Commit | Line | Data |
---|---|---|
68dc0745 | 1 | =head1 NAME |
2 | ||
bc06af74 | 3 | perlfaq3 - Programming Tools ($Revision: 1.6 $, $Date: 2001/10/03 23:06:15 $) |
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 | |
25 | Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html | |
26 | (not a man-page but still useful) | |
27 | ||
3958b146 | 28 | A crude table of contents for the Perl manpage 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 | |
3958b146 | 33 | perldebug(1) manpage, 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 | ||
55e174a4 JH |
44 | In general, not yet. There is psh available at |
45 | ||
46 | http://www.focusresearch.com/gregor/psh | |
47 | ||
48 | Which includes the following description: | |
49 | ||
50 | The Perl Shell is a shell that combines the interactive nature | |
51 | of a Unix shell with the power of Perl. The goal is to eventually | |
52 | have a full featured shell that behaves as expected for normal | |
53 | shell activity. But, the Perl Shell will use Perl syntax and | |
54 | functionality for for control-flow statements and other things. | |
55 | ||
56 | The Shell.pm module (distributed with Perl) makes Perl try commands | |
57 | which aren't part of the Perl language as shell commands. perlsh | |
58 | from the source distribution is simplistic and uninteresting, but | |
59 | may still be what you want. | |
68dc0745 | 60 | |
61 | =head2 How do I debug my Perl programs? | |
62 | ||
9f1b1f2d | 63 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
a6dd486b | 64 | to detect dubious practices. |
68dc0745 | 65 | |
92c2ed05 GS |
66 | Have you tried C<use strict>? It prevents you from using symbolic |
67 | references, makes you predeclare any subroutines that you call as bare | |
68 | words, and (probably most importantly) forces you to predeclare your | |
a6dd486b | 69 | variables with C<my>, C<our>, or C<use vars>. |
68dc0745 | 70 | |
a6dd486b JB |
71 | Did you check the return values of each and every system call? The operating |
72 | system (and thus Perl) tells you whether they worked, and if not | |
92c2ed05 | 73 | why. |
68dc0745 | 74 | |
92c2ed05 GS |
75 | open(FH, "> /etc/cantwrite") |
76 | or die "Couldn't write to /etc/cantwrite: $!\n"; | |
68dc0745 | 77 | |
92c2ed05 | 78 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
a6dd486b | 79 | programmers and even has sections for those of you who are upgrading |
92c2ed05 GS |
80 | from languages like I<awk> and I<C>. |
81 | ||
82 | Have you tried the Perl debugger, described in L<perldebug>? You can | |
83 | step through your program and see what it's doing and thus work out | |
84 | why what it's doing isn't what it should be doing. | |
68dc0745 | 85 | |
86 | =head2 How do I profile my Perl programs? | |
87 | ||
e083a89c | 88 | You should get the Devel::DProf module from the standard distribution |
733271b5 PK |
89 | (or separately on CPAN) and also use Benchmark.pm from the standard |
90 | distribution. The Benchmark module lets you time specific portions of | |
91 | your code, while Devel::DProf gives detailed breakdowns of where your | |
e083a89c | 92 | code spends its time. |
68dc0745 | 93 | |
92c2ed05 GS |
94 | Here's a sample use of Benchmark: |
95 | ||
96 | use Benchmark; | |
97 | ||
98 | @junk = `cat /etc/motd`; | |
99 | $count = 10_000; | |
100 | ||
101 | timethese($count, { | |
102 | 'map' => sub { my @a = @junk; | |
103 | map { s/a/b/ } @a; | |
104 | return @a | |
105 | }, | |
106 | 'for' => sub { my @a = @junk; | |
107 | local $_; | |
108 | for (@a) { s/a/b/ }; | |
109 | return @a }, | |
110 | }); | |
111 | ||
112 | This is what it prints (on one machine--your results will be dependent | |
113 | on your hardware, operating system, and the load on your machine): | |
114 | ||
115 | Benchmark: timing 10000 iterations of for, map... | |
116 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) | |
117 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) | |
118 | ||
65acb1b1 | 119 | Be aware that a good benchmark is very hard to write. It only tests the |
a6dd486b | 120 | data you give it and proves little about the differing complexities |
65acb1b1 TC |
121 | of contrasting algorithms. |
122 | ||
68dc0745 | 123 | =head2 How do I cross-reference my Perl programs? |
124 | ||
125 | The B::Xref module, shipped with the new, alpha-release Perl compiler | |
5a964f20 TC |
126 | (not the general distribution prior to the 5.005 release), can be used |
127 | to generate cross-reference reports 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 |
65acb1b1 | 155 | http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz |
92c2ed05 | 156 | |
65acb1b1 | 157 | If you are used to using the I<vgrind> program for printing out nice code |
92c2ed05 | 158 | to a laser printer, you can take a stab at this using |
68dc0745 | 159 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
160 | results are not particularly satisfying for sophisticated code. | |
161 | ||
87275199 | 162 | The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things |
65acb1b1 TC |
163 | related to generating nicely printed output of documents. |
164 | ||
d92eb7b0 | 165 | =head2 Is there a ctags for Perl? |
