1perlfaq3(3) User Contributed Perl Documentation perlfaq3(3)
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6 perlfaq3 - Programming Tools
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9 version 5.20190126
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12 This section of the FAQ answers questions related to programmer tools
13 and programming support.
14 How do I do (anything)?
16 Have you looked at CPAN (see perlfaq2)? The chances are that someone
17 has already written a module that can solve your problem. Have you
18 read the appropriate manpages? Here's a brief index:
19 Basics
21 perldata - Perl data types
22 perlvar - Perl pre-defined variables
23 perlsyn - Perl syntax
24 perlop - Perl operators and precedence
25 perlsub - Perl subroutines
26 Execution
27 perlrun - how to execute the Perl interpreter
28 perldebug - Perl debugging
29 Functions
30 perlfunc - Perl builtin functions
31 Objects
32 perlref - Perl references and nested data structures
33 perlmod - Perl modules (packages and symbol tables)
34 perlobj - Perl objects
35 perltie - how to hide an object class in a simple variable
36 Data Structures
37 perlref - Perl references and nested data structures
38 perllol - Manipulating arrays of arrays in Perl
39 perldsc - Perl Data Structures Cookbook
40 Modules
41 perlmod - Perl modules (packages and symbol tables)
42 perlmodlib - constructing new Perl modules and finding existing
43 ones
44 Regexes
45 perlre - Perl regular expressions
46 perlfunc - Perl builtin functions>
47 perlop - Perl operators and precedence
48 perllocale - Perl locale handling (internationalization and
49 localization)
50 Moving to perl5
51 perltrap - Perl traps for the unwary
52 perl
53 Linking with C
54 perlxstut - Tutorial for writing XSUBs
55 perlxs - XS language reference manual
56 perlcall - Perl calling conventions from C
57 perlguts - Introduction to the Perl API
58 perlembed - how to embed perl in your C program
59 Various
60 <http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz> (not a man-page but
61 still useful, a collection of various essays on Perl techniques)
62 A crude table of contents for the Perl manpage set is found in perltoc.
64 How can I use Perl interactively?
66 The typical approach uses the Perl debugger, described in the
67 perldebug(1) manpage, on an "empty" program, like this:
68 perl -de 42
70 Now just type in any legal Perl code, and it will be immediately
72 evaluated. You can also examine the symbol table, get stack backtraces,
73 check variable values, set breakpoints, and other operations typically
74 found in symbolic debuggers.
75 You can also use Devel::REPL which is an interactive shell for Perl,
77 commonly known as a REPL - Read, Evaluate, Print, Loop. It provides
78 various handy features.
79 How do I find which modules are installed on my system?
81 From the command line, you can use the "cpan" command's "-l" switch:
82 $ cpan -l
84 You can also use "cpan"'s "-a" switch to create an autobundle file that
86 "CPAN.pm" understands and can use to re-install every module:
87 $ cpan -a
89 Inside a Perl program, you can use the ExtUtils::Installed module to
91 show all installed distributions, although it can take awhile to do its
92 magic. The standard library which comes with Perl just shows up as
93 "Perl" (although you can get those with Module::CoreList).
94 use ExtUtils::Installed;
96 my $inst = ExtUtils::Installed->new();
98 my @modules = $inst->modules();
99 If you want a list of all of the Perl module filenames, you can use
101 File::Find::Rule:
102 use File::Find::Rule;
104 my @files = File::Find::Rule->
106 extras({follow => 1})->
107 file()->
108 name( '*.pm' )->
109 in( @INC )
110 ;
111 If you do not have that module, you can do the same thing with
113 File::Find which is part of the standard library:
114 use File::Find;
116 my @files;
117 find(
119 {
120 wanted => sub {
121 push @files, $File::Find::fullname
122 if -f $File::Find::fullname && /\.pm$/
123 },
124 follow => 1,
125 follow_skip => 2,
126 },
127 @INC
128 );
129 print join "\n", @files;
131 If you simply need to check quickly to see if a module is available,
133 you can check for its documentation. If you can read the documentation
134 the module is most likely installed. If you cannot read the
135 documentation, the module might not have any (in rare cases):
136 $ perldoc Module::Name
138 You can also try to include the module in a one-liner to see if perl
140 finds it:
141 $ perl -MModule::Name -e1
143 (If you don't receive a "Can't locate ... in @INC" error message, then
145 Perl found the module name you asked for.)
146 How do I debug my Perl programs?
148 (contributed by brian d foy)
149 Before you do anything else, you can help yourself by ensuring that you
151 let Perl tell you about problem areas in your code. By turning on
152 warnings and strictures, you can head off many problems before they get
153 too big. You can find out more about these in strict and warnings.
