3 perlfaq3 - Programming Tools ($Revision: 1.10 $, $Date: 2001/11/19 17:09:37 $)
7 This section of the FAQ answers questions related to programmer tools
8 and programming support.
10 =head2 How do I do (anything)?
12 Have you looked at CPAN (see L<perlfaq2>)? The chances are that
13 someone has already written a module that can solve your problem.
14 Have you read the appropriate manpages? Here's a brief index:
16 Basics perldata, perlvar, perlsyn, perlop, perlsub
17 Execution perlrun, perldebug
19 Objects perlref, perlmod, perlobj, perltie
20 Data Structures perlref, perllol, perldsc
21 Modules perlmod, perlmodlib, perlsub
22 Regexes perlre, perlfunc, perlop, perllocale
23 Moving to perl5 perltrap, perl
24 Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed
25 Various http://www.cpan.org/doc/FMTEYEWTK/index.html
26 (not a man-page but still useful)
28 A crude table of contents for the Perl manpage set is found in L<perltoc>.
30 =head2 How can I use Perl interactively?
32 The typical approach uses the Perl debugger, described in the
33 perldebug(1) manpage, on an ``empty'' program, like this:
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
40 operations typically found in symbolic debuggers.
42 =head2 Is there a Perl shell?
44 In general, not yet. There is psh available at
46 http://www.focusresearch.com/gregor/psh
48 Which includes the following description:
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 control-flow statements and other things.
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.
61 =head2 How do I debug my Perl programs?
63 Have you tried C<use warnings> or used C<-w>? They enable warnings
64 to detect dubious practices.
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
69 variables with C<my>, C<our>, or C<use vars>.
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
75 open(FH, "> /etc/cantwrite")
76 or die "Couldn't write to /etc/cantwrite: $!\n";
78 Did you read L<perltrap>? It's full of gotchas for old and new Perl
79 programmers and even has sections for those of you who are upgrading
80 from languages like I<awk> and I<C>.
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.
86 =head2 How do I profile my Perl programs?
88 You should get the Devel::DProf module from the standard distribution
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
94 Here's a sample use of Benchmark:
98 @junk = `cat /etc/motd`;
102 'map' => sub { my @a = @junk;
106 'for' => sub { my @a = @junk;
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):
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)
119 Be aware that a good benchmark is very hard to write. It only tests the
120 data you give it and proves little about the differing complexities
121 of contrasting algorithms.
123 =head2 How do I cross-reference my Perl programs?
125 The B::Xref module, shipped with the new, alpha-release Perl compiler
126 (not the general distribution prior to the 5.005 release), can be used
127 to generate cross-reference reports for Perl programs.
129 perl -MO=Xref[,OPTIONS] scriptname.plx
131 =head2 Is there a pretty-printer (formatter) for Perl?
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
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:
151 Put that in your F<.exrc> file (replacing the caret characters
152 with control characters) and away you go. In insert mode, ^T is
153 for indenting, ^D is for undenting, and ^O is for blockdenting--
154 as it were. A more complete example, with comments, can be found at
155 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
157 If you are used to using the I<vgrind> program for printing out nice code
158 to a laser printer, you can take a stab at this using
159 http://www.cpan.org/doc/misc/tips/working.vgrind.entry, but the
160 results are not particularly satisfying for sophisticated code.
162 The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things
163 related to generating nicely printed output of documents.
165 =head2 Is there a ctags for Perl?
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.
171 There is also a simple one at
172 http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
173 the trick. It can be easy to hack this into what you want.
175 =head2 Is there an IDE or Windows Perl Editor?
177 Perl programs are just plain text, so any editor will do.
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.
183 If you want an IDE, check the following:
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)).
196 =item The Object System
198 (http://www.castlelink.co.uk/object_system/) is a Perl web
199 applications development IDE, apparently for any platform
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.
211 (http://www.solutionsoft.com/perl.htm) is an integrated development
212 environment for Windows that supports Perl development.
216 ( http://helpconsulting.net/visiperl/ )
217 From Help Consulting, for Windows.
221 For Windows there's also the
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.
234 For editors: if you're on Unix you probably have vi or a vi clone already,
235 and possibly an emacs too, so you may not need to download anything.