68dc0745 | 166 | |
bc06af74 JH |
167 | Recent versions of ctags do much more than older versions did. |
168 | EXUBERANT CTAGS is available from http://ctags.sourceforge.net/ | |
169 | and does a good job of making tags files for perl code. | |
170 | ||
171 | There is also a simple one at | |
68dc0745 | 172 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
bc06af74 | 173 | the trick. It can be easy to hack this into what you want. |
65acb1b1 TC |
174 | |
175 | =head2 Is there an IDE or Windows Perl Editor? | |
176 | ||
6641ed39 JH |
177 | Perl programs are just plain text, so any editor will do. |
178 | ||
6641ed39 JH |
179 | If you're on Unix, you already have an IDE--Unix itself. The UNIX |
180 | philosophy is the philosophy of several small tools that each do one | |
181 | thing and do it well. It's like a carpenter's toolbox. | |
182 | ||
5ca69f12 | 183 | If you want an IDE, check the following: |
68fbfbd7 JH |
184 | |
185 | =over 4 | |
186 | ||
68fbfbd7 JH |
187 | =item Komodo |
188 | ||
5ca69f12 JH |
189 | ActiveState's cross-platform (as of April 2001 Windows and Linux), |
190 | multi-language IDE has Perl support, including a regular expression | |
191 | debugger and remote debugging | |
192 | (http://www.ActiveState.com/Products/Komodo/index.html). (Visual | |
193 | Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta | |
194 | (http://www.ActiveState.com/Products/VisualPerl/index.html)). | |
68fbfbd7 | 195 | |
06e809ab JH |
196 | =item The Object System |
197 | ||
198 | (http://www.castlelink.co.uk/object_system/) is a Perl web | |
199 | applications development IDE, apparently for any platform | |
200 | that runs Perl. | |
201 | ||
ac1094a1 JH |
202 | =item Open Perl IDE |
203 | ||
204 | ( http://open-perl-ide.sourceforge.net/ ) | |
205 | Open Perl IDE is an integrated development environment for writing | |
206 | and debugging Perl scripts with ActiveState's ActivePerl distribution | |
207 | under Windows 95/98/NT/2000. | |
208 | ||
5ca69f12 JH |
209 | =item PerlBuilder |
210 | ||
211 | (http://www.solutionsoft.com/perl.htm) is an integrated development | |
212 | environment for Windows that supports Perl development. | |
8782d048 | 213 | |
68fbfbd7 JH |
214 | =item visiPerl+ |
215 | ||
ac1094a1 JH |
216 | ( http://helpconsulting.net/visiperl/ ) |
217 | From Help Consulting, for Windows. | |
68fbfbd7 JH |
218 | |
219 | =back | |
220 | ||
06e809ab JH |
221 | For Windows there's also the |
222 | ||
223 | =over 4 | |
224 | ||
225 | =item CodeMagicCD | |
226 | ||
227 | ( http://www.codemagiccd.com/ ) Collection of various programming | |
228 | tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming | |
229 | tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP | |
230 | GNU C/C++ compiler, Cint C interpreter, YaBasic. | |
231 | ||
232 | =back | |
233 | ||
5a13f98a | 234 | For editors: if you're on Unix you probably have vi or a vi clone already, |
6641ed39 | 235 | and possibly an emacs too, so you may not need to download anything. |
5a13f98a | 236 | In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the |
6641ed39 JH |
237 | best available Perl editing mode in any editor. |
238 | ||
68fbfbd7 JH |
239 | For Windows editors: you can download an Emacs |
240 | ||
241 | =over 4 | |
242 | ||
243 | =item GNU Emacs | |
244 | ||
245 | http://www.gnu.org/software/emacs/windows/ntemacs.html | |
246 | ||
247 | =item MicroEMACS | |
248 | ||
249 | http://members.nbci.com/uemacs/ | |
250 | ||
251 | =item XEmacs | |
252 | ||
253 | http://www.xemacs.org/Download/index.html | |
254 | ||
255 | =back | |
256 | ||
257 | or a vi clone such as | |
258 | ||
259 | =over 4 | |
260 | ||
261 | =item Elvis | |
262 | ||
263 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ | |
264 | ||
265 | =item Vile | |
266 | ||
267 | http://vile.cx/ | |
268 | ||
269 | =item Vim | |
270 | ||
271 | http://www.vim.org/ | |
272 | ||
273 | win32: http://www.cs.vu.nl/%7Etmgil/vi.html | |
274 | ||
275 | =back | |
276 | ||
5a13f98a JH |
277 | For vi lovers in general, Windows or elsewhere: |
278 | http://www.thomer.com/thomer/vi/vi.html. | |
6641ed39 JH |
279 | |
280 | nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is | |
5a13f98a | 281 | yet another vi clone, unfortunately not available for Windows, but in |
6641ed39 JH |
282 | UNIX platforms you might be interested in trying it out, firstly because |
283 | strictly speaking it is not a vi clone, it is the real vi, or the new | |
284 | incarnation of it, and secondly because you can embed Perl inside it | |
285 | to use Perl as the scripting language. nvi is not alone in this, | |
7c82de66 | 286 | though: at least also vim and vile offer an embedded Perl. |
614a1598 | 287 | |
68fbfbd7 JH |
288 | The following are Win32 multilanguage editor/IDESs that support Perl: |
289 | ||
290 | =over 4 | |
291 | ||
292 | =item Codewright | |
293 | ||
294 | http://www.starbase.com/ | |
295 | ||
296 | =item MultiEdit | |
297 | ||
298 | http://www.MultiEdit.com/ | |
299 | ||
300 | =item SlickEdit | |
301 | ||
302 | http://www.slickedit.com/ | |
303 | ||
304 | =back | |
8782d048 | 305 | |
6641ed39 JH |
306 | There is also a toyedit Text widget based editor written in Perl |