154 #!/usr/bin/perl
156 use strict;
157 use warnings;
158 Beyond that, the simplest debugger is the "print" function. Use it to
160 look at values as you run your program:
161 print STDERR "The value is [$value]\n";
163 The Data::Dumper module can pretty-print Perl data structures:
165 use Data::Dumper qw( Dumper );
167 print STDERR "The hash is " . Dumper( \%hash ) . "\n";
168 Perl comes with an interactive debugger, which you can start with the
170 "-d" switch. It's fully explained in perldebug.
171 If you'd like a graphical user interface and you have Tk, you can use
173 "ptkdb". It's on CPAN and available for free.
174 If you need something much more sophisticated and controllable, Leon
176 Brocard's Devel::ebug (which you can call with the "-D" switch as
177 "-Debug") gives you the programmatic hooks into everything you need to
178 write your own (without too much pain and suffering).
179 You can also use a commercial debugger such as Affrus (Mac OS X),
181 Komodo from Activestate (Windows and Mac OS X), or EPIC (most
182 platforms).
183 How do I profile my Perl programs?
185 (contributed by brian d foy, updated Fri Jul 25 12:22:26 PDT 2008)
186 The "Devel" namespace has several modules which you can use to profile
188 your Perl programs.
189 The Devel::NYTProf (New York Times Profiler) does both statement and
191 subroutine profiling. It's available from CPAN and you also invoke it
192 with the "-d" switch:
193 perl -d:NYTProf some_perl.pl
195 It creates a database of the profile information that you can turn into
197 reports. The "nytprofhtml" command turns the data into an HTML report
198 similar to the Devel::Cover report:
199 nytprofhtml
201 You might also be interested in using the Benchmark to measure and
203 compare code snippets.
204 You can read more about profiling in Programming Perl, chapter 20, or
206 Mastering Perl, chapter 5.
207 perldebguts documents creating a custom debugger if you need to create
209 a special sort of profiler. brian d foy describes the process in The
210 Perl Journal, "Creating a Perl Debugger",
211 <http://www.ddj.com/184404522> , and "Profiling in Perl"
212 <http://www.ddj.com/184404580> .
213 Perl.com has two interesting articles on profiling: "Profiling Perl",
215 by Simon Cozens, <http://www.perl.com/lpt/a/850> and "Debugging and
216 Profiling mod_perl Applications", by Frank Wiles,
217 <http://www.perl.com/pub/a/2006/02/09/debug_mod_perl.html> .
218 Randal L. Schwartz writes about profiling in "Speeding up Your Perl
220 Programs" for Unix Review,
221 <http://www.stonehenge.com/merlyn/UnixReview/col49.html> , and
222 "Profiling in Template Toolkit via Overriding" for Linux Magazine,
223 <http://www.stonehenge.com/merlyn/LinuxMag/col75.html> .
224 How do I cross-reference my Perl programs?
226 The B::Xref module can be used to generate cross-reference reports for
227 Perl programs.
228 perl -MO=Xref[,OPTIONS] scriptname.plx
230 Is there a pretty-printer (formatter) for Perl?
232 Perl::Tidy comes with a perl script perltidy which indents and
233 reformats Perl scripts to make them easier to read by trying to follow
234 the rules of the perlstyle. If you write Perl, or spend much time
235 reading Perl, you will probably find it useful.
236 Of course, if you simply follow the guidelines in perlstyle, you
238 shouldn't need to reformat. The habit of formatting your code as you
239 write it will help prevent bugs. Your editor can and should help you
240 with this. The perl-mode or newer cperl-mode for emacs can provide
241 remarkable amounts of help with most (but not all) code, and even less
242 programmable editors can provide significant assistance. Tom
243 Christiansen and many other VI users swear by the following settings in
244 vi and its clones:
245 set ai sw=4
247 map! ^O {^M}^[O^T
248 Put that in your .exrc file (replacing the caret characters with
250 control characters) and away you go. In insert mode, ^T is for
251 indenting, ^D is for undenting, and ^O is for blockdenting--as it were.
252 A more complete example, with comments, can be found at
253 <http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz>
254 Is there an IDE or Windows Perl Editor?
256 Perl programs are just plain text, so any editor will do.
257 If you're on Unix, you already have an IDE--Unix itself. The Unix
259 philosophy is the philosophy of several small tools that each do one
260 thing and do it well. It's like a carpenter's toolbox.
