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68dc0745 | 1 | =head1 NAME |
2 | ||
83ded9ee | 3 | perlfaq3 - Programming Tools ($Revision: 1.13 $, $Date: 2002/02/08 22:32:47 $) |
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. | |
3958b146 | 14 | Have you read the appropriate manpages? 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 | |
06a5f41f JH |
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) | |
68dc0745 | 28 | |
3958b146 | 29 | A crude table of contents for the Perl manpage set is found in L<perltoc>. |
68dc0745 | 30 | |
31 | =head2 How can I use Perl interactively? | |
32 | ||
33 | The typical approach uses the Perl debugger, described in the | |
3958b146 | 34 | perldebug(1) manpage, on an ``empty'' program, like this: |
68dc0745 | 35 | |
36 | perl -de 42 | |
37 | ||
38 | Now just type in any legal Perl code, and it will be immediately | |
39 | evaluated. You can also examine the symbol table, get stack | |
40 | backtraces, check variable values, set breakpoints, and other | |
92c2ed05 | 41 | operations typically found in symbolic debuggers. |
68dc0745 | 42 | |
43 | =head2 Is there a Perl shell? | |
44 | ||
55e174a4 JH |
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 | |
da75cd15 | 55 | functionality for control-flow statements and other things. |
55e174a4 JH |
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. | |
68dc0745 | 61 | |
62 | =head2 How do I debug my Perl programs? | |
63 | ||
9f1b1f2d | 64 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
a6dd486b | 65 | to detect dubious practices. |
68dc0745 | 66 | |
92c2ed05 GS |
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 | |
a6dd486b | 70 | variables with C<my>, C<our>, or C<use vars>. |
68dc0745 | 71 | |
a6dd486b JB |
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 | |
92c2ed05 | 74 | why. |
68dc0745 | 75 | |
92c2ed05 GS |
76 | open(FH, "> /etc/cantwrite") |
77 | or die "Couldn't write to /etc/cantwrite: $!\n"; | |
68dc0745 | 78 | |
92c2ed05 | 79 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
a6dd486b | 80 | programmers and even has sections for those of you who are upgrading |
92c2ed05 GS |
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. | |
68dc0745 | 86 | |
87 | =head2 How do I profile my Perl programs? | |
88 | ||
e083a89c | 89 | You should get the Devel::DProf module from the standard distribution |
733271b5 PK |
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 | |
e083a89c | 93 | code spends its time. |
68dc0745 | 94 | |
92c2ed05 GS |
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 | ||
65acb1b1 | 120 | Be aware that a good benchmark is very hard to write. It only tests the |
a6dd486b | 121 | data you give it and proves little about the differing complexities |
65acb1b1 TC |
122 | of contrasting algorithms. |
123 | ||
68dc0745 | 124 | =head2 How do I cross-reference my Perl programs? |
125 | ||
83ded9ee JH |
126 | The B::Xref module can be used to generate cross-reference reports |
127 | for Perl programs. | |
68dc0745 | 128 | |
c8db1d39 | 129 | perl -MO=Xref[,OPTIONS] scriptname.plx |
68dc0745 | 130 | |
131 | =head2 Is there a pretty-printer (formatter) for Perl? | |
132 | ||
55e174a4 JH |
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: | |
65acb1b1 TC |
147 | |
148 | set ai sw=4 | |
d92eb7b0 | 149 | map! ^O {^M}^[O^T |
65acb1b1 | 150 | |
55e174a4 | 151 | Put that in your F<.exrc> file (replacing the caret characters |
65acb1b1 | 152 | with control characters) and away you go. In insert mode, ^T is |
a6dd486b | 153 | for indenting, ^D is for undenting, and ^O is for blockdenting-- |
55e174a4 | 154 | as it were. A more complete example, with comments, can be found at |
213329dd | 155 | http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz |
92c2ed05 | 156 | |
06a5f41f JH |
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/. | |
65acb1b1 | 160 | |
d92eb7b0 | 161 | =head2 Is there a ctags for Perl? |
68dc0745 | 162 | |
bc06af74 JH |
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 | |
a93751fa | 168 | http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do |
bc06af74 | 169 | the trick. It can be easy to hack this into what you want. |
65acb1b1 TC |
170 | |
171 | =head2 Is there an IDE or Windows Perl Editor? | |
172 | ||
6641ed39 JH |
173 | Perl programs are just plain text, so any editor will do. |
174 | ||
6641ed39 JH |
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 | ||
5ca69f12 | 179 | If you want an IDE, check the following: |
68fbfbd7 JH |
180 | |
181 | =over 4 | |
182 | ||
68fbfbd7 JH |
183 | =item Komodo |
184 | ||
5ca69f12 JH |
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)). | |
68fbfbd7 | 191 | |
06e809ab JH |
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 | ||
ac1094a1 JH |
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 | ||
5ca69f12 JH |
205 | =item PerlBuilder |
206 | ||
207 | (http://www.solutionsoft.com/perl.htm) is an integrated development | |