307 | that is distributed with the Tk module on CPAN. The ptkdb | |
8782d048 JH |
308 | (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that |
309 | acts as a development environment of sorts. Perl Composer | |
e083a89c JH |
310 | (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk |
311 | GUI creation. | |
312 | ||
8782d048 | 313 | In addition to an editor/IDE you might be interested in a more |
68fbfbd7 JH |
314 | powerful shell environment for Win32. Your options include |
315 | ||
316 | =over 4 | |
317 | ||
318 | =item Bash | |
319 | ||
320 | from the Cygwin package (http://sources.redhat.com/cygwin/) | |
321 | ||
322 | =item Ksh | |
323 | ||
324 | from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of | |
325 | the U/WIN environment (http://www.research.att.com/sw/tools/uwin/) | |
326 | ||
327 | =item Tcsh | |
328 | ||
329 | ftp://ftp.astron.com/pub/tcsh/, see also | |
330 | http://www.primate.wisc.edu/software/csh-tcsh-book/ | |
331 | ||
332 | =item Zsh | |
333 | ||
334 | ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/ | |
335 | ||
336 | =back | |
337 | ||
614a1598 JH |
338 | MKS and U/WIN are commercial (U/WIN is free for educational and |
339 | research purposes), Cygwin is covered by the GNU Public License (but | |
340 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all | |
341 | contain (in addition to the shells) a comprehensive set of standard | |
342 | UNIX toolkit utilities. | |
8782d048 | 343 | |
5a13f98a JH |
344 | If you're transferring text files between Unix and Windows using FTP |
345 | be sure to transfer them in ASCII mode so the ends of lines are | |
346 | appropriately converted. | |
347 | ||
e083a89c JH |
348 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
349 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application | |
733271b5 | 350 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
68fbfbd7 JH |
351 | no 32k limit). |
352 | ||
353 | =over 4 | |
354 | ||
355 | =item BBEdit and BBEdit Lite | |
356 | ||
357 | are text editors for Mac OS that have a Perl sensitivity mode | |
358 | (http://web.barebones.com/). | |
359 | ||
360 | =item Alpha | |
361 | ||
362 | is an editor, written and extensible in Tcl, that nonetheless has | |
733271b5 | 363 | built in support for several popular markup and programming languages |
68fbfbd7 JH |
364 | including Perl and HTML (http://alpha.olm.net/). |
365 | ||
366 | =back | |
367 | ||
368 | Pepper and Pe are programming language sensitive text editors for Mac | |
369 | OS X and BeOS respectively (http://www.hekkelman.com/). | |
68dc0745 | 370 | |
371 | =head2 Where can I get Perl macros for vi? | |
372 | ||
373 | For a complete version of Tom Christiansen's vi configuration file, | |
a6dd486b JB |
374 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
375 | the standard benchmark file for vi emulators. The file runs best with nvi, | |
5a964f20 | 376 | the current version of vi out of Berkeley, which incidentally can be built |
a6dd486b | 377 | with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc. |
68dc0745 | 378 | |
379 | =head2 Where can I get perl-mode for emacs? | |
380 | ||
381 | Since Emacs version 19 patchlevel 22 or so, there have been both a | |
87275199 | 382 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 | 383 | come with the standard Emacs 19 distribution. |
384 | ||
87275199 | 385 | In the Perl source directory, you'll find a directory called "emacs", |
68dc0745 | 386 | which contains a cperl-mode that color-codes keywords, provides |
387 | context-sensitive help, and other nifty things. | |
388 | ||
92c2ed05 | 389 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 | 390 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 | 391 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 | 392 | shouldn't be an issue. |
68dc0745 | 393 | |
394 | =head2 How can I use curses with Perl? | |
395 | ||
396 | The Curses module from CPAN provides a dynamically loadable object | |
5a964f20 TC |
397 | module interface to a curses library. A small demo can be found at the |
398 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; | |
399 | this program repeats a command and updates the screen as needed, rendering | |
400 | B<rep ps axu> similar to B<top>. | |
68dc0745 | 401 | |
402 | =head2 How can I use X or Tk with Perl? | |
403 | ||
5a964f20 TC |
404 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
405 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface | |
406 | to the Athena Widget set. Both are available from CPAN. See the | |
407 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ | |
68dc0745 | 408 | |
a6dd486b | 409 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
87275199 | 410 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
92c2ed05 GS |
411 | Guide available at |
412 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the | |
413 | online manpages at | |
87275199 | 414 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 | 415 | |
68dc0745 | 416 | =head2 How can I generate simple menus without using CGI or Tk? |
417 | ||
418 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz | |
419 | module, which is curses-based, can help with this. | |
420 | ||
68dc0745 | 421 | =head2 What is undump? |
422 | ||
a6dd486b | 423 | See the next question on ``How can I make my Perl program run faster?'' |
68dc0745 | 424 | |
425 | =head2 How can I make my Perl program run faster? | |
426 | ||
92c2ed05 | 427 | The best way to do this is to come up with a better algorithm. This |
b73a15ae | 428 | can often make a dramatic difference. Jon Bentley's book |
92c2ed05 GS |
429 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
430 | on optimization, too. Advice on benchmarking boils down to: benchmark | |
431 | and profile to make sure you're optimizing the right part, look for | |
432 | better algorithms instead of microtuning your code, and when all else | |
57b19278 JS |
433 | fails consider just buying faster hardware. You will probably want to |
434 | read the answer to the earlier question ``How do I profile my Perl programs?'' | |
435 | if you haven't done so already. | |
68dc0745 | 436 | |
92c2ed05 | 437 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 | 438 | AutoSplit and AutoLoader modules in the standard distribution for |
439 | that. Or you could locate the bottleneck and think about writing just | |
440 | that part in C, the way we used to take bottlenecks in C code and | |
a6dd486b JB |
441 | write them in assembler. Similar to rewriting in C, |
442 | modules that have critical sections can be written in C (for instance, the | |
68dc0745 | 443 | PDL module from CPAN). |
444 | ||
445 | In some cases, it may be worth it to use the backend compiler to | |
446 | produce byte code (saving compilation time) or compile into C, which | |
447 | will certainly save compilation time and sometimes a small amount (but | |
448 | not much) execution time. See the question about compiling your Perl | |
92c2ed05 GS |
449 | programs for more on the compiler--the wins aren't as obvious as you'd |
450 | hope. | |
68dc0745 | 451 | |
92c2ed05 | 452 | If you're currently linking your perl executable to a shared I<libc.so>, |
68dc0745 | 453 | you can often gain a 10-25% performance benefit by rebuilding it to |
454 | link with a static libc.a instead. This will make a bigger perl | |
455 | executable, but your Perl programs (and programmers) may thank you for | |
456 | it. See the F<INSTALL> file in the source distribution for more | |
457 | information. | |
458 | ||
459 | Unsubstantiated reports allege that Perl interpreters that use sfio | |
87275199 | 460 | outperform those that don't (for I/O intensive applications). To try |
68dc0745 | 461 | this, see the F<INSTALL> file in the source distribution, especially |
87275199 | 462 | the ``Selecting File I/O mechanisms'' section. |
68dc0745 | 463 | |
464 | The undump program was an old attempt to speed up your Perl program | |
465 | by storing the already-compiled form to disk. This is no longer | |
466 | a viable option, as it only worked on a few architectures, and | |
467 | wasn't a good solution anyway. | |
468 | ||
469 | =head2 How can I make my Perl program take less memory? | |
470 | ||
471 | When it comes to time-space tradeoffs, Perl nearly always prefers to | |
472 | throw memory at a problem. Scalars in Perl use more memory than | |
65acb1b1 | 473 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 | 474 | there's still a lot to be done, recent releases have been addressing |
475 | these issues. For example, as of 5.004, duplicate hash keys are | |
476 | shared amongst all hashes using them, so require no reallocation. | |
477 | ||
478 | In some cases, using substr() or vec() to simulate arrays can be | |
479 | highly beneficial. For example, an array of a thousand booleans will | |
480 | take at least 20,000 bytes of space, but it can be turned into one | |
a6dd486b | 481 | 125-byte bit vector--a considerable memory savings. The standard |
68dc0745 | 482 | Tie::SubstrHash module can also help for certain types of data |
483 | structure. If you're working with specialist data structures | |
484 | (matrices, for instance) modules that implement these in C may use | |
485 | less memory than equivalent Perl modules. | |
486 | ||
487 | Another thing to try is learning whether your Perl was compiled with | |
54310121 | 488 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 | 489 | is, try using the other one and see whether this makes a difference. |
490 | Information about malloc is in the F<INSTALL> file in the source | |
491 | distribution. You can find out whether you are using perl's malloc by | |
492 | typing C<perl -V:usemymalloc>. | |
493 | ||
24f1ba9b JH |
494 | Of course, the best way to save memory is to not do anything to waste |
495 | it in the first place. Good programming practices can go a long way | |
496 | toward this: | |
497 | ||
498 | =over 4 | |
499 | ||
500 | =item * Don't slurp! | |
501 | ||
502 | Don't read an entire file into memory if you can process it line | |
503 | by line. Or more concretely, use a loop like this: | |
504 | ||
505 | # | |
506 | # Good Idea | |
507 | # | |
508 | while (<FILE>) { | |
509 | # ... | |
510 | } | |
511 | ||
512 | instead of this: | |
513 | ||
514 | # | |
515 | # Bad Idea | |
