1PERLFAQ3(1) Perl Programmers Reference Guide PERLFAQ3(1)
2
6 perlfaq3 - Programming Tools
7
9 This section of the FAQ answers questions related to programmer tools
10 and programming support.
11 How do I do (anything)?
13 Have you looked at CPAN (see perlfaq2)? The chances are that someone
14 has already written a module that can solve your problem. Have you
15 read the appropriate manpages? Here's a brief index:
16 Basics
18 perldata - Perl data types
19 perlvar - Perl pre-defined variables
20 perlsyn - Perl syntax
21 perlop - Perl operators and precedence
22 perlsub - Perl subroutines
23 Execution
24 perlrun - how to execute the Perl interpreter
25 perldebug - Perl debugging
26 Functions
27 perlfunc - Perl builtin functions
28 Objects
29 perlref - Perl references and nested data structures
30 perlmod - Perl modules (packages and symbol tables)
31 perlobj - Perl objects
32 perltie - how to hide an object class in a simple variable
33 Data Structures
34 perlref - Perl references and nested data structures
35 perllol - Manipulating arrays of arrays in Perl
36 perldsc - Perl Data Structures Cookbook
37 Modules
38 perlmod - Perl modules (packages and symbol tables)
39 perlmodlib - constructing new Perl modules and finding existing
40 ones
41 Regexes
42 perlre - Perl regular expressions
43 perlfunc - Perl builtin functions>
44 perlop - Perl operators and precedence
45 perllocale - Perl locale handling (internationalization and
46 localization)
47 Moving to perl5
48 perltrap - Perl traps for the unwary
49 perl
50 Linking with C
51 perlxstut - Tutorial for writing XSUBs
52 perlxs - XS language reference manual
53 perlcall - Perl calling conventions from C
54 perlguts - Introduction to the Perl API
55 perlembed - how to embed perl in your C program
56 Various
57 <http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz> (not a man-page but
58 still useful, a collection of various essays on Perl techniques)
59 A crude table of contents for the Perl manpage set is found in perltoc.
61 How can I use Perl interactively?
63 The typical approach uses the Perl debugger, described in the
64 perldebug(1) manpage, on an "empty" program, like this:
65 perl -de 42
67 Now just type in any legal Perl code, and it will be immediately
69 evaluated. You can also examine the symbol table, get stack backtraces,
70 check variable values, set breakpoints, and other operations typically
71 found in symbolic debuggers.
72 You can also use Devel::REPL which is an interactive shell for Perl,
74 commonly known as a REPL - Read, Evaluate, Print, Loop. It provides
75 various handy features.
76 How do I find which modules are installed on my system?
78 From the command line, you can use the "cpan" command's "-l" switch:
79 $ cpan -l
81 You can also use "cpan"'s "-a" switch to create an autobundle file that
83 "CPAN.pm" understands and can use to re-install every module:
84 $ cpan -a
86 Inside a Perl program, you can use the ExtUtils::Installed module to
88 show all installed distributions, although it can take awhile to do its
89 magic. The standard library which comes with Perl just shows up as
90 "Perl" (although you can get those with Module::CoreList).
91 use ExtUtils::Installed;
93 my $inst = ExtUtils::Installed->new();
95 my @modules = $inst->modules();
96 If you want a list of all of the Perl module filenames, you can use
98 File::Find::Rule:
99 use File::Find::Rule;
101 my @files = File::Find::Rule->
103 extras({follow => 1})->
104 file()->
105 name( '*.pm' )->
106 in( @INC )
107 ;
108 If you do not have that module, you can do the same thing with
110 File::Find which is part of the standard library:
111 use File::Find;
113 my @files;
114 find(
116 {
117 wanted => sub {
118 push @files, $File::Find::fullname
119 if -f $File::Find::fullname && /\.pm$/
120 },
121 follow => 1,
122 follow_skip => 2,
123 },
124 @INC
125 );
126 print join "\n", @files;
128 If you simply need to check quickly to see if a module is available,
130 you can check for its documentation. If you can read the documentation
131 the module is most likely installed. If you cannot read the
132 documentation, the module might not have any (in rare cases):
133 $ perldoc Module::Name
135 You can also try to include the module in a one-liner to see if perl
137 finds it:
138 $ perl -MModule::Name -e1
140 (If you don't receive a "Can't locate ... in @INC" error message, then
142 Perl found the module name you asked for.)
143 How do I debug my Perl programs?
145 (contributed by brian d foy)
146 Before you do anything else, you can help yourself by ensuring that you
148 let Perl tell you about problem areas in your code. By turning on
149 warnings and strictures, you can head off many problems before they get
150 too big. You can find out more about these in strict and warnings.
