1PERLFAQ3(1) Perl Programmers Reference Guide PERLFAQ3(1)
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6 perlfaq3 - Programming Tools ($Revision: 1.56 $, $Date: 2005/12/31
7 00:54:37 $)
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10 This section of the FAQ answers questions related to programmer tools
11 and programming support.
12 How do I do (anything)?
14 Have you looked at CPAN (see perlfaq2)? The chances are that someone
16 has already written a module that can solve your problem. Have you
17 read the appropriate manpages? Here's a brief index:
18 Basics perldata, perlvar, perlsyn, perlop, perlsub
20 Execution perlrun, perldebug
21 Functions perlfunc
22 Objects perlref, perlmod, perlobj, perltie
23 Data Structures perlref, perllol, perldsc
24 Modules perlmod, perlmodlib, perlsub
25 Regexes perlre, perlfunc, perlop, perllocale
26 Moving to perl5 perltrap, perl
27 Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed
28 Various http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz
29 (not a man-page but still useful, a collection
30 of various essays on Perl techniques)
31 A crude table of contents for the Perl manpage set is found in perltoc.
33 How can I use Perl interactively?
35 The typical approach uses the Perl debugger, described in the perlde‐
37 bug(1) manpage, on an "empty" program, like this:
38 perl -de 42
40 Now just type in any legal Perl code, and it will be immediately evalu‐
42 ated. You can also examine the symbol table, get stack backtraces,
43 check variable values, set breakpoints, and other operations typically
44 found in symbolic debuggers.
45 Is there a Perl shell?
47 The psh (Perl sh) is currently at version 1.8. The Perl Shell is a
49 shell that combines the interactive nature of a Unix shell with the
50 power of Perl. The goal is a full featured shell that behaves as
51 expected for normal shell activity and uses Perl syntax and functional‐
52 ity for control-flow statements and other things. You can get psh at
53 http://sourceforge.net/projects/psh/ .
54 Zoidberg is a similar project and provides a shell written in perl,
56 configured in perl and operated in perl. It is intended as a login
57 shell and development environment. It can be found at http://zoid‐
58 berg.sf.net/ or your local CPAN mirror.
59 The Shell.pm module (distributed with Perl) makes Perl try commands
61 which aren't part of the Perl language as shell commands. perlsh from
62 the source distribution is simplistic and uninteresting, but may still
63 be what you want.
64 How do I find which modules are installed on my system?
66 You can use the ExtUtils::Installed module to show all installed dis‐
68 tributions, although it can take awhile to do its magic. The standard
69 library which comes with Perl just shows up as "Perl" (although you can
70 get those with Module::CoreList).
71 use ExtUtils::Installed;
73 my $inst = ExtUtils::Installed->new();
75 my @modules = $inst->modules();
76 If you want a list of all of the Perl module filenames, you can use
78 File::Find::Rule.
79 use File::Find::Rule;
81 my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC );
83 If you do not have that module, you can do the same thing with
85 File::Find which is part of the standard library.
86 use File::Find;
88 my @files;
89 find(
91 sub {
92 push @files, $File::Find::name
93 if -f $File::Find::name && /\.pm$/
94 },
95 @INC
97 );
98 print join "\n", @files;
100 If you simply need to quickly check to see if a module is available,
102 you can check for its documentation. If you can read the documentation
103 the module is most likely installed. If you cannot read the documenta‐
104 tion, the module might not have any (in rare cases).
105 prompt% perldoc Module::Name
107 You can also try to include the module in a one-liner to see if perl
109 finds it.
110 perl -MModule::Name -e1
112 How do I debug my Perl programs?
114 Have you tried "use warnings" or used "-w"? They enable warnings to
116 detect dubious practices.
117 Have you tried "use strict"? It prevents you from using symbolic ref‐
119 erences, makes you predeclare any subroutines that you call as bare
120 words, and (probably most importantly) forces you to predeclare your
121 variables with "my", "our", or "use vars".
122 Did you check the return values of each and every system call? The
124 operating system (and thus Perl) tells you whether they worked, and if
125 not why.