516 | # | |
517 | @data = <FILE>; | |
518 | foreach (@data) { | |
519 | # ... | |
520 | } | |
521 | ||
522 | When the files you're processing are small, it doesn't much matter which | |
523 | way you do it, but it makes a huge difference when they start getting | |
524 | larger. | |
525 | ||
bc06af74 JH |
526 | =item * Use map and grep selectively |
527 | ||
528 | Remember that both map and grep expect a LIST argument, so doing this: | |
529 | ||
530 | @wanted = grep {/pattern/} <FILE>; | |
531 | ||
532 | will cause the entire file to be slurped. For large files, it's better | |
533 | to loop: | |
534 | ||
535 | while (<FILE>) { | |
536 | push(@wanted, $_) if /pattern/; | |
537 | } | |
538 | ||
539 | =item * Avoid unnecessary quotes and stringification | |
540 | ||
541 | Don't quote large strings unless absolutely necessary: | |
542 | ||
543 | my $copy = "$large_string"; | |
544 | ||
545 | makes 2 copies of $large_string (one for $copy and another for the | |
546 | quotes), whereas | |
547 | ||
548 | my $copy = $large_string; | |
549 | ||
550 | only makes one copy. | |
551 | ||
552 | Ditto for stringifying large arrays: | |
553 | ||
554 | { | |
555 | local $, = "\n"; | |
556 | print @big_array; | |
557 | } | |
558 | ||
559 | is much more memory-efficient than either | |
560 | ||
561 | print join "\n", @big_array; | |
562 | ||
563 | or | |
564 | ||
565 | { | |
566 | local $" = "\n"; | |
567 | print "@big_array"; | |
568 | } | |
569 | ||
570 | ||
24f1ba9b JH |
571 | =item * Pass by reference |
572 | ||
573 | Pass arrays and hashes by reference, not by value. For one thing, it's | |
574 | the only way to pass multiple lists or hashes (or both) in a single | |
575 | call/return. It also avoids creating a copy of all the contents. This | |
576 | requires some judgment, however, because any changes will be propagated | |
577 | back to the original data. If you really want to mangle (er, modify) a | |
578 | copy, you'll have to sacrifice the memory needed to make one. | |
579 | ||
580 | =item * Tie large variables to disk. | |
581 | ||
582 | For "big" data stores (i.e. ones that exceed available memory) consider | |
583 | using one of the DB modules to store it on disk instead of in RAM. This | |
584 | will incur a penalty in access time, but that's probably better that | |
585 | causing your hard disk to thrash due to massive swapping. | |
586 | ||
587 | =back | |
588 | ||
68dc0745 | 589 | =head2 Is it unsafe to return a pointer to local data? |
590 | ||
591 | No, Perl's garbage collection system takes care of this. | |
592 | ||
593 | sub makeone { | |
594 | my @a = ( 1 .. 10 ); | |
595 | return \@a; | |
596 | } | |
597 | ||
598 | for $i ( 1 .. 10 ) { | |
599 | push @many, makeone(); | |
600 | } | |
601 | ||
602 | print $many[4][5], "\n"; | |
603 | ||
604 | print "@many\n"; | |
605 | ||
606 | =head2 How can I free an array or hash so my program shrinks? | |
607 | ||
c8db1d39 TC |
608 | You can't. On most operating systems, memory allocated to a program |
609 | can never be returned to the system. That's why long-running programs | |
65acb1b1 TC |
610 | sometimes re-exec themselves. Some operating systems (notably, |
611 | FreeBSD and Linux) allegedly reclaim large chunks of memory that is no | |
612 | longer used, but it doesn't appear to happen with Perl (yet). The Mac | |
613 | appears to be the only platform that will reliably (albeit, slowly) | |
614 | return memory to the OS. | |
615 | ||
616 | We've had reports that on Linux (Redhat 5.1) on Intel, C<undef | |
617 | $scalar> will return memory to the system, while on Solaris 2.6 it | |
618 | won't. In general, try it yourself and see. | |
68dc0745 | 619 | |
620 | However, judicious use of my() on your variables will help make sure | |
a6dd486b | 621 | that they go out of scope so that Perl can free up that space for |
92c2ed05 | 622 | use in other parts of your program. A global variable, of course, never |
68dc0745 | 623 | goes out of scope, so you can't get its space automatically reclaimed, |
624 | although undef()ing and/or delete()ing it will achieve the same effect. | |
46fc3d4c | 625 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 | 626 | or should be worrying about much in Perl, but even this capability |
627 | (preallocation of data types) is in the works. | |
628 | ||
629 | =head2 How can I make my CGI script more efficient? | |
630 | ||
631 | Beyond the normal measures described to make general Perl programs | |
632 | faster or smaller, a CGI program has additional issues. It may be run | |
633 | several times per second. Given that each time it runs it will need | |
46fc3d4c | 634 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 | 635 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c | 636 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 | 637 | |
92c2ed05 GS |
638 | There are two popular ways to avoid this overhead. One solution |
639 | involves running the Apache HTTP server (available from | |
68dc0745 | 640 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
92c2ed05 GS |
641 | plugin modules. |
642 | ||
643 | With mod_perl and the Apache::Registry module (distributed with | |