151 #!/usr/bin/perl
153 use strict;
154 use warnings;
155 Beyond that, the simplest debugger is the "print" function. Use it to
157 look at values as you run your program:
158 print STDERR "The value is [$value]\n";
160 The Data::Dumper module can pretty-print Perl data structures:
162 use Data::Dumper qw( Dumper );
164 print STDERR "The hash is " . Dumper( \%hash ) . "\n";
165 Perl comes with an interactive debugger, which you can start with the
167 "-d" switch. It's fully explained in perldebug.
168 If you'd like a graphical user interface and you have Tk, you can use
170 "ptkdb". It's on CPAN and available for free.
171 If you need something much more sophisticated and controllable, Leon
173 Brocard's Devel::ebug (which you can call with the "-D" switch as
174 "-Debug") gives you the programmatic hooks into everything you need to
175 write your own (without too much pain and suffering).
176 You can also use a commercial debugger such as Affrus (Mac OS X),
178 Komodo from Activestate (Windows and Mac OS X), or EPIC (most
179 platforms).
180 How do I profile my Perl programs?
182 (contributed by brian d foy, updated Fri Jul 25 12:22:26 PDT 2008)
183 The "Devel" namespace has several modules which you can use to profile
185 your Perl programs.
186 The Devel::NYTProf (New York Times Profiler) does both statement and
188 subroutine profiling. It's available from CPAN and you also invoke it
189 with the "-d" switch:
190 perl -d:NYTProf some_perl.pl
192 It creates a database of the profile information that you can turn into
194 reports. The "nytprofhtml" command turns the data into an HTML report
195 similar to the Devel::Cover report:
196 nytprofhtml
198 You might also be interested in using the Benchmark to measure and
200 compare code snippets.
201 You can read more about profiling in Programming Perl, chapter 20, or
203 Mastering Perl, chapter 5.
204 perldebguts documents creating a custom debugger if you need to create
206 a special sort of profiler. brian d foy describes the process in The
207 Perl Journal, "Creating a Perl Debugger",
208 <http://www.ddj.com/184404522> , and "Profiling in Perl"
209 <http://www.ddj.com/184404580> .
210 Perl.com has two interesting articles on profiling: "Profiling Perl",
212 by Simon Cozens, <http://www.perl.com/lpt/a/850> and "Debugging and
213 Profiling mod_perl Applications", by Frank Wiles,
214 <http://www.perl.com/pub/a/2006/02/09/debug_mod_perl.html> .
215 Randal L. Schwartz writes about profiling in "Speeding up Your Perl
217 Programs" for Unix Review,
218 <http://www.stonehenge.com/merlyn/UnixReview/col49.html> , and
219 "Profiling in Template Toolkit via Overriding" for Linux Magazine,
220 <http://www.stonehenge.com/merlyn/LinuxMag/col75.html> .
221 How do I cross-reference my Perl programs?
223 The B::Xref module can be used to generate cross-reference reports for
224 Perl programs.
225 perl -MO=Xref[,OPTIONS] scriptname.plx
227 Is there a pretty-printer (formatter) for Perl?
229 Perl::Tidy comes with a perl script perltidy which indents and
230 reformats Perl scripts to make them easier to read by trying to follow
231 the rules of the perlstyle. If you write Perl, or spend much time
232 reading Perl, you will probably find it useful.
233 Of course, if you simply follow the guidelines in perlstyle, you
235 shouldn't need to reformat. The habit of formatting your code as you
236 write it will help prevent bugs. Your editor can and should help you
237 with this. The perl-mode or newer cperl-mode for emacs can provide
238 remarkable amounts of help with most (but not all) code, and even less
239 programmable editors can provide significant assistance. Tom
240 Christiansen and many other VI users swear by the following settings in
241 vi and its clones:
242 set ai sw=4
244 map! ^O {^M}^[O^T
245 Put that in your .exrc file (replacing the caret characters with
247 control characters) and away you go. In insert mode, ^T is for
248 indenting, ^D is for undenting, and ^O is for blockdenting--as it were.
249 A more complete example, with comments, can be found at
250 <http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz>
251 Is there an IDE or Windows Perl Editor?
253 Perl programs are just plain text, so any editor will do.
254 If you're on Unix, you already have an IDE--Unix itself. The Unix
256 philosophy is the philosophy of several small tools that each do one
257 thing and do it well. It's like a carpenter's toolbox.
258 If you want an IDE, check the following (in alphabetical order, not
260 order of preference):
261 Eclipse
263 http://e-p-i-c.sf.net/ <http://e-p-i-c.sf.net/>
264 The Eclipse Perl Integration Project integrates Perl
266 editing/debugging with Eclipse.
