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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
        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 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})->
                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;

                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 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, 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.


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:


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", 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 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):



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 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 95/98/NT/2000.



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



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 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 ActiveState.



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 te