3 perlfaq3 - Programming Tools
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 C<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 C<psh> (Perl sh) is currently at version 1.8. The Perl Shell is a shell
46 that combines the interactive nature of a Unix shell with the power of
47 Perl. The goal is a full-featured shell that behaves as expected for
48 normal shell activity and uses Perl syntax and functionality for
49 control-flow statements and other things. You can get C<psh> at
50 http://sourceforge.net/projects/psh/ .
52 C<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
55 http://pardus-larus.student.utwente.nl/~pardus/projects/zoidberg/
56 or your local CPAN mirror.
58 The C<Shell.pm> module (distributed with Perl) makes Perl try commands
59 which aren't part of the Perl language as shell commands. C<perlsh> from
60 the source distribution is simplistic and uninteresting, but may still
63 =head2 How do I find which modules are installed on my system?
65 From the command line, you can use the C<cpan> command's C<-l> switch:
69 You can also use C<cpan>'s C<-a> switch to create an autobundle file
70 that C<CPAN.pm> understands and can use to re-install every module:
74 Inside a Perl program, you can use the C<ExtUtils::Installed> module to
75 show all installed distributions, although it can take awhile to do
76 its magic. The standard library which comes with Perl just shows up
77 as "Perl" (although you can get those with C<Module::CoreList>).
79 use ExtUtils::Installed;
81 my $inst = ExtUtils::Installed->new();
82 my @modules = $inst->modules();
84 If you want a list of all of the Perl module filenames, you
85 can use C<File::Find::Rule>:
89 my @files = File::Find::Rule->
90 extras({follow => 1})->
96 If you do not have that module, you can do the same thing
97 with C<File::Find> which is part of the standard library:
105 push @files, $File::Find::fullname
106 if -f $File::Find::fullname && /\.pm$/
114 print join "\n", @files;
116 If you simply need to check quickly to see if a module is
117 available, you can check for its documentation. If you can
118 read the documentation the module is most likely installed.
119 If you cannot read the documentation, the module might not
120 have any (in rare cases):
122 $ perldoc Module::Name
124 You can also try to include the module in a one-liner to see if
127 $ perl -MModule::Name -e1
129 =head2 How do I debug my Perl programs?
131 (contributed by brian d foy)
133 Before you do anything else, you can help yourself by ensuring that
134 you let Perl tell you about problem areas in your code. By turning
135 on warnings and strictures, you can head off many problems before
136 they get too big. You can find out more about these in L<strict>
143 Beyond that, the simplest debugger is the C<print> function. Use it
144 to look at values as you run your program:
146 print STDERR "The value is [$value]\n";
148 The C<Data::Dumper> module can pretty-print Perl data structures:
150 use Data::Dumper qw( Dumper );
151 print STDERR "The hash is " . Dumper( \%hash ) . "\n";
153 Perl comes with an interactive debugger, which you can start with the
154 C<-d> switch. It's fully explained in L<perldebug>.
156 If you'd like a graphical user interface and you have C<Tk>, you can use
157 C<ptkdb>. It's on CPAN and available for free.
159 If you need something much more sophisticated and controllable, Leon
160 Brocard's C<Devel::ebug> (which you can call with the C<-D> switch as C<-Debug>)
161 gives you the programmatic hooks into everything you need to write your
162 own (without too much pain and suffering).
164 You can also use a commercial debugger such as Affrus (Mac OS X), Komodo
165 from Activestate (Windows and Mac OS X), or EPIC (most platforms).
167 =head2 How do I profile my Perl programs?
169 (contributed by brian d foy, updated Fri Jul 25 12:22:26 PDT 2008)
171 The C<Devel> namespace has several modules which you can use to
172 profile your Perl programs.