208 | environment for Windows that supports Perl development. | |
8782d048 | 209 | |
68fbfbd7 JH |
210 | =item visiPerl+ |
211 | ||
ac1094a1 JH |
212 | ( http://helpconsulting.net/visiperl/ ) |
213 | From Help Consulting, for Windows. | |
68fbfbd7 JH |
214 | |
215 | =back | |
216 | ||
06e809ab JH |
217 | For Windows there's also the |
218 | ||
219 | =over 4 | |
220 | ||
221 | =item CodeMagicCD | |
222 | ||
223 | ( http://www.codemagiccd.com/ ) Collection of various programming | |
224 | tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming | |
225 | tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP | |
226 | GNU C/C++ compiler, Cint C interpreter, YaBasic. | |
227 | ||
228 | =back | |
229 | ||
5a13f98a | 230 | For editors: if you're on Unix you probably have vi or a vi clone already, |
6641ed39 | 231 | and possibly an emacs too, so you may not need to download anything. |
5a13f98a | 232 | In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the |
6641ed39 JH |
233 | best available Perl editing mode in any editor. |
234 | ||
cc30d1a7 JH |
235 | If you are using Windows, you can use any editor that lets |
236 | you work with plain text, such as NotePad or WordPad. Word | |
237 | processors, such as Microsoft Word or WordPerfect, typically | |
238 | do not work since they insert all sorts of behind-the-scenes | |
239 | information, although some allow you to save files as "Text | |
240 | Only". You can also download text editors designed | |
241 | specifically for programming, such as Textpad | |
242 | (http://www.textpad.com/) and UltraEdit | |
243 | (http://www.ultraedit.com), among others. | |
244 | ||
245 | If you are using MacOS, the same concerns apply. MacPerl | |
246 | (for Classic environments) comes with a simple editor. | |
247 | Popular external editors are BBEdit (http://www.bbedit.com) | |
248 | or Alpha (http://alpha.olm.net/). MacOS X users can use Unix | |
249 | editors as well. | |
68fbfbd7 JH |
250 | |
251 | =over 4 | |
252 | ||
253 | =item GNU Emacs | |
254 | ||
255 | http://www.gnu.org/software/emacs/windows/ntemacs.html | |
256 | ||
257 | =item MicroEMACS | |
258 | ||
259 | http://members.nbci.com/uemacs/ | |
260 | ||
261 | =item XEmacs | |
262 | ||
263 | http://www.xemacs.org/Download/index.html | |
264 | ||
265 | =back | |
266 | ||
267 | or a vi clone such as | |
268 | ||
269 | =over 4 | |
270 | ||
271 | =item Elvis | |
272 | ||
273 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ | |
274 | ||
275 | =item Vile | |
276 | ||
277 | http://vile.cx/ | |
278 | ||
279 | =item Vim | |
280 | ||
281 | http://www.vim.org/ | |
282 | ||
283 | win32: http://www.cs.vu.nl/%7Etmgil/vi.html | |
284 | ||
285 | =back | |
286 | ||
5a13f98a JH |
287 | For vi lovers in general, Windows or elsewhere: |
288 | http://www.thomer.com/thomer/vi/vi.html. | |
6641ed39 JH |
289 | |
290 | nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is | |
5a13f98a | 291 | yet another vi clone, unfortunately not available for Windows, but in |
6641ed39 JH |
292 | UNIX platforms you might be interested in trying it out, firstly because |
293 | strictly speaking it is not a vi clone, it is the real vi, or the new | |
294 | incarnation of it, and secondly because you can embed Perl inside it | |
295 | to use Perl as the scripting language. nvi is not alone in this, | |
7c82de66 | 296 | though: at least also vim and vile offer an embedded Perl. |
614a1598 | 297 | |
68fbfbd7 JH |
298 | The following are Win32 multilanguage editor/IDESs that support Perl: |
299 | ||
300 | =over 4 | |
301 | ||
302 | =item Codewright | |
303 | ||
304 | http://www.starbase.com/ | |
305 | ||
306 | =item MultiEdit | |
307 | ||
308 | http://www.MultiEdit.com/ | |
309 | ||
310 | =item SlickEdit | |
311 | ||
312 | http://www.slickedit.com/ | |
313 | ||
314 | =back | |
8782d048 | 315 | |
6641ed39 JH |
316 | There is also a toyedit Text widget based editor written in Perl |
317 | that is distributed with the Tk module on CPAN. The ptkdb | |
8782d048 JH |
318 | (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that |
319 | acts as a development environment of sorts. Perl Composer | |
e083a89c JH |
320 | (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk |
321 | GUI creation. | |
322 | ||
8782d048 | 323 | In addition to an editor/IDE you might be interested in a more |
68fbfbd7 JH |
324 | powerful shell environment for Win32. Your options include |
325 | ||
326 | =over 4 | |
327 | ||
328 | =item Bash | |
329 | ||
330 | from the Cygwin package (http://sources.redhat.com/cygwin/) | |
331 | ||
332 | =item Ksh | |
333 | ||
334 | from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of | |
335 | the U/WIN environment (http://www.research.att.com/sw/tools/uwin/) | |
336 | ||
337 | =item Tcsh | |
338 | ||
339 | ftp://ftp.astron.com/pub/tcsh/, see also | |
340 | http://www.primate.wisc.edu/software/csh-tcsh-book/ | |
341 | ||
342 | =item Zsh | |
343 | ||
