


PERLFAQ3(1)      Perl Programmers Reference Guide     PERLFAQ3(1)


NAME
       perlfaq3 - Programming Tools

DESCRIPTION
       This section of the FAQ answers questions related to
       programmer tools and programming support.

   How do I do (anything)?
       Have you looked at CPAN (see perlfaq2)?  The chances are
       that someone has already written a module that can solve
       your problem.  Have you read the appropriate manpages?
       Here's a brief index:

               Basics          perldata, perlvar, perlsyn, perlop, perlsub
               Execution       perlrun, perldebug
               Functions       perlfunc
               Objects         perlref, perlmod, perlobj, perltie
               Data Structures perlref, perllol, perldsc
               Modules         perlmod, perlmodlib, perlsub
               Regexes         perlre, perlfunc, perlop, perllocale
               Moving to perl5 perltrap, perl
               Linking w/C     perlxstut, perlxs, perlcall, perlguts, perlembed
               Various         http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz
                               (not a man-page but still useful, a collection
                                of various essays on Perl techniques)

       A crude table of contents for the Perl manpage set is
       found in perltoc.

   How can I use Perl interactively?
       The typical approach uses the Perl debugger, described in
       the perldebug(1) manpage, on an "empty" program, like
       this:

           perl -de 42

       Now just type in any legal Perl code, and it will be
       immediately evaluated.  You can also examine the symbol
       table, get stack backtraces, check variable values, set
       breakpoints, and other operations typically found in
       symbolic debuggers.

   Is there a Perl shell?
       The psh (Perl sh) is currently at version 1.8. The Perl
       Shell is a shell that combines the interactive nature of a
       Unix shell with the power of Perl. The goal is a full
       featured shell that behaves as expected for normal shell
       activity and uses Perl syntax and functionality for
       control-flow statements and other things. You can get psh
       at http://sourceforge.net/projects/psh/ .

       Zoidberg is a similar project and provides a shell written
       in perl, configured in perl and operated in perl. It is
       intended as a login shell and development environment. It



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       can be found at
       http://pardus-larus.student.utwente.nl/~pardus/projects/zoidberg/
       or your local CPAN mirror.

       The Shell.pm module (distributed with Perl) makes Perl try
       commands which aren't part of the Perl language as shell
       commands.  perlsh from the source distribution is
       simplistic and uninteresting, but may still be what you
       want.

   How do I find which modules are installed on my system?
       From the command line, you can use the "cpan" command's
       "-l" switch:

               $ cpan -l

       You can also use "cpan"'s "-a" switch to create an
       autobundle file that "CPAN.pm" understands and cna use to
       re-install every module:

               $ cpan -a

       Inside a Perl program, you can use the ExtUtils::Installed
       module to show all installed distributions, although it
       can take awhile to do its magic.  The standard library
       which comes with Perl just shows up as "Perl" (although
       you can get those with Module::CoreList).

               use ExtUtils::Installed;

               my $inst    = ExtUtils::Installed->new();
               my @modules = $inst->modules();

       If you want a list of all of the Perl module filenames,
       you can use File::Find::Rule.

               use File::Find::Rule;

               my @files = File::Find::Rule->
                       extras({follow => 1})->
                       file()->
                       name( '*.pm' )->
                       in( @INC )
                       ;

       If you do not have that module, you can do the same thing
       with File::Find which is part of the standard library.

               use File::Find;
               my @files;

               find(
                   {
                       wanted => sub {



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                           push @files, $File::Find::fullname
                               if -f $File::Find::fullname && /\.pm$/
                       },
                       follow => 1,
                       follow_skip => 2,
                   },
                   @INC
               );

               print join "\n", @files;

       If you simply need to quickly check to see if a module is
       available, you can check for its documentation.  If you
       can read the documentation the module is most likely
       installed.  If you cannot read the documentation, the
       module might not have any (in rare cases).

               $ perldoc Module::Name

       You can also try to include the module in a one-liner to
       see if perl finds it.

               $ perl -MModule::Name -e1

   How do I debug my Perl programs?
       (contributed by brian d foy)

       Before you do anything else, you can help yourself by
       ensuring that you let Perl tell you about problem areas in
       your code. By turning on warnings and strictures, you can
       head off many problems before they get too big. You can
       find out more about these in strict and warnings.

               #!/usr/bin/perl
               use strict;
               use warnings;

       Beyond that, the simplest debugger is the "print"
       function. Use it to look at values as you run your
       program:

               print STDERR "The value is [$value]\n";

       The "Data::Dumper" module can pretty-print Perl data
       structures:

               use Data::Dumper qw( Dumper );
               print STDERR "The hash is " . Dumper( \%hash ) . "\n";

       Perl comes with an interactive debugger, which you can
       start with the "-d" switch. It's fully explained in
       perldebug.

