3 perlfaq3 - Programming Tools ($Revision: 1.40 $, $Date: 2004/10/19 17:02:27 $)
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/misc/olddoc/FMTEYEWTK.tgz
26 (not a man-page but still useful, a collection
27 of various essays on Perl techniques)
29 A crude table of contents for the Perl manpage set is found in L<perltoc>.
31 =head2 How can I use Perl interactively?
33 The typical approach uses the Perl debugger, described in the
34 perldebug(1) manpage, on an ``empty'' program, like this:
38 Now just type in any legal Perl code, and it will be immediately
39 evaluated. You can also examine the symbol table, get stack
40 backtraces, check variable values, set breakpoints, and other
41 operations typically found in symbolic debuggers.
43 =head2 Is there a Perl shell?
45 The psh (Perl sh) is currently at version 1.8. The Perl Shell is a
46 shell that combines the interactive nature of a Unix shell with the
47 power of Perl. The goal is a full featured shell that behaves as
48 expected for normal shell activity and uses Perl syntax and
49 functionality for control-flow statements and other things.
50 You can get psh at http://www.focusresearch.com/gregor/psh/ .
52 Zoidberg is a similar project and provides a shell written in perl,
53 configured in perl and operated in perl. It is intended as a login shell
54 and development environment. It can be found at http://zoidberg.sf.net/
55 or your local CPAN mirror.
57 The Shell.pm module (distributed with Perl) makes Perl try commands
58 which aren't part of the Perl language as shell commands. perlsh
59 from the source distribution is simplistic and uninteresting, but
60 may still be what you want.
62 =head2 How do I find which modules are installed on my system?
64 You can use the ExtUtils::Installed module to show all
65 installed distributions, although it can take awhile to do
66 its magic. The standard library which comes with Perl just
67 shows up as "Perl" (although you can get those with
70 use ExtUtils::Installed;
72 my $inst = ExtUtils::Installed->new();
73 my @modules = $inst->modules();
75 If you want a list of all of the Perl module filenames, you
76 can use File::Find::Rule.
80 my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC );
82 If you do not have that module, you can do the same thing
83 with File::Find which is part of the standard library.
88 find sub { push @files, $File::Find::name if -f _ && /\.pm$/ },
91 print join "\n", @files;
93 If you simply need to quickly check to see if a module is
94 available, you can check for its documentation. If you can
95 read the documentation the module is most likely installed.
96 If you cannot read the documentation, the module might not
97 have any (in rare cases).
99 prompt% perldoc Module::Name
101 You can also try to include the module in a one-liner to see if
104 perl -MModule::Name -e1
106 =head2 How do I debug my Perl programs?
108 Have you tried C<use warnings> or used C<-w>? They enable warnings
109 to detect dubious practices.
111 Have you tried C<use strict>? It prevents you from using symbolic
112 references, makes you predeclare any subroutines that you call as bare
113 words, and (probably most importantly) forces you to predeclare your
114 variables with C<my>, C<our>, or C<use vars>.
116 Did you check the return values of each and every system call? The operating
117 system (and thus Perl) tells you whether they worked, and if not
120 open(FH, "> /etc/cantwrite")
121 or die "Couldn't write to /etc/cantwrite: $!\n";
123 Did you read L<perltrap>? It's full of gotchas for old and new Perl
124 programmers and even has sections for those of you who are upgrading
125 from languages like I<awk> and I<C>.
127 Have you tried the Perl debugger, described in L<perldebug>? You can
128 step through your program and see what it's doing and thus work out
129 why what it's doing isn't what it should be doing.
131 =head2 How do I profile my Perl programs?
133 You should get the Devel::DProf module from the standard distribution
134 (or separately on CPAN) and also use Benchmark.pm from the standard
135 distribution. The Benchmark module lets you time specific portions of
136 your code, while Devel::DProf gives detailed breakdowns of where your
137 code spends its time.
