its clones: | |
147 | ||
148 | set ai sw=4 | |
149 | map! ^O {^M}^[O^T | |
150 | ||
151 | Put that in your F<.exrc> file (replacing the caret characters | |
152 | with control characters) and away you go. In insert mode, ^T is | |
153 | for indenting, ^D is for undenting, and ^O is for blockdenting-- | |
154 | as it were. A more complete example, with comments, can be found at | |
155 | http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz | |
156 | ||
157 | The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps does | |
158 | lots of things related to generating nicely printed output of | |
159 | documents, as does enscript at http://people.ssh.fi/mtr/genscript/ . | |
160 | ||
161 | =head2 Is there a ctags for Perl? | |
162 | ||
163 | Recent versions of ctags do much more than older versions did. | |
164 | EXUBERANT CTAGS is available from http://ctags.sourceforge.net/ | |
165 | and does a good job of making tags files for perl code. | |
166 | ||
167 | There is also a simple one at | |
168 | http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do | |
169 | the trick. It can be easy to hack this into what you want. | |
170 | ||
171 | =head2 Is there an IDE or Windows Perl Editor? | |
172 | ||
173 | Perl programs are just plain text, so any editor will do. | |
174 | ||
175 | If you're on Unix, you already have an IDE--Unix itself. The UNIX | |
176 | philosophy is the philosophy of several small tools that each do one | |
177 | thing and do it well. It's like a carpenter's toolbox. | |
178 | ||
179 | If you want an IDE, check the following: | |
180 | ||
181 | =over 4 | |
182 | ||
183 | =item Komodo | |
184 | ||
185 | ActiveState's cross-platform (as of April 2001 Windows and Linux), | |
186 | multi-language IDE has Perl support, including a regular expression | |
187 | debugger and remote debugging | |
188 | ( http://www.ActiveState.com/Products/Komodo/index.html ). (Visual | |
189 | Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta | |
190 | ( http://www.ActiveState.com/Products/VisualPerl/index.html )). | |
191 | ||
192 | =item The Object System | |
193 | ||
194 | ( http://www.castlelink.co.uk/object_system/ ) is a Perl web | |
195 | applications development IDE, apparently for any platform | |
196 | that runs Perl. | |
197 | ||
198 | =item Open Perl IDE | |
199 | ||
200 | ( http://open-perl-ide.sourceforge.net/ ) | |
201 | Open Perl IDE is an integrated development environment for writing | |
202 | and debugging Perl scripts with ActiveState's ActivePerl distribution | |
203 | under Windows 95/98/NT/2000. | |
204 | ||
205 | =item PerlBuilder | |
206 | ||
207 | ( http://www.solutionsoft.com/perl.htm ) is an integrated development | |
208 | environment for Windows that supports Perl development. | |
209 | ||
210 | =item visiPerl+ | |
211 | ||
212 | ( http://helpconsulting.net/visiperl/ ) | |
213 | From Help Consulting, for Windows. | |
214 | ||
215 | =item OptiPerl | |
216 | ||
217 | ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI | |
218 | environment, including debugger and syntax highlighting editor. | |
219 | ||
220 | =back | |
221 | ||
222 | For Windows there's also the | |
223 | ||
224 | =over 4 | |
225 | ||
226 | =item CodeMagicCD | |
227 | ||
228 | ( http://www.codemagiccd.com/ ) Collection of various programming | |
229 | tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming | |
230 | tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP | |
231 | GNU C/C++ compiler, Cint C interpreter, YaBasic. | |
232 | ||
233 | =back | |
234 | ||
235 | For editors: if you're on Unix you probably have vi or a vi clone already, | |
236 | and possibly an emacs too, so you may not need to download anything. | |
237 | In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the | |
238 | best available Perl editing mode in any editor. | |
239 | ||
240 | If you are using Windows, you can use any editor that lets | |
241 | you work with plain text, such as NotePad or WordPad. Word | |
242 | processors, such as Microsoft Word or WordPerfect, typically | |
243 | do not work since they insert all sorts of behind-the-scenes | |
244 | information, although some allow you to save files as "Text | |
245 | Only". You can also download text editors designed | |
246 | specifically for programming, such as Textpad | |
247 | ( http://www.textpad.com/ ) and UltraEdit | |
248 | ( http://www.ultraedit.com/ ), among others. | |
249 | ||
250 | If you are using Mac OS, the same concerns apply. MacPerl | |