261 If you want an IDE, check the following (in alphabetical order, not
263 order of preference):
264 Eclipse
266 <http://e-p-i-c.sf.net/>
267 The Eclipse Perl Integration Project integrates Perl
269 editing/debugging with Eclipse.
270 Enginsite
272 <http://www.enginsite.com/>
273 Perl Editor by EngInSite is a complete integrated development
275 environment (IDE) for creating, testing, and debugging Perl
276 scripts; the tool runs on Windows 9x/NT/2000/XP or later.
277 IntelliJ IDEA
279 <https://plugins.jetbrains.com/plugin/7796>
280 Camelcade plugin provides Perl5 support in IntelliJ IDEA and other
282 JetBrains IDEs.
283 Kephra
285 <http://kephra.sf.net>
286 GUI editor written in Perl using wxWidgets and Scintilla with lots
288 of smaller features. Aims for a UI based on Perl principles like
289 TIMTOWTDI and "easy things should be easy, hard things should be
290 possible".
291 Komodo
293 <http://www.ActiveState.com/Products/Komodo/>
294 ActiveState's cross-platform (as of October 2004, that's Windows,
296 Linux, and Solaris), multi-language IDE has Perl support, including
297 a regular expression debugger and remote debugging.
298 Notepad++
300 <http://notepad-plus.sourceforge.net/>
301 Open Perl IDE
303 <http://open-perl-ide.sourceforge.net/>
304 Open Perl IDE is an integrated development environment for writing
306 and debugging Perl scripts with ActiveState's ActivePerl
307 distribution under Windows 95/98/NT/2000.
308 OptiPerl
310 <http://www.optiperl.com/>
311 OptiPerl is a Windows IDE with simulated CGI environment, including
313 debugger and syntax-highlighting editor.
314 Padre
316 <http://padre.perlide.org/>
317 Padre is cross-platform IDE for Perl written in Perl using
319 wxWidgets to provide a native look and feel. It's open source under
320 the Artistic License. It is one of the newer Perl IDEs.
321 PerlBuilder
323 <http://www.solutionsoft.com/perl.htm>
324 PerlBuilder is an integrated development environment for Windows
326 that supports Perl development.
327 visiPerl+
329 <http://helpconsulting.net/visiperl/index.html>
330 From Help Consulting, for Windows.
332 Visual Perl
334 <http://www.activestate.com/Products/Visual_Perl/>
335 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
337 Zeus
339 <http://www.zeusedit.com/lookmain.html>
340 Zeus for Windows is another Win32 multi-language editor/IDE that
342 comes with support for Perl.
343 For editors: if you're on Unix you probably have vi or a vi clone
345 already, and possibly an emacs too, so you may not need to download
346 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
347 perhaps the best available Perl editing mode in any editor.
348 If you are using Windows, you can use any editor that lets you work
350 with plain text, such as NotePad or WordPad. Word processors, such as
351 Microsoft Word or WordPerfect, typically do not work since they insert
352 all sorts of behind-the-scenes information, although some allow you to
353 save files as "Text Only". You can also download text editors designed
354 specifically for programming, such as Textpad (
355 <http://www.textpad.com/> ) and UltraEdit ( <http://www.ultraedit.com/>
356 ), among others.
357 If you are using MacOS, the same concerns apply. MacPerl (for Classic
359 environments) comes with a simple editor. Popular external editors are
360 BBEdit ( <http://www.barebones.com/products/bbedit/> ) or Alpha (
361 <http://www.his.com/~jguyer/Alpha/Alpha8.html> ). MacOS X users can use
362 Unix editors as well.
363 GNU Emacs
365 <http://www.gnu.org/software/emacs/windows/ntemacs.html>
366 MicroEMACS
368 <http://www.microemacs.de/>
369 XEmacs
371 <http://www.xemacs.org/Download/index.html>
372 Jed <http://space.mit.edu/~davis/jed/>
374 or a vi clone such as
376 Vim <http://www.vim.org/>
378 Vile
380 <http://dickey.his.com/vile/vile.html>
381 The following are Win32 multilanguage editor/IDEs that support Perl:
383 MultiEdit
385 <http://www.MultiEdit.com/>
386 SlickEdit
388 <http://www.slickedit.com/>
389 ConTEXT
391 <http://www.contexteditor.org/>
392 There is also a toyedit Text widget based editor written in Perl that
394 is distributed with the Tk module on CPAN. The ptkdb (
395 <http://ptkdb.sourceforge.net/> ) is a Perl/Tk-based debugger that acts
396 as a development environment of sorts. Perl Composer (
397 <http://perlcomposer.sourceforge.net/> ) is an IDE for Perl/Tk GUI
398 creation.