174 The C<Devel::NYTProf> (New York Times Profiler) does both statement
175 and subroutine profiling. It's available from CPAN and you also invoke
176 it with the C<-d> switch:
178 perl -d:NYTProf some_perl.pl
180 It creates a database of the profile information that you can turn into
181 reports. The C<nytprofhtml> command turns the data into an HTML report
182 similar to the C<Devel::Cover> report:
186 CPAN has several other profilers that you can invoke in the same
187 fashion. You might also be interested in using the C<Benchmark> to
188 measure and compare code snippets.
190 You can read more about profiling in I<Programming Perl>, chapter 20,
191 or I<Mastering Perl>, chapter 5.
193 L<perldebguts> documents creating a custom debugger if you need to
194 create a special sort of profiler. brian d foy describes the process
195 in I<The Perl Journal>, "Creating a Perl Debugger",
196 http://www.ddj.com/184404522 , and "Profiling in Perl"
197 http://www.ddj.com/184404580 .
199 Perl.com has two interesting articles on profiling: "Profiling Perl",
200 by Simon Cozens, http://www.perl.com/lpt/a/850 and "Debugging and
201 Profiling mod_perl Applications", by Frank Wiles,
202 http://www.perl.com/pub/a/2006/02/09/debug_mod_perl.html .
204 Randal L. Schwartz writes about profiling in "Speeding up Your Perl
205 Programs" for I<Unix Review>,
206 http://www.stonehenge.com/merlyn/UnixReview/col49.html , and "Profiling
207 in Template Toolkit via Overriding" for I<Linux Magazine>,
208 http://www.stonehenge.com/merlyn/LinuxMag/col75.html .
210 =head2 How do I cross-reference my Perl programs?
212 The C<B::Xref> module can be used to generate cross-reference reports
215 perl -MO=Xref[,OPTIONS] scriptname.plx
217 =head2 Is there a pretty-printer (formatter) for Perl?
219 C<Perltidy> is a Perl script which indents and reformats Perl scripts
220 to make them easier to read by trying to follow the rules of the
221 L<perlstyle>. If you write Perl scripts, or spend much time reading
222 them, you will probably find it useful. It is available at
223 http://perltidy.sourceforge.net .
225 Of course, if you simply follow the guidelines in L<perlstyle>,
226 you shouldn't need to reformat. The habit of formatting your code
227 as you write it will help prevent bugs. Your editor can and should
228 help you with this. The perl-mode or newer cperl-mode for emacs
229 can provide remarkable amounts of help with most (but not all)
230 code, and even less programmable editors can provide significant
231 assistance. Tom Christiansen and many other VI users swear by
232 the following settings in vi and its clones:
237 Put that in your F<.exrc> file (replacing the caret characters
238 with control characters) and away you go. In insert mode, ^T is
239 for indenting, ^D is for undenting, and ^O is for blockdenting--as
240 it were. A more complete example, with comments, can be found at
241 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
243 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
244 lots of things related to generating nicely printed output of
247 =head2 Is there a ctags for Perl?
249 (contributed by brian d foy)
251 Ctags uses an index to quickly find things in source code, and many
252 popular editors support ctags for several different languages,
255 Exuberant ctags supports Perl: http://ctags.sourceforge.net/
257 You might also try pltags: http://www.mscha.com/pltags.zip
259 =head2 Is there an IDE or Windows Perl Editor?
261 Perl programs are just plain text, so any editor will do.
263 If you're on Unix, you already have an IDE--Unix itself. The Unix
264 philosophy is the philosophy of several small tools that each do one
265 thing and do it well. It's like a carpenter's toolbox.
267 If you want an IDE, check the following (in alphabetical order, not
268 order of preference):
274 http://e-p-i-c.sf.net/
276 The Eclipse Perl Integration Project integrates Perl
277 editing/debugging with Eclipse.
281 http://www.enginsite.com/
283 Perl Editor by EngInSite is a complete integrated development
284 environment (IDE) for creating, testing, and debugging Perl scripts;
285 the tool runs on Windows 9x/NT/2000/XP or later.
289 http://www.ActiveState.com/Products/Komodo/
291 ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
292 and Solaris), multi-language IDE has Perl support, including a regular expression
293 debugger and remote debugging.