251 | (for Classic environments) comes with a simple editor. | |
252 | Popular external editors are BBEdit ( http://www.bbedit.com/ ) | |
253 | or Alpha ( http://www.kelehers.org/alpha/ ). Mac OS X users can | |
254 | use Unix editors as well. | |
255 | ||
256 | =over 4 | |
257 | ||
258 | =item GNU Emacs | |
259 | ||
260 | http://www.gnu.org/software/emacs/windows/ntemacs.html | |
261 | ||
262 | =item MicroEMACS | |
263 | ||
264 | http://members.nbci.com/uemacs/ | |
265 | ||
266 | =item XEmacs | |
267 | ||
268 | http://www.xemacs.org/Download/index.html | |
269 | ||
270 | =back | |
271 | ||
272 | or a vi clone such as | |
273 | ||
274 | =over 4 | |
275 | ||
276 | =item Elvis | |
277 | ||
278 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ | |
279 | ||
280 | =item Vile | |
281 | ||
282 | http://vile.cx/ | |
283 | ||
284 | =item Vim | |
285 | ||
286 | http://www.vim.org/ | |
287 | ||
288 | win32: http://www.cs.vu.nl/%7Etmgil/vi.html | |
289 | ||
290 | =back | |
291 | ||
292 | For vi lovers in general, Windows or elsewhere: | |
293 | ||
294 | http://www.thomer.com/thomer/vi/vi.html | |
295 | ||
296 | nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is | |
297 | yet another vi clone, unfortunately not available for Windows, but in | |
298 | UNIX platforms you might be interested in trying it out, firstly because | |
299 | strictly speaking it is not a vi clone, it is the real vi, or the new | |
300 | incarnation of it, and secondly because you can embed Perl inside it | |
301 | to use Perl as the scripting language. nvi is not alone in this, | |
302 | though: at least also vim and vile offer an embedded Perl. | |
303 | ||
304 | The following are Win32 multilanguage editor/IDESs that support Perl: | |
305 | ||
306 | =over 4 | |
307 | ||
308 | =item Codewright | |
309 | ||
310 | http://www.starbase.com/ | |
311 | ||
312 | =item MultiEdit | |
313 | ||
314 | http://www.MultiEdit.com/ | |
315 | ||
316 | =item SlickEdit | |
317 | ||
318 | http://www.slickedit.com/ | |
319 | ||
320 | =back | |
321 | ||
322 | There is also a toyedit Text widget based editor written in Perl | |
323 | that is distributed with the Tk module on CPAN. The ptkdb | |
324 | ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that | |
325 | acts as a development environment of sorts. Perl Composer | |
326 | ( http://perlcomposer.sourceforge.net/vperl.html ) is an IDE for Perl/Tk | |
327 | GUI creation. | |
328 | ||
329 | In addition to an editor/IDE you might be interested in a more | |
330 | powerful shell environment for Win32. Your options include | |
331 | ||
332 | =over 4 | |
333 | ||
334 | =item Bash | |
335 | ||
336 | from the Cygwin package ( http://sources.redhat.com/cygwin/ ) | |
337 | ||
338 | =item Ksh | |
339 | ||
340 | from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of | |
341 | the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ ) | |
342 | ||
343 | =item Tcsh | |
344 | ||
345 | ftp://ftp.astron.com/pub/tcsh/ , see also | |
346 | http://www.primate.wisc.edu/software/csh-tcsh-book/ | |
347 | ||
348 | =item Zsh | |
349 | ||
350 | ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/ | |
351 | ||
352 | =back | |
353 | ||
354 | MKS and U/WIN are commercial (U/WIN is free for educational and | |
355 | research purposes), Cygwin is covered by the GNU Public License (but | |
356 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all | |
357 | contain (in addition to the shells) a comprehensive set of standard | |
358 | UNIX toolkit utilities. | |
359 | ||
360 | If you're transferring text files between Unix and Windows using FTP | |
361 | be sure to transfer them in ASCII mode so the ends of lines are | |
362 | appropriately converted. | |
363 | ||
364 | On Mac OS the MacPerl Application comes with a simple 32k text editor | |
365 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application | |
366 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with | |
367 | no 32k limit). | |
368 | ||
369 | =over 4 | |
370 | ||
371 | =item BBEdit and BBEdit Lite | |
372 | ||
373 | are text editors for Mac OS that have a Perl sensitivity mode | |
374 | ( http://web.barebones.com/ ). | |
375 | ||
376 | =item Alpha | |
377 | ||
378 | is an editor, written and extensible in Tcl, that nonetheless has | |
379 | built in support for several popular markup and programming languages | |
380 | including Perl and HTML ( http://alpha.olm.net/ ). | |
381 | ||
382 | =back | |
383 | ||
384 | Pepper and Pe are programming language sensitive text editors for Mac | |