344 | ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/ | |
345 | ||
346 | =back | |
347 | ||
614a1598 JH |
348 | MKS and U/WIN are commercial (U/WIN is free for educational and |
349 | research purposes), Cygwin is covered by the GNU Public License (but | |
350 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all | |
351 | contain (in addition to the shells) a comprehensive set of standard | |
352 | UNIX toolkit utilities. | |
8782d048 | 353 | |
5a13f98a JH |
354 | If you're transferring text files between Unix and Windows using FTP |
355 | be sure to transfer them in ASCII mode so the ends of lines are | |
356 | appropriately converted. | |
357 | ||
e083a89c JH |
358 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
359 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application | |
733271b5 | 360 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
68fbfbd7 JH |
361 | no 32k limit). |
362 | ||
363 | =over 4 | |
364 | ||
365 | =item BBEdit and BBEdit Lite | |
366 | ||
367 | are text editors for Mac OS that have a Perl sensitivity mode | |
368 | (http://web.barebones.com/). | |
369 | ||
370 | =item Alpha | |
371 | ||
372 | is an editor, written and extensible in Tcl, that nonetheless has | |
733271b5 | 373 | built in support for several popular markup and programming languages |
68fbfbd7 JH |
374 | including Perl and HTML (http://alpha.olm.net/). |
375 | ||
376 | =back | |
377 | ||
378 | Pepper and Pe are programming language sensitive text editors for Mac | |
379 | OS X and BeOS respectively (http://www.hekkelman.com/). | |
68dc0745 | 380 | |
381 | =head2 Where can I get Perl macros for vi? | |
382 | ||
383 | For a complete version of Tom Christiansen's vi configuration file, | |
a93751fa | 384 | see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
a6dd486b | 385 | the standard benchmark file for vi emulators. The file runs best with nvi, |
5a964f20 | 386 | the current version of vi out of Berkeley, which incidentally can be built |
a93751fa | 387 | with an embedded Perl interpreter--see http://www.cpan.org/src/misc. |
68dc0745 | 388 | |
389 | =head2 Where can I get perl-mode for emacs? | |
390 | ||
391 | Since Emacs version 19 patchlevel 22 or so, there have been both a | |
87275199 | 392 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 | 393 | come with the standard Emacs 19 distribution. |
394 | ||
87275199 | 395 | In the Perl source directory, you'll find a directory called "emacs", |
68dc0745 | 396 | which contains a cperl-mode that color-codes keywords, provides |
397 | context-sensitive help, and other nifty things. | |
398 | ||
92c2ed05 | 399 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 | 400 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 | 401 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 | 402 | shouldn't be an issue. |
68dc0745 | 403 | |
404 | =head2 How can I use curses with Perl? | |
405 | ||
406 | The Curses module from CPAN provides a dynamically loadable object | |
5a964f20 | 407 | module interface to a curses library. A small demo can be found at the |
a93751fa | 408 | directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep; |
5a964f20 TC |
409 | this program repeats a command and updates the screen as needed, rendering |
410 | B<rep ps axu> similar to B<top>. | |
68dc0745 | 411 | |
412 | =head2 How can I use X or Tk with Perl? | |
413 | ||
5a964f20 TC |
414 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
415 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface | |
416 | to the Athena Widget set. Both are available from CPAN. See the | |
a93751fa | 417 | directory http://www.cpan.org/modules/by-category/08_User_Interfaces/ |
68dc0745 | 418 | |
a6dd486b | 419 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
87275199 | 420 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
92c2ed05 | 421 | Guide available at |
213329dd | 422 | http://www.cpan.org/authors/Stephen_O_Lidie/ , and the |
92c2ed05 | 423 | online manpages at |
87275199 | 424 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 | 425 | |
68dc0745 | 426 | =head2 How can I generate simple menus without using CGI or Tk? |
427 | ||
a93751fa | 428 | The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz |
68dc0745 | 429 | module, which is curses-based, can help with this. |
430 | ||
68dc0745 | 431 | =head2 How can I make my Perl program run faster? |
432 | ||
92c2ed05 | 433 | The best way to do this is to come up with a better algorithm. This |
b73a15ae | 434 | can often make a dramatic difference. Jon Bentley's book |
92c2ed05 GS |
435 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
436 | on optimization, too. Advice on benchmarking boils down to: benchmark | |
437 | and profile to make sure you're optimizing the right part, look for | |
438 | better algorithms instead of microtuning your code, and when all else | |
57b19278 JS |
439 | fails consider just buying faster hardware. You will probably want to |