297 http://notepad-plus.sourceforge.net/
301 http://open-perl-ide.sourceforge.net/
303 Open Perl IDE is an integrated development environment for writing
304 and debugging Perl scripts with ActiveState's ActivePerl distribution
305 under Windows 95/98/NT/2000.
309 http://www.optiperl.com/
311 OptiPerl is a Windows IDE with simulated CGI environment, including
312 debugger and syntax-highlighting editor.
316 http://padre.perlide.org/
318 Padre is cross-platform IDE for Perl written in Perl using wxWidgets to provide
319 a native look and feel. It's open source under the Artistic License.
323 http://www.solutionsoft.com/perl.htm
325 PerlBuilder is an integrated development environment for Windows that
326 supports Perl development.
330 http://helpconsulting.net/visiperl/
332 From Help Consulting, for Windows.
336 http://www.activestate.com/Products/Visual_Perl/
338 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
342 http://www.zeusedit.com/lookmain.html
344 Zeus for Window is another Win32 multi-language editor/IDE
345 that comes with support for Perl.
349 For editors: if you're on Unix you probably have vi or a vi clone
350 already, and possibly an emacs too, so you may not need to download
351 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
352 perhaps the best available Perl editing mode in any editor.
354 If you are using Windows, you can use any editor that lets you work
355 with plain text, such as NotePad or WordPad. Word processors, such as
356 Microsoft Word or WordPerfect, typically do not work since they insert
357 all sorts of behind-the-scenes information, although some allow you to
358 save files as "Text Only". You can also download text editors designed
359 specifically for programming, such as Textpad (
360 http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ),
363 If you are using MacOS, the same concerns apply. MacPerl (for Classic
364 environments) comes with a simple editor. Popular external editors are
365 BBEdit ( http://www.bbedit.com/ ) or Alpha (
366 http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use
367 Unix editors as well.
373 http://www.gnu.org/software/emacs/windows/ntemacs.html
377 http://www.microemacs.de/
381 http://www.xemacs.org/Download/index.html
385 http://space.mit.edu/~davis/jed/
389 or a vi clone such as
395 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
399 http://dickey.his.com/vile/vile.html
407 For vi lovers in general, Windows or elsewhere:
409 http://www.thomer.com/thomer/vi/vi.html
411 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
412 yet another vi clone, unfortunately not available for Windows, but in
413 Unix platforms you might be interested in trying it out, firstly because
414 strictly speaking it is not a vi clone, it is the real vi, or the new
415 incarnation of it, and secondly because you can embed Perl inside it
416 to use Perl as the scripting language. nvi is not alone in this,
417 though: at least also vim and vile offer an embedded Perl.
419 The following are Win32 multilanguage editor/IDEs that support Perl:
425 http://www.borland.com/codewright/
429 http://www.MultiEdit.com/
433 http://www.slickedit.com/
437 http://www.contexteditor.org/
441 There is also a toyedit Text widget based editor written in Perl
442 that is distributed with the Tk module on CPAN. The ptkdb
443 ( http://ptkdb.sourceforge.net/ ) is a Perl/Tk-based debugger that
444 acts as a development environment of sorts. Perl Composer
445 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
448 In addition to an editor/IDE you might be interested in a more
449 powerful shell environment for Win32. Your options include
455 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
459 from the MKS Toolkit ( http://www.mkssoftware.com/ ), or the Bourne shell of
460 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
464 ftp://ftp.astron.com/pub/tcsh/ , see also
465 http://www.primate.wisc.edu/software/csh-tcsh-book/
473 MKS and U/WIN are commercial (U/WIN is free for educational and
474 research purposes), Cygwin is covered by the GNU General Public
475 License (but that shouldn't matter for Perl use). The Cygwin, MKS,
476 and U/WIN all contain (in addition to the shells) a comprehensive set
477 of standard Unix toolkit utilities.