385 | OS X and BeOS respectively ( http://www.hekkelman.com/ ). | |
386 | ||
387 | =head2 Where can I get Perl macros for vi? | |
388 | ||
389 | For a complete version of Tom Christiansen's vi configuration file, | |
390 | see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz , | |
391 | the standard benchmark file for vi emulators. The file runs best with nvi, | |
392 | the current version of vi out of Berkeley, which incidentally can be built | |
393 | with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ . | |
394 | ||
395 | =head2 Where can I get perl-mode for emacs? | |
396 | ||
397 | Since Emacs version 19 patchlevel 22 or so, there have been both a | |
398 | perl-mode.el and support for the Perl debugger built in. These should | |
399 | come with the standard Emacs 19 distribution. | |
400 | ||
401 | In the Perl source directory, you'll find a directory called "emacs", | |
402 | which contains a cperl-mode that color-codes keywords, provides | |
403 | context-sensitive help, and other nifty things. | |
404 | ||
405 | Note that the perl-mode of emacs will have fits with C<"main'foo"> | |
406 | (single quote), and mess up the indentation and highlighting. You | |
407 | are probably using C<"main::foo"> in new Perl code anyway, so this | |
408 | shouldn't be an issue. | |
409 | ||
410 | =head2 How can I use curses with Perl? | |
411 | ||
412 | The Curses module from CPAN provides a dynamically loadable object | |
413 | module interface to a curses library. A small demo can be found at the | |
414 | directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep ; | |
415 | this program repeats a command and updates the screen as needed, rendering | |
416 | B<rep ps axu> similar to B<top>. | |
417 | ||
418 | =head2 How can I use X or Tk with Perl? | |
419 | ||
420 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit | |
421 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface | |
422 | to the Athena Widget set. Both are available from CPAN. See the | |
423 | directory http://www.cpan.org/modules/by-category/08_User_Interfaces/ | |
424 | ||
425 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at | |
426 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference | |
427 | Guide available at | |
428 | http://www.cpan.org/authors/Stephen_O_Lidie/ , and the | |
429 | online manpages at | |
430 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . | |
431 | ||
432 | =head2 How can I generate simple menus without using CGI or Tk? | |
433 | ||
434 | The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz | |
435 | module, which is curses-based, can help with this. | |
436 | ||
437 | =head2 How can I make my Perl program run faster? | |
438 | ||
439 | The best way to do this is to come up with a better algorithm. This | |
440 | can often make a dramatic difference. Jon Bentley's book | |
441 | ``Programming Pearls'' (that's not a misspelling!) has some good tips | |
442 | on optimization, too. Advice on benchmarking boils down to: benchmark | |
443 | and profile to make sure you're optimizing the right part, look for | |
444 | better algorithms instead of microtuning your code, and when all else | |
445 | fails consider just buying faster hardware. You will probably want to | |
446 | read the answer to the earlier question ``How do I profile my Perl programs?'' | |
447 | if you haven't done so already. | |
448 | ||
449 | A different approach is to autoload seldom-used Perl code. See the | |
450 | AutoSplit and AutoLoader modules in the standard distribution for | |
451 | that. Or you could locate the bottleneck and think about writing just | |
452 | that part in C, the way we used to take bottlenecks in C code and | |
453 | write them in assembler. Similar to rewriting in C, | |
454 | modules that have critical sections can be written in C (for instance, the | |
455 | PDL module from CPAN). | |
456 | ||
457 | In some cases, it may be worth it to use the backend compiler to | |
458 | produce byte code (saving compilation time) or compile into C, which | |
459 | will certainly save compilation time and sometimes a small amount (but | |
460 | not much) execution time. See the question about compiling your Perl | |
461 | programs for more on the compiler--the wins aren't as obvious as you'd | |
462 | hope. | |
463 | ||
464 | If you're currently linking your perl executable to a shared I<libc.so>, | |
465 | you can often gain a 10-25% performance benefit by rebuilding it to | |