       If you'd like a graphical user interface and you have Tk,



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       you can use "ptkdb". It's on CPAN and available for free.

       If you need something much more sophisticated and
       controllable, Leon Brocard's Devel::ebug (which you can
       call with the -D switch as -Debug) gives you the
       programmatic hooks into everything you need to write your
       own (without too much pain and suffering).

       You can also use a commercial debugger such as Affrus (Mac
       OS X), Komodo from Activestate (Windows and Mac OS X), or
       EPIC (most platforms).

   How do I profile my Perl programs?
       (contributed by brian d foy, updated Fri Jul 25 12:22:26
       PDT 2008)

       The "Devel" namespace has several modules which you can
       use to profile your Perl programs. The "Devel::DProf"
       module comes with Perl and you can invoke it with the "-d"
       switch:

               perl -d:DProf program.pl

       After running your program under "DProf", you'll get a
       tmon.out file with the profile data. To look at the data,
       you can turn it into a human-readable report with the
       "dprofpp" program that comes with "Devel::DProf".

               dprofpp

       You can also do the profiling and reporting in one step
       with the "-p" switch to <dprofpp>:

               dprofpp -p program.pl

       The "Devel::NYTProf" (New York Times Profiler) does both
       statement and subroutine profiling. It's available from
       CPAN and you also invoke it with the "-d" switch:

               perl -d:NYTProf some_perl.pl

       Like "DProf", it creates a database of the profile
       information that you can turn into reports. The
       "nytprofhtml" command turns the data into an HTML report
       similar to the "Devel::Cover" report:

               nytprofhtml

       CPAN has several other profilers that you can invoke in
       the same fashion. You might also be interested in using
       the "Benchmark" to measure and compare code snippets.

       You can read more about profiling in Programming Perl,
       chapter 20, or Mastering Perl, chapter 5.



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       perldebguts documents creating a custom debugger if you
       need to create a special sort of profiler. brian d foy
       describes the process in The Perl Journal, "Creating a
       Perl Debugger", http://www.ddj.com/184404522 , and
       "Profiling in Perl" http://www.ddj.com/184404580 .

       Perl.com has two interesting articles on profiling:
       "Profiling Perl", by Simon Cozens,
       http://www.perl.com/lpt/a/850 and "Debugging and Profiling
       mod_perl Applications", by Frank Wiles,
       http://www.perl.com/pub/a/2006/02/09/debug_mod_perl.html .

       Randal L. Schwartz writes about profiling in "Speeding up
       Your Perl Programs" for Unix Review,
       http://www.stonehenge.com/merlyn/UnixReview/col49.html ,
       and "Profiling in Template Toolkit via Overriding" for
       Linux Magazine,
       http://www.stonehenge.com/merlyn/LinuxMag/col75.html .

   How do I cross-reference my Perl programs?
       The B::Xref module can be used to generate cross-reference
       reports for Perl programs.

           perl -MO=Xref[,OPTIONS] scriptname.plx

   Is there a pretty-printer (formatter) for Perl?
       Perltidy is a Perl script which indents and reformats Perl
       scripts to make them easier to read by trying to follow
       the rules of the perlstyle. If you write Perl scripts, or
       spend much time reading them, you will probably find it
       useful.  It is available at
       http://perltidy.sourceforge.net

       Of course, if you simply follow the guidelines in
       perlstyle, you shouldn't need to reformat.  The habit of
       formatting your code as you write it will help prevent
       bugs.  Your editor can and should help you with this.  The
       perl-mode or newer cperl-mode for emacs can provide
       remarkable amounts of help with most (but not all) code,
       and even less programmable editors can provide significant
       assistance.  Tom Christiansen and many other VI users
       swear by the following settings in vi and its clones:

           set ai sw=4
           map! ^O {^M}^[O^T

       Put that in your .exrc file (replacing the caret
       characters with control characters) and away you go.  In
       insert mode, ^T is for indenting, ^D is for undenting, and
       ^O is for blockdenting--as it were.  A more complete
       example, with comments, can be found at
       http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz

       The a2ps



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       http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz
       does lots of things related to generating nicely printed
       output of documents.

   Is there a ctags for Perl?
       (contributed by brian d foy)

       Ctags uses an index to quickly find things in source code,
       and many popular editors support ctags for several
       different languages, including Perl.

