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:
22 =item L<perldata> - Perl data types
24 =item L<perlvar> - Perl pre-defined variables
26 =item L<perlsyn> - Perl syntax
28 =item L<perlop> - Perl operators and precedence
30 =item L<perlsub> - Perl subroutines
39 =item L<perlrun> - how to execute the Perl interpreter
41 =item L<perldebug> - Perl debugging
50 =item L<perlfunc> - Perl builtin functions
58 =item L<perlref> - Perl references and nested data structures
60 =item L<perlmod> - Perl modules (packages and symbol tables)
62 =item L<perlobj> - Perl objects
64 =item L<perltie> - how to hide an object class in a simple variable
73 =item L<perlref> - Perl references and nested data structures
75 =item L<perllol> - Manipulating arrays of arrays in Perl
77 =item L<perldsc> - Perl Data Structures Cookbook
85 =item L<perlmod> - Perl modules (packages and symbol tables)
87 =item L<perlmodlib> - constructing new Perl modules and finding existing ones
96 =item L<perlre> - Perl regular expressions
98 =item L<perlfunc> - Perl builtin functions>
100 =item L<perlop> - Perl operators and precedence
102 =item L<perllocale> - Perl locale handling (internationalization and localization)
107 =item Moving to perl5
111 =item L<perltrap> - Perl traps for the unwary
122 =item L<perlxstut> - Tutorial for writing XSUBs
124 =item L<perlxs> - XS language reference manual
126 =item L<perlcall> - Perl calling conventions from C
128 =item L<perlguts> - Introduction to the Perl API
130 =item L<perlembed> - how to embed perl in your C program
136 L<http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz>
137 (not a man-page but still useful, a collection of various essays on
142 A crude table of contents for the Perl manpage set is found in L<perltoc>.
144 =head2 How can I use Perl interactively?
146 The typical approach uses the Perl debugger, described in the
147 L<perldebug(1)> manpage, on an "empty" program, like this:
151 Now just type in any legal Perl code, and it will be immediately
152 evaluated. You can also examine the symbol table, get stack
153 backtraces, check variable values, set breakpoints, and other
154 operations typically found in symbolic debuggers.
156 You can also use L<Devel::REPL> which is an interactive shell for Perl,
157 commonly known as a REPL - Read, Evaluate, Print, Loop. It provides
158 various handy features.
160 =head2 How do I find which modules are installed on my system?
162 From the command line, you can use the C<cpan> command's C<-l> switch:
166 You can also use C<cpan>'s C<-a> switch to create an autobundle file
167 that C<CPAN.pm> understands and can use to re-install every module:
171 Inside a Perl program, you can use the L<ExtUtils::Installed> module to
172 show all installed distributions, although it can take awhile to do
173 its magic. The standard library which comes with Perl just shows up
174 as "Perl" (although you can get those with L<Module::CoreList>).
176 use ExtUtils::Installed;
178 my $inst = ExtUtils::Installed->new();
179 my @modules = $inst->modules();
181 If you want a list of all of the Perl module filenames, you
182 can use L<File::Find::Rule>:
184 use File::Find::Rule;
186 my @files = File::Find::Rule->
187 extras({follow => 1})->
193 If you do not have that module, you can do the same thing
194 with L<File::Find> which is part of the standard library:
202 push @files, $File::Find::fullname
203 if -f $File::Find::fullname && /\.pm$/
211 print join "\n", @files;
213 If you simply need to check quickly to see if a module is
214 available, you can check for its documentation. If you can
215 read the documentation the module is most likely installed.
216 If you cannot read the documentation, the module might not
217 have any (in rare cases):
219 $ perldoc Module::Name
221 You can also try to include the module in a one-liner to see if
224 $ perl -MModule::Name -e1
226 (If you don't receive a "Can't locate ... in @INC" error message, then Perl
227 found the module name you asked for.)
229 =head2 How do I debug my Perl programs?