236 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
237 best available Perl editing mode in any editor.
239 If you are using Windows, you can use any editor that lets
240 you work with plain text, such as NotePad or WordPad. Word
241 processors, such as Microsoft Word or WordPerfect, typically
242 do not work since they insert all sorts of behind-the-scenes
243 information, although some allow you to save files as "Text
244 Only". You can also download text editors designed
245 specifically for programming, such as Textpad
246 (http://www.textpad.com/) and UltraEdit
247 (http://www.ultraedit.com), among others.
249 If you are using MacOS, the same concerns apply. MacPerl
250 (for Classic environments) comes with a simple editor.
251 Popular external editors are BBEdit (http://www.bbedit.com)
252 or Alpha (http://alpha.olm.net/). MacOS X users can use Unix
259 http://www.gnu.org/software/emacs/windows/ntemacs.html
263 http://members.nbci.com/uemacs/
267 http://www.xemacs.org/Download/index.html
271 or a vi clone such as
277 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
287 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
291 For vi lovers in general, Windows or elsewhere:
292 http://www.thomer.com/thomer/vi/vi.html.
294 nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
295 yet another vi clone, unfortunately not available for Windows, but in
296 UNIX platforms you might be interested in trying it out, firstly because
297 strictly speaking it is not a vi clone, it is the real vi, or the new
298 incarnation of it, and secondly because you can embed Perl inside it
299 to use Perl as the scripting language. nvi is not alone in this,
300 though: at least also vim and vile offer an embedded Perl.
302 The following are Win32 multilanguage editor/IDESs that support Perl:
308 http://www.starbase.com/
312 http://www.MultiEdit.com/
316 http://www.slickedit.com/
320 There is also a toyedit Text widget based editor written in Perl
321 that is distributed with the Tk module on CPAN. The ptkdb
322 (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
323 acts as a development environment of sorts. Perl Composer
324 (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
327 In addition to an editor/IDE you might be interested in a more
328 powerful shell environment for Win32. Your options include
334 from the Cygwin package (http://sources.redhat.com/cygwin/)
338 from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
339 the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
343 ftp://ftp.astron.com/pub/tcsh/, see also
344 http://www.primate.wisc.edu/software/csh-tcsh-book/
348 ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
352 MKS and U/WIN are commercial (U/WIN is free for educational and
353 research purposes), Cygwin is covered by the GNU Public License (but
354 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
355 contain (in addition to the shells) a comprehensive set of standard
356 UNIX toolkit utilities.
358 If you're transferring text files between Unix and Windows using FTP
359 be sure to transfer them in ASCII mode so the ends of lines are
360 appropriately converted.
362 On Mac OS the MacPerl Application comes with a simple 32k text editor
363 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
364 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
369 =item BBEdit and BBEdit Lite
371 are text editors for Mac OS that have a Perl sensitivity mode
372 (http://web.barebones.com/).
376 is an editor, written and extensible in Tcl, that nonetheless has
377 built in support for several popular markup and programming languages
378 including Perl and HTML (http://alpha.olm.net/).
382 Pepper and Pe are programming language sensitive text editors for Mac
383 OS X and BeOS respectively (http://www.hekkelman.com/).
385 =head2 Where can I get Perl macros for vi?
387 For a complete version of Tom Christiansen's vi configuration file,
388 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
389 the standard benchmark file for vi emulators. The file runs best with nvi,
390 the current version of vi out of Berkeley, which incidentally can be built
391 with an embedded Perl interpreter--see http://www.cpan.org/src/misc.
393 =head2 Where can I get perl-mode for emacs?
395 Since Emacs version 19 patchlevel 22 or so, there have been both a
396 perl-mode.el and support for the Perl debugger built in. These should
397 come with the standard Emacs 19 distribution.
399 In the Perl source directory, you'll find a directory called "emacs",
400 which contains a cperl-mode that color-codes keywords, provides
401 context-sensitive help, and other nifty things.
403 Note that the perl-mode of emacs will have fits with C<"main'foo">
404 (single quote), and mess up the indentation and highlighting. You
405 are probably using C<"main::foo"> in new Perl code anyway, so this
406 shouldn't be an issue.
408 =head2 How can I use curses with Perl?
