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Module::ScanDeps - Recursively scan Perl code for dependencies


Via the command-line program

    % *.pm          # Print PREREQ_PM section for *.pm
    % -e "use utf8" # Read script from command line
    % -B *.pm       # Include core modules
    % -V *.pm       # Show autoload/shared/data files

Used in a program;

    use Module::ScanDeps;

    # standard usage
    my $hash_ref = scan_deps(
        files   => [ '', '' ],
        recurse => 1,

    # shorthand; assume recurse == 1
    my $hash_ref = scan_deps( '', '' );

    # App::Packer::Frontend compatible interface
    # see App::Packer::Frontend for the structure returned by get_files
    my $scan = Module::ScanDeps->new;
    $scan->set_file( '' );
    $scan->set_options( add_modules => [ 'Test::More' ] );
    my $files = $scan->get_files;


This module scans potential modules used by perl programs, and returns a hash reference; its keys are the module names as appears in %INC (e.g. Test/; the values are hash references with this structure:

        file    => '/usr/local/lib/perl5/5.8.0/Test/',
        key     => 'Test/',
        type    => 'module',    # or 'autoload', 'data', 'shared'
        used_by => [ 'Test/', ... ],
        uses    => [ 'Test/', ... ],

One function, scan_deps, is exported by default. Other functions such as (scan_line, scan_chunk, add_deps, path_to_inc_name) are exported upon request.

Users of App::Packer may also use this module as the dependency-checking frontend, by tweaking their like below:

    use Module::ScanDeps;
    my $packer = App::Packer->new( frontend => 'Module::ScanDeps' );

Please see App::Packer::Frontend for detailed explanation on the structure returned by get_files.


    $rv_ref = scan_deps(
        files      => \@files,     recurse => $recurse,
        rv         => \%rv,        skip    => \%skip,
        compile    => $compile,    execute => $execute,
    $rv_ref = scan_deps(@files); # shorthand, with recurse => 1

This function scans each file in @files, registering their dependencies into %rv, and returns a reference to the updated %rv. The meaning of keys and values are explained above.

If $recurse is true, scan_deps will call itself recursively, to perform a breadth-first search on text files (as defined by the -T operator) found in %rv.

If the \%skip is specified, files that exists as its keys are skipped. This is used internally to avoid infinite recursion.

If $compile or $execute is true, runs files in either compile-only or normal mode, then inspects their %INC after termination to determine additional runtime dependencies.

If $execute is an array reference, passes @$execute as arguments to each file in @files when it is run.

If performance of the scanning process is a concern, cache_file can be set to a filename. The scanning results will be cached and written to the file. This will speed up the scanning process on subsequent runs.

Additionally, an option warn_missing is recognized. If set to true, scan_deps issues a warning to STDERR for every module file that the scanned code depends but that wasn't found. Please note that this may also report numerous false positives. That is why by default, the heuristic silently drops all dependencies it cannot find.


Like scan_deps, but skips the static scanning part.


    @modules = scan_line($line);

Splits a line into chunks (currently with the semicolon characters), and return the union of scan_chunk calls of them.

If the line is __END__ or __DATA__, a single __END__ element is returned to signify the end of the program.

Similarly, it returns a single __POD__ if the line matches /^=\w/; the caller is responsible for skipping appropriate number of lines until =cut, before calling scan_line again.


    $module = scan_chunk($chunk);
    @modules = scan_chunk($chunk);

Apply various heuristics to $chunk to find and return the module name(s) it contains. In scalar context, returns only the first module or undef.


    $rv_ref = add_deps( rv => \%rv, modules => \@modules );
    $rv_ref = add_deps( @modules ); # shorthand, without rv

Resolves a list of module names to its actual on-disk location, by finding in @INC and @Module::ScanDeps::IncludeLibs; modules that cannot be found are skipped.

This function populates the %rv hash with module/filename pairs, and returns a reference to it.


    $perl_name = path_to_inc_name($path, $warn)

Assumes $path refers to a perl file and does it's best to return the name as it would appear in %INC. Returns undef if no match was found and a prints a warning to STDERR if $warn is true.

E.g. if $path = perl/site/lib/Module/ then $perl_name will be Module/



You can set this global variable to specify additional directories in which to search modules without modifying @INC itself.


You can set this global variable to specify a regular expression to identify what files to scan. By default it includes all files of the following types: .pm, .pl, .t and .al. Additionally, all files without a suffix are considered.

For instance, if you want to scan all files then use the following:

$Module::ScanDeps::ScanFileRE = qr/./


This module intentionally ignores the BSDPAN hack on FreeBSD -- the additional directory is removed from @INC altogether.

The static-scanning heuristic is not likely to be 100% accurate, especially on modules that dynamically load other modules.

Chunks that span multiple lines are not handled correctly. For example, this one works:

    use base 'Foo::Bar';

But this one does not:

    use base

SEE ALSO is a bundled utility that writes PREREQ_PM section for a number of files.

An application of Module::ScanDeps is to generate executables from scripts that contains prerequisite modules; this module supports two such projects, PAR and App::Packer. Please see their respective documentations on CPAN for further information.

Other modules which accomplish the same goal with different approach: Module::ExtractUse, Perl::PrereqScanner, Perl::PrereqScanner::Lite, Perl::PrereqScanner::NotQuiteLite.


Audrey Tang <>

To a lesser degree: Steffen Mueller <>

Parts of heuristics were deduced from:

The scan_deps_runtime function is contributed by Edward S. Peschko.

You can write to the mailing list at <>, or send an empty mail to <> to participate in the discussion.

Please submit bug reports to <>.


Copyright 2002-2008 by Audrey Tang <>; 2005-2010 by Steffen Mueller <>.

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