231 (contributed by brian d foy)
233 Before you do anything else, you can help yourself by ensuring that
234 you let Perl tell you about problem areas in your code. By turning
235 on warnings and strictures, you can head off many problems before
236 they get too big. You can find out more about these in L<strict>
243 Beyond that, the simplest debugger is the C<print> function. Use it
244 to look at values as you run your program:
246 print STDERR "The value is [$value]\n";
248 The L<Data::Dumper> module can pretty-print Perl data structures:
250 use Data::Dumper qw( Dumper );
251 print STDERR "The hash is " . Dumper( \%hash ) . "\n";
253 Perl comes with an interactive debugger, which you can start with the
254 C<-d> switch. It's fully explained in L<perldebug>.
256 If you'd like a graphical user interface and you have L<Tk>, you can use
257 C<ptkdb>. It's on CPAN and available for free.
259 If you need something much more sophisticated and controllable, Leon
260 Brocard's L<Devel::ebug> (which you can call with the C<-D> switch as C<-Debug>)
261 gives you the programmatic hooks into everything you need to write your
262 own (without too much pain and suffering).
264 You can also use a commercial debugger such as Affrus (Mac OS X), Komodo
265 from Activestate (Windows and Mac OS X), or EPIC (most platforms).
267 =head2 How do I profile my Perl programs?
269 (contributed by brian d foy, updated Fri Jul 25 12:22:26 PDT 2008)
271 The C<Devel> namespace has several modules which you can use to
272 profile your Perl programs.
274 The L<Devel::NYTProf> (New York Times Profiler) does both statement
275 and subroutine profiling. It's available from CPAN and you also invoke
276 it with the C<-d> switch:
278 perl -d:NYTProf some_perl.pl
280 It creates a database of the profile information that you can turn into
281 reports. The C<nytprofhtml> command turns the data into an HTML report
282 similar to the L<Devel::Cover> report:
286 You might also be interested in using the L<Benchmark> to
287 measure and compare code snippets.
289 You can read more about profiling in I<Programming Perl>, chapter 20,
290 or I<Mastering Perl>, chapter 5.
292 L<perldebguts> documents creating a custom debugger if you need to
293 create a special sort of profiler. brian d foy describes the process
294 in I<The Perl Journal>, "Creating a Perl Debugger",
295 L<http://www.ddj.com/184404522> , and "Profiling in Perl"
296 L<http://www.ddj.com/184404580> .
298 Perl.com has two interesting articles on profiling: "Profiling Perl",
299 by Simon Cozens, L<http://www.perl.com/lpt/a/850> and "Debugging and
300 Profiling mod_perl Applications", by Frank Wiles,
301 L<http://www.perl.com/pub/a/2006/02/09/debug_mod_perl.html> .
303 Randal L. Schwartz writes about profiling in "Speeding up Your Perl
304 Programs" for I<Unix Review>,
305 L<http://www.stonehenge.com/merlyn/UnixReview/col49.html> , and "Profiling
306 in Template Toolkit via Overriding" for I<Linux Magazine>,
307 L<http://www.stonehenge.com/merlyn/LinuxMag/col75.html> .
309 =head2 How do I cross-reference my Perl programs?
311 The L<B::Xref> module can be used to generate cross-reference reports
314 perl -MO=Xref[,OPTIONS] scriptname.plx
316 =head2 Is there a pretty-printer (formatter) for Perl?
318 L<Perl::Tidy> comes with a perl script L<perltidy> which indents and
319 reformats Perl scripts to make them easier to read by trying to follow
320 the rules of the L<perlstyle>. If you write Perl, or spend much time reading
321 Perl, you will probably find it useful.
323 Of course, if you simply follow the guidelines in L<perlstyle>,
324 you shouldn't need to reformat. The habit of formatting your code
325 as you write it will help prevent bugs. Your editor can and should
326 help you with this. The perl-mode or newer cperl-mode for emacs
327 can provide remarkable amounts of help with most (but not all)
328 code, and even less programmable editors can provide significant
329 assistance. Tom Christiansen and many other VI users swear by
330 the following settings in vi and its clones:
335 Put that in your F<.exrc> file (replacing the caret characters
336 with control characters) and away you go. In insert mode, ^T is
337 for indenting, ^D is for undenting, and ^O is for blockdenting--as
338 it were. A more complete example, with comments, can be found at
339 L<http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz>
341 =head2 Is there an IDE or Windows Perl Editor?
343 Perl programs are just plain text, so any editor will do.
345 If you're on Unix, you already have an IDE--Unix itself. The Unix
346 philosophy is the philosophy of several small tools that each do one
347 thing and do it well. It's like a carpenter's toolbox.