       Exuberent ctags supports Perl:
       http://ctags.sourceforge.net/

       You might also try pltags: http://www.mscha.com/pltags.zip

   Is there an IDE or Windows Perl Editor?
       Perl programs are just plain text, so any editor will do.

       If you're on Unix, you already have an IDE--Unix itself.
       The UNIX philosophy is the philosophy of several small
       tools that each do one thing and do it well.  It's like a
       carpenter's toolbox.

       If you want an IDE, check the following (in alphabetical
       order, not order of preference):

       Eclipse
           http://e-p-i-c.sf.net/

           The Eclipse Perl Integration Project integrates Perl
           editing/debugging with Eclipse.

       Enginsite
           http://www.enginsite.com/

           Perl Editor by EngInSite is a complete integrated
           development environment (IDE) for creating, testing,
           and  debugging  Perl scripts; the tool runs on Windows
           9x/NT/2000/XP or later.

       Komodo
           http://www.ActiveState.com/Products/Komodo/

           ActiveState's cross-platform (as of October 2004,
           that's Windows, Linux, and Solaris), multi-language
           IDE has Perl support, including a regular expression
           debugger and remote debugging.

       Open Perl IDE
           http://open-perl-ide.sourceforge.net/

           Open Perl IDE is an integrated development environment
           for writing and debugging Perl scripts with



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           ActiveState's ActivePerl distribution under Windows
           95/98/NT/2000.

       OptiPerl
           http://www.optiperl.com/

           OptiPerl is a Windows IDE with simulated CGI
           environment, including debugger and syntax
           highlighting editor.

       Padre
           http://padre.perlide.org/

           Padre is cross-platform IDE for Perl written in Perl
           using the the wxWidgets to provide a native look and
           feel. It's open source under the Artistic License.

       PerlBuilder
           http://www.solutionsoft.com/perl.htm

           PerlBuilder is an integrated development environment
           for Windows that supports Perl development.

       visiPerl+
           http://helpconsulting.net/visiperl/

           From Help Consulting, for Windows.

       Visual Perl
           http://www.activestate.com/Products/Visual_Perl/

           Visual Perl is a Visual Studio.NET plug-in from
           ActiveState.

       Zeus
           http://www.zeusedit.com/lookmain.html

           Zeus for Window is another Win32 multi-language
           editor/IDE that comes with support for Perl:

       For editors: if you're on Unix you probably have vi or a
       vi clone already, and possibly an emacs too, so you may
       not need to download anything. In any emacs the cperl-mode
       (M-x cperl-mode) gives you perhaps the best available Perl
       editing mode in any editor.

       If you are using Windows, you can use any editor that lets
       you work with plain text, such as NotePad or WordPad.
       Word processors, such as Microsoft Word or WordPerfect,
       typically do not work since they insert all sorts of
       behind-the-scenes information, although some allow you to
       save files as "Text Only". You can also download text
       editors designed specifically for programming, such as
       Textpad ( http://www.textpad.com/ ) and UltraEdit (



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       http://www.ultraedit.com/ ), among others.

       If you are using MacOS, the same concerns apply.  MacPerl
       (for Classic environments) comes with a simple editor.
       Popular external editors are BBEdit (
       http://www.bbedit.com/ ) or Alpha (
       http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X
       users can use Unix editors as well.

       GNU Emacs
           http://www.gnu.org/software/emacs/windows/ntemacs.html

       MicroEMACS
           http://www.microemacs.de/

       XEmacs
           http://www.xemacs.org/Download/index.html

       Jed http://space.mit.edu/~davis/jed/

       or a vi clone such as

       Elvis
           ftp://ftp.cs.pdx.edu/pub/elvis/
           http://www.fh-wedel.de/elvis/

       Vile
           http://dickey.his.com/vile/vile.html

       Vim http://www.vim.org/

       For vi lovers in general, Windows or elsewhere:

               http://www.thomer.com/thomer/vi/vi.html

       nvi ( http://www.bostic.com/vi/ , available from CPAN in
       src/misc/) is yet another vi clone, unfortunately not
       available for Windows, but in UNIX platforms you might be
       interested in trying it out, firstly because strictly
       speaking it is not a vi clone, it is the real vi, or the
       new incarnation of it, and secondly because you can embed
       Perl inside it to use Perl as the scripting language.  nvi
       is not alone in this, though: at least also vim and vile
       offer an embedded Perl.