267 Enginsite
269 <http://www.enginsite.com/>
270 Perl Editor by EngInSite is a complete integrated development
272 environment (IDE) for creating, testing, and debugging Perl
273 scripts; the tool runs on Windows 9x/NT/2000/XP or later.
274 Komodo
276 <http://www.ActiveState.com/Products/Komodo/>
277 ActiveState's cross-platform (as of October 2004, that's Windows,
279 Linux, and Solaris), multi-language IDE has Perl support, including
280 a regular expression debugger and remote debugging.
281 Notepad++
283 http://notepad-plus.sourceforge.net/ <http://notepad-
284 plus.sourceforge.net/>
285 Open Perl IDE
287 http://open-perl-ide.sourceforge.net/ <http://open-perl-
288 ide.sourceforge.net/>
289 Open Perl IDE is an integrated development environment for writing
291 and debugging Perl scripts with ActiveState's ActivePerl
292 distribution under Windows 95/98/NT/2000.
293 OptiPerl
295 <http://www.optiperl.com/>
296 OptiPerl is a Windows IDE with simulated CGI environment, including
298 debugger and syntax-highlighting editor.
299 Padre
301 <http://padre.perlide.org/>
302 Padre is cross-platform IDE for Perl written in Perl using
304 wxWidgets to provide a native look and feel. It's open source under
305 the Artistic License. It is one of the newer Perl IDEs.
306 PerlBuilder
308 <http://www.solutionsoft.com/perl.htm>
309 PerlBuilder is an integrated development environment for Windows
311 that supports Perl development.
312 visiPerl+
314 <http://helpconsulting.net/visiperl/index.html>
315 From Help Consulting, for Windows.
317 Visual Perl
319 <http://www.activestate.com/Products/Visual_Perl/>
320 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
322 Zeus
324 <http://www.zeusedit.com/lookmain.html>
325 Zeus for Window is another Win32 multi-language editor/IDE that
327 comes with support for Perl.
328 For editors: if you're on Unix you probably have vi or a vi clone
330 already, and possibly an emacs too, so you may not need to download
331 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
332 perhaps the best available Perl editing mode in any editor.
333 If you are using Windows, you can use any editor that lets you work
335 with plain text, such as NotePad or WordPad. Word processors, such as
336 Microsoft Word or WordPerfect, typically do not work since they insert
337 all sorts of behind-the-scenes information, although some allow you to
338 save files as "Text Only". You can also download text editors designed
339 specifically for programming, such as Textpad (
340 <http://www.textpad.com/> ) and UltraEdit ( <http://www.ultraedit.com/>
341 ), among others.
342 If you are using MacOS, the same concerns apply. MacPerl (for Classic
344 environments) comes with a simple editor. Popular external editors are
345 BBEdit ( <http://www.bbedit.com/> ) or Alpha (
346 <http://www.his.com/~jguyer/Alpha/Alpha8.html> ). MacOS X users can use
347 Unix editors as well.
348 GNU Emacs
350 <http://www.gnu.org/software/emacs/windows/ntemacs.html>
351 MicroEMACS
353 <http://www.microemacs.de/>
354 XEmacs
356 <http://www.xemacs.org/Download/index.html>
357 Jed <http://space.mit.edu/~davis/jed/>
359 or a vi clone such as
361 Vim <http://www.vim.org/>
363 Vile
365 <http://dickey.his.com/vile/vile.html>
366 The following are Win32 multilanguage editor/IDEs that support Perl:
368 Codewright
370 <http://www.borland.com/codewright/>
371 MultiEdit
373 <http://www.MultiEdit.com/>
374 SlickEdit
376 <http://www.slickedit.com/>
377 ConTEXT
379 <http://www.contexteditor.org/>
380 There is also a toyedit Text widget based editor written in Perl that
382 is distributed with the Tk module on CPAN. The ptkdb (
383 <http://ptkdb.sourceforge.net/> ) is a Perl/Tk-based debugger that acts
384 as a development environment of sorts. Perl Composer (
385 <http://perlcomposer.sourceforge.net/> ) is an IDE for Perl/Tk GUI
386 creation.