349 If you want an IDE, check the following (in alphabetical order, not
350 order of preference):
356 L<http://e-p-i-c.sf.net/>
358 The Eclipse Perl Integration Project integrates Perl
359 editing/debugging with Eclipse.
363 L<http://www.enginsite.com/>
365 Perl Editor by EngInSite is a complete integrated development
366 environment (IDE) for creating, testing, and debugging Perl scripts;
367 the tool runs on Windows 9x/NT/2000/XP or later.
371 L<http://kephra.sf.net>
373 GUI editor written in Perl using wxWidgets and Scintilla with lots of smaller features.
374 Aims for a UI based on Perl principles like TIMTOWTDI and "easy things should be easy,
375 hard things should be possible".
379 L<http://www.ActiveState.com/Products/Komodo/>
381 ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
382 and Solaris), multi-language IDE has Perl support, including a regular expression
383 debugger and remote debugging.
387 L<http://notepad-plus.sourceforge.net/>
391 L<http://open-perl-ide.sourceforge.net/>
393 Open Perl IDE is an integrated development environment for writing
394 and debugging Perl scripts with ActiveState's ActivePerl distribution
395 under Windows 95/98/NT/2000.
399 L<http://www.optiperl.com/>
401 OptiPerl is a Windows IDE with simulated CGI environment, including
402 debugger and syntax-highlighting editor.
406 L<http://padre.perlide.org/>
408 Padre is cross-platform IDE for Perl written in Perl using wxWidgets to provide
409 a native look and feel. It's open source under the Artistic License. It
410 is one of the newer Perl IDEs.
414 L<http://www.solutionsoft.com/perl.htm>
416 PerlBuilder is an integrated development environment for Windows that
417 supports Perl development.
421 L<http://helpconsulting.net/visiperl/index.html>
423 From Help Consulting, for Windows.
427 L<http://www.activestate.com/Products/Visual_Perl/>
429 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
433 L<http://www.zeusedit.com/lookmain.html>
435 Zeus for Windows is another Win32 multi-language editor/IDE
436 that comes with support for Perl.
440 For editors: if you're on Unix you probably have vi or a vi clone
441 already, and possibly an emacs too, so you may not need to download
442 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
443 perhaps the best available Perl editing mode in any editor.
445 If you are using Windows, you can use any editor that lets you work
446 with plain text, such as NotePad or WordPad. Word processors, such as
447 Microsoft Word or WordPerfect, typically do not work since they insert
448 all sorts of behind-the-scenes information, although some allow you to
449 save files as "Text Only". You can also download text editors designed
450 specifically for programming, such as Textpad (
451 L<http://www.textpad.com/> ) and UltraEdit ( L<http://www.ultraedit.com/> ),
454 If you are using MacOS, the same concerns apply. MacPerl (for Classic
455 environments) comes with a simple editor. Popular external editors are
456 BBEdit ( L<http://www.barebones.com/products/bbedit/> ) or Alpha (
457 L<http://www.his.com/~jguyer/Alpha/Alpha8.html> ). MacOS X users can use
458 Unix editors as well.
464 L<http://www.gnu.org/software/emacs/windows/ntemacs.html>
468 L<http://www.microemacs.de/>
472 L<http://www.xemacs.org/Download/index.html>
476 L<http://space.mit.edu/~davis/jed/>
480 or a vi clone such as
486 L<http://www.vim.org/>
490 L<http://dickey.his.com/vile/vile.html>
494 The following are Win32 multilanguage editor/IDEs that support Perl:
500 L<http://www.borland.com/codewright/>
504 L<http://www.MultiEdit.com/>
508 L<http://www.slickedit.com/>
512 L<http://www.contexteditor.org/>
516 There is also a toyedit Text widget based editor written in Perl
517 that is distributed with the Tk module on CPAN. The ptkdb
518 ( L<http://ptkdb.sourceforge.net/> ) is a Perl/Tk-based debugger that
519 acts as a development environment of sorts. Perl Composer
520 ( L<http://perlcomposer.sourceforge.net/> ) is an IDE for Perl/Tk
523 In addition to an editor/IDE you might be interested in a more
524 powerful shell environment for Win32. Your options include
530 from the Cygwin package ( L<http://sources.redhat.com/cygwin/> )
534 from the MKS Toolkit ( L<http://www.mkssoftware.com/> ), or the Bourne shell of
535 the U/WIN environment ( L<http://www.research.att.com/sw/tools/uwin/> )
539 L<ftp://ftp.astron.com/pub/tcsh/> , see also
540 L<http://www.primate.wisc.edu/software/csh-tcsh-book/>
544 L<http://www.zsh.org/>
548 MKS and U/WIN are commercial (U/WIN is free for educational and
549 research purposes), Cygwin is covered by the GNU General Public
550 License (but that shouldn't matter for Perl use). The Cygwin, MKS,
551 and U/WIN all contain (in addition to the shells) a comprehensive set
552 of standard Unix toolkit utilities.