139 Here's a sample use of Benchmark:
143 @junk = `cat /etc/motd`;
147 'map' => sub { my @a = @junk;
150 'for' => sub { my @a = @junk;
155 This is what it prints (on one machine--your results will be dependent
156 on your hardware, operating system, and the load on your machine):
158 Benchmark: timing 10000 iterations of for, map...
159 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
160 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
162 Be aware that a good benchmark is very hard to write. It only tests the
163 data you give it and proves little about the differing complexities
164 of contrasting algorithms.
166 =head2 How do I cross-reference my Perl programs?
168 The B::Xref module can be used to generate cross-reference reports
171 perl -MO=Xref[,OPTIONS] scriptname.plx
173 =head2 Is there a pretty-printer (formatter) for Perl?
175 Perltidy is a Perl script which indents and reformats Perl scripts
176 to make them easier to read by trying to follow the rules of the
177 L<perlstyle>. If you write Perl scripts, or spend much time reading
178 them, you will probably find it useful. It is available at
179 http://perltidy.sourceforge.net
181 Of course, if you simply follow the guidelines in L<perlstyle>,
182 you shouldn't need to reformat. The habit of formatting your code
183 as you write it will help prevent bugs. Your editor can and should
184 help you with this. The perl-mode or newer cperl-mode for emacs
185 can provide remarkable amounts of help with most (but not all)
186 code, and even less programmable editors can provide significant
187 assistance. Tom Christiansen and many other VI users swear by
188 the following settings in vi and its clones:
193 Put that in your F<.exrc> file (replacing the caret characters
194 with control characters) and away you go. In insert mode, ^T is
195 for indenting, ^D is for undenting, and ^O is for blockdenting--
196 as it were. A more complete example, with comments, can be found at
197 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
199 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
200 lots of things related to generating nicely printed output of
201 documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
203 =head2 Is there a ctags for Perl?
205 Recent versions of ctags do much more than older versions did.
206 EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
207 and does a good job of making tags files for perl code.
209 There is also a simple one at
210 http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
211 the trick. It can be easy to hack this into what you want.
213 =head2 Is there an IDE or Windows Perl Editor?
215 Perl programs are just plain text, so any editor will do.
217 If you're on Unix, you already have an IDE--Unix itself. The UNIX
218 philosophy is the philosophy of several small tools that each do one
219 thing and do it well. It's like a carpenter's toolbox.
221 If you want an IDE, check the following:
227 ActiveState's cross-platform (as of April 2001 Windows and Linux),
228 multi-language IDE has Perl support, including a regular expression
229 debugger and remote debugging
230 ( http://www.ActiveState.com/Products/Komodo/ ). (Visual
231 Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta
232 ( http://www.ActiveState.com/Products/VisualPerl/index.html )).
236 ( http://open-perl-ide.sourceforge.net/ )
237 Open Perl IDE is an integrated development environment for writing
238 and debugging Perl scripts with ActiveState's ActivePerl distribution
239 under Windows 95/98/NT/2000.
243 ( http://www.solutionsoft.com/perl.htm ) is an integrated development
244 environment for Windows that supports Perl development.
248 ( http://helpconsulting.net/visiperl/ )
249 From Help Consulting, for Windows.
253 ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
254 environment, including debugger and syntax highlighting editor.
258 For editors: if you're on Unix you probably have vi or a vi clone already,
259 and possibly an emacs too, so you may not need to download anything.
260 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
261 best available Perl editing mode in any editor.
263 If you are using Windows, you can use any editor that lets
264 you work with plain text, such as NotePad or WordPad. Word
265 processors, such as Microsoft Word or WordPerfect, typically
266 do not work since they insert all sorts of behind-the-scenes
267 information, although some allow you to save files as "Text
268 Only". You can also download text editors designed
269 specifically for programming, such as Textpad
270 ( http://www.textpad.com/ ) and UltraEdit
271 ( http://www.ultraedit.com/ ), among others.
273 If you are using MacOS, the same concerns apply. MacPerl
274 (for Classic environments) comes with a simple editor.
275 Popular external editors are BBEdit ( http://www.bbedit.com/ )
276 or Alpha ( http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can
277 use Unix editors as well.