126 open(FH, "> /etc/cantwrite")
128 or die "Couldn't write to /etc/cantwrite: $!\n";
129 Did you read perltrap? It's full of gotchas for old and new Perl pro‐
131 grammers and even has sections for those of you who are upgrading from
132 languages like awk and C.
133 Have you tried the Perl debugger, described in perldebug? You can step
135 through your program and see what it's doing and thus work out why what
136 it's doing isn't what it should be doing.
137 How do I profile my Perl programs?
139 You should get the Devel::DProf module from the standard distribution
141 (or separately on CPAN) and also use Benchmark.pm from the standard
142 distribution. The Benchmark module lets you time specific portions of
143 your code, while Devel::DProf gives detailed breakdowns of where your
144 code spends its time.
145 Here's a sample use of Benchmark:
147 use Benchmark;
149 @junk = `cat /etc/motd`;
151 $count = 10_000;
152 timethese($count, {
154 'map' => sub { my @a = @junk;
155 map { s/a/b/ } @a;
156 return @a },
157 'for' => sub { my @a = @junk;
158 for (@a) { s/a/b/ };
159 return @a },
160 });
161 This is what it prints (on one machine--your results will be dependent
163 on your hardware, operating system, and the load on your machine):
164 Benchmark: timing 10000 iterations of for, map...
166 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
167 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
168 Be aware that a good benchmark is very hard to write. It only tests
170 the data you give it and proves little about the differing complexities
171 of contrasting algorithms.
172 How do I cross-reference my Perl programs?
174 The B::Xref module can be used to generate cross-reference reports for
176 Perl programs.
177 perl -MO=Xref[,OPTIONS] scriptname.plx
179 Is there a pretty-printer (formatter) for Perl?
181 Perltidy is a Perl script which indents and reformats Perl scripts to
183 make them easier to read by trying to follow the rules of the perl‐
184 style. If you write Perl scripts, or spend much time reading them, you
185 will probably find it useful. It is available at
186 http://perltidy.sourceforge.net
187 Of course, if you simply follow the guidelines in perlstyle, you
189 shouldn't need to reformat. The habit of formatting your code as you
190 write it will help prevent bugs. Your editor can and should help you
191 with this. The perl-mode or newer cperl-mode for emacs can provide
192 remarkable amounts of help with most (but not all) code, and even less
193 programmable editors can provide significant assistance. Tom Chris‐
194 tiansen and many other VI users swear by the following settings in vi
195 and its clones:
196 set ai sw=4
198 map! ^O {^M}^[O^T
199 Put that in your .exrc file (replacing the caret characters with con‐
201 trol characters) and away you go. In insert mode, ^T is for indenting,
202 ^D is for undenting, and ^O is for blockdenting-- as it were. A more
203 complete example, with comments, can be found at
204 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
205 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
207 lots of things related to generating nicely printed output of docu‐
208 ments, as does enscript at http://people.ssh.fi/mtr/genscript/ .
209 Is there a ctags for Perl?
211 (contributed by brian d foy)
213 Exuberent ctags supports Perl: http://ctags.sourceforge.net/
215 You might also try pltags: http://www.mscha.com/pltags.zip
217 Is there an IDE or Windows Perl Editor?
219 Perl programs are just plain text, so any editor will do.
221 If you're on Unix, you already have an IDE--Unix itself. The UNIX phi‐
223 losophy is the philosophy of several small tools that each do one thing
224 and do it well. It's like a carpenter's toolbox.
225 If you want an IDE, check the following (in alphabetical order, not
227 order of preference):
228 Eclipse
230 http://e-p-i-c.sf.net/
231 The Eclipse Perl Integration Project integrates Perl editing/debug‐
233 ging with Eclipse.
234 Enginsite
236 http://www.enginsite.com/
237 Perl Editor by EngInSite is a complete integrated development envi‐
239 ronment (IDE) for creating, testing, and debugging Perl scripts;
240 the tool runs on Windows 9x/NT/2000/XP or later.
241 Komodo
243 http://www.ActiveState.com/Products/Komodo/
244 ActiveState's cross-platform (as of October 2004, that's Windows,
246 Linux, and Solaris), multi-language IDE has Perl support, including
247 a regular expression debugger and remote debugging.