479 If you're transferring text files between Unix and Windows using FTP
480 be sure to transfer them in ASCII mode so the ends of lines are
481 appropriately converted.
483 On Mac OS the MacPerl Application comes with a simple 32k text editor
484 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
485 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
492 is a full Perl development environment with full debugger support
493 ( http://www.latenightsw.com ).
497 is an editor, written and extensible in Tcl, that nonetheless has
498 built-in support for several popular markup and programming languages,
499 including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).
501 =item BBEdit and BBEdit Lite
503 are text editors for Mac OS that have a Perl sensitivity mode
504 ( http://web.barebones.com/ ).
508 =head2 Where can I get Perl macros for vi?
510 For a complete version of Tom Christiansen's vi configuration file,
511 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
512 the standard benchmark file for vi emulators. The file runs best with nvi,
513 the current version of vi out of Berkeley, which incidentally can be built
514 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
516 =head2 Where can I get perl-mode or cperl-mode for emacs?
519 Since Emacs version 19 patchlevel 22 or so, there have been both a
520 perl-mode.el and support for the Perl debugger built in. These should
521 come with the standard Emacs 19 distribution.
523 Note that the perl-mode of emacs will have fits with C<"main'foo">
524 (single quote), and mess up the indentation and highlighting. You
525 are probably using C<"main::foo"> in new Perl code anyway, so this
526 shouldn't be an issue.
528 For CPerlMode, see http://www.emacswiki.org/cgi-bin/wiki/CPerlMode
530 =head2 How can I use curses with Perl?
532 The Curses module from CPAN provides a dynamically loadable object
533 module interface to a curses library. A small demo can be found at the
534 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
535 this program repeats a command and updates the screen as needed, rendering
536 B<rep ps axu> similar to B<top>.
538 =head2 How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
539 X<GUI> X<Tk> X<Wx> X<WxWidgets> X<Gtk> X<Gtk2> X<CamelBones> X<Qt>
541 (contributed by Ben Morrow)
543 There are a number of modules which let you write GUIs in Perl. Most
544 GUI toolkits have a perl interface: an incomplete list follows.
550 This works under Unix and Windows, and the current version doesn't
551 look half as bad under Windows as it used to. Some of the gui elements
552 still don't 'feel' quite right, though. The interface is very natural
553 and 'perlish', making it easy to use in small scripts that just need a
554 simple gui. It hasn't been updated in a while.
558 This is a Perl binding for the cross-platform wxWidgets toolkit
559 ( http://www.wxwidgets.org ). It works under Unix, Win32 and Mac OS X,
560 using native widgets (Gtk under Unix). The interface follows the C++
561 interface closely, but the documentation is a little sparse for someone
562 who doesn't know the library, mostly just referring you to the C++
567 These are Perl bindings for the Gtk toolkit ( http://www.gtk.org ). The
568 interface changed significantly between versions 1 and 2 so they have
569 separate Perl modules. It runs under Unix, Win32 and Mac OS X (currently
570 it requires an X server on Mac OS, but a 'native' port is underway), and
571 the widgets look the same on every platform: i.e., they don't match the
572 native widgets. As with Wx, the Perl bindings follow the C API closely,
573 and the documentation requires you to read the C documentation to
578 This provides access to most of the Win32 GUI widgets from Perl.
579 Obviously, it only runs under Win32, and uses native widgets. The Perl
580 interface doesn't really follow the C interface: it's been made more
581 Perlish, and the documentation is pretty good. More advanced stuff may
582 require familiarity with the C Win32 APIs, or reference to MSDN.
586 CamelBones ( http://camelbones.sourceforge.net ) is a Perl interface to
587 Mac OS X's Cocoa GUI toolkit, and as such can be used to produce native
588 GUIs on Mac OS X. It's not on CPAN, as it requires frameworks that
589 CPAN.pm doesn't know how to install, but installation is via the
590 standard OSX package installer. The Perl API is, again, very close to
591 the ObjC API it's wrapping, and the documentation just tells you how to
592 translate from one to the other.