554 If you're transferring text files between Unix and Windows using FTP
555 be sure to transfer them in ASCII mode so the ends of lines are
556 appropriately converted.
558 On Mac OS the MacPerl Application comes with a simple 32k text editor
559 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
560 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
567 is a full Perl development environment with full debugger support
568 ( L<http://www.latenightsw.com> ).
572 is an editor, written and extensible in Tcl, that nonetheless has
573 built-in support for several popular markup and programming languages,
574 including Perl and HTML ( L<http://www.his.com/~jguyer/Alpha/Alpha8.html> ).
576 =item BBEdit and TextWrangler
578 are text editors for Mac OS that have a Perl sensitivity mode
579 ( L<http://www.barebones.com/> ).
583 =head2 Where can I get Perl macros for vi?
585 For a complete version of Tom Christiansen's vi configuration file,
586 see L<http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz> ,
587 the standard benchmark file for vi emulators. The file runs best with nvi,
588 the current version of vi out of Berkeley, which incidentally can be built
589 with an embedded Perl interpreter--see L<http://www.cpan.org/src/misc/> .
591 =head2 Where can I get perl-mode or cperl-mode for emacs?
594 Since Emacs version 19 patchlevel 22 or so, there have been both a
595 perl-mode.el and support for the Perl debugger built in. These should
596 come with the standard Emacs 19 distribution.
598 Note that the perl-mode of emacs will have fits with C<"main'foo">
599 (single quote), and mess up the indentation and highlighting. You
600 are probably using C<"main::foo"> in new Perl code anyway, so this
601 shouldn't be an issue.
603 For CPerlMode, see L<http://www.emacswiki.org/cgi-bin/wiki/CPerlMode>
605 =head2 How can I use curses with Perl?
607 The Curses module from CPAN provides a dynamically loadable object
608 module interface to a curses library. A small demo can be found at the
609 directory L<http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz> ;
610 this program repeats a command and updates the screen as needed, rendering
611 B<rep ps axu> similar to B<top>.
613 =head2 How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
614 X<GUI> X<Tk> X<Wx> X<WxWidgets> X<Gtk> X<Gtk2> X<CamelBones> X<Qt>
616 (contributed by Ben Morrow)
618 There are a number of modules which let you write GUIs in Perl. Most
619 GUI toolkits have a perl interface: an incomplete list follows.
625 This works under Unix and Windows, and the current version doesn't
626 look half as bad under Windows as it used to. Some of the gui elements
627 still don't 'feel' quite right, though. The interface is very natural
628 and 'perlish', making it easy to use in small scripts that just need a
629 simple gui. It hasn't been updated in a while.
633 This is a Perl binding for the cross-platform wxWidgets toolkit
634 ( L<http://www.wxwidgets.org> ). It works under Unix, Win32 and Mac OS X,
635 using native widgets (Gtk under Unix). The interface follows the C++
636 interface closely, but the documentation is a little sparse for someone
637 who doesn't know the library, mostly just referring you to the C++
642 These are Perl bindings for the Gtk toolkit ( L<http://www.gtk.org> ). The
643 interface changed significantly between versions 1 and 2 so they have
644 separate Perl modules. It runs under Unix, Win32 and Mac OS X (currently
645 it requires an X server on Mac OS, but a 'native' port is underway), and
646 the widgets look the same on every platform: i.e., they don't match the
647 native widgets. As with Wx, the Perl bindings follow the C API closely,
648 and the documentation requires you to read the C documentation to
653 This provides access to most of the Win32 GUI widgets from Perl.
654 Obviously, it only runs under Win32, and uses native widgets. The Perl
655 interface doesn't really follow the C interface: it's been made more
656 Perlish, and the documentation is pretty good. More advanced stuff may
657 require familiarity with the C Win32 APIs, or reference to MSDN.