283 http://www.gnu.org/software/emacs/windows/ntemacs.html
287 http://www.microemacs.de/
291 http://www.xemacs.org/Download/index.html
295 http://space.mit.edu/~davis/jed/
299 or a vi clone such as
305 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
309 http://dickey.his.com/vile/vile.html
317 For vi lovers in general, Windows or elsewhere:
319 http://www.thomer.com/thomer/vi/vi.html
321 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
322 yet another vi clone, unfortunately not available for Windows, but in
323 UNIX platforms you might be interested in trying it out, firstly because
324 strictly speaking it is not a vi clone, it is the real vi, or the new
325 incarnation of it, and secondly because you can embed Perl inside it
326 to use Perl as the scripting language. nvi is not alone in this,
327 though: at least also vim and vile offer an embedded Perl.
329 The following are Win32 multilanguage editor/IDESs that support Perl:
335 http://www.borland.com/codewright/
339 http://www.MultiEdit.com/
343 http://www.slickedit.com/
347 There is also a toyedit Text widget based editor written in Perl
348 that is distributed with the Tk module on CPAN. The ptkdb
349 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
350 acts as a development environment of sorts. Perl Composer
351 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
354 In addition to an editor/IDE you might be interested in a more
355 powerful shell environment for Win32. Your options include
361 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
365 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
366 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
370 ftp://ftp.astron.com/pub/tcsh/ , see also
371 http://www.primate.wisc.edu/software/csh-tcsh-book/
375 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
379 MKS and U/WIN are commercial (U/WIN is free for educational and
380 research purposes), Cygwin is covered by the GNU Public License (but
381 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
382 contain (in addition to the shells) a comprehensive set of standard
383 UNIX toolkit utilities.
385 If you're transferring text files between Unix and Windows using FTP
386 be sure to transfer them in ASCII mode so the ends of lines are
387 appropriately converted.
389 On Mac OS the MacPerl Application comes with a simple 32k text editor
390 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
391 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
398 is a full Perl development enivornment with full debugger support (
399 http://www.latenightsw.com ).
403 is an editor, written and extensible in Tcl, that nonetheless has
404 built in support for several popular markup and programming languages
405 including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).
407 =item BBEdit and BBEdit Lite
409 are text editors for Mac OS that have a Perl sensitivity mode
410 ( http://web.barebones.com/ ).
415 Pepper and Pe are programming language sensitive text editors for Mac
416 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
418 =head2 Where can I get Perl macros for vi?
420 For a complete version of Tom Christiansen's vi configuration file,
421 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
422 the standard benchmark file for vi emulators. The file runs best with nvi,
423 the current version of vi out of Berkeley, which incidentally can be built
424 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
426 =head2 Where can I get perl-mode for emacs?
428 Since Emacs version 19 patchlevel 22 or so, there have been both a
429 perl-mode.el and support for the Perl debugger built in. These should
430 come with the standard Emacs 19 distribution.
432 In the Perl source directory, you'll find a directory called "emacs",
433 which contains a cperl-mode that color-codes keywords, provides
434 context-sensitive help, and other nifty things.
436 Note that the perl-mode of emacs will have fits with C<"main'foo">
437 (single quote), and mess up the indentation and highlighting. You
438 are probably using C<"main::foo"> in new Perl code anyway, so this
439 shouldn't be an issue.
441 =head2 How can I use curses with Perl?
443 The Curses module from CPAN provides a dynamically loadable object
444 module interface to a curses library. A small demo can be found at the
445 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
446 this program repeats a command and updates the screen as needed, rendering
447 B<rep ps axu> similar to B<top>.
449 =head2 How can I use X or Tk with Perl?
451 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
452 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
453 to the Athena Widget set. Both are available from CPAN. See the
454 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
456 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
457 http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
459 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
461 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
463 =head2 How can I generate simple menus without using CGI or Tk?
465 The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
466 module, which is curses-based, can help with this.
468 =head2 How can I make my Perl program run faster?