248 Open Perl IDE
250 http://open-perl-ide.sourceforge.net/
251 Open Perl IDE is an integrated development environment for writing
253 and debugging Perl scripts with ActiveState's ActivePerl distribu‐
254 tion under Windows 95/98/NT/2000.
255 OptiPerl
257 http://www.optiperl.com/
258 OptiPerl is a Windows IDE with simulated CGI environment, including
260 debugger and syntax highlighting editor.
261 PerlBuilder
263 http://www.solutionsoft.com/perl.htm
264 PerlBuidler is an integrated development environment for Windows
266 that supports Perl development.
267 visiPerl+
269 http://helpconsulting.net/visiperl/
270 From Help Consulting, for Windows.
272 Visual Perl
274 http://www.activestate.com/Products/Visual_Perl/
275 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
277 Zeus
279 http://www.zeusedit.com/lookmain.html
280 Zeus for Window is another Win32 multi-language editor/IDE that
282 comes with support for Perl:
283 For editors: if you're on Unix you probably have vi or a vi clone
285 already, and possibly an emacs too, so you may not need to download
286 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you per‐
287 haps the best available Perl editing mode in any editor.
288 If you are using Windows, you can use any editor that lets you work
290 with plain text, such as NotePad or WordPad. Word processors, such as
291 Microsoft Word or WordPerfect, typically do not work since they insert
292 all sorts of behind-the-scenes information, although some allow you to
293 save files as "Text Only". You can also download text editors designed
294 specifically for programming, such as Textpad ( http://www.textpad.com/
295 ) and UltraEdit ( http://www.ultraedit.com/ ), among others.
296 If you are using MacOS, the same concerns apply. MacPerl (for Classic
298 environments) comes with a simple editor. Popular external editors are
299 BBEdit ( http://www.bbedit.com/ ) or Alpha (
300 http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use
301 Unix editors as well. Neil Bowers (the man behind Geekcruises) has a
302 list of Mac editors that can handle Perl ( http://www.neilbow‐
303 ers.org/macperleditors.html ).
304 GNU Emacs
306 http://www.gnu.org/software/emacs/windows/ntemacs.html
307 MicroEMACS
309 http://www.microemacs.de/
310 XEmacs
312 http://www.xemacs.org/Download/index.html
313 Jed http://space.mit.edu/~davis/jed/
315 or a vi clone such as
317 Elvis
319 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
320 Vile
322 http://dickey.his.com/vile/vile.html
323 Vim http://www.vim.org/
325 For vi lovers in general, Windows or elsewhere:
327 http://www.thomer.com/thomer/vi/vi.html
329 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
331 yet another vi clone, unfortunately not available for Windows, but in
332 UNIX platforms you might be interested in trying it out, firstly
333 because strictly speaking it is not a vi clone, it is the real vi, or
334 the new incarnation of it, and secondly because you can embed Perl
335 inside it to use Perl as the scripting language. nvi is not alone in
336 this, though: at least also vim and vile offer an embedded Perl.
337 The following are Win32 multilanguage editor/IDESs that support Perl:
339 Codewright
341 http://www.borland.com/codewright/
342 MultiEdit
344 http://www.MultiEdit.com/
345 SlickEdit
347 http://www.slickedit.com/
348 There is also a toyedit Text widget based editor written in Perl that
350 is distributed with the Tk module on CPAN. The ptkdb (
351 http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
352 acts as a development environment of sorts. Perl Composer (
353 http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk GUI cre‐
354 ation.
355 In addition to an editor/IDE you might be interested in a more powerful
357 shell environment for Win32. Your options include
358 Bash
360 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
361 Ksh from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell
363 of the U/WIN environment (
364 http://www.research.att.com/sw/tools/uwin/ )
365 Tcsh
367 ftp://ftp.astron.com/pub/tcsh/ , see also http://www.pri‐
368 mate.wisc.edu/software/csh-tcsh-book/
369 Zsh ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
371 MKS and U/WIN are commercial (U/WIN is free for educational and
373 research purposes), Cygwin is covered by the GNU Public License (but
374 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
375 contain (in addition to the shells) a comprehensive set of standard
376 UNIX toolkit utilities.
377 If you're transferring text files between Unix and Windows using FTP be
379 sure to transfer them in ASCII mode so the ends of lines are appropri‐
380 ately converted.