387 In addition to an editor/IDE you might be interested in a more powerful
389 shell environment for Win32. Your options include
390 Bash
392 from the Cygwin package ( <http://sources.redhat.com/cygwin/> )
393 Ksh from the MKS Toolkit ( <http://www.mkssoftware.com/> ), or the
395 Bourne shell of the U/WIN environment (
396 <http://www.research.att.com/sw/tools/uwin/> )
397 Tcsh
399 <ftp://ftp.astron.com/pub/tcsh/> , see also
400 http://www.primate.wisc.edu/software/csh-tcsh-book/
401 <http://www.primate.wisc.edu/software/csh-tcsh-book/>
402 Zsh <http://www.zsh.org/>
404 MKS and U/WIN are commercial (U/WIN is free for educational and
406 research purposes), Cygwin is covered by the GNU General Public License
407 (but that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN
408 all contain (in addition to the shells) a comprehensive set of standard
409 Unix toolkit utilities.
410 If you're transferring text files between Unix and Windows using FTP be
412 sure to transfer them in ASCII mode so the ends of lines are
413 appropriately converted.
414 On Mac OS the MacPerl Application comes with a simple 32k text editor
416 that behaves like a rudimentary IDE. In contrast to the MacPerl
417 Application the MPW Perl tool can make use of the MPW Shell itself as
418 an editor (with no 32k limit).
419 Affrus
421 is a full Perl development environment with full debugger support (
422 <http://www.latenightsw.com> ).
423 Alpha
425 is an editor, written and extensible in Tcl, that nonetheless has
426 built-in support for several popular markup and programming
427 languages, including Perl and HTML (
428 <http://www.his.com/~jguyer/Alpha/Alpha8.html> ).
429 BBEdit and BBEdit Lite
431 are text editors for Mac OS that have a Perl sensitivity mode (
432 <http://web.barebones.com/> ).
433 Where can I get Perl macros for vi?
435 For a complete version of Tom Christiansen's vi configuration file, see
436 <http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz> ,
437 the standard benchmark file for vi emulators. The file runs best with
438 nvi, the current version of vi out of Berkeley, which incidentally can
439 be built with an embedded Perl interpreter--see
440 <http://www.cpan.org/src/misc/> .
441 Where can I get perl-mode or cperl-mode for emacs?
443 Since Emacs version 19 patchlevel 22 or so, there have been both a
444 perl-mode.el and support for the Perl debugger built in. These should
445 come with the standard Emacs 19 distribution.
446 Note that the perl-mode of emacs will have fits with "main'foo" (single
448 quote), and mess up the indentation and highlighting. You are probably
449 using "main::foo" in new Perl code anyway, so this shouldn't be an
450 issue.
451 For CPerlMode, see http://www.emacswiki.org/cgi-bin/wiki/CPerlMode
453 <http://www.emacswiki.org/cgi-bin/wiki/CPerlMode>
454 How can I use curses with Perl?
456 The Curses module from CPAN provides a dynamically loadable object
457 module interface to a curses library. A small demo can be found at the
458 directory <http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz>
459 ; this program repeats a command and updates the screen as needed,
460 rendering rep ps axu similar to top.
461 How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
463 (contributed by Ben Morrow)
464 There are a number of modules which let you write GUIs in Perl. Most
466 GUI toolkits have a perl interface: an incomplete list follows.
467 Tk This works under Unix and Windows, and the current version doesn't
469 look half as bad under Windows as it used to. Some of the gui
470 elements still don't 'feel' quite right, though. The interface is
471 very natural and 'perlish', making it easy to use in small scripts
472 that just need a simple gui. It hasn't been updated in a while.
473 Wx This is a Perl binding for the cross-platform wxWidgets toolkit (
475 <http://www.wxwidgets.org> ). It works under Unix, Win32 and Mac OS
476 X, using native widgets (Gtk under Unix). The interface follows the
477 C++ interface closely, but the documentation is a little sparse for
478 someone who doesn't know the library, mostly just referring you to
479 the C++ documentation.
480 Gtk and Gtk2
482 These are Perl bindings for the Gtk toolkit ( <http://www.gtk.org>
483 ). The interface changed significantly between versions 1 and 2 so
484 they have separate Perl modules. It runs under Unix, Win32 and Mac
485 OS X (currently it requires an X server on Mac OS, but a 'native'
486 port is underway), and the widgets look the same on every platform:
487 i.e., they don't match the native widgets. As with Wx, the Perl
488 bindings follow the C API closely, and the documentation requires
489 you to read the C documentation to understand it.
490 Win32::GUI
492 This provides access to most of the Win32 GUI widgets from Perl.
493 Obviously, it only runs under Win32, and uses native widgets. The
494 Perl interface doesn't really follow the C interface: it's been
495 made more Perlish, and the documentation is pretty good. More
496 advanced stuff may require familiarity with the C Win32 APIs, or
497 reference to MSDN.