470 The best way to do this is to come up with a better algorithm. This
471 can often make a dramatic difference. Jon Bentley's book
472 I<Programming Pearls> (that's not a misspelling!) has some good tips
473 on optimization, too. Advice on benchmarking boils down to: benchmark
474 and profile to make sure you're optimizing the right part, look for
475 better algorithms instead of microtuning your code, and when all else
476 fails consider just buying faster hardware. You will probably want to
477 read the answer to the earlier question ``How do I profile my Perl
478 programs?'' if you haven't done so already.
480 A different approach is to autoload seldom-used Perl code. See the
481 AutoSplit and AutoLoader modules in the standard distribution for
482 that. Or you could locate the bottleneck and think about writing just
483 that part in C, the way we used to take bottlenecks in C code and
484 write them in assembler. Similar to rewriting in C, modules that have
485 critical sections can be written in C (for instance, the PDL module
488 If you're currently linking your perl executable to a shared
489 I<libc.so>, you can often gain a 10-25% performance benefit by
490 rebuilding it to link with a static libc.a instead. This will make a
491 bigger perl executable, but your Perl programs (and programmers) may
492 thank you for it. See the F<INSTALL> file in the source distribution
493 for more information.
495 The undump program was an ancient attempt to speed up Perl program by
496 storing the already-compiled form to disk. This is no longer a viable
497 option, as it only worked on a few architectures, and wasn't a good
500 =head2 How can I make my Perl program take less memory?
502 When it comes to time-space tradeoffs, Perl nearly always prefers to
503 throw memory at a problem. Scalars in Perl use more memory than
504 strings in C, arrays take more than that, and hashes use even more. While
505 there's still a lot to be done, recent releases have been addressing
506 these issues. For example, as of 5.004, duplicate hash keys are
507 shared amongst all hashes using them, so require no reallocation.
509 In some cases, using substr() or vec() to simulate arrays can be
510 highly beneficial. For example, an array of a thousand booleans will
511 take at least 20,000 bytes of space, but it can be turned into one
512 125-byte bit vector--a considerable memory savings. The standard
513 Tie::SubstrHash module can also help for certain types of data
514 structure. If you're working with specialist data structures
515 (matrices, for instance) modules that implement these in C may use
516 less memory than equivalent Perl modules.
518 Another thing to try is learning whether your Perl was compiled with
519 the system malloc or with Perl's builtin malloc. Whichever one it
520 is, try using the other one and see whether this makes a difference.
521 Information about malloc is in the F<INSTALL> file in the source
522 distribution. You can find out whether you are using perl's malloc by
523 typing C<perl -V:usemymalloc>.
525 Of course, the best way to save memory is to not do anything to waste
526 it in the first place. Good programming practices can go a long way
533 Don't read an entire file into memory if you can process it line
534 by line. Or more concretely, use a loop like this:
553 When the files you're processing are small, it doesn't much matter which
554 way you do it, but it makes a huge difference when they start getting
557 =item * Use map and grep selectively
559 Remember that both map and grep expect a LIST argument, so doing this:
561 @wanted = grep {/pattern/} <FILE>;
563 will cause the entire file to be slurped. For large files, it's better
567 push(@wanted, $_) if /pattern/;
570 =item * Avoid unnecessary quotes and stringification
572 Don't quote large strings unless absolutely necessary:
574 my $copy = "$large_string";
576 makes 2 copies of $large_string (one for $copy and another for the
579 my $copy = $large_string;
583 Ditto for stringifying large arrays:
590 is much more memory-efficient than either
592 print join "\n", @big_array;
602 =item * Pass by reference
604 Pass arrays and hashes by reference, not by value. For one thing, it's
605 the only way to pass multiple lists or hashes (or both) in a single
606 call/return. It also avoids creating a copy of all the contents. This
607 requires some judgment, however, because any changes will be propagated
608 back to the original data. If you really want to mangle (er, modify) a
609 copy, you'll have to sacrifice the memory needed to make one.
611 =item * Tie large variables to disk.
613 For "big" data stores (i.e. ones that exceed available memory) consider
614 using one of the DB modules to store it on disk instead of in RAM. This
615 will incur a penalty in access time, but that's probably better than
616 causing your hard disk to thrash due to massive swapping.