381 On Mac OS the MacPerl Application comes with a simple 32k text editor
383 that behaves like a rudimentary IDE. In contrast to the MacPerl Appli‐
384 cation the MPW Perl tool can make use of the MPW Shell itself as an
385 editor (with no 32k limit).
386 Affrus
388 is a full Perl development environment with full debugger support (
389 http://www.latenightsw.com ).
390 Alpha
392 is an editor, written and extensible in Tcl, that nonetheless has
393 built in support for several popular markup and programming lan‐
394 guages including Perl and HTML (
395 http://www.his.com/~jguyer/Alpha/Alpha8.html ).
396 BBEdit and BBEdit Lite
398 are text editors for Mac OS that have a Perl sensitivity mode (
399 http://web.barebones.com/ ).
400 Pepper and Pe are programming language sensitive text editors for Mac
402 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
403 Where can I get Perl macros for vi?
405 For a complete version of Tom Christiansen's vi configuration file, see
407 http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz , the
408 standard benchmark file for vi emulators. The file runs best with nvi,
409 the current version of vi out of Berkeley, which incidentally can be
410 built with an embedded Perl interpreter--see
411 http://www.cpan.org/src/misc/ .
412 Where can I get perl-mode for emacs?
414 Since Emacs version 19 patchlevel 22 or so, there have been both a
416 perl-mode.el and support for the Perl debugger built in. These should
417 come with the standard Emacs 19 distribution.
418 In the Perl source directory, you'll find a directory called "emacs",
420 which contains a cperl-mode that color-codes keywords, provides con‐
421 text-sensitive help, and other nifty things.
422 Note that the perl-mode of emacs will have fits with "main'foo" (single
424 quote), and mess up the indentation and highlighting. You are probably
425 using "main::foo" in new Perl code anyway, so this shouldn't be an
426 issue.
427 How can I use curses with Perl?
429 The Curses module from CPAN provides a dynamically loadable object mod‐
431 ule interface to a curses library. A small demo can be found at the
432 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
433 this program repeats a command and updates the screen as needed, ren‐
434 dering rep ps axu similar to top.
435 How can I use X or Tk with Perl?
437 Tk is a completely Perl-based, object-oriented interface to the Tk
439 toolkit that doesn't force you to use Tcl just to get at Tk. Sx is an
440 interface to the Athena Widget set. Both are available from CPAN. See
441 the directory http://www.cpan.org/modules/by-category/08_User_Inter‐
442 faces/
443 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at http://pha‐
445 seit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
446 Guide available at http://www.cpan.org/authors/Stephen_O_Lidie/ , and
447 the online manpages at http://www-users.cs.umn.edu/%7Eamund‐
448 son/perl/perltk/toc.html .
449 How can I make my Perl program run faster?
451 The best way to do this is to come up with a better algorithm. This
453 can often make a dramatic difference. Jon Bentley's book Programming
454 Pearls (that's not a misspelling!) has some good tips on optimization,
455 too. Advice on benchmarking boils down to: benchmark and profile to
456 make sure you're optimizing the right part, look for better algorithms
457 instead of microtuning your code, and when all else fails consider just
458 buying faster hardware. You will probably want to read the answer to
459 the earlier question "How do I profile my Perl programs?" if you
460 haven't done so already.
461 A different approach is to autoload seldom-used Perl code. See the
463 AutoSplit and AutoLoader modules in the standard distribution for that.
464 Or you could locate the bottleneck and think about writing just that
465 part in C, the way we used to take bottlenecks in C code and write them
466 in assembler. Similar to rewriting in C, modules that have critical
467 sections can be written in C (for instance, the PDL module from CPAN).
468 If you're currently linking your perl executable to a shared libc.so,
470 you can often gain a 10-25% performance benefit by rebuilding it to
471 link with a static libc.a instead. This will make a bigger perl exe‐
472 cutable, but your Perl programs (and programmers) may thank you for it.