410 The Curses module from CPAN provides a dynamically loadable object
411 module interface to a curses library. A small demo can be found at the
412 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep;
413 this program repeats a command and updates the screen as needed, rendering
414 B<rep ps axu> similar to B<top>.
416 =head2 How can I use X or Tk with Perl?
418 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
419 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
420 to the Athena Widget set. Both are available from CPAN. See the
421 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
423 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
424 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
426 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
428 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
430 =head2 How can I generate simple menus without using CGI or Tk?
432 The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
433 module, which is curses-based, can help with this.
435 =head2 How can I make my Perl program run faster?
437 The best way to do this is to come up with a better algorithm. This
438 can often make a dramatic difference. Jon Bentley's book
439 ``Programming Pearls'' (that's not a misspelling!) has some good tips
440 on optimization, too. Advice on benchmarking boils down to: benchmark
441 and profile to make sure you're optimizing the right part, look for
442 better algorithms instead of microtuning your code, and when all else
443 fails consider just buying faster hardware. You will probably want to
444 read the answer to the earlier question ``How do I profile my Perl programs?''
445 if you haven't done so already.
447 A different approach is to autoload seldom-used Perl code. See the
448 AutoSplit and AutoLoader modules in the standard distribution for
449 that. Or you could locate the bottleneck and think about writing just
450 that part in C, the way we used to take bottlenecks in C code and
451 write them in assembler. Similar to rewriting in C,
452 modules that have critical sections can be written in C (for instance, the
453 PDL module from CPAN).
455 In some cases, it may be worth it to use the backend compiler to
456 produce byte code (saving compilation time) or compile into C, which
457 will certainly save compilation time and sometimes a small amount (but
458 not much) execution time. See the question about compiling your Perl
459 programs for more on the compiler--the wins aren't as obvious as you'd
462 If you're currently linking your perl executable to a shared I<libc.so>,
463 you can often gain a 10-25% performance benefit by rebuilding it to
464 link with a static libc.a instead. This will make a bigger perl
465 executable, but your Perl programs (and programmers) may thank you for
466 it. See the F<INSTALL> file in the source distribution for more
469 Unsubstantiated reports allege that Perl interpreters that use sfio
470 outperform those that don't (for I/O intensive applications). To try
471 this, see the F<INSTALL> file in the source distribution, especially
472 the ``Selecting File I/O mechanisms'' section.
474 The undump program was an old attempt to speed up your Perl program
475 by storing the already-compiled form to disk. This is no longer
476 a viable option, as it only worked on a few architectures, and
477 wasn't a good solution anyway.
479 =head2 How can I make my Perl program take less memory?
481 When it comes to time-space tradeoffs, Perl nearly always prefers to
482 throw memory at a problem. Scalars in Perl use more memory than
483 strings in C, arrays take more than that, and hashes use even more. While
484 there's still a lot to be done, recent releases have been addressing
485 these issues. For example, as of 5.004, duplicate hash keys are
486 shared amongst all hashes using them, so require no reallocation.
488 In some cases, using substr() or vec() to simulate arrays can be
489 highly beneficial. For example, an array of a thousand booleans will
490 take at least 20,000 bytes of space, but it can be turned into one
491 125-byte bit vector--a considerable memory savings. The standard
492 Tie::SubstrHash module can also help for certain types of data
493 structure. If you're working with specialist data structures
494 (matrices, for instance) modules that implement these in C may use
495 less memory than equivalent Perl modules.
497 Another thing to try is learning whether your Perl was compiled with
498 the system malloc or with Perl's builtin malloc. Whichever one it
499 is, try using the other one and see whether this makes a difference.
500 Information about malloc is in the F<INSTALL> file in the source
501 distribution. You can find out whether you are using perl's malloc by
502 typing C<perl -V:usemymalloc>.