620 =head2 Is it safe to return a reference to local or lexical data?
622 Yes. Perl's garbage collection system takes care of this so
623 everything works out right.
631 push @many, makeone();
634 print $many[4][5], "\n";
638 =head2 How can I free an array or hash so my program shrinks?
640 You usually can't. On most operating systems, memory
641 allocated to a program can never be returned to the system.
642 That's why long-running programs sometimes re-exec
643 themselves. Some operating systems (notably, systems that
644 use mmap(2) for allocating large chunks of memory) can
645 reclaim memory that is no longer used, but on such systems,
646 perl must be configured and compiled to use the OS's malloc,
649 However, judicious use of my() on your variables will help make sure
650 that they go out of scope so that Perl can free up that space for
651 use in other parts of your program. A global variable, of course, never
652 goes out of scope, so you can't get its space automatically reclaimed,
653 although undef()ing and/or delete()ing it will achieve the same effect.
654 In general, memory allocation and de-allocation isn't something you can
655 or should be worrying about much in Perl, but even this capability
656 (preallocation of data types) is in the works.
658 =head2 How can I make my CGI script more efficient?
660 Beyond the normal measures described to make general Perl programs
661 faster or smaller, a CGI program has additional issues. It may be run
662 several times per second. Given that each time it runs it will need
663 to be re-compiled and will often allocate a megabyte or more of system
664 memory, this can be a killer. Compiling into C B<isn't going to help
665 you> because the process start-up overhead is where the bottleneck is.
667 There are two popular ways to avoid this overhead. One solution
668 involves running the Apache HTTP server (available from
669 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
672 With mod_perl and the Apache::Registry module (distributed with
673 mod_perl), httpd will run with an embedded Perl interpreter which
674 pre-compiles your script and then executes it within the same address
675 space without forking. The Apache extension also gives Perl access to
676 the internal server API, so modules written in Perl can do just about
677 anything a module written in C can. For more on mod_perl, see
678 http://perl.apache.org/
680 With the FCGI module (from CPAN) and the mod_fastcgi
681 module (available from http://www.fastcgi.com/ ) each of your Perl
682 programs becomes a permanent CGI daemon process.
684 Both of these solutions can have far-reaching effects on your system
685 and on the way you write your CGI programs, so investigate them with
688 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
690 A non-free, commercial product, ``The Velocity Engine for Perl'',
691 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
692 might also be worth looking at. It will allow you to increase the
693 performance of your Perl programs, running programs up to 25 times
694 faster than normal CGI Perl when running in persistent Perl mode or 4
695 to 5 times faster without any modification to your existing CGI
696 programs. Fully functional evaluation copies are available from the
699 =head2 How can I hide the source for my Perl program?
701 Delete it. :-) Seriously, there are a number of (mostly
702 unsatisfactory) solutions with varying levels of ``security''.
704 First of all, however, you I<can't> take away read permission, because
705 the source code has to be readable in order to be compiled and
706 interpreted. (That doesn't mean that a CGI script's source is
707 readable by people on the web, though--only by people with access to
708 the filesystem.) So you have to leave the permissions at the socially
711 Some people regard this as a security problem. If your program does
712 insecure things and relies on people not knowing how to exploit those
713 insecurities, it is not secure. It is often possible for someone to
714 determine the insecure things and exploit them without viewing the
715 source. Security through obscurity, the name for hiding your bugs
716 instead of fixing them, is little security indeed.
718 You can try using encryption via source filters (Starting from Perl
719 5.8 the Filter::Simple and Filter::Util::Call modules are included in
720 the standard distribution), but any decent programmer will be able to
721 decrypt it. You can try using the byte code compiler and interpreter
722 described below, but the curious might still be able to de-compile it.
723 You can try using the native-code compiler described below, but
724 crackers might be able to disassemble it. These pose varying degrees
725 of difficulty to people wanting to get at your code, but none can
726 definitively conceal it (true of every language, not just Perl).