466 | link with a static libc.a instead. This will make a bigger perl | |
467 | executable, but your Perl programs (and programmers) may thank you for | |
468 | it. See the F<INSTALL> file in the source distribution for more | |
469 | information. | |
470 | ||
471 | Unsubstantiated reports allege that Perl interpreters that use sfio | |
472 | outperform those that don't (for I/O intensive applications). To try | |
473 | this, see the F<INSTALL> file in the source distribution, especially | |
474 | the ``Selecting File I/O mechanisms'' section. | |
475 | ||
476 | The undump program was an old attempt to speed up your Perl program | |
477 | by storing the already-compiled form to disk. This is no longer | |
478 | a viable option, as it only worked on a few architectures, and | |
479 | wasn't a good solution anyway. | |
480 | ||
481 | =head2 How can I make my Perl program take less memory? | |
482 | ||
483 | When it comes to time-space tradeoffs, Perl nearly always prefers to | |
484 | throw memory at a problem. Scalars in Perl use more memory than | |
485 | strings in C, arrays take more than that, and hashes use even more. While | |
486 | there's still a lot to be done, recent releases have been addressing | |
487 | these issues. For example, as of 5.004, duplicate hash keys are | |
488 | shared amongst all hashes using them, so require no reallocation. | |
489 | ||
490 | In some cases, using substr() or vec() to simulate arrays can be | |
491 | highly beneficial. For example, an array of a thousand booleans will | |
492 | take at least 20,000 bytes of space, but it can be turned into one | |
493 | 125-byte bit vector--a considerable memory savings. The standard | |
494 | Tie::SubstrHash module can also help for certain types of data | |
495 | structure. If you're working with specialist data structures | |
496 | (matrices, for instance) modules that implement these in C may use | |
497 | less memory than equivalent Perl modules. | |
498 | ||
499 | Another thing to try is learning whether your Perl was compiled with | |
500 | the system malloc or with Perl's builtin malloc. Whichever one it | |
501 | is, try using the other one and see whether this makes a difference. | |
502 | Information about malloc is in the F<INSTALL> file in the source | |
503 | distribution. You can find out whether you are using perl's malloc by | |
504 | typing C<perl -V:usemymalloc>. | |
505 | ||
506 | Of course, the best way to save memory is to not do anything to waste | |
507 | it in the first place. Good programming practices can go a long way | |
508 | toward this: | |
509 | ||
510 | =over 4 | |
511 | ||
512 | =item * Don't slurp! | |
513 | ||
514 | Don't read an entire file into memory if you can process it line | |
515 | by line. Or more concretely, use a loop like this: | |
516 | ||
517 | # | |
518 | # Good Idea | |
519 | # | |
520 | while (<FILE>) { | |
521 | # ... | |
522 | } | |
523 | ||
524 | instead of this: | |
525 | ||
526 | # | |
527 | # Bad Idea | |
528 | # | |
529 | @data = <FILE>; | |
530 | foreach (@data) { | |
531 | # ... | |
532 | } | |
533 | ||
534 | When the files you're processing are small, it doesn't much matter which | |
535 | way you do it, but it makes a huge difference when they start getting | |
536 | larger. | |
537 | ||
538 | =item * Use map and grep selectively | |
539 | ||
540 | Remember that both map and grep expect a LIST argument, so doing this: | |
541 | ||
542 | @wanted = grep {/pattern/} <FILE>; | |
543 | ||
544 | will cause the entire file to be slurped. For large files, it's better | |
545 | to loop: | |
546 | ||
547 | while (<FILE>) { | |
548 | push(@wanted, $_) if /pattern/; | |
549 | } | |
550 | ||
551 | =item * Avoid unnecessary quotes and stringification | |
552 | ||
553 | Don't quote large strings unless absolutely necessary: | |
554 | ||
555 | my $copy = "$large_string"; | |
556 | ||
557 | makes 2 copies of $large_string (one for $copy and another for the | |
558 | quotes), whereas | |
559 | ||
560 | my $copy = $large_string; | |
561 | ||
562 | only makes one copy. | |
563 | ||
564 | Ditto for stringifying large arrays: | |
565 | ||
566 | { | |
567 | local $, = "\n"; | |
568 | print @big_array; | |
569 | } | |
570 | ||
571 | is much more memory-efficient than either | |
572 | ||
573 | print join "\n", @big_array; | |
574 | ||
575 | or | |
576 | ||
577 | { | |
578 | local $" = "\n"; | |
579 | print "@big_array"; | |
580 | } | |
581 | ||
582 | ||
583 | =item * Pass by reference | |
584 | ||