504 Of course, the best way to save memory is to not do anything to waste
505 it in the first place. Good programming practices can go a long way
512 Don't read an entire file into memory if you can process it line
513 by line. Or more concretely, use a loop like this:
532 When the files you're processing are small, it doesn't much matter which
533 way you do it, but it makes a huge difference when they start getting
536 =item * Use map and grep selectively
538 Remember that both map and grep expect a LIST argument, so doing this:
540 @wanted = grep {/pattern/} <FILE>;
542 will cause the entire file to be slurped. For large files, it's better
546 push(@wanted, $_) if /pattern/;
549 =item * Avoid unnecessary quotes and stringification
551 Don't quote large strings unless absolutely necessary:
553 my $copy = "$large_string";
555 makes 2 copies of $large_string (one for $copy and another for the
558 my $copy = $large_string;
562 Ditto for stringifying large arrays:
569 is much more memory-efficient than either
571 print join "\n", @big_array;
581 =item * Pass by reference
583 Pass arrays and hashes by reference, not by value. For one thing, it's
584 the only way to pass multiple lists or hashes (or both) in a single
585 call/return. It also avoids creating a copy of all the contents. This
586 requires some judgment, however, because any changes will be propagated
587 back to the original data. If you really want to mangle (er, modify) a
588 copy, you'll have to sacrifice the memory needed to make one.
590 =item * Tie large variables to disk.
592 For "big" data stores (i.e. ones that exceed available memory) consider
593 using one of the DB modules to store it on disk instead of in RAM. This
594 will incur a penalty in access time, but that's probably better that
595 causing your hard disk to thrash due to massive swapping.
599 =head2 Is it unsafe to return a pointer to local data?
601 No, Perl's garbage collection system takes care of this.
609 push @many, makeone();
612 print $many[4][5], "\n";
616 =head2 How can I free an array or hash so my program shrinks?
618 You can't. On most operating systems, memory allocated to a program
619 can never be returned to the system. That's why long-running programs
620 sometimes re-exec themselves. Some operating systems (notably,
621 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
622 longer used, but it doesn't appear to happen with Perl (yet). The Mac
623 appears to be the only platform that will reliably (albeit, slowly)
624 return memory to the OS.
626 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
627 $scalar> will return memory to the system, while on Solaris 2.6 it
628 won't. In general, try it yourself and see.
630 However, judicious use of my() on your variables will help make sure
631 that they go out of scope so that Perl can free up that space for
632 use in other parts of your program. A global variable, of course, never
633 goes out of scope, so you can't get its space automatically reclaimed,
634 although undef()ing and/or delete()ing it will achieve the same effect.
635 In general, memory allocation and de-allocation isn't something you can
636 or should be worrying about much in Perl, but even this capability
637 (preallocation of data types) is in the works.
639 =head2 How can I make my CGI script more efficient?
641 Beyond the normal measures described to make general Perl programs
642 faster or smaller, a CGI program has additional issues. It may be run
643 several times per second. Given that each time it runs it will need
644 to be re-compiled and will often allocate a megabyte or more of system
645 memory, this can be a killer. Compiling into C B<isn't going to help
646 you> because the process start-up overhead is where the bottleneck is.
648 There are two popular ways to avoid this overhead. One solution
649 involves running the Apache HTTP server (available from
650 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
653 With mod_perl and the Apache::Registry module (distributed with
654 mod_perl), httpd will run with an embedded Perl interpreter which
655 pre-compiles your script and then executes it within the same address
656 space without forking. The Apache extension also gives Perl access to
657 the internal server API, so modules written in Perl can do just about
658 anything a module written in C can. For more on mod_perl, see
659 http://perl.apache.org/
661 With the FCGI module (from CPAN) and the mod_fastcgi
662 module (available from http://www.fastcgi.com/) each of your Perl
663 programs becomes a permanent CGI daemon process.
665 Both of these solutions can have far-reaching effects on your system
666 and on the way you write your CGI programs, so investigate them with
669 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
671 A non-free, commercial product, ``The Velocity Engine for Perl'',
672 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
673 might also be worth looking at. It will allow you to increase the
674 performance of your Perl programs, running programs up to 25 times
675 faster than normal CGI Perl when running in persistent Perl mode or 4
676 to 5 times faster without any modification to your existing CGI
677 programs. Fully functional evaluation copies are available from the
680 =head2 How can I hide the source for my Perl program?
682 Delete it. :-) Seriously, there are a number of (mostly
683 unsatisfactory) solutions with varying levels of ``security''.