728 It is very easy to recover the source of Perl programs. You simply
729 feed the program to the perl interpreter and use the modules in
730 the B:: hierarchy. The B::Deparse module should be able to
731 defeat most attempts to hide source. Again, this is not
734 If you're concerned about people profiting from your code, then the
735 bottom line is that nothing but a restrictive license will give you
736 legal security. License your software and pepper it with threatening
737 statements like ``This is unpublished proprietary software of XYZ Corp.
738 Your access to it does not give you permission to use it blah blah
739 blah.'' We are not lawyers, of course, so you should see a lawyer if
740 you want to be sure your license's wording will stand up in court.
742 =head2 How can I compile my Perl program into byte code or C?
744 Malcolm Beattie has written a multifunction backend compiler,
745 available from CPAN, that can do both these things. It is included
746 in the perl5.005 release, but is still considered experimental.
747 This means it's fun to play with if you're a programmer but not
748 really for people looking for turn-key solutions.
750 Merely compiling into C does not in and of itself guarantee that your
751 code will run very much faster. That's because except for lucky cases
752 where a lot of native type inferencing is possible, the normal Perl
753 run-time system is still present and so your program will take just as
754 long to run and be just as big. Most programs save little more than
755 compilation time, leaving execution no more than 10-30% faster. A few
756 rare programs actually benefit significantly (even running several times
757 faster), but this takes some tweaking of your code.
759 You'll probably be astonished to learn that the current version of the
760 compiler generates a compiled form of your script whose executable is
761 just as big as the original perl executable, and then some. That's
762 because as currently written, all programs are prepared for a full
763 eval() statement. You can tremendously reduce this cost by building a
764 shared I<libperl.so> library and linking against that. See the
765 F<INSTALL> podfile in the Perl source distribution for details. If
766 you link your main perl binary with this, it will make it minuscule.
767 For example, on one author's system, F</usr/bin/perl> is only 11k in
770 In general, the compiler will do nothing to make a Perl program smaller,
771 faster, more portable, or more secure. In fact, it can make your
772 situation worse. The executable will be bigger, your VM system may take
773 longer to load the whole thing, the binary is fragile and hard to fix,
774 and compilation never stopped software piracy in the form of crackers,
775 viruses, or bootleggers. The real advantage of the compiler is merely
776 packaging, and once you see the size of what it makes (well, unless
777 you use a shared I<libperl.so>), you'll probably want a complete
780 =head2 How can I compile Perl into Java?
782 You can also integrate Java and Perl with the
783 Perl Resource Kit from O'Reilly Media. See
784 http://www.oreilly.com/catalog/prkunix/ .
786 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
787 development, allows Perl code to be called from Java. See jpl/README
788 in the Perl source tree.
790 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
794 extproc perl -S -your_switches
796 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
797 `extproc' handling). For DOS one should first invent a corresponding
798 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
799 F<dosish.h> file in the source distribution for more information).
801 The Win95/NT installation, when using the ActiveState port of Perl,
802 will modify the Registry to associate the C<.pl> extension with the
803 perl interpreter. If you install another port, perhaps even building
804 your own Win95/NT Perl from the standard sources by using a Windows port
805 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
806 the Registry yourself. In addition to associating C<.pl> with the
807 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
808 run the program C<install-linux.pl> merely by typing C<install-linux>.
810 Macintosh Perl programs will have the appropriate Creator and
811 Type, so that double-clicking them will invoke the Perl application.
813 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
814 throw the perl interpreter into your cgi-bin directory, in order to
815 get your programs working for a web server. This is an EXTREMELY big
816 security risk. Take the time to figure out how to do it correctly.
818 =head2 Can I write useful Perl programs on the command line?
820 Yes. Read L<perlrun> for more information. Some examples follow.
821 (These assume standard Unix shell quoting rules.)