498 CamelBones
500 CamelBones ( <http://camelbones.sourceforge.net> ) is a Perl
501 interface to Mac OS X's Cocoa GUI toolkit, and as such can be used
502 to produce native GUIs on Mac OS X. It's not on CPAN, as it
503 requires frameworks that CPAN.pm doesn't know how to install, but
504 installation is via the standard OSX package installer. The Perl
505 API is, again, very close to the ObjC API it's wrapping, and the
506 documentation just tells you how to translate from one to the
507 other.
508 Qt There is a Perl interface to TrollTech's Qt toolkit, but it does
510 not appear to be maintained.
511 Athena
513 Sx is an interface to the Athena widget set which comes with X, but
514 again it appears not to be much used nowadays.
515 How can I make my Perl program run faster?
517 The best way to do this is to come up with a better algorithm. This can
518 often make a dramatic difference. Jon Bentley's book Programming Pearls
519 (that's not a misspelling!) has some good tips on optimization, too.
520 Advice on benchmarking boils down to: benchmark and profile to make
521 sure you're optimizing the right part, look for better algorithms
522 instead of microtuning your code, and when all else fails consider just
523 buying faster hardware. You will probably want to read the answer to
524 the earlier question "How do I profile my Perl programs?" if you
525 haven't done so already.
526 A different approach is to autoload seldom-used Perl code. See the
528 AutoSplit and AutoLoader modules in the standard distribution for that.
529 Or you could locate the bottleneck and think about writing just that
530 part in C, the way we used to take bottlenecks in C code and write them
531 in assembler. Similar to rewriting in C, modules that have critical
532 sections can be written in C (for instance, the PDL module from CPAN).
533 If you're currently linking your perl executable to a shared libc.so,
535 you can often gain a 10-25% performance benefit by rebuilding it to
536 link with a static libc.a instead. This will make a bigger perl
537 executable, but your Perl programs (and programmers) may thank you for
538 it. See the INSTALL file in the source distribution for more
539 information.
540 The undump program was an ancient attempt to speed up Perl program by
542 storing the already-compiled form to disk. This is no longer a viable
543 option, as it only worked on a few architectures, and wasn't a good
544 solution anyway.
545 How can I make my Perl program take less memory?
547 When it comes to time-space tradeoffs, Perl nearly always prefers to
548 throw memory at a problem. Scalars in Perl use more memory than strings
549 in C, arrays take more than that, and hashes use even more. While
550 there's still a lot to be done, recent releases have been addressing
551 these issues. For example, as of 5.004, duplicate hash keys are shared
552 amongst all hashes using them, so require no reallocation.
553 In some cases, using substr() or vec() to simulate arrays can be highly
555 beneficial. For example, an array of a thousand booleans will take at
556 least 20,000 bytes of space, but it can be turned into one 125-byte bit
557 vector--a considerable memory savings. The standard Tie::SubstrHash
558 module can also help for certain types of data structure. If you're
559 working with specialist data structures (matrices, for instance)
560 modules that implement these in C may use less memory than equivalent
561 Perl modules.
562 Another thing to try is learning whether your Perl was compiled with
564 the system malloc or with Perl's builtin malloc. Whichever one it is,
565 try using the other one and see whether this makes a difference.
566 Information about malloc is in the INSTALL file in the source
567 distribution. You can find out whether you are using perl's malloc by
568 typing "perl -V:usemymalloc".
569 Of course, the best way to save memory is to not do anything to waste
571 it in the first place. Good programming practices can go a long way
572 toward this:
573 Don't slurp!
575 Don't read an entire file into memory if you can process it line by
576 line. Or more concretely, use a loop like this:
577 #
579 # Good Idea
580 #
581 while (my $line = <$file_handle>) {
582 # ...
583 }
584 instead of this:
586 #
588 # Bad Idea
589 #
590 my @data = <$file_handle>;
591 foreach (@data) {
592 # ...
593 }
594 When the files you're processing are small, it doesn't much matter
596 which way you do it, but it makes a huge difference when they start
597 getting larger.
598 Use map and grep selectively
600 Remember that both map and grep expect a LIST argument, so doing
601 this:
602 @wanted = grep {/pattern/} <$file_handle>;
604 will cause the entire file to be slurped. For large files, it's
606 better to loop:
607 while (<$file_handle>) {
609 push(@wanted, $_) if /pattern/;
610 }
611 Avoid unnecessary quotes and stringification
613 Don't quote large strings unless absolutely necessary:
614 my $copy = "$large_string";
616 makes 2 copies of $large_string (one for $copy and another for the
618 quotes), whereas
619 my $copy = $large_string;
621 only makes one copy.