685 First of all, however, you I<can't> take away read permission, because
686 the source code has to be readable in order to be compiled and
687 interpreted. (That doesn't mean that a CGI script's source is
688 readable by people on the web, though--only by people with access to
689 the filesystem.) So you have to leave the permissions at the socially
692 Some people regard this as a security problem. If your program does
693 insecure things and relies on people not knowing how to exploit those
694 insecurities, it is not secure. It is often possible for someone to
695 determine the insecure things and exploit them without viewing the
696 source. Security through obscurity, the name for hiding your bugs
697 instead of fixing them, is little security indeed.
699 You can try using encryption via source filters (Starting from Perl
700 5.8 the Filter::Simple and Filter::Util::Call modules are included in
701 the standard distribution), but any decent programmer will be able to
702 decrypt it. You can try using the byte code compiler and interpreter
703 described below, but the curious might still be able to de-compile it.
704 You can try using the native-code compiler described below, but
705 crackers might be able to disassemble it. These pose varying degrees
706 of difficulty to people wanting to get at your code, but none can
707 definitively conceal it (true of every language, not just Perl).
709 If you're concerned about people profiting from your code, then the
710 bottom line is that nothing but a restrictive license will give you
711 legal security. License your software and pepper it with threatening
712 statements like ``This is unpublished proprietary software of XYZ Corp.
713 Your access to it does not give you permission to use it blah blah
714 blah.'' We are not lawyers, of course, so you should see a lawyer if
715 you want to be sure your license's wording will stand up in court.
717 =head2 How can I compile my Perl program into byte code or C?
719 Malcolm Beattie has written a multifunction backend compiler,
720 available from CPAN, that can do both these things. It is included
721 in the perl5.005 release, but is still considered experimental.
722 This means it's fun to play with if you're a programmer but not
723 really for people looking for turn-key solutions.
725 Merely compiling into C does not in and of itself guarantee that your
726 code will run very much faster. That's because except for lucky cases
727 where a lot of native type inferencing is possible, the normal Perl
728 run-time system is still present and so your program will take just as
729 long to run and be just as big. Most programs save little more than
730 compilation time, leaving execution no more than 10-30% faster. A few
731 rare programs actually benefit significantly (even running several times
732 faster), but this takes some tweaking of your code.
734 You'll probably be astonished to learn that the current version of the
735 compiler generates a compiled form of your script whose executable is
736 just as big as the original perl executable, and then some. That's
737 because as currently written, all programs are prepared for a full
738 eval() statement. You can tremendously reduce this cost by building a
739 shared I<libperl.so> library and linking against that. See the
740 F<INSTALL> podfile in the Perl source distribution for details. If
741 you link your main perl binary with this, it will make it minuscule.
742 For example, on one author's system, F</usr/bin/perl> is only 11k in
745 In general, the compiler will do nothing to make a Perl program smaller,
746 faster, more portable, or more secure. In fact, it can make your
747 situation worse. The executable will be bigger, your VM system may take
748 longer to load the whole thing, the binary is fragile and hard to fix,
749 and compilation never stopped software piracy in the form of crackers,
750 viruses, or bootleggers. The real advantage of the compiler is merely
751 packaging, and once you see the size of what it makes (well, unless
752 you use a shared I<libperl.so>), you'll probably want a complete
755 =head2 How can I compile Perl into Java?
757 You can also integrate Java and Perl with the
758 Perl Resource Kit from O'Reilly and Associates. See
759 http://www.oreilly.com/catalog/prkunix/ .
761 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
762 development, allows Perl code to be called from Java. See jpl/README
763 in the Perl source tree.
765 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
769 extproc perl -S -your_switches
771 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
772 `extproc' handling). For DOS one should first invent a corresponding
773 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
774 F<INSTALL> file in the source distribution for more information).
776 The Win95/NT installation, when using the ActiveState port of Perl,
777 will modify the Registry to associate the C<.pl> extension with the
778 perl interpreter. If you install another port, perhaps even building
779 your own Win95/NT Perl from the standard sources by using a Windows port
780 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
781 the Registry yourself. In addition to associating C<.pl> with the
782 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
783 run the program C<install-linux.pl> merely by typing C<install-linux>.