       The following are Win32 multilanguage editor/IDEs that
       support Perl:

       Codewright
           http://www.borland.com/codewright/

       MultiEdit
           http://www.MultiEdit.com/




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       SlickEdit
           http://www.slickedit.com/

       ConTEXT
           http://www.contexteditor.org/

       There is also a toyedit Text widget based editor written
       in Perl that is distributed with the Tk module on CPAN.
       The ptkdb ( http://ptkdb.sourceforge.net/ ) is a Perl/tk
       based debugger that acts as a development environment of
       sorts.  Perl Composer (
       http://perlcomposer.sourceforge.net/ ) is an IDE for
       Perl/Tk GUI creation.

       In addition to an editor/IDE you might be interested in a
       more powerful shell environment for Win32.  Your options
       include

       Bash
           from the Cygwin package (
           http://sources.redhat.com/cygwin/ )

       Ksh from the MKS Toolkit ( http://www.mkssoftware.com/ ),
           or the Bourne shell of the U/WIN environment (
           http://www.research.att.com/sw/tools/uwin/ )

       Tcsh
           ftp://ftp.astron.com/pub/tcsh/ , see also
           http://www.primate.wisc.edu/software/csh-tcsh-book/

       Zsh http://www.zsh.org/

       MKS and U/WIN are commercial (U/WIN is free for
       educational and research purposes), Cygwin is covered by
       the GNU General Public License (but that shouldn't matter
       for Perl use).  The Cygwin, MKS, and U/WIN all contain (in
       addition to the shells) a comprehensive set of standard
       UNIX toolkit utilities.

       If you're transferring text files between Unix and Windows
       using FTP be sure to transfer them in ASCII mode so the
       ends of lines are appropriately converted.

       On Mac OS the MacPerl Application comes with a simple 32k
       text editor that behaves like a rudimentary IDE.  In
       contrast to the MacPerl Application the MPW Perl tool can
       make use of the MPW Shell itself as an editor (with no 32k
       limit).

       Affrus
           is a full Perl development environment with full
           debugger support ( http://www.latenightsw.com ).





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       Alpha
           is an editor, written and extensible in Tcl, that
           nonetheless has built in support for several popular
           markup and programming languages including Perl and
           HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).

       BBEdit and BBEdit Lite
           are text editors for Mac OS that have a Perl
           sensitivity mode ( http://web.barebones.com/ ).

   Where can I get Perl macros for vi?
       For a complete version of Tom Christiansen's vi
       configuration file, see
       http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz
       , the standard benchmark file for vi emulators.  The file
       runs best with nvi, the current version of vi out of
       Berkeley, which incidentally can be built with an embedded
       Perl interpreter--see http://www.cpan.org/src/misc/ .

   Where can I get perl-mode for emacs?
       Since Emacs version 19 patchlevel 22 or so, there have
       been both a perl-mode.el and support for the Perl debugger
       built in.  These should come with the standard Emacs 19
       distribution.

       In the Perl source directory, you'll find a directory
       called "emacs", which contains a cperl-mode that color-
       codes keywords, provides context-sensitive help, and other
       nifty things.

       Note that the perl-mode of emacs will have fits with
       "main'foo" (single quote), and mess up the indentation and
       highlighting.  You are probably using "main::foo" in new
       Perl code anyway, so this shouldn't be an issue.

   How can I use curses with Perl?
       The Curses module from CPAN provides a dynamically
       loadable object module interface to a curses library.  A
       small demo can be found at the directory
       http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz
       ; this program repeats a command and updates the screen as
       needed, rendering rep ps axu similar to top.

   How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
       (contributed by Ben Morrow)

       There are a number of modules which let you write GUIs in
       Perl. Most GUI toolkits have a perl interface: an
       incomplete list follows.

       Tk  This works under Unix and Windows, and the current
           version doesn't look half as bad under Windows as it
           used to. Some of the gui elements still don't 'feel'
           quite right, though. The interface is very natural and



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           'perlish', making it easy to use in small scripts that
           just need a simple gui. It hasn't been updated in a
           while.

       Wx  This is a Perl binding for the cross-platform
           wxWidgets toolkit ( http://www.wxwidgets.org ). It
           works under Unix, Win32 and Mac OS X, using native
           widgets (Gtk under Unix). The interface follows the
           C++ interface closely, but the documentation is a
           little sparse for someone who doesn't know the
           library, mostly just referring you to the C++
           documentation.

       Gtk and Gtk2
           These are Perl bindings for the Gtk toolkit (
           http://www.gtk.org ). The interface changed
           significantly between versions 1 and 2 so they have
           separate Perl modules. It runs under Unix, Win32 and
           Mac OS X (currently it requires an X server on Mac OS,
           but a 'native' port is underway), and the widgets look
           the same on every plaform: i.e., they don't match the
           native widgets. As with Wx, the Perl bindings follow
           the C API closely, and the documentation requires you
           to read the C documentation to understand it.