585 | Pass arrays and hashes by reference, not by value. For one thing, it's | |
586 | the only way to pass multiple lists or hashes (or both) in a single | |
587 | call/return. It also avoids creating a copy of all the contents. This | |
588 | requires some judgment, however, because any changes will be propagated | |
589 | back to the original data. If you really want to mangle (er, modify) a | |
590 | copy, you'll have to sacrifice the memory needed to make one. | |
591 | ||
592 | =item * Tie large variables to disk. | |
593 | ||
594 | For "big" data stores (i.e. ones that exceed available memory) consider | |
595 | using one of the DB modules to store it on disk instead of in RAM. This | |
596 | will incur a penalty in access time, but that's probably better than | |
597 | causing your hard disk to thrash due to massive swapping. | |
598 | ||
599 | =back | |
600 | ||
601 | =head2 Is it unsafe to return a pointer to local data? | |
602 | ||
603 | No, Perl's garbage collection system takes care of this. | |
604 | ||
605 | sub makeone { | |
606 | my @a = ( 1 .. 10 ); | |
607 | return \@a; | |
608 | } | |
609 | ||
610 | for $i ( 1 .. 10 ) { | |
611 | push @many, makeone(); | |
612 | } | |
613 | ||
614 | print $many[4][5], "\n"; | |
615 | ||
616 | print "@many\n"; | |
617 | ||
618 | =head2 How can I free an array or hash so my program shrinks? | |
619 | ||
620 | You usually can't. On most operating systems, memory | |
621 | allocated to a program can never be returned to the system. | |
622 | That's why long-running programs sometimes re-exec | |
623 | themselves. Some operating systems (notably, systems that | |
624 | use mmap(2) for allocating large chunks of memory) can | |
625 | reclaim memory that is no longer used, but on such systems, | |
626 | perl must be configured and compiled to use the OS's malloc, | |
627 | not perl's. | |
628 | ||
629 | However, judicious use of my() on your variables will help make sure | |
630 | that they go out of scope so that Perl can free up that space for | |
631 | use in other parts of your program. A global variable, of course, never | |
632 | goes out of scope, so you can't get its space automatically reclaimed, | |
633 | although undef()ing and/or delete()ing it will achieve the same effect. | |
634 | In general, memory allocation and de-allocation isn't something you can | |
635 | or should be worrying about much in Perl, but even this capability | |
636 | (preallocation of data types) is in the works. | |
637 | ||
638 | =head2 How can I make my CGI script more efficient? | |
639 | ||
640 | Beyond the normal measures described to make general Perl programs | |
641 | faster or smaller, a CGI program has additional issues. It may be run | |
642 | several times per second. Given that each time it runs it will need | |
643 | to be re-compiled and will often allocate a megabyte or more of system | |
644 | memory, this can be a killer. Compiling into C B<isn't going to help | |
645 | you> because the process start-up overhead is where the bottleneck is. | |
646 | ||
647 | There are two popular ways to avoid this overhead. One solution | |
648 | involves running the Apache HTTP server (available from | |
649 | http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi | |
650 | plugin modules. | |
651 | ||
652 | With mod_perl and the Apache::Registry module (distributed with | |
653 | mod_perl), httpd will run with an embedded Perl interpreter which | |
654 | pre-compiles your script and then executes it within the same address | |
655 | space without forking. The Apache extension also gives Perl access to | |
656 | the internal server API, so modules written in Perl can do just about | |
657 | anything a module written in C can. For more on mod_perl, see | |
658 | http://perl.apache.org/ | |
659 | ||
660 | With the FCGI module (from CPAN) and the mod_fastcgi | |
661 | module (available from http://www.fastcgi.com/ ) each of your Perl | |
662 | programs becomes a permanent CGI daemon process. | |
663 | ||
664 | Both of these solutions can have far-reaching effects on your system | |
665 | and on the way you write your CGI programs, so investigate them with | |
666 | care. | |
667 | ||
668 | See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . | |
669 | ||
670 | A non-free, commercial product, ``The Velocity Engine for Perl'', | |
671 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ ) | |
672 | might also be worth looking at. It will allow you to increase the | |
673 | performance of your Perl programs, running programs up to 25 times | |