440 | read the answer to the earlier question ``How do I profile my Perl programs?'' | |
441 | if you haven't done so already. | |
68dc0745 | 442 | |
92c2ed05 | 443 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 | 444 | AutoSplit and AutoLoader modules in the standard distribution for |
445 | that. Or you could locate the bottleneck and think about writing just | |
446 | that part in C, the way we used to take bottlenecks in C code and | |
a6dd486b JB |
447 | write them in assembler. Similar to rewriting in C, |
448 | modules that have critical sections can be written in C (for instance, the | |
68dc0745 | 449 | PDL module from CPAN). |
450 | ||
451 | In some cases, it may be worth it to use the backend compiler to | |
452 | produce byte code (saving compilation time) or compile into C, which | |
453 | will certainly save compilation time and sometimes a small amount (but | |
454 | not much) execution time. See the question about compiling your Perl | |
92c2ed05 GS |
455 | programs for more on the compiler--the wins aren't as obvious as you'd |
456 | hope. | |
68dc0745 | 457 | |
92c2ed05 | 458 | If you're currently linking your perl executable to a shared I<libc.so>, |
68dc0745 | 459 | you can often gain a 10-25% performance benefit by rebuilding it to |
460 | link with a static libc.a instead. This will make a bigger perl | |
461 | executable, but your Perl programs (and programmers) may thank you for | |
462 | it. See the F<INSTALL> file in the source distribution for more | |
463 | information. | |
464 | ||
465 | Unsubstantiated reports allege that Perl interpreters that use sfio | |
87275199 | 466 | outperform those that don't (for I/O intensive applications). To try |
68dc0745 | 467 | this, see the F<INSTALL> file in the source distribution, especially |
87275199 | 468 | the ``Selecting File I/O mechanisms'' section. |
68dc0745 | 469 | |
470 | The undump program was an old attempt to speed up your Perl program | |
471 | by storing the already-compiled form to disk. This is no longer | |
472 | a viable option, as it only worked on a few architectures, and | |
473 | wasn't a good solution anyway. | |
474 | ||
475 | =head2 How can I make my Perl program take less memory? | |
476 | ||
477 | When it comes to time-space tradeoffs, Perl nearly always prefers to | |
478 | throw memory at a problem. Scalars in Perl use more memory than | |
65acb1b1 | 479 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 | 480 | there's still a lot to be done, recent releases have been addressing |
481 | these issues. For example, as of 5.004, duplicate hash keys are | |
482 | shared amongst all hashes using them, so require no reallocation. | |
483 | ||
484 | In some cases, using substr() or vec() to simulate arrays can be | |
485 | highly beneficial. For example, an array of a thousand booleans will | |
486 | take at least 20,000 bytes of space, but it can be turned into one | |
a6dd486b | 487 | 125-byte bit vector--a considerable memory savings. The standard |
68dc0745 | 488 | Tie::SubstrHash module can also help for certain types of data |
489 | structure. If you're working with specialist data structures | |
490 | (matrices, for instance) modules that implement these in C may use | |
491 | less memory than equivalent Perl modules. | |
492 | ||
493 | Another thing to try is learning whether your Perl was compiled with | |
54310121 | 494 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 | 495 | is, try using the other one and see whether this makes a difference. |
496 | Information about malloc is in the F<INSTALL> file in the source | |
497 | distribution. You can find out whether you are using perl's malloc by | |
498 | typing C<perl -V:usemymalloc>. | |
499 | ||
24f1ba9b JH |
500 | Of course, the best way to save memory is to not do anything to waste |
501 | it in the first place. Good programming practices can go a long way | |
502 | toward this: | |
503 | ||
504 | =over 4 | |
505 | ||
506 | =item * Don't slurp! | |
507 | ||
508 | Don't read an entire file into memory if you can process it line | |
509 | by line. Or more concretely, use a loop like this: | |
510 | ||
511 | # | |
512 | # Good Idea | |
513 | # | |
514 | while (<FILE>) { | |
515 | # ... | |
516 | } | |
517 | ||
518 | instead of this: | |
519 | ||
520 | # | |
521 | # Bad Idea | |
522 | # | |
523 | @data = <FILE>; | |
524 | foreach (@data) { | |
525 | # ... | |
526 | } | |
527 | ||
528 | When the files you're processing are small, it doesn't much matter which | |
529 | way you do it, but it makes a huge difference when they start getting | |
530 | larger. | |
531 | ||
bc06af74 JH |
532 | =item * Use map and grep selectively |
533 | ||
534 | Remember that both map and grep expect a LIST argument, so doing this: | |
535 | ||
536 | @wanted = grep {/pattern/} <FILE>; | |
537 | ||
538 | will cause the entire file to be slurped. For large files, it's better | |
539 | to loop: | |
540 | ||