644 | mod_perl), httpd will run with an embedded Perl interpreter which | |
645 | pre-compiles your script and then executes it within the same address | |
646 | space without forking. The Apache extension also gives Perl access to | |
647 | the internal server API, so modules written in Perl can do just about | |
648 | anything a module written in C can. For more on mod_perl, see | |
649 | http://perl.apache.org/ | |
650 | ||
65acb1b1 | 651 | With the FCGI module (from CPAN) and the mod_fastcgi |
87275199 GS |
652 | module (available from http://www.fastcgi.com/) each of your Perl |
653 | programs becomes a permanent CGI daemon process. | |
68dc0745 | 654 | |
655 | Both of these solutions can have far-reaching effects on your system | |
87275199 | 656 | and on the way you write your CGI programs, so investigate them with |
68dc0745 | 657 | care. |
658 | ||
92c2ed05 | 659 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 | 660 | |
65acb1b1 | 661 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
a6dd486b JB |
662 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ ) |
663 | might also be worth looking at. It will allow you to increase the | |
664 | performance of your Perl programs, running programs up to 25 times | |
665 | faster than normal CGI Perl when running in persistent Perl mode or 4 | |
666 | to 5 times faster without any modification to your existing CGI | |
667 | programs. Fully functional evaluation copies are available from the | |
668 | web site. | |
c8db1d39 | 669 | |
68dc0745 | 670 | =head2 How can I hide the source for my Perl program? |
671 | ||
672 | Delete it. :-) Seriously, there are a number of (mostly | |
92c2ed05 | 673 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 | 674 | |
675 | First of all, however, you I<can't> take away read permission, because | |
676 | the source code has to be readable in order to be compiled and | |
677 | interpreted. (That doesn't mean that a CGI script's source is | |
a6dd486b JB |
678 | readable by people on the web, though--only by people with access to |
679 | the filesystem.) So you have to leave the permissions at the socially | |
92c2ed05 | 680 | friendly 0755 level. |
68dc0745 | 681 | |
682 | Some people regard this as a security problem. If your program does | |
a6dd486b | 683 | insecure things and relies on people not knowing how to exploit those |
68dc0745 | 684 | insecurities, it is not secure. It is often possible for someone to |
685 | determine the insecure things and exploit them without viewing the | |
686 | source. Security through obscurity, the name for hiding your bugs | |
687 | instead of fixing them, is little security indeed. | |
688 | ||
83df6a1d JH |
689 | You can try using encryption via source filters (Starting from Perl |
690 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in | |
691 | the standard distribution), but any decent programmer will be able to | |
692 | decrypt it. You can try using the byte code compiler and interpreter | |
693 | described below, but the curious might still be able to de-compile it. | |
694 | You can try using the native-code compiler described below, but | |
695 | crackers might be able to disassemble it. These pose varying degrees | |
696 | of difficulty to people wanting to get at your code, but none can | |
697 | definitively conceal it (true of every language, not just Perl). | |
68dc0745 | 698 | |
699 | If you're concerned about people profiting from your code, then the | |
d92eb7b0 | 700 | bottom line is that nothing but a restrictive license will give you |
68dc0745 | 701 | legal security. License your software and pepper it with threatening |
92c2ed05 | 702 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 | 703 | Your access to it does not give you permission to use it blah blah |
92c2ed05 | 704 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 | 705 | you want to be sure your license's wording will stand up in court. |
68dc0745 | 706 | |
54310121 | 707 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 | 708 | |
709 | Malcolm Beattie has written a multifunction backend compiler, | |
5e3006a4 GS |
710 | available from CPAN, that can do both these things. It is included |
711 | in the perl5.005 release, but is still considered experimental. | |
712 | This means it's fun to play with if you're a programmer but not | |
713 | really for people looking for turn-key solutions. | |
68dc0745 | 714 | |
92c2ed05 GS |
715 | Merely compiling into C does not in and of itself guarantee that your |
716 | code will run very much faster. That's because except for lucky cases | |
717 | where a lot of native type inferencing is possible, the normal Perl | |
a6dd486b | 718 | run-time system is still present and so your program will take just as |
92c2ed05 GS |
719 | long to run and be just as big. Most programs save little more than |
720 | compilation time, leaving execution no more than 10-30% faster. A few | |
a6dd486b | 721 | rare programs actually benefit significantly (even running several times |
92c2ed05 | 722 | faster), but this takes some tweaking of your code. |
68dc0745 | 723 | |
68dc0745 | 724 | You'll probably be astonished to learn that the current version of the |