674 | faster than normal CGI Perl when running in persistent Perl mode or 4 | |
675 | to 5 times faster without any modification to your existing CGI | |
676 | programs. Fully functional evaluation copies are available from the | |
677 | web site. | |
678 | ||
679 | =head2 How can I hide the source for my Perl program? | |
680 | ||
681 | Delete it. :-) Seriously, there are a number of (mostly | |
682 | unsatisfactory) solutions with varying levels of ``security''. | |
683 | ||
684 | First of all, however, you I<can't> take away read permission, because | |
685 | the source code has to be readable in order to be compiled and | |
686 | interpreted. (That doesn't mean that a CGI script's source is | |
687 | readable by people on the web, though--only by people with access to | |
688 | the filesystem.) So you have to leave the permissions at the socially | |
689 | friendly 0755 level. | |
690 | ||
691 | Some people regard this as a security problem. If your program does | |
692 | insecure things and relies on people not knowing how to exploit those | |
693 | insecurities, it is not secure. It is often possible for someone to | |
694 | determine the insecure things and exploit them without viewing the | |
695 | source. Security through obscurity, the name for hiding your bugs | |
696 | instead of fixing them, is little security indeed. | |
697 | ||
698 | You can try using encryption via source filters (Starting from Perl | |
699 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in | |
700 | the standard distribution), but any decent programmer will be able to | |
701 | decrypt it. You can try using the byte code compiler and interpreter | |
702 | described below, but the curious might still be able to de-compile it. | |
703 | You can try using the native-code compiler described below, but | |
704 | crackers might be able to disassemble it. These pose varying degrees | |
705 | of difficulty to people wanting to get at your code, but none can | |
706 | definitively conceal it (true of every language, not just Perl). | |
707 | ||
708 | If you're concerned about people profiting from your code, then the | |
709 | bottom line is that nothing but a restrictive license will give you | |
710 | legal security. License your software and pepper it with threatening | |
711 | statements like ``This is unpublished proprietary software of XYZ Corp. | |
712 | Your access to it does not give you permission to use it blah blah | |
713 | blah.'' We are not lawyers, of course, so you should see a lawyer if | |
714 | you want to be sure your license's wording will stand up in court. | |
715 | ||
716 | =head2 How can I compile my Perl program into byte code or C? | |
717 | ||
718 | Malcolm Beattie has written a multifunction backend compiler, | |
719 | available from CPAN, that can do both these things. It is included | |
720 | in the perl5.005 release, but is still considered experimental. | |
721 | This means it's fun to play with if you're a programmer but not | |
722 | really for people looking for turn-key solutions. | |
723 | ||
724 | Merely compiling into C does not in and of itself guarantee that your | |
725 | code will run very much faster. That's because except for lucky cases | |
726 | where a lot of native type inferencing is possible, the normal Perl | |
727 | run-time system is still present and so your program will take just as | |
728 | long to run and be just as big. Most programs save little more than | |
729 | compilation time, leaving execution no more than 10-30% faster. A few | |
730 | rare programs actually benefit significantly (even running several times | |
731 | faster), but this takes some tweaking of your code. | |
732 | ||
733 | You'll probably be astonished to learn that the current version of the | |
734 | compiler generates a compiled form of your script whose executable is | |
735 | just as big as the original perl executable, and then some. That's | |
736 | because as currently written, all programs are prepared for a full | |
737 | eval() statement. You can tremendously reduce this cost by building a | |
738 | shared I<libperl.so> library and linking against that. See the | |
739 | F<INSTALL> podfile in the Perl source distribution for details. If | |
740 | you link your main perl binary with this, it will make it minuscule. | |
741 | For example, on one author's system, F</usr/bin/perl> is only 11k in | |
742 | size! | |
743 | ||
744 | In general, the compiler will do nothing to make a Perl program smaller, | |