       Win32::GUI
           This provides access to most of the Win32 GUI widgets
           from Perl.  Obviously, it only runs under Win32, and
           uses native widgets. The Perl interface doesn't really
           follow the C interface: it's been made more Perlish,
           and the documentation is pretty good. More advanced
           stuff may require familiarity with the C Win32 APIs,
           or reference to MSDN.

       CamelBones
           CamelBones ( http://camelbones.sourceforge.net ) is a
           Perl interface to Mac OS X's Cocoa GUI toolkit, and as
           such can be used to produce native GUIs on Mac OS X.
           It's not on CPAN, as it requires frameworks that
           CPAN.pm doesn't know how to install, but installation
           is via the standard OSX package installer. The Perl
           API is, again, very close to the ObjC API it's
           wrapping, and the documentation just tells you how to
           translate from one to the other.

       Qt  There is a Perl interface to TrollTech's Qt toolkit,
           but it does not appear to be maintained.

       Athena
           Sx is an interface to the Athena widget set which
           comes with X, but again it appears not to be much used
           nowadays.





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   How can I make my Perl program run faster?
       The best way to do this is to come up with a better
       algorithm.  This can often make a dramatic difference.
       Jon Bentley's book Programming Pearls (that's not a
       misspelling!)  has some good tips on optimization, too.
       Advice on benchmarking boils down to: benchmark and
       profile to make sure you're optimizing the right part,
       look for better algorithms instead of microtuning your
       code, and when all else fails consider just buying faster
       hardware.  You will probably want to read the answer to
       the earlier question "How do I profile my Perl programs?"
       if you haven't done so already.

       A different approach is to autoload seldom-used Perl code.
       See the AutoSplit and AutoLoader modules in the standard
       distribution for that.  Or you could locate the bottleneck
       and think about writing just that part in C, the way we
       used to take bottlenecks in C code and write them in
       assembler.  Similar to rewriting in C, modules that have
       critical sections can be written in C (for instance, the
       PDL module from CPAN).

       If you're currently linking your perl executable to a
       shared libc.so, you can often gain a 10-25% performance
       benefit by rebuilding it to link with a static libc.a
       instead.  This will make a bigger perl executable, but
       your Perl programs (and programmers) may thank you for it.
       See the INSTALL file in the source distribution for more
       information.

       The undump program was an ancient attempt to speed up Perl
       program by storing the already-compiled form to disk.
       This is no longer a viable option, as it only worked on a
       few architectures, and wasn't a good solution anyway.

   How can I make my Perl program take less memory?
       When it comes to time-space tradeoffs, Perl nearly always
       prefers to throw memory at a problem.  Scalars in Perl use
       more memory than strings in C, arrays take more than that,
       and hashes use even more.  While there's still a lot to be
       done, recent releases have been addressing these issues.
       For example, as of 5.004, duplicate hash keys are shared
       amongst all hashes using them, so require no reallocation.

       In some cases, using substr() or vec() to simulate arrays
       can be highly beneficial.  For example, an array of a
       thousand booleans will take at least 20,000 bytes of
       space, but it can be turned into one 125-byte bit
       vector--a considerable memory savings.  The standard
       Tie::SubstrHash module can also help for certain types of
       data structure.  If you're working with specialist data
       structures (matrices, for instance) modules that implement
       these in C may use less memory than equivalent Perl
       modules.



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       Another thing to try is learning whether your Perl was
       compiled with the system malloc or with Perl's builtin
       malloc.  Whichever one it is, try using the other one and
       see whether this makes a difference.  Information about
       malloc is in the INSTALL file in the source distribution.
       You can find out whether you are using perl's malloc by
       typing "perl -V:usemymalloc".

       Of course, the best way to save memory is to not do
       anything to waste it in the first place. Good programming
       practices can go a long way toward this:

       o   Don't slurp!

           Don't read an entire file into memory if you can
           process it line by line. Or more concretely, use a
           loop like this:

                   #
                   # Good Idea
                   #
                   while (<FILE>) {
                      # ...
                   }

           instead of this:

                   #
                   # Bad Idea
                   #
                   @data = <FILE>;
                   foreach (@data) {
                       # ...
                   }

           When the files you're processing are small, it doesn't
           much matter which way you do it, but it makes a huge
           difference when they start getting larger.

       o   Use map and grep selectively

           Remember that both map and grep expect a LIST
           argument, so doing this:

                   @wanted = grep {/pattern/} <FILE>;

           will cause the entire file to be slurped. For large
           files, it's better to loop:

                   while (<FILE>) {
                           push(@wanted, $_) if /pattern/;
                   }

       o   Avoid unnecessary quotes and stringification



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           Don't quote large strings unless absolutely necessary:

                   my $copy = "$large_string";

           makes 2 copies of $large_string (one for $copy and
           another for the quotes), whereas

                   my $copy = $large_string;

           only makes one copy.