541 | while (<FILE>) { | |
542 | push(@wanted, $_) if /pattern/; | |
543 | } | |
544 | ||
545 | =item * Avoid unnecessary quotes and stringification | |
546 | ||
547 | Don't quote large strings unless absolutely necessary: | |
548 | ||
549 | my $copy = "$large_string"; | |
550 | ||
551 | makes 2 copies of $large_string (one for $copy and another for the | |
552 | quotes), whereas | |
553 | ||
554 | my $copy = $large_string; | |
555 | ||
556 | only makes one copy. | |
557 | ||
558 | Ditto for stringifying large arrays: | |
559 | ||
560 | { | |
561 | local $, = "\n"; | |
562 | print @big_array; | |
563 | } | |
564 | ||
565 | is much more memory-efficient than either | |
566 | ||
567 | print join "\n", @big_array; | |
568 | ||
569 | or | |
570 | ||
571 | { | |
572 | local $" = "\n"; | |
573 | print "@big_array"; | |
574 | } | |
575 | ||
576 | ||
24f1ba9b JH |
577 | =item * Pass by reference |
578 | ||
579 | Pass arrays and hashes by reference, not by value. For one thing, it's | |
580 | the only way to pass multiple lists or hashes (or both) in a single | |
581 | call/return. It also avoids creating a copy of all the contents. This | |
582 | requires some judgment, however, because any changes will be propagated | |
583 | back to the original data. If you really want to mangle (er, modify) a | |
584 | copy, you'll have to sacrifice the memory needed to make one. | |
585 | ||
586 | =item * Tie large variables to disk. | |
587 | ||
588 | For "big" data stores (i.e. ones that exceed available memory) consider | |
589 | using one of the DB modules to store it on disk instead of in RAM. This | |
590 | will incur a penalty in access time, but that's probably better that | |
591 | causing your hard disk to thrash due to massive swapping. | |
592 | ||
593 | =back | |
594 | ||
68dc0745 | 595 | =head2 Is it unsafe to return a pointer to local data? |
596 | ||
597 | No, Perl's garbage collection system takes care of this. | |
598 | ||
599 | sub makeone { | |
600 | my @a = ( 1 .. 10 ); | |
601 | return \@a; | |
602 | } | |
603 | ||
604 | for $i ( 1 .. 10 ) { | |
605 | push @many, makeone(); | |
606 | } | |
607 | ||
608 | print $many[4][5], "\n"; | |
609 | ||
610 | print "@many\n"; | |
611 | ||
612 | =head2 How can I free an array or hash so my program shrinks? | |
613 | ||
c8db1d39 TC |
614 | You can't. On most operating systems, memory allocated to a program |
615 | can never be returned to the system. That's why long-running programs | |
65acb1b1 TC |
616 | sometimes re-exec themselves. Some operating systems (notably, |
617 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no | |
618 | longer used, but it doesn't appear to happen with Perl (yet). The Mac | |
619 | appears to be the only platform that will reliably (albeit, slowly) | |
620 | return memory to the OS. | |
621 | ||
622 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef | |
623 | $scalar> will return memory to the system, while on Solaris 2.6 it | |
624 | won't. In general, try it yourself and see. | |
68dc0745 | 625 | |
626 | However, judicious use of my() on your variables will help make sure | |
a6dd486b | 627 | that they go out of scope so that Perl can free up that space for |
92c2ed05 | 628 | use in other parts of your program. A global variable, of course, never |
68dc0745 | 629 | goes out of scope, so you can't get its space automatically reclaimed, |
630 | although undef()ing and/or delete()ing it will achieve the same effect. | |
46fc3d4c | 631 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 | 632 | or should be worrying about much in Perl, but even this capability |
633 | (preallocation of data types) is in the works. | |
634 | ||
635 | =head2 How can I make my CGI script more efficient? | |
636 | ||
637 | Beyond the normal measures described to make general Perl programs | |
638 | faster or smaller, a CGI program has additional issues. It may be run | |
639 | several times per second. Given that each time it runs it will need | |
46fc3d4c | 640 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 | 641 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c | 642 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 | 643 | |
92c2ed05 GS |
644 | There are two popular ways to avoid this overhead. One solution |
645 | involves running the Apache HTTP server (available from | |
68dc0745 | 646 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
92c2ed05 GS |
647 | plugin modules. |
648 | ||
649 | With mod_perl and the Apache::Registry module (distributed with | |
650 | mod_perl), httpd will run with an embedded Perl interpreter which | |
651 | pre-compiles your script and then executes it within the same address | |
652 | space without forking. The Apache extension also gives Perl access to | |
653 | the internal server API, so modules written in Perl can do just about | |
654 | anything a module written in C can. For more on mod_perl, see | |
655 | http://perl.apache.org/ | |
656 | ||