725 | compiler generates a compiled form of your script whose executable is | |
726 | just as big as the original perl executable, and then some. That's | |
727 | because as currently written, all programs are prepared for a full | |
728 | eval() statement. You can tremendously reduce this cost by building a | |
92c2ed05 | 729 | shared I<libperl.so> library and linking against that. See the |
87275199 | 730 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 | 731 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 | 732 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 | 733 | size! |
734 | ||
5a964f20 | 735 | In general, the compiler will do nothing to make a Perl program smaller, |
a6dd486b JB |
736 | faster, more portable, or more secure. In fact, it can make your |
737 | situation worse. The executable will be bigger, your VM system may take | |
5a964f20 TC |
738 | longer to load the whole thing, the binary is fragile and hard to fix, |
739 | and compilation never stopped software piracy in the form of crackers, | |
740 | viruses, or bootleggers. The real advantage of the compiler is merely | |
741 | packaging, and once you see the size of what it makes (well, unless | |
742 | you use a shared I<libperl.so>), you'll probably want a complete | |
5e3006a4 | 743 | Perl install anyway. |
5a964f20 | 744 | |
65acb1b1 TC |
745 | =head2 How can I compile Perl into Java? |
746 | ||
a6dd486b | 747 | You can also integrate Java and Perl with the |
65acb1b1 | 748 | Perl Resource Kit from O'Reilly and Associates. See |
a6dd486b JB |
749 | http://www.oreilly.com/catalog/prkunix/ . |
750 | ||
751 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in | |
752 | development, allows Perl code to be called from Java. See jpl/README | |
753 | in the Perl source tree. | |
65acb1b1 | 754 | |
92c2ed05 | 755 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 | 756 | |
757 | For OS/2 just use | |
758 | ||
759 | extproc perl -S -your_switches | |
760 | ||
761 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's | |
46fc3d4c | 762 | `extproc' handling). For DOS one should first invent a corresponding |
a6dd486b | 763 | batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the |
68dc0745 | 764 | F<INSTALL> file in the source distribution for more information). |
765 | ||
92c2ed05 GS |
766 | The Win95/NT installation, when using the ActiveState port of Perl, |
767 | will modify the Registry to associate the C<.pl> extension with the | |
d92eb7b0 GS |
768 | perl interpreter. If you install another port, perhaps even building |
769 | your own Win95/NT Perl from the standard sources by using a Windows port | |
d702ae42 | 770 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 GS |
771 | the Registry yourself. In addition to associating C<.pl> with the |
772 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them | |
773 | run the program C<install-linux.pl> merely by typing C<install-linux>. | |
68dc0745 | 774 | |
87275199 GS |
775 | Macintosh Perl programs will have the appropriate Creator and |
776 | Type, so that double-clicking them will invoke the Perl application. | |
68dc0745 | 777 | |
778 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just | |
779 | throw the perl interpreter into your cgi-bin directory, in order to | |
87275199 | 780 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 | 781 | security risk. Take the time to figure out how to do it correctly. |
782 | ||
87275199 | 783 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 | 784 | |
785 | Yes. Read L<perlrun> for more information. Some examples follow. | |
786 | (These assume standard Unix shell quoting rules.) | |
787 | ||
788 | # sum first and last fields | |
5a964f20 | 789 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 | 790 | |
791 | # identify text files | |
792 | perl -le 'for(@ARGV) {print if -f && -T _}' * | |
793 | ||
5a964f20 | 794 | # remove (most) comments from C program |
68dc0745 | 795 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
796 | ||
797 | # make file a month younger than today, defeating reaper daemons | |
798 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * | |
799 | ||
800 | # find first unused uid | |
801 | perl -le '$i++ while getpwuid($i); print $i' | |
802 | ||
803 | # display reasonable manpath | |
804 | echo $PATH | perl -nl -072 -e ' | |
805 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' | |
806 | ||
87275199 | 807 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 | 808 | |
87275199 | 809 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 | 810 | |
811 | The problem is usually that the command interpreters on those systems | |
812 | have rather different ideas about quoting than the Unix shells under | |
813 | which the one-liners were created. On some systems, you may have to | |
814 | change single-quotes to double ones, which you must I<NOT> do on Unix | |
815 | or Plan9 systems. You might also have to change a single % to a %%. | |
816 | ||
817 | For example: | |
818 | ||
819 | # Unix | |
820 | perl -e 'print "Hello world\n"' | |
821 | ||
46fc3d4c | 822 | # DOS, etc. |
68dc0745 | 823 | perl -e "print \"Hello world\n\"" |