661 CamelBones ( L<http://camelbones.sourceforge.net> ) is a Perl interface to
662 Mac OS X's Cocoa GUI toolkit, and as such can be used to produce native
663 GUIs on Mac OS X. It's not on CPAN, as it requires frameworks that
664 CPAN.pm doesn't know how to install, but installation is via the
665 standard OSX package installer. The Perl API is, again, very close to
666 the ObjC API it's wrapping, and the documentation just tells you how to
667 translate from one to the other.
671 There is a Perl interface to TrollTech's Qt toolkit, but it does not
672 appear to be maintained.
676 Sx is an interface to the Athena widget set which comes with X, but
677 again it appears not to be much used nowadays.
681 =head2 How can I make my Perl program run faster?
683 The best way to do this is to come up with a better algorithm. This
684 can often make a dramatic difference. Jon Bentley's book
685 I<Programming Pearls> (that's not a misspelling!) has some good tips
686 on optimization, too. Advice on benchmarking boils down to: benchmark
687 and profile to make sure you're optimizing the right part, look for
688 better algorithms instead of microtuning your code, and when all else
689 fails consider just buying faster hardware. You will probably want to
690 read the answer to the earlier question "How do I profile my Perl
691 programs?" if you haven't done so already.
693 A different approach is to autoload seldom-used Perl code. See the
694 AutoSplit and AutoLoader modules in the standard distribution for
695 that. Or you could locate the bottleneck and think about writing just
696 that part in C, the way we used to take bottlenecks in C code and
697 write them in assembler. Similar to rewriting in C, modules that have
698 critical sections can be written in C (for instance, the PDL module
701 If you're currently linking your perl executable to a shared
702 I<libc.so>, you can often gain a 10-25% performance benefit by
703 rebuilding it to link with a static libc.a instead. This will make a
704 bigger perl executable, but your Perl programs (and programmers) may
705 thank you for it. See the F<INSTALL> file in the source distribution
706 for more information.
708 The undump program was an ancient attempt to speed up Perl program by
709 storing the already-compiled form to disk. This is no longer a viable
710 option, as it only worked on a few architectures, and wasn't a good
713 =head2 How can I make my Perl program take less memory?
715 When it comes to time-space tradeoffs, Perl nearly always prefers to
716 throw memory at a problem. Scalars in Perl use more memory than
717 strings in C, arrays take more than that, and hashes use even more. While
718 there's still a lot to be done, recent releases have been addressing
719 these issues. For example, as of 5.004, duplicate hash keys are
720 shared amongst all hashes using them, so require no reallocation.
722 In some cases, using substr() or vec() to simulate arrays can be
723 highly beneficial. For example, an array of a thousand booleans will
724 take at least 20,000 bytes of space, but it can be turned into one
725 125-byte bit vector--a considerable memory savings. The standard
726 Tie::SubstrHash module can also help for certain types of data
727 structure. If you're working with specialist data structures
728 (matrices, for instance) modules that implement these in C may use
729 less memory than equivalent Perl modules.
731 Another thing to try is learning whether your Perl was compiled with
732 the system malloc or with Perl's builtin malloc. Whichever one it
733 is, try using the other one and see whether this makes a difference.
734 Information about malloc is in the F<INSTALL> file in the source
735 distribution. You can find out whether you are using perl's malloc by
736 typing C<perl -V:usemymalloc>.
738 Of course, the best way to save memory is to not do anything to waste
739 it in the first place. Good programming practices can go a long way
746 Don't read an entire file into memory if you can process it line
747 by line. Or more concretely, use a loop like this:
752 while (my $line = <$file_handle>) {
761 my @data = <$file_handle>;
766 When the files you're processing are small, it doesn't much matter which
767 way you do it, but it makes a huge difference when they start getting
770 =item Use map and grep selectively
772 Remember that both map and grep expect a LIST argument, so doing this:
774 @wanted = grep {/pattern/} <$file_handle>;
776 will cause the entire file to be slurped. For large files, it's better
779 while (<$file_handle>) {
780 push(@wanted, $_) if /pattern/;
783 =item Avoid unnecessary quotes and stringification
785 Don't quote large strings unless absolutely necessary:
787 my $copy = "$large_string";
789 makes 2 copies of $large_string (one for $copy and another for the
792 my $copy = $large_string;
796 Ditto for stringifying large arrays:
803 is much more memory-efficient than either
805 print join "\n", @big_array;
815 =item Pass by reference
817 Pass arrays and hashes by reference, not by value. For one thing, it's
818 the only way to pass multiple lists or hashes (or both) in a single
819 call/return. It also avoids creating a copy of all the contents. This
820 requires some judgement, however, because any changes will be propagated
821 back to the original data. If you really want to mangle (er, modify) a
822 copy, you'll have to sacrifice the memory needed to make one.