399 In addition to an editor/IDE you might be interested in a more powerful
401 shell environment for Win32. Your options include
402 bash
404 from the Cygwin package ( <http://cygwin.com/> )
405 zsh <http://www.zsh.org/>
407 Cygwin is covered by the GNU General Public License (but that shouldn't
409 matter for Perl use). Cygwin contains (in addition to the shell) a
410 comprehensive set of standard Unix toolkit utilities.
411 BBEdit and TextWrangler
413 are text editors for OS X that have a Perl sensitivity mode (
414 <http://www.barebones.com/> ).
415 Where can I get Perl macros for vi?
417 For a complete version of Tom Christiansen's vi configuration file, see
418 <http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz> ,
419 the standard benchmark file for vi emulators. The file runs best with
420 nvi, the current version of vi out of Berkeley, which incidentally can
421 be built with an embedded Perl interpreter--see
422 <http://www.cpan.org/src/misc/> .
423 Where can I get perl-mode or cperl-mode for emacs?
425 Since Emacs version 19 patchlevel 22 or so, there have been both a
426 perl-mode.el and support for the Perl debugger built in. These should
427 come with the standard Emacs 19 distribution.
428 Note that the perl-mode of emacs will have fits with "main'foo" (single
430 quote), and mess up the indentation and highlighting. You are probably
431 using "main::foo" in new Perl code anyway, so this shouldn't be an
432 issue.
433 For CPerlMode, see <http://www.emacswiki.org/cgi-bin/wiki/CPerlMode>
435 How can I use curses with Perl?
437 The Curses module from CPAN provides a dynamically loadable object
438 module interface to a curses library. A small demo can be found at the
439 directory <http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz>
440 ; this program repeats a command and updates the screen as needed,
441 rendering rep ps axu similar to top.
442 How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
444 (contributed by Ben Morrow)
445 There are a number of modules which let you write GUIs in Perl. Most
447 GUI toolkits have a perl interface: an incomplete list follows.
448 Tk This works under Unix and Windows, and the current version doesn't
450 look half as bad under Windows as it used to. Some of the gui
451 elements still don't 'feel' quite right, though. The interface is
452 very natural and 'perlish', making it easy to use in small scripts
453 that just need a simple gui. It hasn't been updated in a while.
454 Wx This is a Perl binding for the cross-platform wxWidgets toolkit (
456 <http://www.wxwidgets.org> ). It works under Unix, Win32 and Mac OS
457 X, using native widgets (Gtk under Unix). The interface follows the
458 C++ interface closely, but the documentation is a little sparse for
459 someone who doesn't know the library, mostly just referring you to
460 the C++ documentation.
461 Gtk and Gtk2
463 These are Perl bindings for the Gtk toolkit ( <http://www.gtk.org>
464 ). The interface changed significantly between versions 1 and 2 so
465 they have separate Perl modules. It runs under Unix, Win32 and Mac
466 OS X (currently it requires an X server on Mac OS, but a 'native'
467 port is underway), and the widgets look the same on every platform:
468 i.e., they don't match the native widgets. As with Wx, the Perl
469 bindings follow the C API closely, and the documentation requires
470 you to read the C documentation to understand it.
471 Win32::GUI
473 This provides access to most of the Win32 GUI widgets from Perl.
474 Obviously, it only runs under Win32, and uses native widgets. The
475 Perl interface doesn't really follow the C interface: it's been
476 made more Perlish, and the documentation is pretty good. More
477 advanced stuff may require familiarity with the C Win32 APIs, or
478 reference to MSDN.
479 CamelBones
481 CamelBones ( <http://camelbones.sourceforge.net> ) is a Perl
482 interface to Mac OS X's Cocoa GUI toolkit, and as such can be used
483 to produce native GUIs on Mac OS X. It's not on CPAN, as it
484 requires frameworks that CPAN.pm doesn't know how to install, but
485 installation is via the standard OSX package installer. The Perl
486 API is, again, very close to the ObjC API it's wrapping, and the
487 documentation just tells you how to translate from one to the
488 other.
489 Qt There is a Perl interface to TrollTech's Qt toolkit, but it does
491 not appear to be maintained.