785 Macintosh Perl programs will have the appropriate Creator and
786 Type, so that double-clicking them will invoke the Perl application.
788 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
789 throw the perl interpreter into your cgi-bin directory, in order to
790 get your programs working for a web server. This is an EXTREMELY big
791 security risk. Take the time to figure out how to do it correctly.
793 =head2 Can I write useful Perl programs on the command line?
795 Yes. Read L<perlrun> for more information. Some examples follow.
796 (These assume standard Unix shell quoting rules.)
798 # sum first and last fields
799 perl -lane 'print $F[0] + $F[-1]' *
801 # identify text files
802 perl -le 'for(@ARGV) {print if -f && -T _}' *
804 # remove (most) comments from C program
805 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
807 # make file a month younger than today, defeating reaper daemons
808 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
810 # find first unused uid
811 perl -le '$i++ while getpwuid($i); print $i'
813 # display reasonable manpath
814 echo $PATH | perl -nl -072 -e '
815 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
817 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
819 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
821 The problem is usually that the command interpreters on those systems
822 have rather different ideas about quoting than the Unix shells under
823 which the one-liners were created. On some systems, you may have to
824 change single-quotes to double ones, which you must I<NOT> do on Unix
825 or Plan9 systems. You might also have to change a single % to a %%.
830 perl -e 'print "Hello world\n"'
833 perl -e "print \"Hello world\n\""
836 print "Hello world\n"
837 (then Run "Myscript" or Shift-Command-R)
840 perl -e "print ""Hello world\n"""
842 The problem is that none of these examples are reliable: they depend on the
843 command interpreter. Under Unix, the first two often work. Under DOS,
844 it's entirely possible that neither works. If 4DOS was the command shell,
845 you'd probably have better luck like this:
847 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
849 Under the Mac, it depends which environment you are using. The MacPerl
850 shell, or MPW, is much like Unix shells in its support for several
851 quoting variants, except that it makes free use of the Mac's non-ASCII
852 characters as control characters.
854 Using qq(), q(), and qx(), instead of "double quotes", 'single
855 quotes', and `backticks`, may make one-liners easier to write.
857 There is no general solution to all of this. It is a mess, pure and
858 simple. Sucks to be away from Unix, huh? :-)
860 [Some of this answer was contributed by Kenneth Albanowski.]
862 =head2 Where can I learn about CGI or Web programming in Perl?
864 For modules, get the CGI or LWP modules from CPAN. For textbooks,
865 see the two especially dedicated to web stuff in the question on
866 books. For problems and questions related to the web, like ``Why
867 do I get 500 Errors'' or ``Why doesn't it run from the browser right
868 when it runs fine on the command line'', see the troubleshooting
869 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
871 http://www.perl.org/CGI_MetaFAQ.html
873 =head2 Where can I learn about object-oriented Perl programming?
875 A good place to start is L<perltoot>, and you can use L<perlobj>,
876 L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out
877 until the 5.004 release; you can get a copy (in pod, html, or
878 postscript) from http://www.cpan.org/doc/FMTEYEWTK/ .
880 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
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.
889 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
890 my C program; what am I doing wrong?
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
894 fail, see L<perlbug> and send a bug report with the output of
895 C<make test TEST_VERBOSE=1> along with C<perl -V>.
897 =head2 When I tried to run my script, I got this message. What does it
900 A complete list of Perl's error messages and warnings with explanatory
901 text can be found in L<perldiag>. You can also use the splain program
902 (distributed with Perl) to explain the error messages:
904 perl program 2>diag.out
905 splain [-v] [-p] diag.out
907 or change your program to explain the messages for you:
913 use diagnostics -verbose;
915 =head2 What's MakeMaker?
917 This module (part of the standard Perl distribution) is designed to
918 write a Makefile for an extension module from a Makefile.PL. For more
919 information, see L<ExtUtils::MakeMaker>.
921 =head1 AUTHOR AND COPYRIGHT
923 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
926 This documentation is free; you can redistribute it and/or modify it
927 under the same terms as Perl itself.
929 Irrespective of its distribution, all code examples here are in the public
930 domain. You are permitted and encouraged to use this code and any
931 derivatives thereof in your own programs for fun or for profit as you
932 see fit. A simple comment in the code giving credit to the FAQ would
933 be courteous but is not required.