596 There is a Perl interface to TrollTech's Qt toolkit, but it does not
597 appear to be maintained.
601 Sx is an interface to the Athena widget set which comes with X, but
602 again it appears not to be much used nowadays.
606 =head2 How can I make my Perl program run faster?
608 The best way to do this is to come up with a better algorithm. This
609 can often make a dramatic difference. Jon Bentley's book
610 I<Programming Pearls> (that's not a misspelling!) has some good tips
611 on optimization, too. Advice on benchmarking boils down to: benchmark
612 and profile to make sure you're optimizing the right part, look for
613 better algorithms instead of microtuning your code, and when all else
614 fails consider just buying faster hardware. You will probably want to
615 read the answer to the earlier question "How do I profile my Perl
616 programs?" if you haven't done so already.
618 A different approach is to autoload seldom-used Perl code. See the
619 AutoSplit and AutoLoader modules in the standard distribution for
620 that. Or you could locate the bottleneck and think about writing just
621 that part in C, the way we used to take bottlenecks in C code and
622 write them in assembler. Similar to rewriting in C, modules that have
623 critical sections can be written in C (for instance, the PDL module
626 If you're currently linking your perl executable to a shared
627 I<libc.so>, you can often gain a 10-25% performance benefit by
628 rebuilding it to link with a static libc.a instead. This will make a
629 bigger perl executable, but your Perl programs (and programmers) may
630 thank you for it. See the F<INSTALL> file in the source distribution
631 for more information.
633 The undump program was an ancient attempt to speed up Perl program by
634 storing the already-compiled form to disk. This is no longer a viable
635 option, as it only worked on a few architectures, and wasn't a good
638 =head2 How can I make my Perl program take less memory?
640 When it comes to time-space tradeoffs, Perl nearly always prefers to
641 throw memory at a problem. Scalars in Perl use more memory than
642 strings in C, arrays take more than that, and hashes use even more. While
643 there's still a lot to be done, recent releases have been addressing
644 these issues. For example, as of 5.004, duplicate hash keys are
645 shared amongst all hashes using them, so require no reallocation.
647 In some cases, using substr() or vec() to simulate arrays can be
648 highly beneficial. For example, an array of a thousand booleans will
649 take at least 20,000 bytes of space, but it can be turned into one
650 125-byte bit vector--a considerable memory savings. The standard
651 Tie::SubstrHash module can also help for certain types of data
652 structure. If you're working with specialist data structures
653 (matrices, for instance) modules that implement these in C may use
654 less memory than equivalent Perl modules.
656 Another thing to try is learning whether your Perl was compiled with
657 the system malloc or with Perl's builtin malloc. Whichever one it
658 is, try using the other one and see whether this makes a difference.
659 Information about malloc is in the F<INSTALL> file in the source
660 distribution. You can find out whether you are using perl's malloc by
661 typing C<perl -V:usemymalloc>.
663 Of course, the best way to save memory is to not do anything to waste
664 it in the first place. Good programming practices can go a long way
671 Don't read an entire file into memory if you can process it line
672 by line. Or more concretely, use a loop like this:
691 When the files you're processing are small, it doesn't much matter which
692 way you do it, but it makes a huge difference when they start getting
695 =item * Use map and grep selectively
697 Remember that both map and grep expect a LIST argument, so doing this:
699 @wanted = grep {/pattern/} <FILE>;
701 will cause the entire file to be slurped. For large files, it's better
705 push(@wanted, $_) if /pattern/;
708 =item * Avoid unnecessary quotes and stringification
710 Don't quote large strings unless absolutely necessary:
712 my $copy = "$large_string";
714 makes 2 copies of $large_string (one for $copy and another for the
717 my $copy = $large_string;
721 Ditto for stringifying large arrays:
728 is much more memory-efficient than either
730 print join "\n", @big_array;
740 =item * Pass by reference
742 Pass arrays and hashes by reference, not by value. For one thing, it's
743 the only way to pass multiple lists or hashes (or both) in a single
744 call/return. It also avoids creating a copy of all the contents. This
745 requires some judgement, however, because any changes will be propagated
746 back to the original data. If you really want to mangle (er, modify) a
747 copy, you'll have to sacrifice the memory needed to make one.