824 =item Tie large variables to disk
826 For "big" data stores (i.e. ones that exceed available memory) consider
827 using one of the DB modules to store it on disk instead of in RAM. This
828 will incur a penalty in access time, but that's probably better than
829 causing your hard disk to thrash due to massive swapping.
833 =head2 Is it safe to return a reference to local or lexical data?
835 Yes. Perl's garbage collection system takes care of this so
836 everything works out right.
844 push @many, makeone();
847 print $many[4][5], "\n";
851 =head2 How can I free an array or hash so my program shrinks?
853 (contributed by Michael Carman)
855 You usually can't. Memory allocated to lexicals (i.e. my() variables)
856 cannot be reclaimed or reused even if they go out of scope. It is
857 reserved in case the variables come back into scope. Memory allocated
858 to global variables can be reused (within your program) by using
859 undef() and/or delete().
861 On most operating systems, memory allocated to a program can never be
862 returned to the system. That's why long-running programs sometimes re-
863 exec themselves. Some operating systems (notably, systems that use
864 mmap(2) for allocating large chunks of memory) can reclaim memory that
865 is no longer used, but on such systems, perl must be configured and
866 compiled to use the OS's malloc, not perl's.
868 In general, memory allocation and de-allocation isn't something you can
869 or should be worrying about much in Perl.
871 See also "How can I make my Perl program take less memory?"
873 =head2 How can I make my CGI script more efficient?
875 Beyond the normal measures described to make general Perl programs
876 faster or smaller, a CGI program has additional issues. It may be run
877 several times per second. Given that each time it runs it will need
878 to be re-compiled and will often allocate a megabyte or more of system
879 memory, this can be a killer. Compiling into C B<isn't going to help
880 you> because the process start-up overhead is where the bottleneck is.
882 There are three popular ways to avoid this overhead. One solution
883 involves running the Apache HTTP server (available from
884 L<http://www.apache.org/> ) with either of the mod_perl or mod_fastcgi
887 With mod_perl and the Apache::Registry module (distributed with
888 mod_perl), httpd will run with an embedded Perl interpreter which
889 pre-compiles your script and then executes it within the same address
890 space without forking. The Apache extension also gives Perl access to
891 the internal server API, so modules written in Perl can do just about
892 anything a module written in C can. For more on mod_perl, see
893 L<http://perl.apache.org/>
895 With the FCGI module (from CPAN) and the mod_fastcgi
896 module (available from L<http://www.fastcgi.com/> ) each of your Perl
897 programs becomes a permanent CGI daemon process.
899 Finally, L<Plack> is a Perl module and toolkit that contains PSGI middleware,
900 helpers and adapters to web servers, allowing you to easily deploy scripts which
901 can continue running, and provides flexibility with regards to which web server
902 you use. It can allow existing CGI scripts to enjoy this flexibility and
903 performance with minimal changes, or can be used along with modern Perl web
904 frameworks to make writing and deploying web services with Perl a breeze.
906 These solutions can have far-reaching effects on your system and on the way you
907 write your CGI programs, so investigate them with care.
910 L<http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/> .
912 =head2 How can I hide the source for my Perl program?
914 Delete it. :-) Seriously, there are a number of (mostly
915 unsatisfactory) solutions with varying levels of "security".
917 First of all, however, you I<can't> take away read permission, because
918 the source code has to be readable in order to be compiled and
919 interpreted. (That doesn't mean that a CGI script's source is
920 readable by people on the web, though--only by people with access to
921 the filesystem.) So you have to leave the permissions at the socially
924 Some people regard this as a security problem. If your program does
925 insecure things and relies on people not knowing how to exploit those
926 insecurities, it is not secure. It is often possible for someone to
927 determine the insecure things and exploit them without viewing the
928 source. Security through obscurity, the name for hiding your bugs
929 instead of fixing them, is little security indeed.