65acb1b1 | 657 | With the FCGI module (from CPAN) and the mod_fastcgi |
87275199 GS |
658 | module (available from http://www.fastcgi.com/) each of your Perl |
659 | programs becomes a permanent CGI daemon process. | |
68dc0745 | 660 | |
661 | Both of these solutions can have far-reaching effects on your system | |
87275199 | 662 | and on the way you write your CGI programs, so investigate them with |
68dc0745 | 663 | care. |
664 | ||
a93751fa | 665 | See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 | 666 | |
65acb1b1 | 667 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
a6dd486b JB |
668 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ ) |
669 | might also be worth looking at. It will allow you to increase the | |
670 | performance of your Perl programs, running programs up to 25 times | |
671 | faster than normal CGI Perl when running in persistent Perl mode or 4 | |
672 | to 5 times faster without any modification to your existing CGI | |
673 | programs. Fully functional evaluation copies are available from the | |
674 | web site. | |
c8db1d39 | 675 | |
68dc0745 | 676 | =head2 How can I hide the source for my Perl program? |
677 | ||
678 | Delete it. :-) Seriously, there are a number of (mostly | |
92c2ed05 | 679 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 | 680 | |
681 | First of all, however, you I<can't> take away read permission, because | |
682 | the source code has to be readable in order to be compiled and | |
683 | interpreted. (That doesn't mean that a CGI script's source is | |
a6dd486b JB |
684 | readable by people on the web, though--only by people with access to |
685 | the filesystem.) So you have to leave the permissions at the socially | |
92c2ed05 | 686 | friendly 0755 level. |
68dc0745 | 687 | |
688 | Some people regard this as a security problem. If your program does | |
a6dd486b | 689 | insecure things and relies on people not knowing how to exploit those |
68dc0745 | 690 | insecurities, it is not secure. It is often possible for someone to |
691 | determine the insecure things and exploit them without viewing the | |
692 | source. Security through obscurity, the name for hiding your bugs | |
693 | instead of fixing them, is little security indeed. | |
694 | ||
83df6a1d JH |
695 | You can try using encryption via source filters (Starting from Perl |
696 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in | |
697 | the standard distribution), but any decent programmer will be able to | |
698 | decrypt it. You can try using the byte code compiler and interpreter | |
699 | described below, but the curious might still be able to de-compile it. | |
700 | You can try using the native-code compiler described below, but | |
701 | crackers might be able to disassemble it. These pose varying degrees | |
702 | of difficulty to people wanting to get at your code, but none can | |
703 | definitively conceal it (true of every language, not just Perl). | |
68dc0745 | 704 | |
705 | If you're concerned about people profiting from your code, then the | |
d92eb7b0 | 706 | bottom line is that nothing but a restrictive license will give you |
68dc0745 | 707 | legal security. License your software and pepper it with threatening |
92c2ed05 | 708 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 | 709 | Your access to it does not give you permission to use it blah blah |
92c2ed05 | 710 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 | 711 | you want to be sure your license's wording will stand up in court. |
68dc0745 | 712 | |
54310121 | 713 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 | 714 | |
715 | Malcolm Beattie has written a multifunction backend compiler, | |
5e3006a4 GS |
716 | available from CPAN, that can do both these things. It is included |
717 | in the perl5.005 release, but is still considered experimental. | |
718 | This means it's fun to play with if you're a programmer but not | |
719 | really for people looking for turn-key solutions. | |
68dc0745 | 720 | |
92c2ed05 GS |
721 | Merely compiling into C does not in and of itself guarantee that your |
722 | code will run very much faster. That's because except for lucky cases | |
723 | where a lot of native type inferencing is possible, the normal Perl | |
a6dd486b | 724 | run-time system is still present and so your program will take just as |
92c2ed05 GS |
725 | long to run and be just as big. Most programs save little more than |
726 | compilation time, leaving execution no more than 10-30% faster. A few | |
a6dd486b | 727 | rare programs actually benefit significantly (even running several times |
92c2ed05 | 728 | faster), but this takes some tweaking of your code. |
68dc0745 | 729 | |
68dc0745 | 730 | You'll probably be astonished to learn that the current version of the |
731 | compiler generates a compiled form of your script whose executable is | |
732 | just as big as the original perl executable, and then some. That's | |