745 | faster, more portable, or more secure. In fact, it can make your | |
746 | situation worse. The executable will be bigger, your VM system may take | |
747 | longer to load the whole thing, the binary is fragile and hard to fix, | |
748 | and compilation never stopped software piracy in the form of crackers, | |
749 | viruses, or bootleggers. The real advantage of the compiler is merely | |
750 | packaging, and once you see the size of what it makes (well, unless | |
751 | you use a shared I<libperl.so>), you'll probably want a complete | |
752 | Perl install anyway. | |
753 | ||
754 | =head2 How can I compile Perl into Java? | |
755 | ||
756 | You can also integrate Java and Perl with the | |
757 | Perl Resource Kit from O'Reilly and Associates. See | |
758 | http://www.oreilly.com/catalog/prkunix/ . | |
759 | ||
760 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in | |
761 | development, allows Perl code to be called from Java. See jpl/README | |
762 | in the Perl source tree. | |
763 | ||
764 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? | |
765 | ||
766 | For OS/2 just use | |
767 | ||
768 | extproc perl -S -your_switches | |
769 | ||
770 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's | |
771 | `extproc' handling). For DOS one should first invent a corresponding | |
772 | batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the | |
773 | F<INSTALL> file in the source distribution for more information). | |
774 | ||
775 | The Win95/NT installation, when using the ActiveState port of Perl, | |
776 | will modify the Registry to associate the C<.pl> extension with the | |
777 | perl interpreter. If you install another port, perhaps even building | |
778 | your own Win95/NT Perl from the standard sources by using a Windows port | |
779 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify | |
780 | the Registry yourself. In addition to associating C<.pl> with the | |
781 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them | |
782 | run the program C<install-linux.pl> merely by typing C<install-linux>. | |
783 | ||
784 | Macintosh Perl programs will have the appropriate Creator and | |
785 | Type, so that double-clicking them will invoke the Perl application. | |
786 | ||
787 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just | |
788 | throw the perl interpreter into your cgi-bin directory, in order to | |
789 | get your programs working for a web server. This is an EXTREMELY big | |
790 | security risk. Take the time to figure out how to do it correctly. | |
791 | ||
792 | =head2 Can I write useful Perl programs on the command line? | |
793 | ||
794 | Yes. Read L<perlrun> for more information. Some examples follow. | |
795 | (These assume standard Unix shell quoting rules.) | |
796 | ||
797 | # sum first and last fields | |
798 | perl -lane 'print $F[0] + $F[-1]' * | |
799 | ||
800 | # identify text files | |
801 | perl -le 'for(@ARGV) {print if -f && -T _}' * | |
802 | ||
803 | # remove (most) comments from C program | |
804 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c | |
805 | ||
806 | # make file a month younger than today, defeating reaper daemons | |
807 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * | |
808 | ||
809 | # find first unused uid | |
810 | perl -le '$i++ while getpwuid($i); print $i' | |
811 | ||
812 | # display reasonable manpath | |
813 | echo $PATH | perl -nl -072 -e ' | |
814 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' | |
815 | ||
816 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) | |
817 | ||
818 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? | |
819 | ||
820 | The problem is usually that the command interpreters on those systems | |
821 | have rather different ideas about quoting than the Unix shells under | |
822 | which the one-liners were created. On some systems, you may have to | |
823 | change single-quotes to double ones, which you must I<NOT> do on Unix | |
824 | or Plan9 systems. You might also have to change a single % to a %%. | |
825 | ||
826 | For example: | |
827 | ||
828 | # Unix | |
829 | perl -e 'print "Hello world\n"' | |
830 | ||
831 | # DOS, etc. | |
832 | perl -e "print \"Hello world\n\"" | |
833 | ||
834 | # Mac | |
835 | print "Hello world\n" | |
836 | (then Run "Myscript" or Shift-Command-R) | |
837 | ||
838 | # MPW | |
839 | perl -e 'print "Hello world\n"' | |
840 | ||
841 | # VMS | |
842 | perl -e "print ""Hello world\n""" | |
843 | ||