473 See the INSTALL file in the source distribution for more information.
474 The undump program was an ancient attempt to speed up Perl program by
476 storing the already-compiled form to disk. This is no longer a viable
477 option, as it only worked on a few architectures, and wasn't a good
478 solution anyway.
479 How can I make my Perl program take less memory?
481 When it comes to time-space tradeoffs, Perl nearly always prefers to
483 throw memory at a problem. Scalars in Perl use more memory than
484 strings in C, arrays take more than that, and hashes use even more.
485 While there's still a lot to be done, recent releases have been
486 addressing these issues. For example, as of 5.004, duplicate hash keys
487 are shared amongst all hashes using them, so require no reallocation.
488 In some cases, using substr() or vec() to simulate arrays can be highly
490 beneficial. For example, an array of a thousand booleans will take at
491 least 20,000 bytes of space, but it can be turned into one 125-byte bit
492 vector--a considerable memory savings. The standard Tie::SubstrHash
493 module can also help for certain types of data structure. If you're
494 working with specialist data structures (matrices, for instance) mod‐
495 ules that implement these in C may use less memory than equivalent Perl
496 modules.
497 Another thing to try is learning whether your Perl was compiled with
499 the system malloc or with Perl's builtin malloc. Whichever one it is,
500 try using the other one and see whether this makes a difference.
501 Information about malloc is in the INSTALL file in the source distribu‐
502 tion. You can find out whether you are using perl's malloc by typing
503 "perl -V:usemymalloc".
504 Of course, the best way to save memory is to not do anything to waste
506 it in the first place. Good programming practices can go a long way
507 toward this:
508 * Don't slurp!
510 Don't read an entire file into memory if you can process it line by
511 line. Or more concretely, use a loop like this:
512 #
514 # Good Idea
515 #
516 while (<FILE>) {
517 # ...
518 }
519 instead of this:
521 #
523 # Bad Idea
524 #
525 @data = <FILE>;
526 foreach (@data) {
527 # ...
528 }
529 When the files you're processing are small, it doesn't much matter
531 which way you do it, but it makes a huge difference when they start
532 getting larger.
533 * Use map and grep selectively
535 Remember that both map and grep expect a LIST argument, so doing
536 this:
537 @wanted = grep {/pattern/} <FILE>;
539 will cause the entire file to be slurped. For large files, it's
541 better to loop:
542 while (<FILE>) {
544 push(@wanted, $_) if /pattern/;
545 }
546 * Avoid unnecessary quotes and stringification
548 Don't quote large strings unless absolutely necessary:
549 my $copy = "$large_string";
551 makes 2 copies of $large_string (one for $copy and another for the
553 quotes), whereas
554 my $copy = $large_string;
556 only makes one copy.
558 Ditto for stringifying large arrays:
560 {
562 local $, = "\n";
563 print @big_array;
564 }
565 is much more memory-efficient than either
567 print join "\n", @big_array;
569 or
571 {
573 local $" = "\n";
574 print "@big_array";
575 }
576 * Pass by reference
578 Pass arrays and hashes by reference, not by value. For one thing,
579 it's the only way to pass multiple lists or hashes (or both) in a
580 single call/return. It also avoids creating a copy of all the con‐
581 tents. This requires some judgment, however, because any changes
582 will be propagated back to the original data. If you really want to
583 mangle (er, modify) a copy, you'll have to sacrifice the memory
584 needed to make one.
585 * Tie large variables to disk.
587 For "big" data stores (i.e. ones that exceed available memory) con‐
588 sider using one of the DB modules to store it on disk instead of in
589 RAM. This will incur a penalty in access time, but that's probably
590 better than causing your hard disk to thrash due to massive swap‐
591 ping.
592 Is it safe to return a reference to local or lexical data?
594 Yes. Perl's garbage collection system takes care of this so everything
596 works out right.
597 sub makeone {
599 my @a = ( 1 .. 10 );
600 return \@a;
601 }
602 for ( 1 .. 10 ) {
604 push @many, makeone();
605 }
606 print $many[4][5], "\n";
608 print "@many\n";
610 How can I free an array or hash so my program shrinks?
612 (contributed by Michael Carman)
614 You usually can't. Memory allocated to lexicals (i.e. my() variables)
616 cannot be reclaimed or reused even if they go out of scope. It is
617 reserved in case the variables come back into scope. Memory allocated
618 to global variables can be reused (within your program) by using
619 undef()ing and/or delete().