733 | because as currently written, all programs are prepared for a full | |
734 | eval() statement. You can tremendously reduce this cost by building a | |
92c2ed05 | 735 | shared I<libperl.so> library and linking against that. See the |
87275199 | 736 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 | 737 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 | 738 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 | 739 | size! |
740 | ||
5a964f20 | 741 | In general, the compiler will do nothing to make a Perl program smaller, |
a6dd486b JB |
742 | faster, more portable, or more secure. In fact, it can make your |
743 | situation worse. The executable will be bigger, your VM system may take | |
5a964f20 TC |
744 | longer to load the whole thing, the binary is fragile and hard to fix, |
745 | and compilation never stopped software piracy in the form of crackers, | |
746 | viruses, or bootleggers. The real advantage of the compiler is merely | |
747 | packaging, and once you see the size of what it makes (well, unless | |
748 | you use a shared I<libperl.so>), you'll probably want a complete | |
5e3006a4 | 749 | Perl install anyway. |
5a964f20 | 750 | |
65acb1b1 TC |
751 | =head2 How can I compile Perl into Java? |
752 | ||
a6dd486b | 753 | You can also integrate Java and Perl with the |
65acb1b1 | 754 | Perl Resource Kit from O'Reilly and Associates. See |
a6dd486b JB |
755 | http://www.oreilly.com/catalog/prkunix/ . |
756 | ||
757 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in | |
758 | development, allows Perl code to be called from Java. See jpl/README | |
759 | in the Perl source tree. | |
65acb1b1 | 760 | |
92c2ed05 | 761 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 | 762 | |
763 | For OS/2 just use | |
764 | ||
765 | extproc perl -S -your_switches | |
766 | ||
767 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's | |
46fc3d4c | 768 | `extproc' handling). For DOS one should first invent a corresponding |
a6dd486b | 769 | batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the |
68dc0745 | 770 | F<INSTALL> file in the source distribution for more information). |
771 | ||
92c2ed05 GS |
772 | The Win95/NT installation, when using the ActiveState port of Perl, |
773 | will modify the Registry to associate the C<.pl> extension with the | |
d92eb7b0 GS |
774 | perl interpreter. If you install another port, perhaps even building |
775 | your own Win95/NT Perl from the standard sources by using a Windows port | |
d702ae42 | 776 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 GS |
777 | the Registry yourself. In addition to associating C<.pl> with the |
778 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them | |
779 | run the program C<install-linux.pl> merely by typing C<install-linux>. | |
68dc0745 | 780 | |
87275199 GS |
781 | Macintosh Perl programs will have the appropriate Creator and |
782 | Type, so that double-clicking them will invoke the Perl application. | |
68dc0745 | 783 | |
784 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just | |
785 | throw the perl interpreter into your cgi-bin directory, in order to | |
87275199 | 786 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 | 787 | security risk. Take the time to figure out how to do it correctly. |
788 | ||
87275199 | 789 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 | 790 | |
791 | Yes. Read L<perlrun> for more information. Some examples follow. | |
792 | (These assume standard Unix shell quoting rules.) | |
793 | ||
794 | # sum first and last fields | |
5a964f20 | 795 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 | 796 | |
797 | # identify text files | |
798 | perl -le 'for(@ARGV) {print if -f && -T _}' * | |
799 | ||
5a964f20 | 800 | # remove (most) comments from C program |
68dc0745 | 801 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
802 | ||
803 | # make file a month younger than today, defeating reaper daemons | |
804 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * | |
805 | ||
806 | # find first unused uid | |
807 | perl -le '$i++ while getpwuid($i); print $i' | |
808 | ||
809 | # display reasonable manpath | |
810 | echo $PATH | perl -nl -072 -e ' | |
811 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' | |
812 | ||
87275199 | 813 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 | 814 | |
87275199 | 815 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 | 816 | |
817 | The problem is usually that the command interpreters on those systems | |
818 | have rather different ideas about quoting than the Unix shells under | |
819 | which the one-liners were created. On some systems, you may have to | |
820 | change single-quotes to double ones, which you must I<NOT> do on Unix | |
821 | or Plan9 systems. You might also have to change a single % to a %%. | |
822 | ||
823 | For example: | |
824 | ||
825 | # Unix | |
826 | perl -e 'print "Hello world\n"' | |
827 | ||
46fc3d4c | 828 | # DOS, etc. |