623 Ditto for stringifying large arrays:
625 {
627 local $, = "\n";
628 print @big_array;
629 }
630 is much more memory-efficient than either
632 print join "\n", @big_array;
634 or
636 {
638 local $" = "\n";
639 print "@big_array";
640 }
641 Pass by reference
643 Pass arrays and hashes by reference, not by value. For one thing,
644 it's the only way to pass multiple lists or hashes (or both) in a
645 single call/return. It also avoids creating a copy of all the
646 contents. This requires some judgement, however, because any
647 changes will be propagated back to the original data. If you really
648 want to mangle (er, modify) a copy, you'll have to sacrifice the
649 memory needed to make one.
650 Tie large variables to disk
652 For "big" data stores (i.e. ones that exceed available memory)
653 consider using one of the DB modules to store it on disk instead of
654 in RAM. This will incur a penalty in access time, but that's
655 probably better than causing your hard disk to thrash due to
656 massive swapping.
657 Is it safe to return a reference to local or lexical data?
659 Yes. Perl's garbage collection system takes care of this so everything
660 works out right.
661 sub makeone {
663 my @a = ( 1 .. 10 );
664 return \@a;
665 }
666 for ( 1 .. 10 ) {
668 push @many, makeone();
669 }
670 print $many[4][5], "\n";
672 print "@many\n";
674 How can I free an array or hash so my program shrinks?
676 (contributed by Michael Carman)
677 You usually can't. Memory allocated to lexicals (i.e. my() variables)
679 cannot be reclaimed or reused even if they go out of scope. It is
680 reserved in case the variables come back into scope. Memory allocated
681 to global variables can be reused (within your program) by using
682 undef() and/or delete().
683 On most operating systems, memory allocated to a program can never be
685 returned to the system. That's why long-running programs sometimes re-
686 exec themselves. Some operating systems (notably, systems that use
687 mmap(2) for allocating large chunks of memory) can reclaim memory that
688 is no longer used, but on such systems, perl must be configured and
689 compiled to use the OS's malloc, not perl's.
690 In general, memory allocation and de-allocation isn't something you can
692 or should be worrying about much in Perl.
693 See also "How can I make my Perl program take less memory?"
695 How can I make my CGI script more efficient?
697 Beyond the normal measures described to make general Perl programs
698 faster or smaller, a CGI program has additional issues. It may be run
699 several times per second. Given that each time it runs it will need to
700 be re-compiled and will often allocate a megabyte or more of system
701 memory, this can be a killer. Compiling into C isn't going to help you
702 because the process start-up overhead is where the bottleneck is.
703 There are three popular ways to avoid this overhead. One solution
705 involves running the Apache HTTP server (available from
706 <http://www.apache.org/> ) with either of the mod_perl or mod_fastcgi
707 plugin modules.
708 With mod_perl and the Apache::Registry module (distributed with
710 mod_perl), httpd will run with an embedded Perl interpreter which pre-
711 compiles your script and then executes it within the same address space
712 without forking. The Apache extension also gives Perl access to the
713 internal server API, so modules written in Perl can do just about
714 anything a module written in C can. For more on mod_perl, see
715 <http://perl.apache.org/>
716 With the FCGI module (from CPAN) and the mod_fastcgi module (available
718 from <http://www.fastcgi.com/> ) each of your Perl programs becomes a
719 permanent CGI daemon process.
720 Finally, Plack is a Perl module and toolkit that contains PSGI
722 middleware, helpers and adapters to web servers, allowing you to easily
723 deploy scripts which can continue running, and provides flexibility
724 with regards to which web server you use. It can allow existing CGI
725 scripts to enjoy this flexibility and performance with minimal changes,
726 or can be used along with modern Perl web frameworks to make writing
727 and deploying web services with Perl a breeze.
728 These solutions can have far-reaching effects on your system and on the
730 way you write your CGI programs, so investigate them with care.
731 See also
733 http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/
734 <http://www.cpan.org/modules/by-
735 category/15_World_Wide_Web_HTML_HTTP_CGI/> .
736 How can I hide the source for my Perl program?
738 Delete it. :-) Seriously, there are a number of (mostly unsatisfactory)
739 solutions with varying levels of "security".
740 First of all, however, you can't take away read permission, because the
742 source code has to be readable in order to be compiled and interpreted.
743 (That doesn't mean that a CGI script's source is readable by people on
744 the web, though--only by people with access to the filesystem.) So you
745 have to leave the permissions at the socially friendly 0755 level.
746 Some people regard this as a security problem. If your program does
748 insecure things and relies on people not knowing how to exploit those
749 insecurities, it is not secure. It is often possible for someone to
750 determine the insecure things and exploit them without viewing the
751 source. Security through obscurity, the name for hiding your bugs
752 instead of fixing them, is little security indeed.