620 On most operating systems, memory allocated to a program can never be
622 returned to the system. That's why long-running programs sometimes re-
623 exec themselves. Some operating systems (notably, systems that use
624 mmap(2) for allocating large chunks of memory) can reclaim memory that
625 is no longer used, but on such systems, perl must be configured and
626 compiled to use the OS's malloc, not perl's.
627 In general, memory allocation and de-allocation isn't something you can
629 or should be worrying about much in Perl.
630 See also "How can I make my Perl program take less memory?"
632 How can I make my CGI script more efficient?
634 Beyond the normal measures described to make general Perl programs
636 faster or smaller, a CGI program has additional issues. It may be run
637 several times per second. Given that each time it runs it will need to
638 be re-compiled and will often allocate a megabyte or more of system
639 memory, this can be a killer. Compiling into C isn't going to help you
640 because the process start-up overhead is where the bottleneck is.
641 There are two popular ways to avoid this overhead. One solution
643 involves running the Apache HTTP server (available from
644 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
645 plugin modules.
646 With mod_perl and the Apache::Registry module (distributed with
648 mod_perl), httpd will run with an embedded Perl interpreter which pre-
649 compiles your script and then executes it within the same address space
650 without forking. The Apache extension also gives Perl access to the
651 internal server API, so modules written in Perl can do just about any‐
652 thing a module written in C can. For more on mod_perl, see
653 http://perl.apache.org/
654 With the FCGI module (from CPAN) and the mod_fastcgi module (available
656 from http://www.fastcgi.com/ ) each of your Perl programs becomes a
657 permanent CGI daemon process.
658 Both of these solutions can have far-reaching effects on your system
660 and on the way you write your CGI programs, so investigate them with
661 care.
662 See http://www.cpan.org/modules/by-cate‐
664 gory/15_World_Wide_Web_HTML_HTTP_CGI/ .
665 How can I hide the source for my Perl program?
667 Delete it. :-) Seriously, there are a number of (mostly unsatisfactory)
669 solutions with varying levels of "security".
670 First of all, however, you can't take away read permission, because the
672 source code has to be readable in order to be compiled and interpreted.
673 (That doesn't mean that a CGI script's source is readable by people on
674 the web, though--only by people with access to the filesystem.) So you
675 have to leave the permissions at the socially friendly 0755 level.
676 Some people regard this as a security problem. If your program does
678 insecure things and relies on people not knowing how to exploit those
679 insecurities, it is not secure. It is often possible for someone to
680 determine the insecure things and exploit them without viewing the
681 source. Security through obscurity, the name for hiding your bugs
682 instead of fixing them, is little security indeed.
683 You can try using encryption via source filters (Starting from Perl 5.8
685 the Filter::Simple and Filter::Util::Call modules are included in the
686 standard distribution), but any decent programmer will be able to
687 decrypt it. You can try using the byte code compiler and interpreter
688 described below, but the curious might still be able to de-compile it.
689 You can try using the native-code compiler described below, but crack‐
690 ers might be able to disassemble it. These pose varying degrees of
691 difficulty to people wanting to get at your code, but none can defini‐
692 tively conceal it (true of every language, not just Perl).
693 It is very easy to recover the source of Perl programs. You simply
695 feed the program to the perl interpreter and use the modules in the B::
696 hierarchy. The B::Deparse module should be able to defeat most
697 attempts to hide source. Again, this is not unique to Perl.
698 If you're concerned about people profiting from your code, then the
700 bottom line is that nothing but a restrictive license will give you
701 legal security. License your software and pepper it with threatening
702 statements like "This is unpublished proprietary software of XYZ Corp.
703 Your access to it does not give you permission to use it blah blah
704 blah." We are not lawyers, of course, so you should see a lawyer if
705 you want to be sure your license's wording will stand up in court.