492 Athena
494 Sx is an interface to the Athena widget set which comes with X, but
495 again it appears not to be much used nowadays.
496 How can I make my Perl program run faster?
498 The best way to do this is to come up with a better algorithm. This can
499 often make a dramatic difference. Jon Bentley's book Programming Pearls
500 (that's not a misspelling!) has some good tips on optimization, too.
501 Advice on benchmarking boils down to: benchmark and profile to make
502 sure you're optimizing the right part, look for better algorithms
503 instead of microtuning your code, and when all else fails consider just
504 buying faster hardware. You will probably want to read the answer to
505 the earlier question "How do I profile my Perl programs?" if you
506 haven't done so already.
507 A different approach is to autoload seldom-used Perl code. See the
509 AutoSplit and AutoLoader modules in the standard distribution for that.
510 Or you could locate the bottleneck and think about writing just that
511 part in C, the way we used to take bottlenecks in C code and write them
512 in assembler. Similar to rewriting in C, modules that have critical
513 sections can be written in C (for instance, the PDL module from CPAN).
514 If you're currently linking your perl executable to a shared libc.so,
516 you can often gain a 10-25% performance benefit by rebuilding it to
517 link with a static libc.a instead. This will make a bigger perl
518 executable, but your Perl programs (and programmers) may thank you for
519 it. See the INSTALL file in the source distribution for more
520 information.
521 The undump program was an ancient attempt to speed up Perl program by
523 storing the already-compiled form to disk. This is no longer a viable
524 option, as it only worked on a few architectures, and wasn't a good
525 solution anyway.
526 How can I make my Perl program take less memory?
528 When it comes to time-space tradeoffs, Perl nearly always prefers to
529 throw memory at a problem. Scalars in Perl use more memory than strings
530 in C, arrays take more than that, and hashes use even more. While
531 there's still a lot to be done, recent releases have been addressing
532 these issues. For example, as of 5.004, duplicate hash keys are shared
533 amongst all hashes using them, so require no reallocation.
534 In some cases, using substr() or vec() to simulate arrays can be highly
536 beneficial. For example, an array of a thousand booleans will take at
537 least 20,000 bytes of space, but it can be turned into one 125-byte bit
538 vector--a considerable memory savings. The standard Tie::SubstrHash
539 module can also help for certain types of data structure. If you're
540 working with specialist data structures (matrices, for instance)
541 modules that implement these in C may use less memory than equivalent
542 Perl modules.
543 Another thing to try is learning whether your Perl was compiled with
545 the system malloc or with Perl's builtin malloc. Whichever one it is,
546 try using the other one and see whether this makes a difference.
547 Information about malloc is in the INSTALL file in the source
548 distribution. You can find out whether you are using perl's malloc by
549 typing "perl -V:usemymalloc".
550 Of course, the best way to save memory is to not do anything to waste
552 it in the first place. Good programming practices can go a long way
553 toward this:
554 Don't slurp!
556 Don't read an entire file into memory if you can process it line by
557 line. Or more concretely, use a loop like this:
558 #
560 # Good Idea
561 #
562 while (my $line = <$file_handle>) {
563 # ...
564 }
565 instead of this:
567 #
569 # Bad Idea
570 #
571 my @data = <$file_handle>;
572 foreach (@data) {
573 # ...
574 }
575 When the files you're processing are small, it doesn't much matter
577 which way you do it, but it makes a huge difference when they start
578 getting larger.
579 Use map and grep selectively
581 Remember that both map and grep expect a LIST argument, so doing
582 this:
583 @wanted = grep {/pattern/} <$file_handle>;
585 will cause the entire file to be slurped. For large files, it's
587 better to loop:
588 while (<$file_handle>) {
590 push(@wanted, $_) if /pattern/;
591 }
592 Avoid unnecessary quotes and stringification
594 Don't quote large strings unless absolutely necessary:
595 my $copy = "$large_string";
597 makes 2 copies of $large_string (one for $copy and another for the
599 quotes), whereas
600 my $copy = $large_string;
602 only makes one copy.
604 Ditto for stringifying large arrays:
606 {
608 local $, = "\n";
609 print @big_array;
610 }
611 is much more memory-efficient than either
613 print join "\n", @big_array;
615 or
617 {
619 local $" = "\n";
620 print "@big_array";
621 }
622 Pass by reference
624 Pass arrays and hashes by reference, not by value. For one thing,
625 it's the only way to pass multiple lists or hashes (or both) in a
626 single call/return. It also avoids creating a copy of all the
627 contents. This requires some judgement, however, because any
628 changes will be propagated back to the original data. If you really
629 want to mangle (er, modify) a copy, you'll have to sacrifice the
630 memory needed to make one.
