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perlfaq3 (1)


perlfaq3 - Programming Tools


Please see following description for synopsis


Perl Programmers Reference Guide                      PERLFAQ3(1)

     perlfaq3 - Programming Tools

     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
                             (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 .

     "Zoidberg" is a similar project and provides a shell written
     in perl, configured in perl and operated in perl. It is

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     intended as a login shell and development environment. It
     can be found at
     or your local CPAN mirror.

     The "" 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

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

             $ cpan -l

     You can also use "cpan"'s "-a" switch to create an
     autobundle file that "" understands and can 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})->
                     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;

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                     wanted => sub {
                         push @files, $File::Find::fullname
                             if -f $File::Find::fullname && /\.pm$/
                     follow => 1,
                     follow_skip => 2,

             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.

             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

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

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     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",
     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

     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

     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".


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

             dprofpp -p

     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

     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:


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     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.

     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", , and "Profiling in Perl" . has two interesting articles on profiling:
     "Profiling Perl", by Simon Cozens, and "Debugging and Profiling
     mod_perl Applications", by Frank Wiles, .

     Randal L. Schwartz writes about profiling in "Speeding up
     Your Perl Programs" for Unix Review, , and
     "Profiling in Template Toolkit via Overriding" for Linux
     Magazine, .

  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 .

     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

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     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

     The a2ps
     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:

     You might also try pltags:

  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):


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


         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.


         ActiveState's cross-platform (as of October 2004, that's

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         Windows, Linux, and Solaris), multi-language IDE has
         Perl support, including a regular expression debugger
         and remote debugging.


     Open Perl IDE

         Open Perl IDE is an integrated development environment
         for writing and debugging Perl scripts with
         ActiveState's ActivePerl distribution under Windows


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


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


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


         From Help Consulting, for Windows.

     Visual Perl

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


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

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     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 ( ) and UltraEdit ( ), 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 (
     ) or Alpha ( ).
     MacOS X users can use Unix editors as well.

     GNU Emacs




     or a vi clone such as




     For vi lovers in general, Windows or elsewhere:


     nvi ( , 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

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     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:





     There is also a toyedit Text widget based editor written in
     Perl that is distributed with the Tk module on CPAN.  The
     ptkdb ( ) is a Perl/tk based
     debugger that acts as a development environment of sorts.
     Perl Composer ( ) 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

         from the Cygwin package ( )

     Ksh from the MKS Toolkit ( ), or
         the Bourne shell of the U/WIN environment ( )

     Tcsh , see also


     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

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     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

         is a full Perl development environment with full
         debugger support ( ).

         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
         ( ).

     BBEdit and BBEdit Lite
         are text editors for Mac OS that have a Perl sensitivity
         mode ( ).

  Where can I get Perl macros for vi?
     For a complete version of Tom Christiansen's vi
     configuration file, see
     , 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 .

  Where can I get perl-mode or cperl-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

     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.

     For CPerlMode, see

  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

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

     Wx  This is a Perl binding for the cross-platform wxWidgets
         toolkit ( ). 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 ( ). 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.

         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 ( ) 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

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         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.

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

  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, 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,

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     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.

     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

                 # 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

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         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

         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;


                 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

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         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.

         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

     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.

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     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 ) with either of the mod_perl or
     mod_fastcgi plugin modules.

     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,

     With the FCGI module (from CPAN) and the mod_fastcgi module
     (available from ) 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.


  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

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     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).

     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 ( ) is Perl's
     analog to Java's JAR.  It's freely available and on CPAN ( ).

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

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     The Perl Dev Kit ( ) from
     ActiveState can "Turn your Perl programs into ready-to-run
     executables for HP-UX, Linux, Solaris and Windows."

     Perl2Exe ( ) is a
     command line program for converting perl scripts to
     executable files.  It targets both Windows and Unix

  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
     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 "" 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: .

     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]' *

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         # 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 '

     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
     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:

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       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

     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 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:


  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?

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Perl Programmers Reference Guide                      PERLFAQ3(1)

     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

  When I tried to run my script, I got this message. What does it
     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;


         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.

     Copyright (c) 1997-2010 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.

     See attributes(5) for descriptions of the following

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Perl Programmers Reference Guide                      PERLFAQ3(1)

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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