823 # sum first and last fields
824 perl -lane 'print $F[0] + $F[-1]' *
826 # identify text files
827 perl -le 'for(@ARGV) {print if -f && -T _}' *
829 # remove (most) comments from C program
830 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
832 # make file a month younger than today, defeating reaper daemons
833 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
835 # find first unused uid
836 perl -le '$i++ while getpwuid($i); print $i'
838 # display reasonable manpath
839 echo $PATH | perl -nl -072 -e '
840 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
842 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
844 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
846 The problem is usually that the command interpreters on those systems
847 have rather different ideas about quoting than the Unix shells under
848 which the one-liners were created. On some systems, you may have to
849 change single-quotes to double ones, which you must I<NOT> do on Unix
850 or Plan9 systems. You might also have to change a single % to a %%.
855 perl -e 'print "Hello world\n"'
858 perl -e "print \"Hello world\n\""
861 print "Hello world\n"
862 (then Run "Myscript" or Shift-Command-R)
865 perl -e 'print "Hello world\n"'
868 perl -e "print ""Hello world\n"""
870 The problem is that none of these examples are reliable: they depend on the
871 command interpreter. Under Unix, the first two often work. Under DOS,
872 it's entirely possible that neither works. If 4DOS was the command shell,
873 you'd probably have better luck like this:
875 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
877 Under the Mac, it depends which environment you are using. The MacPerl
878 shell, or MPW, is much like Unix shells in its support for several
879 quoting variants, except that it makes free use of the Mac's non-ASCII
880 characters as control characters.
882 Using qq(), q(), and qx(), instead of "double quotes", 'single
883 quotes', and `backticks`, may make one-liners easier to write.
885 There is no general solution to all of this. It is a mess.
887 [Some of this answer was contributed by Kenneth Albanowski.]
889 =head2 Where can I learn about CGI or Web programming in Perl?
891 For modules, get the CGI or LWP modules from CPAN. For textbooks,
892 see the two especially dedicated to web stuff in the question on
893 books. For problems and questions related to the web, like ``Why
894 do I get 500 Errors'' or ``Why doesn't it run from the browser right
895 when it runs fine on the command line'', see the troubleshooting
896 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
898 http://www.perl.org/CGI_MetaFAQ.html
900 =head2 Where can I learn about object-oriented Perl programming?
902 A good place to start is L<perltoot>, and you can use L<perlobj>,
903 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
904 (If you are using really old Perl, you may not have all of these,
905 try http://www.perldoc.com/ , but consider upgrading your perl.)
907 A good book on OO on Perl is the "Object-Oriented Perl"
908 by Damian Conway from Manning Publications,
909 http://www.manning.com/Conway/index.html
911 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
913 If you want to call C from Perl, start with L<perlxstut>,
914 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
915 call Perl from C, then read L<perlembed>, L<perlcall>, and
916 L<perlguts>. Don't forget that you can learn a lot from looking at
917 how the authors of existing extension modules wrote their code and
918 solved their problems.
920 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
921 my C program; what am I doing wrong?
923 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
924 the tests pass, read the pods again and again and again. If they
925 fail, see L<perlbug> and send a bug report with the output of
926 C<make test TEST_VERBOSE=1> along with C<perl -V>.
928 =head2 When I tried to run my script, I got this message. What does it mean?
930 A complete list of Perl's error messages and warnings with explanatory
931 text can be found in L<perldiag>. You can also use the splain program
932 (distributed with Perl) to explain the error messages:
934 perl program 2>diag.out
935 splain [-v] [-p] diag.out
937 or change your program to explain the messages for you:
943 use diagnostics -verbose;
945 =head2 What's MakeMaker?
947 This module (part of the standard Perl distribution) is designed to
948 write a Makefile for an extension module from a Makefile.PL. For more
949 information, see L<ExtUtils::MakeMaker>.
951 =head1 AUTHOR AND COPYRIGHT
953 Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
956 This documentation is free; you can redistribute it and/or modify it
957 under the same terms as Perl itself.
959 Irrespective of its distribution, all code examples here are in the public
960 domain. You are permitted and encouraged to use this code and any
961 derivatives thereof in your own programs for fun or for profit as you
962 see fit. A simple comment in the code giving credit to the FAQ would
963 be courteous but is not required.