           Ditto for stringifying large arrays:

                   {
                           local $, = "\n";
                           print @big_array;
                   }

           is much more memory-efficient than either

                   print join "\n", @big_array;

           or

                   {
                           local $" = "\n";
                           print "@big_array";
                   }

       o   Pass by reference

           Pass arrays and hashes by reference, not by value. For
           one thing, it's the only way to pass multiple lists or
           hashes (or both) in a single call/return. It also
           avoids creating a copy of all the contents. This
           requires some judgement, however, because any changes
           will be propagated back to the original data. If you
           really want to mangle (er, modify) a copy, you'll have
           to sacrifice the memory needed to make one.

       o   Tie large variables to disk.

           For "big" data stores (i.e. ones that exceed available
           memory) consider using one of the DB modules to store
           it on disk instead of in RAM. This will incur a
           penalty in access time, but that's probably better
           than causing your hard disk to thrash due to massive
           swapping.

   Is it safe to return a reference to local or lexical data?
       Yes. Perl's garbage collection system takes care of this
       so everything works out right.





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           sub makeone {
               my @a = ( 1 .. 10 );
               return \@a;
           }

           for ( 1 .. 10 ) {
               push @many, makeone();
           }

           print $many[4][5], "\n";

           print "@many\n";

   How can I free an array or hash so my program shrinks?
       (contributed by Michael Carman)

       You usually can't. Memory allocated to lexicals (i.e. my()
       variables) cannot be reclaimed or reused even if they go
       out of scope. It is reserved in case the variables come
       back into scope. Memory allocated to global variables can
       be reused (within your program) by using undef() and/or
       delete().

       On most operating systems, memory allocated to a program
       can never be returned to the system. That's why long-
       running programs sometimes re- exec themselves. Some
       operating systems (notably, systems that use mmap(2) for
       allocating large chunks of memory) can reclaim memory that
       is no longer used, but on such systems, perl must be
       configured and compiled to use the OS's malloc, not
       perl's.

       In general, memory allocation and de-allocation isn't
       something you can or should be worrying about much in
       Perl.

       See also "How can I make my Perl program take less
       memory?"

   How can I make my CGI script more efficient?
       Beyond the normal measures described to make general Perl
       programs faster or smaller, a CGI program has additional
       issues.  It may be run several times per second.  Given
       that each time it runs it will need to be re-compiled and
       will often allocate a megabyte or more of system memory,
       this can be a killer.  Compiling into C isn't going to
       help you because the process start-up overhead is where
       the bottleneck is.

       There are two popular ways to avoid this overhead.  One
       solution involves running the Apache HTTP server
       (available from http://www.apache.org/ ) with either of
       the mod_perl or mod_fastcgi plugin modules.




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       With mod_perl and the Apache::Registry module (distributed
       with mod_perl), httpd will run with an embedded Perl
       interpreter which pre-compiles your script and then
       executes it within the same address space without forking.
       The Apache extension also gives Perl access to the
       internal server API, so modules written in Perl can do
       just about anything a module written in C can.  For more
       on mod_perl, see http://perl.apache.org/

       With the FCGI module (from CPAN) and the mod_fastcgi
       module (available from http://www.fastcgi.com/ ) each of
       your Perl programs becomes a permanent CGI daemon process.

       Both of these solutions can have far-reaching effects on
       your system and on the way you write your CGI programs, so
       investigate them with care.

       See
       http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/
       .

   How can I hide the source for my Perl program?
       Delete it. :-) Seriously, there are a number of (mostly
       unsatisfactory) solutions with varying levels of
       "security".

       First of all, however, you can't take away read
       permission, because the source code has to be readable in
       order to be compiled and interpreted.  (That doesn't mean
       that a CGI script's source is readable by people on the
       web, though--only by people with access to the
       filesystem.)  So you have to leave the permissions at the
       socially friendly 0755 level.

       Some people regard this as a security problem.  If your
       program does insecure things and relies on people not
       knowing how to exploit those insecurities, it is not
       secure.  It is often possible for someone to determine the
       insecure things and exploit them without viewing the
       source.  Security through obscurity, the name for hiding
       your bugs instead of fixing them, is little security
       indeed.