706 How can I compile my Perl program into byte code or C?
708 (contributed by brian d foy)
710 In general, you can't do this. There are some things that may work for
712 your situation though. People usually ask this question because they
713 want to distribute their works without giving away the source code, and
714 most solutions trade disk space for convenience. You probably won't
715 see much of a speed increase either, since most solutions simply bundle
716 a Perl interpreter in the final product (but see "How can I make my
717 Perl program run faster?").
718 The Perl Archive Toolkit ( http://par.perl.org/index.cgi ) is Perl's
720 analog to Java's JAR. It's freely available and on CPAN (
721 http://search.cpan.org/dist/PAR/ ).
722 The B::* namespace, often called "the Perl compiler", but is really a
724 way for Perl programs to peek at its innards rather than create pre-
725 compiled versions of your program. However. the B::Bytecode module can
726 turn your script into a bytecode format that could be loaded later by
727 the ByteLoader module and executed as a regular Perl script.
728 There are also some commercial products that may work for you, although
730 you have to buy a license for them.
731 The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ )
733 from ActiveState can "Turn your Perl programs into ready-to-run exe‐
734 cutables for HP-UX, Linux, Solaris and Windows."
735 Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line
737 program for converting perl scripts to executable files. It targets
738 both Windows and unix platforms.
739 How can I compile Perl into Java?
741 You can also integrate Java and Perl with the Perl Resource Kit from
743 O'Reilly Media. See http://www.oreilly.com/catalog/prkunix/ .
744 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in develop‐
746 ment, allows Perl code to be called from Java. See jpl/README in the
747 Perl source tree.
748 How can I get "#!perl" to work on [MS-DOS,NT,...]?
750 For OS/2 just use
752 extproc perl -S -your_switches
754 as the first line in "*.cmd" file ("-S" due to a bug in cmd.exe's
756 "extproc" handling). For DOS one should first invent a corresponding
757 batch file and codify it in "ALTERNATE_SHEBANG" (see the dosish.h file
758 in the source distribution for more information).
759 The Win95/NT installation, when using the ActiveState port of Perl,
761 will modify the Registry to associate the ".pl" extension with the perl
762 interpreter. If you install another port, perhaps even building your
763 own Win95/NT Perl from the standard sources by using a Windows port of
764 gcc (e.g., with cygwin or mingw32), then you'll have to modify the Reg‐
765 istry yourself. In addition to associating ".pl" with the interpreter,
766 NT people can use: "SET PATHEXT=%PATHEXT%;.PL" to let them run the pro‐
767 gram "install-linux.pl" merely by typing "install-linux".
768 Under "Classic" MacOS, a perl program will have the appropriate Creator
770 and Type, so that double-clicking them will invoke the MacPerl applica‐
771 tion. Under Mac OS X, clickable apps can be made from any "#!" script
772 using Wil Sanchez' DropScript utility: http://www.wsanchez.net/soft‐
773 ware/ .
774 IMPORTANT!: Whatever you do, PLEASE don't get frustrated, and just
776 throw the perl interpreter into your cgi-bin directory, in order to get
777 your programs working for a web server. This is an EXTREMELY big secu‐
778 rity risk. Take the time to figure out how to do it correctly.
779 Can I write useful Perl programs on the command line?
781 Yes. Read perlrun for more information. Some examples follow. (These
783 assume standard Unix shell quoting rules.)
784 # sum first and last fields
786 perl -lane 'print $F[0] + $F[-1]' *
787 # identify text files
789 perl -le 'for(@ARGV) {print if -f && -T _}' *
790 # remove (most) comments from C program
792 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
793 # make file a month younger than today, defeating reaper daemons
795 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
796 # find first unused uid
798 perl -le '$i++ while getpwuid($i); print $i'
799 # display reasonable manpath
801 echo $PATH ⎪ perl -nl -072 -e '
802 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
803 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
805 Why don't Perl one-liners work on my DOS/Mac/VMS system?
807 The problem is usually that the command interpreters on those systems
809 have rather different ideas about quoting than the Unix shells under
810 which the one-liners were created. On some systems, you may have to
811 change single-quotes to double ones, which you must NOT do on Unix or
812 Plan9 systems. You might also have to change a single % to a %%.
813 For example:
815 # Unix
817 perl -e 'print "Hello world\n"'
818 # DOS, etc.