749 =item * Tie large variables to disk
751 For "big" data stores (i.e. ones that exceed available memory) consider
752 using one of the DB modules to store it on disk instead of in RAM. This
753 will incur a penalty in access time, but that's probably better than
754 causing your hard disk to thrash due to massive swapping.
758 =head2 Is it safe to return a reference to local or lexical data?
760 Yes. Perl's garbage collection system takes care of this so
761 everything works out right.
769 push @many, makeone();
772 print $many[4][5], "\n";
776 =head2 How can I free an array or hash so my program shrinks?
778 (contributed by Michael Carman)
780 You usually can't. Memory allocated to lexicals (i.e. my() variables)
781 cannot be reclaimed or reused even if they go out of scope. It is
782 reserved in case the variables come back into scope. Memory allocated
783 to global variables can be reused (within your program) by using
784 undef() and/or delete().
786 On most operating systems, memory allocated to a program can never be
787 returned to the system. That's why long-running programs sometimes re-
788 exec themselves. Some operating systems (notably, systems that use
789 mmap(2) for allocating large chunks of memory) can reclaim memory that
790 is no longer used, but on such systems, perl must be configured and
791 compiled to use the OS's malloc, not perl's.
793 In general, memory allocation and de-allocation isn't something you can
794 or should be worrying about much in Perl.
796 See also "How can I make my Perl program take less memory?"
798 =head2 How can I make my CGI script more efficient?
800 Beyond the normal measures described to make general Perl programs
801 faster or smaller, a CGI program has additional issues. It may be run
802 several times per second. Given that each time it runs it will need
803 to be re-compiled and will often allocate a megabyte or more of system
804 memory, this can be a killer. Compiling into C B<isn't going to help
805 you> because the process start-up overhead is where the bottleneck is.
807 There are two popular ways to avoid this overhead. One solution
808 involves running the Apache HTTP server (available from
809 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
812 With mod_perl and the Apache::Registry module (distributed with
813 mod_perl), httpd will run with an embedded Perl interpreter which
814 pre-compiles your script and then executes it within the same address
815 space without forking. The Apache extension also gives Perl access to
816 the internal server API, so modules written in Perl can do just about
817 anything a module written in C can. For more on mod_perl, see
818 http://perl.apache.org/
820 With the FCGI module (from CPAN) and the mod_fastcgi
821 module (available from http://www.fastcgi.com/ ) each of your Perl
822 programs becomes a permanent CGI daemon process.
824 Both of these solutions can have far-reaching effects on your system
825 and on the way you write your CGI programs, so investigate them with
829 http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
831 =head2 How can I hide the source for my Perl program?
833 Delete it. :-) Seriously, there are a number of (mostly
834 unsatisfactory) solutions with varying levels of "security".
836 First of all, however, you I<can't> take away read permission, because
837 the source code has to be readable in order to be compiled and
838 interpreted. (That doesn't mean that a CGI script's source is
839 readable by people on the web, though--only by people with access to
840 the filesystem.) So you have to leave the permissions at the socially
843 Some people regard this as a security problem. If your program does
844 insecure things and relies on people not knowing how to exploit those
845 insecurities, it is not secure. It is often possible for someone to
846 determine the insecure things and exploit them without viewing the
847 source. Security through obscurity, the name for hiding your bugs
848 instead of fixing them, is little security indeed.