68dc0745 | 829 | perl -e "print \"Hello world\n\"" |
830 | ||
46fc3d4c | 831 | # Mac |
68dc0745 | 832 | print "Hello world\n" |
833 | (then Run "Myscript" or Shift-Command-R) | |
834 | ||
835 | # VMS | |
836 | perl -e "print ""Hello world\n""" | |
837 | ||
a6dd486b | 838 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 | 839 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b | 840 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 | 841 | you'd probably have better luck like this: |
68dc0745 | 842 | |
843 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
844 | ||
46fc3d4c | 845 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 | 846 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c | 847 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 | 848 | characters as control characters. |
849 | ||
65acb1b1 TC |
850 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
851 | quotes', and `backticks`, may make one-liners easier to write. | |
852 | ||
92c2ed05 GS |
853 | There is no general solution to all of this. It is a mess, pure and |
854 | simple. Sucks to be away from Unix, huh? :-) | |
68dc0745 | 855 | |
856 | [Some of this answer was contributed by Kenneth Albanowski.] | |
857 | ||
858 | =head2 Where can I learn about CGI or Web programming in Perl? | |
859 | ||
860 | For modules, get the CGI or LWP modules from CPAN. For textbooks, | |
861 | see the two especially dedicated to web stuff in the question on | |
92c2ed05 GS |
862 | books. For problems and questions related to the web, like ``Why |
863 | do I get 500 Errors'' or ``Why doesn't it run from the browser right | |
8305e449 JH |
864 | when it runs fine on the command line'', see the troubleshooting |
865 | guides and references in L<perlfaq9> or in the CGI MetaFAQ: | |
68dc0745 | 866 | |
8305e449 | 867 | http://www.perl.org/CGI_MetaFAQ.html |
0f542199 | 868 | |
68dc0745 | 869 | =head2 Where can I learn about object-oriented Perl programming? |
870 | ||
a6dd486b | 871 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
06a5f41f JH |
872 | L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference. |
873 | (If you are using really old Perl, you may not have all of these, | |
874 | try http://www.perldoc.com/ , but consider upgrading your perl.) | |
875 | ||
876 | A good book on OO on Perl is the "Object-Oriented Perl" | |
877 | by Damian Conway from Manning Publications, | |
878 | http://www.manning.com/Conway/index.html | |
68dc0745 | 879 | |
880 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
881 | ||
882 | If you want to call C from Perl, start with L<perlxstut>, | |
883 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to | |
884 | call Perl from C, then read L<perlembed>, L<perlcall>, and | |
885 | L<perlguts>. Don't forget that you can learn a lot from looking at | |
886 | how the authors of existing extension modules wrote their code and | |
887 | solved their problems. | |
888 | ||
889 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in | |
a6dd486b | 890 | my C program; what am I doing wrong? |
68dc0745 | 891 | |
892 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If | |
893 | the tests pass, read the pods again and again and again. If they | |
87275199 | 894 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 | 895 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
896 | ||
83ded9ee | 897 | =head2 When I tried to run my script, I got this message. What does it mean? |
68dc0745 | 898 | |
87275199 GS |
899 | A complete list of Perl's error messages and warnings with explanatory |
900 | text can be found in L<perldiag>. You can also use the splain program | |
901 | (distributed with Perl) to explain the error messages: | |
68dc0745 | 902 | |
903 | perl program 2>diag.out | |
904 | splain [-v] [-p] diag.out | |
905 | ||
906 | or change your program to explain the messages for you: | |
907 | ||
908 | use diagnostics; | |
909 | ||
910 | or | |
911 | ||
912 | use diagnostics -verbose; | |
913 | ||
914 | =head2 What's MakeMaker? | |
915 | ||
87275199 | 916 | This module (part of the standard Perl distribution) is designed to |
68dc0745 | 917 | write a Makefile for an extension module from a Makefile.PL. For more |
918 | information, see L<ExtUtils::MakeMaker>. | |
919 | ||
920 | =head1 AUTHOR AND COPYRIGHT | |
921 | ||
0bc0ad85 | 922 | Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington. |
5a964f20 TC |
923 | All rights reserved. |
924 | ||
5a7beb56 JH |
925 | This documentation is free; you can redistribute it and/or modify it |
926 | under the same terms as Perl itself. | |
c8db1d39 | 927 | |
87275199 | 928 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
929 | domain. You are permitted and encouraged to use this code and any |
930 | derivatives thereof in your own programs for fun or for profit as you | |
931 | see fit. A simple comment in the code giving credit to the FAQ would | |
932 | be courteous but is not required. |