820 perl -e "print \"Hello world\n\""
821 # Mac
823 print "Hello world\n"
824 (then Run "Myscript" or Shift-Command-R)
825 # MPW
827 perl -e 'print "Hello world\n"'
828 # VMS
830 perl -e "print ""Hello world\n"""
831 The problem is that none of these examples are reliable: they depend on
833 the command interpreter. Under Unix, the first two often work. Under
834 DOS, it's entirely possible that neither works. If 4DOS was the com‐
835 mand shell, you'd probably have better luck like this:
836 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
838 Under the Mac, it depends which environment you are using. The MacPerl
840 shell, or MPW, is much like Unix shells in its support for several
841 quoting variants, except that it makes free use of the Mac's non-ASCII
842 characters as control characters.
843 Using qq(), q(), and qx(), instead of "double quotes", 'single quotes',
845 and `backticks`, may make one-liners easier to write.
846 There is no general solution to all of this. It is a mess.
848 [Some of this answer was contributed by Kenneth Albanowski.]
850 Where can I learn about CGI or Web programming in Perl?
852 For modules, get the CGI or LWP modules from CPAN. For textbooks, see
854 the two especially dedicated to web stuff in the question on books.
855 For problems and questions related to the web, like "Why do I get 500
856 Errors" or "Why doesn't it run from the browser right when it runs fine
857 on the command line", see the troubleshooting guides and references in
858 perlfaq9 or in the CGI MetaFAQ:
859 http://www.perl.org/CGI_MetaFAQ.html
861 Where can I learn about object-oriented Perl programming?
863 A good place to start is perltoot, and you can use perlobj, perlboot,
865 perltoot, perltooc, and perlbot for reference.
866 A good book on OO on Perl is the "Object-Oriented Perl" by Damian Con‐
868 way from Manning Publications, or "Learning Perl References, Objects, &
869 Modules" by Randal Schwartz and Tom Phoenix from O'Reilly Media.
870 Where can I learn about linking C with Perl?
872 If you want to call C from Perl, start with perlxstut, moving on to
874 perlxs, xsubpp, and perlguts. If you want to call Perl from C, then
875 read perlembed, perlcall, and perlguts. Don't forget that you can
876 learn a lot from looking at how the authors of existing extension mod‐
877 ules wrote their code and solved their problems.
878 You might not need all the power of XS. The Inline::C module lets you
880 put C code directly in your Perl source. It handles all the magic to
881 make it work. You still have to learn at least some of the perl API but
882 you won't have to deal with the complexity of the XS support files.
883 I've read perlembed, perlguts, etc., but I can't embed perl in my C
885 program; what am I doing wrong?
886 Download the ExtUtils::Embed kit from CPAN and run `make test'. If the
888 tests pass, read the pods again and again and again. If they fail, see
889 perlbug and send a bug report with the output of "make test TEST_VER‐
890 BOSE=1" along with "perl -V".
891 When I tried to run my script, I got this message. What does it mean?
893 A complete list of Perl's error messages and warnings with explanatory
895 text can be found in perldiag. You can also use the splain program
896 (distributed with Perl) to explain the error messages:
897 perl program 2>diag.out
899 splain [-v] [-p] diag.out
900 or change your program to explain the messages for you:
902 use diagnostics;
904 or
906 use diagnostics -verbose;
908 What's MakeMaker?
910 This module (part of the standard Perl distribution) is designed to
912 write a Makefile for an extension module from a Makefile.PL. For more
913 information, see ExtUtils::MakeMaker.
914
916 Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and other
917 authors as noted. All rights reserved.
918 This documentation is free; you can redistribute it and/or modify it
920 under the same terms as Perl itself.
921 Irrespective of its distribution, all code examples here are in the
923 public domain. You are permitted and encouraged to use this code and
924 any derivatives thereof in your own programs for fun or for profit as
925 you see fit. A simple comment in the code giving credit to the FAQ
926 would be courteous but is not required.
927perl v5.8.8 2006-01-07 PERLFAQ3(1)