       You can try using encryption via source filters (Starting
       from Perl 5.8 the Filter::Simple and Filter::Util::Call
       modules are included in the standard distribution), but
       any decent programmer will be able to decrypt it.  You can
       try using the byte code compiler and interpreter described
       later in perlfaq3, but the curious might still be able to
       de-compile it. You can try using the native-code compiler
       described later, but crackers might be able to disassemble
       it.  These pose varying degrees of difficulty to people
       wanting to get at your code, but none can definitively
       conceal it (true of every language, not just Perl).



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       It is very easy to recover the source of Perl programs.
       You simply feed the program to the perl interpreter and
       use the modules in the B:: hierarchy.  The B::Deparse
       module should be able to defeat most attempts to hide
       source.  Again, this is not unique to Perl.

       If you're concerned about people profiting from your code,
       then the bottom line is that nothing but a restrictive
       license will give you legal security.  License your
       software and pepper it with threatening statements like
       "This is unpublished proprietary software of XYZ Corp.
       Your access to it does not give you permission to use it
       blah blah blah."  We are not lawyers, of course, so you
       should see a lawyer if you want to be sure your license's
       wording will stand up in court.

   How can I compile my Perl program into byte code or C?
       (contributed by brian d foy)

       In general, you can't do this.  There are some things that
       may work for your situation though.  People usually ask
       this question because they want to distribute their works
       without giving away the source code, and most solutions
       trade disk space for convenience.  You probably won't see
       much of a speed increase either, since most solutions
       simply bundle a Perl interpreter in the final product (but
       see "How can I make my Perl program run faster?").

       The Perl Archive Toolkit ( http://par.perl.org/ ) is
       Perl's analog to Java's JAR.  It's freely available and on
       CPAN ( http://search.cpan.org/dist/PAR/ ).

       There are also some commercial products that may work for
       you, although you have to buy a license for them.

       The Perl Dev Kit (
       http://www.activestate.com/Products/Perl_Dev_Kit/ ) from
       ActiveState can "Turn your Perl programs into ready-to-run
       executables for HP-UX, Linux, Solaris and Windows."

       Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a
       command line program for converting perl scripts to
       executable files.  It targets both Windows and unix
       platforms.

   How can I get "#!perl" to work on [MS-DOS,NT,...]?
       For OS/2 just use

           extproc perl -S -your_switches

       as the first line in "*.cmd" file ("-S" due to a bug in
       cmd.exe's "extproc" handling).  For DOS one should first
       invent a corresponding batch file and codify it in
       "ALTERNATE_SHEBANG" (see the dosish.h file in the source



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       distribution for more information).

       The Win95/NT installation, when using the ActiveState port
       of Perl, will modify the Registry to associate the ".pl"
       extension with the perl interpreter.  If you install
       another port, perhaps even building your own Win95/NT Perl
       from the standard sources by using a Windows port of gcc
       (e.g., with cygwin or mingw32), then you'll have to modify
       the Registry yourself.  In addition to associating ".pl"
       with the interpreter, NT people can use: "SET
       PATHEXT=%PATHEXT%;.PL" to let them run the program
       "install-linux.pl" merely by typing "install-linux".

       Under "Classic" MacOS, a perl program will have the
       appropriate Creator and Type, so that double-clicking them
       will invoke the MacPerl application.  Under Mac OS X,
       clickable apps can be made from any "#!" script using Wil
       Sanchez' DropScript utility:
       http://www.wsanchez.net/software/ .

       IMPORTANT!: Whatever you do, PLEASE don't get frustrated,
       and just throw the perl interpreter into your cgi-bin
       directory, in order to get your programs working for a web
       server.  This is an EXTREMELY big security risk.  Take the
       time to figure out how to do it correctly.

   Can I write useful Perl programs on the command line?
       Yes.  Read perlrun for more information.  Some examples
       follow.  (These assume standard Unix shell quoting rules.)

           # sum first and last fields
           perl -lane 'print $F[0] + $F[-1]' *

           # identify text files
           perl -le 'for(@ARGV) {print if -f && -T _}' *

           # remove (most) comments from C program
           perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c

           # make file a month younger than today, defeating reaper daemons
           perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *

           # find first unused uid
           perl -le '$i++ while getpwuid($i); print $i'

           # display reasonable manpath
           echo $PATH | perl -nl -072 -e '
               s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'

       OK, the last one was actually an Obfuscated Perl Contest
       entry. :-)

   Why don't Perl one-liners work on my DOS/Mac/VMS system?
       The problem is usually that the command interpreters on



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       those systems have rather different ideas about quoting
       than the Unix shells under which the one-liners were
       created.  On some systems, you may have to change single-
       quotes to double ones, which you must NOT do on Unix or
       Plan9 systems.  You might also have to change a single %
       to a %%.