850 You can try using encryption via source filters (Starting from Perl
851 5.8 the Filter::Simple and Filter::Util::Call modules are included in
852 the standard distribution), but any decent programmer will be able to
853 decrypt it. You can try using the byte code compiler and interpreter
854 described later in L<perlfaq3>, but the curious might still be able to
855 de-compile it. You can try using the native-code compiler described
856 later, but crackers might be able to disassemble it. These pose
857 varying degrees of difficulty to people wanting to get at your code,
858 but none can definitively conceal it (true of every language, not just
861 It is very easy to recover the source of Perl programs. You simply
862 feed the program to the perl interpreter and use the modules in
863 the B:: hierarchy. The B::Deparse module should be able to
864 defeat most attempts to hide source. Again, this is not
867 If you're concerned about people profiting from your code, then the
868 bottom line is that nothing but a restrictive license will give you
869 legal security. License your software and pepper it with threatening
870 statements like "This is unpublished proprietary software of XYZ Corp.
871 Your access to it does not give you permission to use it blah blah
872 blah." We are not lawyers, of course, so you should see a lawyer if
873 you want to be sure your license's wording will stand up in court.
875 =head2 How can I compile my Perl program into byte code or C?
877 (contributed by brian d foy)
879 In general, you can't do this. There are some things that may work
880 for your situation though. People usually ask this question
881 because they want to distribute their works without giving away
882 the source code, and most solutions trade disk space for convenience.
883 You probably won't see much of a speed increase either, since most
884 solutions simply bundle a Perl interpreter in the final product
885 (but see L<How can I make my Perl program run faster?>).
887 The Perl Archive Toolkit ( http://par.perl.org/ ) is Perl's
888 analog to Java's JAR. It's freely available and on CPAN (
889 http://search.cpan.org/dist/PAR/ ).
891 There are also some commercial products that may work for you, although
892 you have to buy a license for them.
894 The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ )
895 from ActiveState can "Turn your Perl programs into ready-to-run
896 executables for HP-UX, Linux, Solaris and Windows."
898 Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line
899 program for converting perl scripts to executable files. It targets both
900 Windows and Unix platforms.
902 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
906 extproc perl -S -your_switches
908 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
909 "extproc" handling). For DOS one should first invent a corresponding
910 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
911 F<dosish.h> file in the source distribution for more information).
913 The Win95/NT installation, when using the ActiveState port of Perl,
914 will modify the Registry to associate the C<.pl> extension with the
915 perl interpreter. If you install another port, perhaps even building
916 your own Win95/NT Perl from the standard sources by using a Windows port
917 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
918 the Registry yourself. In addition to associating C<.pl> with the
919 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
920 run the program C<install-linux.pl> merely by typing C<install-linux>.
922 Under "Classic" MacOS, a perl program will have the appropriate Creator and
923 Type, so that double-clicking them will invoke the MacPerl application.
924 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
925 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
927 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
928 throw the perl interpreter into your cgi-bin directory, in order to
929 get your programs working for a web server. This is an EXTREMELY big
930 security risk. Take the time to figure out how to do it correctly.
932 =head2 Can I write useful Perl programs on the command line?
934 Yes. Read L<perlrun> for more information. Some examples follow.
935 (These assume standard Unix shell quoting rules.)
937 # sum first and last fields
938 perl -lane 'print $F[0] + $F[-1]' *
940 # identify text files
941 perl -le 'for(@ARGV) {print if -f && -T _}' *
943 # remove (most) comments from C program
944 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
946 # make file a month younger than today, defeating reaper daemons
947 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
949 # find first unused uid
950 perl -le '$i++ while getpwuid($i); print $i'
952 # display reasonable manpath
953 echo $PATH | perl -nl -072 -e '
954 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
956 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
958 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
960 The problem is usually that the command interpreters on those systems
961 have rather different ideas about quoting than the Unix shells under
962 which the one-liners were created. On some systems, you may have to
963 change single-quotes to double ones, which you must I<NOT> do on Unix
964 or Plan9 systems. You might also have to change a single % to a %%.