931 You can try using encryption via source filters (Starting from Perl
932 5.8 the Filter::Simple and Filter::Util::Call modules are included in
933 the standard distribution), but any decent programmer will be able to
934 decrypt it. You can try using the byte code compiler and interpreter
935 described later in L<perlfaq3>, but the curious might still be able to
936 de-compile it. You can try using the native-code compiler described
937 later, but crackers might be able to disassemble it. These pose
938 varying degrees of difficulty to people wanting to get at your code,
939 but none can definitively conceal it (true of every language, not just
942 It is very easy to recover the source of Perl programs. You simply
943 feed the program to the perl interpreter and use the modules in
944 the B:: hierarchy. The B::Deparse module should be able to
945 defeat most attempts to hide source. Again, this is not
948 If you're concerned about people profiting from your code, then the
949 bottom line is that nothing but a restrictive license will give you
950 legal security. License your software and pepper it with threatening
951 statements like "This is unpublished proprietary software of XYZ Corp.
952 Your access to it does not give you permission to use it blah blah
953 blah." We are not lawyers, of course, so you should see a lawyer if
954 you want to be sure your license's wording will stand up in court.
956 =head2 How can I compile my Perl program into byte code or C?
958 (contributed by brian d foy)
960 In general, you can't do this. There are some things that may work
961 for your situation though. People usually ask this question
962 because they want to distribute their works without giving away
963 the source code, and most solutions trade disk space for convenience.
964 You probably won't see much of a speed increase either, since most
965 solutions simply bundle a Perl interpreter in the final product
966 (but see L<How can I make my Perl program run faster?>).
968 The Perl Archive Toolkit ( L<http://par.perl.org/> ) is Perl's
969 analog to Java's JAR. It's freely available and on CPAN (
970 L<http://search.cpan.org/dist/PAR/> ).
972 There are also some commercial products that may work for you, although
973 you have to buy a license for them.
975 The Perl Dev Kit ( L<http://www.activestate.com/Products/Perl_Dev_Kit/> )
976 from ActiveState can "Turn your Perl programs into ready-to-run
977 executables for HP-UX, Linux, Solaris and Windows."
979 Perl2Exe ( L<http://www.indigostar.com/perl2exe.htm> ) is a command line
980 program for converting perl scripts to executable files. It targets both
981 Windows and Unix platforms.
983 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
987 extproc perl -S -your_switches
989 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
990 "extproc" handling). For DOS one should first invent a corresponding
991 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
992 F<dosish.h> file in the source distribution for more information).
994 The Win95/NT installation, when using the ActiveState port of Perl,
995 will modify the Registry to associate the C<.pl> extension with the
996 perl interpreter. If you install another port, perhaps even building
997 your own Win95/NT Perl from the standard sources by using a Windows port
998 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
999 the Registry yourself. In addition to associating C<.pl> with the
1000 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
1001 run the program C<install-linux.pl> merely by typing C<install-linux>.
1003 Under "Classic" MacOS, a perl program will have the appropriate Creator and
1004 Type, so that double-clicking them will invoke the MacPerl application.
1005 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
1006 Sanchez' DropScript utility: L<http://www.wsanchez.net/software/> .
1008 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
1009 throw the perl interpreter into your cgi-bin directory, in order to
1010 get your programs working for a web server. This is an EXTREMELY big
1011 security risk. Take the time to figure out how to do it correctly.
1013 =head2 Can I write useful Perl programs on the command line?
1015 Yes. Read L<perlrun> for more information. Some examples follow.
1016 (These assume standard Unix shell quoting rules.)
1018 # sum first and last fields
1019 perl -lane 'print $F[0] + $F[-1]' *
1021 # identify text files
1022 perl -le 'for(@ARGV) {print if -f && -T _}' *
1024 # remove (most) comments from C program
1025 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
1027 # make file a month younger than today, defeating reaper daemons
1028 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
1030 # find first unused uid
1031 perl -le '$i++ while getpwuid($i); print $i'
1033 # display reasonable manpath
1034 echo $PATH | perl -nl -072 -e '
1035 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
1037 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
1039 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
1041 The problem is usually that the command interpreters on those systems
1042 have rather different ideas about quoting than the Unix shells under
1043 which the one-liners were created. On some systems, you may have to
1044 change single-quotes to double ones, which you must I<NOT> do on Unix
1045 or Plan9 systems. You might also have to change a single % to a %%.