753 You can try using encryption via source filters (Starting from Perl 5.8
755 the Filter::Simple and Filter::Util::Call modules are included in the
756 standard distribution), but any decent programmer will be able to
757 decrypt it. You can try using the byte code compiler and interpreter
758 described later in perlfaq3, but the curious might still be able to de-
759 compile it. You can try using the native-code compiler described later,
760 but crackers might be able to disassemble it. These pose varying
761 degrees of difficulty to people wanting to get at your code, but none
762 can definitively conceal it (true of every language, not just Perl).
763 It is very easy to recover the source of Perl programs. You simply feed
765 the program to the perl interpreter and use the modules in the B::
766 hierarchy. The B::Deparse module should be able to defeat most attempts
767 to hide source. Again, this is not unique to Perl.
768 If you're concerned about people profiting from your code, then the
770 bottom line is that nothing but a restrictive license will give you
771 legal security. License your software and pepper it with threatening
772 statements like "This is unpublished proprietary software of XYZ Corp.
773 Your access to it does not give you permission to use it blah blah
774 blah." We are not lawyers, of course, so you should see a lawyer if
775 you want to be sure your license's wording will stand up in court.
776 How can I compile my Perl program into byte code or C?
778 (contributed by brian d foy)
779 In general, you can't do this. There are some things that may work for
781 your situation though. People usually ask this question because they
782 want to distribute their works without giving away the source code, and
783 most solutions trade disk space for convenience. You probably won't
784 see much of a speed increase either, since most solutions simply bundle
785 a Perl interpreter in the final product (but see "How can I make my
786 Perl program run faster?").
787 The Perl Archive Toolkit ( <http://par.perl.org/> ) is Perl's analog to
789 Java's JAR. It's freely available and on CPAN (
790 <http://search.cpan.org/dist/PAR/> ).
791 There are also some commercial products that may work for you, although
793 you have to buy a license for them.
794 The Perl Dev Kit ( <http://www.activestate.com/Products/Perl_Dev_Kit/>
796 ) from ActiveState can "Turn your Perl programs into ready-to-run
797 executables for HP-UX, Linux, Solaris and Windows."
798 Perl2Exe ( <http://www.indigostar.com/perl2exe.htm> ) is a command line
800 program for converting perl scripts to executable files. It targets
801 both Windows and Unix platforms.
802 How can I get "#!perl" to work on [MS-DOS,NT,...]?
804 For OS/2 just use
805 extproc perl -S -your_switches
807 as the first line in "*.cmd" file ("-S" due to a bug in cmd.exe's
809 "extproc" handling). For DOS one should first invent a corresponding
810 batch file and codify it in "ALTERNATE_SHEBANG" (see the dosish.h file
811 in the source distribution for more information).
812 The Win95/NT installation, when using the ActiveState port of Perl,
814 will modify the Registry to associate the ".pl" extension with the perl
815 interpreter. If you install another port, perhaps even building your
816 own Win95/NT Perl from the standard sources by using a Windows port of
817 gcc (e.g., with cygwin or mingw32), then you'll have to modify the
818 Registry yourself. In addition to associating ".pl" with the
819 interpreter, NT people can use: "SET PATHEXT=%PATHEXT%;.PL" to let them
820 run the program "install-linux.pl" merely by typing "install-linux".
821 Under "Classic" MacOS, a perl program will have the appropriate Creator
823 and Type, so that double-clicking them will invoke the MacPerl
824 application. Under Mac OS X, clickable apps can be made from any "#!"
825 script using Wil Sanchez' DropScript utility:
826 <http://www.wsanchez.net/software/> .
827 IMPORTANT!: Whatever you do, PLEASE don't get frustrated, and just
829 throw the perl interpreter into your cgi-bin directory, in order to get
830 your programs working for a web server. This is an EXTREMELY big
831 security risk. Take the time to figure out how to do it correctly.
832 Can I write useful Perl programs on the command line?
834 Yes. Read perlrun for more information. Some examples follow. (These
835 assume standard Unix shell quoting rules.)
836 # sum first and last fields
838 perl -lane 'print $F[0] + $F[-1]' *
839 # identify text files
841 perl -le 'for(@ARGV) {print if -f && -T _}' *
842 # remove (most) comments from C program
844 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
845 # make file a month younger than today, defeating reaper daemons
847 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
848 # find first unused uid
850 perl -le '$i++ while getpwuid($i); print $i'
851 # display reasonable manpath
853 echo $PATH | perl -nl -072 -e '
854 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
855 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
857 Why don't Perl one-liners work on my DOS/Mac/VMS system?
859 The problem is usually that the command interpreters on those systems
860 have rather different ideas about quoting than the Unix shells under
861 which the one-liners were created. On some systems, you may have to
862 change single-quotes to double ones, which you must NOT do on Unix or
863 Plan9 systems. You might also have to change a single % to a %%.
864 For example:
866 # Unix (including Mac OS X)
868 perl -e 'print "Hello world\n"'
869 # DOS, etc.