968 # Unix (including Mac OS X)
969 perl -e 'print "Hello world\n"'
972 perl -e "print \"Hello world\n\""
975 print "Hello world\n"
976 (then Run "Myscript" or Shift-Command-R)
979 perl -e 'print "Hello world\n"'
982 perl -e "print ""Hello world\n"""
984 The problem is that none of these examples are reliable: they depend on the
985 command interpreter. Under Unix, the first two often work. Under DOS,
986 it's entirely possible that neither works. If 4DOS was the command shell,
987 you'd probably have better luck like this:
989 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
991 Under the Mac, it depends which environment you are using. The MacPerl
992 shell, or MPW, is much like Unix shells in its support for several
993 quoting variants, except that it makes free use of the Mac's non-ASCII
994 characters as control characters.
996 Using qq(), q(), and qx(), instead of "double quotes", 'single
997 quotes', and `backticks`, may make one-liners easier to write.
999 There is no general solution to all of this. It is a mess.
1001 [Some of this answer was contributed by Kenneth Albanowski.]
1003 =head2 Where can I learn about CGI or Web programming in Perl?
1005 For modules, get the CGI or LWP modules from CPAN. For textbooks,
1006 see the two especially dedicated to web stuff in the question on
1007 books. For problems and questions related to the web, like "Why
1008 do I get 500 Errors" or "Why doesn't it run from the browser right
1009 when it runs fine on the command line", see the troubleshooting
1010 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
1012 http://www.perl.org/CGI_MetaFAQ.html
1014 =head2 Where can I learn about object-oriented Perl programming?
1016 A good place to start is L<perltoot>, and you can use L<perlobj>,
1017 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
1019 A good book on OO on Perl is the "Object-Oriented Perl"
1020 by Damian Conway from Manning Publications, or "Intermediate Perl"
1021 by Randal Schwartz, brian d foy, and Tom Phoenix from O'Reilly Media.
1023 =head2 Where can I learn about linking C with Perl?
1025 If you want to call C from Perl, start with L<perlxstut>,
1026 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
1027 call Perl from C, then read L<perlembed>, L<perlcall>, and
1028 L<perlguts>. Don't forget that you can learn a lot from looking at
1029 how the authors of existing extension modules wrote their code and
1030 solved their problems.
1032 You might not need all the power of XS. The Inline::C module lets
1033 you put C code directly in your Perl source. It handles all the
1034 magic to make it work. You still have to learn at least some of
1035 the perl API but you won't have to deal with the complexity of the
1038 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
1040 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
1041 the tests pass, read the pods again and again and again. If they
1042 fail, see L<perlbug> and send a bug report with the output of
1043 C<make test TEST_VERBOSE=1> along with C<perl -V>.
1045 =head2 When I tried to run my script, I got this message. What does it mean?
1047 A complete list of Perl's error messages and warnings with explanatory
1048 text can be found in L<perldiag>. You can also use the splain program
1049 (distributed with Perl) to explain the error messages:
1051 perl program 2>diag.out
1052 splain [-v] [-p] diag.out
1054 or change your program to explain the messages for you:
1060 use diagnostics -verbose;
1062 =head2 What's MakeMaker?
1064 (contributed by brian d foy)
1066 The C<ExtUtils::MakeMaker> module, better known simply as "MakeMaker",
1067 turns a Perl script, typically called C<Makefile.PL>, into a Makefile.
1068 The Unix tool C<make> uses this file to manage dependencies and actions
1069 to process and install a Perl distribution.
1071 =head1 AUTHOR AND COPYRIGHT
1073 Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and
1074 other authors as noted. All rights reserved.
1076 This documentation is free; you can redistribute it and/or modify it
1077 under the same terms as Perl itself.
1079 Irrespective of its distribution, all code examples here are in the public
1080 domain. You are permitted and encouraged to use this code and any
1081 derivatives thereof in your own programs for fun or for profit as you
1082 see fit. A simple comment in the code giving credit to the FAQ would
1083 be courteous but is not required.