1049 # Unix (including Mac OS X)
1050 perl -e 'print "Hello world\n"'
1053 perl -e "print \"Hello world\n\""
1056 print "Hello world\n"
1057 (then Run "Myscript" or Shift-Command-R)
1060 perl -e 'print "Hello world\n"'
1063 perl -e "print ""Hello world\n"""
1065 The problem is that none of these examples are reliable: they depend on the
1066 command interpreter. Under Unix, the first two often work. Under DOS,
1067 it's entirely possible that neither works. If 4DOS was the command shell,
1068 you'd probably have better luck like this:
1070 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
1072 Under the Mac, it depends which environment you are using. The MacPerl
1073 shell, or MPW, is much like Unix shells in its support for several
1074 quoting variants, except that it makes free use of the Mac's non-ASCII
1075 characters as control characters.
1077 Using qq(), q(), and qx(), instead of "double quotes", 'single
1078 quotes', and `backticks`, may make one-liners easier to write.
1080 There is no general solution to all of this. It is a mess.
1082 [Some of this answer was contributed by Kenneth Albanowski.]
1084 =head2 Where can I learn about CGI or Web programming in Perl?
1086 For modules, get the CGI or LWP modules from CPAN. For textbooks,
1087 see the two especially dedicated to web stuff in the question on
1088 books. For problems and questions related to the web, like "Why
1089 do I get 500 Errors" or "Why doesn't it run from the browser right
1090 when it runs fine on the command line", see the troubleshooting
1091 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
1093 L<http://www.perl.org/CGI_MetaFAQ.html>
1095 Looking in to L<Plack> and modern Perl web frameworks is highly recommended,
1096 though; web programming in Perl has evolved a long way from the old days of
1099 =head2 Where can I learn about object-oriented Perl programming?
1101 A good place to start is L<perlootut>, and you can use L<perlobj> for
1104 A good book on OO on Perl is the "Object-Oriented Perl"
1105 by Damian Conway from Manning Publications, or "Intermediate Perl"
1106 by Randal Schwartz, brian d foy, and Tom Phoenix from O'Reilly Media.
1108 =head2 Where can I learn about linking C with Perl?
1110 If you want to call C from Perl, start with L<perlxstut>,
1111 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
1112 call Perl from C, then read L<perlembed>, L<perlcall>, and
1113 L<perlguts>. Don't forget that you can learn a lot from looking at
1114 how the authors of existing extension modules wrote their code and
1115 solved their problems.
1117 You might not need all the power of XS. The Inline::C module lets
1118 you put C code directly in your Perl source. It handles all the
1119 magic to make it work. You still have to learn at least some of
1120 the perl API but you won't have to deal with the complexity of the
1123 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
1125 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
1126 the tests pass, read the pods again and again and again. If they
1127 fail, see L<perlbug> and send a bug report with the output of
1128 C<make test TEST_VERBOSE=1> along with C<perl -V>.
1130 =head2 When I tried to run my script, I got this message. What does it mean?
1132 A complete list of Perl's error messages and warnings with explanatory
1133 text can be found in L<perldiag>. You can also use the splain program
1134 (distributed with Perl) to explain the error messages:
1136 perl program 2>diag.out
1137 splain [-v] [-p] diag.out
1139 or change your program to explain the messages for you:
1145 use diagnostics -verbose;
1147 =head2 What's MakeMaker?
1149 (contributed by brian d foy)
1151 The L<ExtUtils::MakeMaker> module, better known simply as "MakeMaker",
1152 turns a Perl script, typically called C<Makefile.PL>, into a Makefile.
1153 The Unix tool C<make> uses this file to manage dependencies and actions
1154 to process and install a Perl distribution.
1156 =head1 AUTHOR AND COPYRIGHT
1158 Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and
1159 other authors as noted. All rights reserved.
1161 This documentation is free; you can redistribute it and/or modify it
1162 under the same terms as Perl itself.
1164 Irrespective of its distribution, all code examples here are in the public
1165 domain. You are permitted and encouraged to use this code and any
1166 derivatives thereof in your own programs for fun or for profit as you
1167 see fit. A simple comment in the code giving credit to the FAQ would
1168 be courteous but is not required.