       For example:

           # Unix (including Mac OS X)
           perl -e 'print "Hello world\n"'

           # DOS, etc.
           perl -e "print \"Hello world\n\""

           # Mac Classic
           print "Hello world\n"
            (then Run "Myscript" or Shift-Command-R)

           # MPW
           perl -e 'print "Hello world\n"'

           # VMS
           perl -e "print ""Hello world\n"""

       The problem is that none of these examples are reliable:
       they depend on the command interpreter.  Under Unix, the
       first two often work. Under DOS, it's entirely possible
       that neither works.  If 4DOS was the command shell, you'd
       probably have better luck like this:

         perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""

       Under the Mac, it depends which environment you are using.
       The MacPerl shell, or MPW, is much like Unix shells in its
       support for several quoting variants, except that it makes
       free use of the Mac's non-ASCII characters as control
       characters.

       Using qq(), q(), and qx(), instead of "double quotes",
       'single quotes', and `backticks`, may make one-liners
       easier to write.

       There is no general solution to all of this.  It is a
       mess.

       [Some of this answer was contributed by Kenneth
       Albanowski.]

   Where can I learn about CGI or Web programming in Perl?
       For modules, get the CGI or LWP modules from CPAN.  For
       textbooks, see the two especially dedicated to web stuff
       in the question on books.  For problems and questions
       related to the web, like "Why do I get 500 Errors" or "Why



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       doesn't it run from the browser right when it runs fine on
       the command line", see the troubleshooting guides and
       references in perlfaq9 or in the CGI MetaFAQ:

               http://www.perl.org/CGI_MetaFAQ.html

   Where can I learn about object-oriented Perl programming?
       A good place to start is perltoot, and you can use
       perlobj, perlboot, perltoot, perltooc, and perlbot for
       reference.

       A good book on OO on Perl is the "Object-Oriented Perl" by
       Damian Conway from Manning Publications, or "Intermediate
       Perl" by Randal Schwartz, brian d foy, and Tom Phoenix
       from O'Reilly Media.

   Where can I learn about linking C with Perl?
       If you want to call C from Perl, start with perlxstut,
       moving on to perlxs, xsubpp, and perlguts.  If you want to
       call Perl from C, then read perlembed, perlcall, and
       perlguts.  Don't forget that you can learn a lot from
       looking at how the authors of existing extension modules
       wrote their code and solved their problems.

       You might not need all the power of XS. The Inline::C
       module lets you put C code directly in your Perl source.
       It handles all the magic to make it work. You still have
       to learn at least some of the perl API but you won't have
       to deal with the complexity of the XS support files.

   I've read perlembed, perlguts, etc., but I can't embed perl in
       my C program; what am I doing wrong?
       Download the ExtUtils::Embed kit from CPAN and run `make
       test'.  If the tests pass, read the pods again and again
       and again.  If they fail, see perlbug and send a bug
       report with the output of "make test TEST_VERBOSE=1" along
       with "perl -V".

   When I tried to run my script, I got this message. What does
       it mean?
       A complete list of Perl's error messages and warnings with
       explanatory text can be found in perldiag. You can also
       use the splain program (distributed with Perl) to explain
       the error messages:

           perl program 2>diag.out
           splain [-v] [-p] diag.out

       or change your program to explain the messages for you:

           use diagnostics;

       or




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           use diagnostics -verbose;

   What's MakeMaker?
       (contributed by brian d foy)

       The "ExtUtils::MakeMaker" module, better known simply as
       "MakeMaker", turns a Perl script, typically called
       "Makefile.PL", into a Makefile.  The unix tool "make" uses
       this file to manage dependencies and actions to process
       and install a Perl distribution.

REVISION
       Revision: $Revision: 1.11 $

       Date: $Date: 2009/10/12 18:24:47 $

       See perlfaq for source control details and availability.

AUTHOR AND COPYRIGHT
       Copyright (c) 1997-2009 Tom Christiansen, Nathan
       Torkington, and other authors as noted. All rights
       reserved.

       This documentation is free; you can redistribute it and/or
       modify it under the same terms as Perl itself.

       Irrespective of its distribution, all code examples here
       are in the public domain.  You are permitted and
       encouraged to use this code and any derivatives thereof in
       your own programs for fun or for profit as you see fit.  A
       simple comment in the code giving credit to the FAQ would
       be courteous but is not required.

























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