631 Tie large variables to disk
633 For "big" data stores (i.e. ones that exceed available memory)
634 consider using one of the DB modules to store it on disk instead of
635 in RAM. This will incur a penalty in access time, but that's
636 probably better than causing your hard disk to thrash due to
637 massive swapping.
638 Is it safe to return a reference to local or lexical data?
640 Yes. Perl's garbage collection system takes care of this so everything
641 works out right.
642 sub makeone {
644 my @a = ( 1 .. 10 );
645 return \@a;
646 }
647 for ( 1 .. 10 ) {
649 push @many, makeone();
650 }
651 print $many[4][5], "\n";
653 print "@many\n";
655 How can I free an array or hash so my program shrinks?
657 (contributed by Michael Carman)
658 You usually can't. Memory allocated to lexicals (i.e. my() variables)
660 cannot be reclaimed or reused even if they go out of scope. It is
661 reserved in case the variables come back into scope. Memory allocated
662 to global variables can be reused (within your program) by using
663 undef() and/or delete().
664 On most operating systems, memory allocated to a program can never be
666 returned to the system. That's why long-running programs sometimes re-
667 exec themselves. Some operating systems (notably, systems that use
668 mmap(2) for allocating large chunks of memory) can reclaim memory that
669 is no longer used, but on such systems, perl must be configured and
670 compiled to use the OS's malloc, not perl's.
671 In general, memory allocation and de-allocation isn't something you can
673 or should be worrying about much in Perl.
674 See also "How can I make my Perl program take less memory?"
676 How can I make my CGI script more efficient?
678 Beyond the normal measures described to make general Perl programs
679 faster or smaller, a CGI program has additional issues. It may be run
680 several times per second. Given that each time it runs it will need to
681 be re-compiled and will often allocate a megabyte or more of system
682 memory, this can be a killer. Compiling into C isn't going to help you
683 because the process start-up overhead is where the bottleneck is.
684 There are three popular ways to avoid this overhead. One solution
686 involves running the Apache HTTP server (available from
687 <http://www.apache.org/> ) with either of the mod_perl or mod_fastcgi
688 plugin modules.
689 With mod_perl and the Apache::Registry module (distributed with
691 mod_perl), httpd will run with an embedded Perl interpreter which pre-
692 compiles your script and then executes it within the same address space
693 without forking. The Apache extension also gives Perl access to the
694 internal server API, so modules written in Perl can do just about
695 anything a module written in C can. For more on mod_perl, see
696 <http://perl.apache.org/>
697 With the FCGI module (from CPAN) and the mod_fastcgi module (available
699 from <http://www.fastcgi.com/> ) each of your Perl programs becomes a
700 permanent CGI daemon process.
701 Finally, Plack is a Perl module and toolkit that contains PSGI
703 middleware, helpers and adapters to web servers, allowing you to easily
704 deploy scripts which can continue running, and provides flexibility
705 with regards to which web server you use. It can allow existing CGI
706 scripts to enjoy this flexibility and performance with minimal changes,
707 or can be used along with modern Perl web frameworks to make writing
708 and deploying web services with Perl a breeze.
709 These solutions can have far-reaching effects on your system and on the
711 way you write your CGI programs, so investigate them with care.
712 See also
714 <http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/>
715 .
716 How can I hide the source for my Perl program?
718 Delete it. :-) Seriously, there are a number of (mostly unsatisfactory)
719 solutions with varying levels of "security".
720 First of all, however, you can't take away read permission, because the
722 source code has to be readable in order to be compiled and interpreted.
723 (That doesn't mean that a CGI script's source is readable by people on
724 the web, though--only by people with access to the filesystem.) So you
725 have to leave the permissions at the socially friendly 0755 level.
726 Some people regard this as a security problem. If your program does
728 insecure things and relies on people not knowing how to exploit those
729 insecurities, it is not secure. It is often possible for someone to
730 determine the insecure things and exploit them without viewing the
731 source. Security through obscurity, the name for hiding your bugs
732 instead of fixing them, is little security indeed.