824 | ||
46fc3d4c | 825 | # Mac |
68dc0745 | 826 | print "Hello world\n" |
827 | (then Run "Myscript" or Shift-Command-R) | |
828 | ||
829 | # VMS | |
830 | perl -e "print ""Hello world\n""" | |
831 | ||
a6dd486b | 832 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 | 833 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b | 834 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 | 835 | you'd probably have better luck like this: |
68dc0745 | 836 | |
837 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
838 | ||
46fc3d4c | 839 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 | 840 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c | 841 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 | 842 | characters as control characters. |
843 | ||
65acb1b1 TC |
844 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
845 | quotes', and `backticks`, may make one-liners easier to write. | |
846 | ||
92c2ed05 GS |
847 | There is no general solution to all of this. It is a mess, pure and |
848 | simple. Sucks to be away from Unix, huh? :-) | |
68dc0745 | 849 | |
850 | [Some of this answer was contributed by Kenneth Albanowski.] | |
851 | ||
852 | =head2 Where can I learn about CGI or Web programming in Perl? | |
853 | ||
854 | For modules, get the CGI or LWP modules from CPAN. For textbooks, | |
855 | see the two especially dedicated to web stuff in the question on | |
92c2ed05 GS |
856 | books. For problems and questions related to the web, like ``Why |
857 | do I get 500 Errors'' or ``Why doesn't it run from the browser right | |
858 | when it runs fine on the command line'', see these sources: | |
68dc0745 | 859 | |
5a964f20 TC |
860 | WWW Security FAQ |
861 | http://www.w3.org/Security/Faq/ | |
68dc0745 | 862 | |
5a964f20 TC |
863 | Web FAQ |
864 | http://www.boutell.com/faq/ | |
68dc0745 | 865 | |
5a964f20 | 866 | CGI FAQ |
6cecdcac | 867 | http://www.webthing.com/tutorials/cgifaq.html |
68dc0745 | 868 | |
5a964f20 TC |
869 | HTTP Spec |
870 | http://www.w3.org/pub/WWW/Protocols/HTTP/ | |
871 | ||
872 | HTML Spec | |
873 | http://www.w3.org/TR/REC-html40/ | |
874 | http://www.w3.org/pub/WWW/MarkUp/ | |
875 | ||
876 | CGI Spec | |
877 | http://www.w3.org/CGI/ | |
878 | ||
879 | CGI Security FAQ | |
880 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt | |
68dc0745 | 881 | |
68dc0745 | 882 | =head2 Where can I learn about object-oriented Perl programming? |
883 | ||
a6dd486b JB |
884 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
885 | L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out | |
886 | until the 5.004 release; you can get a copy (in pod, html, or | |
887 | postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ . | |
68dc0745 | 888 | |
889 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
890 | ||
891 | If you want to call C from Perl, start with L<perlxstut>, | |
892 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to | |
893 | call Perl from C, then read L<perlembed>, L<perlcall>, and | |
894 | L<perlguts>. Don't forget that you can learn a lot from looking at | |
895 | how the authors of existing extension modules wrote their code and | |
896 | solved their problems. | |
897 | ||
898 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in | |
a6dd486b | 899 | my C program; what am I doing wrong? |
68dc0745 | 900 | |
901 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If | |
902 | the tests pass, read the pods again and again and again. If they | |
87275199 | 903 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 | 904 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
905 | ||
906 | =head2 When I tried to run my script, I got this message. What does it | |
907 | mean? | |
908 | ||
87275199 GS |
909 | A complete list of Perl's error messages and warnings with explanatory |
910 | text can be found in L<perldiag>. You can also use the splain program | |
911 | (distributed with Perl) to explain the error messages: | |
68dc0745 | 912 | |
913 | perl program 2>diag.out | |
914 | splain [-v] [-p] diag.out | |
915 | ||
916 | or change your program to explain the messages for you: | |
917 | ||
918 | use diagnostics; | |
919 | ||
920 | or | |
921 | ||
922 | use diagnostics -verbose; | |
923 | ||
924 | =head2 What's MakeMaker? | |
925 | ||
87275199 | 926 | This module (part of the standard Perl distribution) is designed to |
68dc0745 | 927 | write a Makefile for an extension module from a Makefile.PL. For more |
928 | information, see L<ExtUtils::MakeMaker>. | |
929 | ||
930 | =head1 AUTHOR AND COPYRIGHT | |
931 | ||
65acb1b1 | 932 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 TC |
933 | All rights reserved. |
934 | ||
5a7beb56 JH |
935 | This documentation is free; you can redistribute it and/or modify it |
936 | under the same terms as Perl itself. | |
c8db1d39 | 937 | |
87275199 | 938 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
939 | domain. You are permitted and encouraged to use this code and any |
940 | derivatives thereof in your own programs for fun or for profit as you | |
941 | see fit. A simple comment in the code giving credit to the FAQ would | |
942 | be courteous but is not required. |