871 perl -e "print \"Hello world\n\""
872 # Mac Classic
874 print "Hello world\n"
875 (then Run "Myscript" or Shift-Command-R)
876 # MPW
878 perl -e 'print "Hello world\n"'
879 # VMS
881 perl -e "print ""Hello world\n"""
882 The problem is that none of these examples are reliable: they depend on
884 the command interpreter. Under Unix, the first two often work. Under
885 DOS, it's entirely possible that neither works. If 4DOS was the command
886 shell, you'd probably have better luck like this:
887 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
889 Under the Mac, it depends which environment you are using. The MacPerl
891 shell, or MPW, is much like Unix shells in its support for several
892 quoting variants, except that it makes free use of the Mac's non-ASCII
893 characters as control characters.
894 Using qq(), q(), and qx(), instead of "double quotes", 'single quotes',
896 and `backticks`, may make one-liners easier to write.
897 There is no general solution to all of this. It is a mess.
899 [Some of this answer was contributed by Kenneth Albanowski.]
901 Where can I learn about CGI or Web programming in Perl?
903 For modules, get the CGI or LWP modules from CPAN. For textbooks, see
904 the two especially dedicated to web stuff in the question on books. For
905 problems and questions related to the web, like "Why do I get 500
906 Errors" or "Why doesn't it run from the browser right when it runs fine
907 on the command line", see the troubleshooting guides and references in
908 perlfaq9 or in the CGI MetaFAQ:
909 L<http://www.perl.org/CGI_MetaFAQ.html>
911 Looking in to Plack and modern Perl web frameworks is highly
913 recommended, though; web programming in Perl has evolved a long way
914 from the old days of simple CGI scripts.
915 Where can I learn about object-oriented Perl programming?
917 A good place to start is perltoot, and you can use perlobj, perlboot,
918 perltoot, perltooc, and perlbot for reference.
919 A good book on OO on Perl is the "Object-Oriented Perl" by Damian
921 Conway from Manning Publications, or "Intermediate Perl" by Randal
922 Schwartz, brian d foy, and Tom Phoenix from O'Reilly Media.
923 Where can I learn about linking C with Perl?
925 If you want to call C from Perl, start with perlxstut, moving on to
926 perlxs, xsubpp, and perlguts. If you want to call Perl from C, then
927 read perlembed, perlcall, and perlguts. Don't forget that you can learn
928 a lot from looking at how the authors of existing extension modules
929 wrote their code and solved their problems.
930 You might not need all the power of XS. The Inline::C module lets you
932 put C code directly in your Perl source. It handles all the magic to
933 make it work. You still have to learn at least some of the perl API but
934 you won't have to deal with the complexity of the XS support files.
935 I've read perlembed, perlguts, etc., but I can't embed perl in my C
937 program; what am I doing wrong?
938 Download the ExtUtils::Embed kit from CPAN and run `make test'. If the
939 tests pass, read the pods again and again and again. If they fail, see
940 perlbug and send a bug report with the output of "make test
941 TEST_VERBOSE=1" along with "perl -V".
942 When I tried to run my script, I got this message. What does it mean?
944 A complete list of Perl's error messages and warnings with explanatory
945 text can be found in perldiag. You can also use the splain program
946 (distributed with Perl) to explain the error messages:
947 perl program 2>diag.out
949 splain [-v] [-p] diag.out
950 or change your program to explain the messages for you:
952 use diagnostics;
954 or
956 use diagnostics -verbose;
958 What's MakeMaker?
960 (contributed by brian d foy)
961 The ExtUtils::MakeMaker module, better known simply as "MakeMaker",
963 turns a Perl script, typically called "Makefile.PL", into a Makefile.
964 The Unix tool "make" uses this file to manage dependencies and actions
965 to process and install a Perl distribution.
966
968 Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and other
969 authors as noted. All rights reserved.
970 This documentation is free; you can redistribute it and/or modify it
972 under the same terms as Perl itself.
973 Irrespective of its distribution, all code examples here are in the
975 public domain. You are permitted and encouraged to use this code and
976 any derivatives thereof in your own programs for fun or for profit as
977 you see fit. A simple comment in the code giving credit to the FAQ
978 would be courteous but is not required.
979perl v5.16.3 2013-03-04 PERLFAQ3(1)