733 You can try using encryption via source filters (Starting from Perl 5.8
735 the Filter::Simple and Filter::Util::Call modules are included in the
736 standard distribution), but any decent programmer will be able to
737 decrypt it. You can try using the byte code compiler and interpreter
738 described later in perlfaq3, but the curious might still be able to de-
739 compile it. You can try using the native-code compiler described later,
740 but crackers might be able to disassemble it. These pose varying
741 degrees of difficulty to people wanting to get at your code, but none
742 can definitively conceal it (true of every language, not just Perl).
743 It is very easy to recover the source of Perl programs. You simply feed
745 the program to the perl interpreter and use the modules in the B::
746 hierarchy. The B::Deparse module should be able to defeat most attempts
747 to hide source. Again, this is not unique to Perl.
748 If you're concerned about people profiting from your code, then the
750 bottom line is that nothing but a restrictive license will give you
751 legal security. License your software and pepper it with threatening
752 statements like "This is unpublished proprietary software of XYZ Corp.
753 Your access to it does not give you permission to use it blah blah
754 blah." We are not lawyers, of course, so you should see a lawyer if
755 you want to be sure your license's wording will stand up in court.
756 How can I compile my Perl program into byte code or C?
758 (contributed by brian d foy)
759 In general, you can't do this. There are some things that may work for
761 your situation though. People usually ask this question because they
762 want to distribute their works without giving away the source code, and
763 most solutions trade disk space for convenience. You probably won't
764 see much of a speed increase either, since most solutions simply bundle
765 a Perl interpreter in the final product (but see "How can I make my
766 Perl program run faster?").
767 The Perl Archive Toolkit is Perl's analog to Java's JAR. It's freely
769 available and on CPAN ( <https://metacpan.org/pod/PAR> ).
770 There are also some commercial products that may work for you, although
772 you have to buy a license for them.
773 The Perl Dev Kit ( <http://www.activestate.com/Products/Perl_Dev_Kit/>
775 ) from ActiveState can "Turn your Perl programs into ready-to-run
776 executables for HP-UX, Linux, Solaris and Windows."
777 Perl2Exe ( <http://www.indigostar.com/perl2exe.htm> ) is a command line
779 program for converting perl scripts to executable files. It targets
780 both Windows and Unix platforms.
781 How can I get "#!perl" to work on [MS-DOS,NT,...]?
783 For OS/2 just use
784 extproc perl -S -your_switches
786 as the first line in "*.cmd" file ("-S" due to a bug in cmd.exe's
788 "extproc" handling). For DOS one should first invent a corresponding
789 batch file and codify it in "ALTERNATE_SHEBANG" (see the dosish.h file
790 in the source distribution for more information).
791 The Win95/NT installation, when using the ActiveState port of Perl,
793 will modify the Registry to associate the ".pl" extension with the perl
794 interpreter. If you install another port, perhaps even building your
795 own Win95/NT Perl from the standard sources by using a Windows port of
796 gcc (e.g., with cygwin or mingw32), then you'll have to modify the
797 Registry yourself. In addition to associating ".pl" with the
798 interpreter, NT people can use: "SET PATHEXT=%PATHEXT%;.PL" to let them
799 run the program "install-linux.pl" merely by typing "install-linux".
800 Under "Classic" MacOS, a perl program will have the appropriate Creator
802 and Type, so that double-clicking them will invoke the MacPerl
803 application. Under Mac OS X, clickable apps can be made from any "#!"
804 script using Wil Sanchez' DropScript utility:
805 <http://www.wsanchez.net/software/> .
806 IMPORTANT!: Whatever you do, PLEASE don't get frustrated, and just
808 throw the perl interpreter into your cgi-bin directory, in order to get
809 your programs working for a web server. This is an EXTREMELY big
810 security risk. Take the time to figure out how to do it correctly.
811 Can I write useful Perl programs on the command line?
813 Yes. Read perlrun for more information. Some examples follow. (These
814 assume standard Unix shell quoting rules.)
815 # sum first and last fields
817 perl -lane 'print $F[0] + $F[-1]' *
818 # identify text files
820 perl -le 'for(@ARGV) {print if -f && -T _}' *
821 # remove (most) comments from C program
823 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
824 # make file a month younger than today, defeating reaper daemons
826 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
827 # find first unused uid
829 perl -le '$i++ while getpwuid($i); print $i'
830 # display reasonable manpath
832 echo $PATH | perl -nl -072 -e '
833 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
834 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
836 Why don't Perl one-liners work on my DOS/Mac/VMS system?
838 The problem is usually that the command interpreters on those systems
839 have rather different ideas about quoting than the Unix shells under
840 which the one-liners were created. On some systems, you may have to
841 change single-quotes to double ones, which you must NOT do on Unix or
842 Plan9 systems. You might also have to change a single % to a %%.
843 For example:
845 # Unix (including Mac OS X)
847 perl -e 'print "Hello world\n"'
848 # DOS, etc.