844 | The problem is that none of these examples are reliable: they depend on the | |
845 | command interpreter. Under Unix, the first two often work. Under DOS, | |
846 | it's entirely possible that neither works. If 4DOS was the command shell, | |
847 | you'd probably have better luck like this: | |
848 | ||
849 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
850 | ||
851 | Under the Mac, it depends which environment you are using. The MacPerl | |
852 | shell, or MPW, is much like Unix shells in its support for several | |
853 | quoting variants, except that it makes free use of the Mac's non-ASCII | |
854 | characters as control characters. | |
855 | ||
856 | Using qq(), q(), and qx(), instead of "double quotes", 'single | |
857 | quotes', and `backticks`, may make one-liners easier to write. | |
858 | ||
859 | There is no general solution to all of this. It is a mess. | |
860 | ||
861 | [Some of this answer was contributed by Kenneth Albanowski.] | |
862 | ||
863 | =head2 Where can I learn about CGI or Web programming in Perl? | |
864 | ||
865 | For modules, get the CGI or LWP modules from CPAN. For textbooks, | |
866 | see the two especially dedicated to web stuff in the question on | |
867 | books. For problems and questions related to the web, like ``Why | |
868 | do I get 500 Errors'' or ``Why doesn't it run from the browser right | |
869 | when it runs fine on the command line'', see the troubleshooting | |
870 | guides and references in L<perlfaq9> or in the CGI MetaFAQ: | |
871 | ||
872 | http://www.perl.org/CGI_MetaFAQ.html | |
873 | ||
874 | =head2 Where can I learn about object-oriented Perl programming? | |
875 | ||
876 | A good place to start is L<perltoot>, and you can use L<perlobj>, | |
877 | L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference. | |
878 | (If you are using really old Perl, you may not have all of these, | |
879 | try http://www.perldoc.com/ , but consider upgrading your perl.) | |
880 | ||
881 | A good book on OO on Perl is the "Object-Oriented Perl" | |
882 | by Damian Conway from Manning Publications, | |
883 | http://www.manning.com/Conway/index.html | |
884 | ||
885 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
886 | ||
887 | If you want to call C from Perl, start with L<perlxstut>, | |
888 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to | |
889 | call Perl from C, then read L<perlembed>, L<perlcall>, and | |
890 | L<perlguts>. Don't forget that you can learn a lot from looking at | |
891 | how the authors of existing extension modules wrote their code and | |
892 | solved their problems. | |
893 | ||
894 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in | |
895 | my C program; what am I doing wrong? | |
896 | ||
897 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If | |
898 | the tests pass, read the pods again and again and again. If they | |
899 | fail, see L<perlbug> and send a bug report with the output of | |
900 | C<make test TEST_VERBOSE=1> along with C<perl -V>. | |
901 | ||
902 | =head2 When I tried to run my script, I got this message. What does it mean? | |
903 | ||
904 | A complete list of Perl's error messages and warnings with explanatory | |
905 | text can be found in L<perldiag>. You can also use the splain program | |
906 | (distributed with Perl) to explain the error messages: | |
907 | ||
908 | perl program 2>diag.out | |
909 | splain [-v] [-p] diag.out | |
910 | ||
911 | or change your program to explain the messages for you: | |
912 | ||
913 | use diagnostics; | |
914 | ||
915 | or | |
916 | ||
917 | use diagnostics -verbose; | |
918 | ||
919 | =head2 What's MakeMaker? | |
920 | ||
921 | This module (part of the standard Perl distribution) is designed to | |
922 | write a Makefile for an extension module from a Makefile.PL. For more | |
923 | information, see L<ExtUtils::MakeMaker>. | |
924 | ||
925 | =head1 AUTHOR AND COPYRIGHT | |
926 | ||
927 | Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington. | |
928 | All rights reserved. | |
929 | ||
930 | This documentation is free; you can redistribute it and/or modify it | |
931 | under the same terms as Perl itself. | |
932 | ||
933 | Irrespective of its distribution, all code examples here are in the public | |
934 | domain. You are permitted and encouraged to use this code and any | |
935 | derivatives thereof in your own programs for fun or for profit as you | |
936 | see fit. A simple comment in the code giving credit to the FAQ would | |
937 | be courteous but is not required. |