850 perl -e "print \"Hello world\n\""
851 # Mac Classic
853 print "Hello world\n"
854 (then Run "Myscript" or Shift-Command-R)
855 # MPW
857 perl -e 'print "Hello world\n"'
858 # VMS
860 perl -e "print ""Hello world\n"""
861 The problem is that none of these examples are reliable: they depend on
863 the command interpreter. Under Unix, the first two often work. Under
864 DOS, it's entirely possible that neither works. If 4DOS was the command
865 shell, you'd probably have better luck like this:
866 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
868 Under the Mac, it depends which environment you are using. The MacPerl
870 shell, or MPW, is much like Unix shells in its support for several
871 quoting variants, except that it makes free use of the Mac's non-ASCII
872 characters as control characters.
873 Using qq(), q(), and qx(), instead of "double quotes", 'single quotes',
875 and `backticks`, may make one-liners easier to write.
876 There is no general solution to all of this. It is a mess.
878 [Some of this answer was contributed by Kenneth Albanowski.]
880 Where can I learn about CGI or Web programming in Perl?
882 For modules, get the CGI or LWP modules from CPAN. For textbooks, see
883 the two especially dedicated to web stuff in the question on books. For
884 problems and questions related to the web, like "Why do I get 500
885 Errors" or "Why doesn't it run from the browser right when it runs fine
886 on the command line", see the troubleshooting guides and references in
887 perlfaq9 or in the CGI MetaFAQ:
888 L<http://www.perl.org/CGI_MetaFAQ.html>
890 Looking in to Plack and modern Perl web frameworks is highly
892 recommended, though; web programming in Perl has evolved a long way
893 from the old days of simple CGI scripts.
894 Where can I learn about object-oriented Perl programming?
896 A good place to start is perlootut, and you can use perlobj for
897 reference.
898 A good book on OO on Perl is the "Object-Oriented Perl" by Damian
900 Conway from Manning Publications, or "Intermediate Perl" by Randal
901 Schwartz, brian d foy, and Tom Phoenix from O'Reilly Media.
902 Where can I learn about linking C with Perl?
904 If you want to call C from Perl, start with perlxstut, moving on to
905 perlxs, xsubpp, and perlguts. If you want to call Perl from C, then
906 read perlembed, perlcall, and perlguts. Don't forget that you can learn
907 a lot from looking at how the authors of existing extension modules
908 wrote their code and solved their problems.
909 You might not need all the power of XS. The Inline::C module lets you
911 put C code directly in your Perl source. It handles all the magic to
912 make it work. You still have to learn at least some of the perl API but
913 you won't have to deal with the complexity of the XS support files.
914 I've read perlembed, perlguts, etc., but I can't embed perl in my C
916 program; what am I doing wrong?
917 Download the ExtUtils::Embed kit from CPAN and run `make test'. If the
918 tests pass, read the pods again and again and again. If they fail, see
919 perlbug and send a bug report with the output of "make test
920 TEST_VERBOSE=1" along with "perl -V".
921 When I tried to run my script, I got this message. What does it mean?
923 A complete list of Perl's error messages and warnings with explanatory
924 text can be found in perldiag. You can also use the splain program
925 (distributed with Perl) to explain the error messages:
926 perl program 2>diag.out
928 splain [-v] [-p] diag.out
929 or change your program to explain the messages for you:
931 use diagnostics;
933 or
935 use diagnostics -verbose;
937 What's MakeMaker?
939 (contributed by brian d foy)
940 The ExtUtils::MakeMaker module, better known simply as "MakeMaker",
942 turns a Perl script, typically called "Makefile.PL", into a Makefile.
943 The Unix tool "make" uses this file to manage dependencies and actions
944 to process and install a Perl distribution.
945
947 Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and other
948 authors as noted. All rights reserved.
949 This documentation is free; you can redistribute it and/or modify it
951 under the same terms as Perl itself.
952 Irrespective of its distribution, all code examples here are in the
954 public domain. You are permitted and encouraged to use this code and
955 any derivatives thereof in your own programs for fun or for profit as
956 you see fit. A simple comment in the code giving credit to the FAQ
957 would be courteous but is not required.
958perl v5.28.1 2019-01-26 perlfaq3(3)