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Emulate Perls internal handling of @INC

README.mkdn

NAME

Path::ScanINC - Emulate Perls internal handling of @INC.

VERSION

version 0.020

SYNOPSIS

The Aim of this module is to fully implement everything Perl does with @INC, to be feature compatible with it, including the behavior with regard to sub refs in @INC.

    use Path::ScanINC;

    # Normal usage.
    my $inc = Path::ScanINC->new( );

    # In case you need something that isn't @INC
    # but works like it

    my $inc = Path::ScanINC->new( inc => \@INC );

    # Freeze the value of @INC at the time of object instantiation
    # with regard to behaviour so later changes to @INC have no effect

    my $inc = Path::ScanINC->new( immutable => 1 );

    # Return the first file in @INC that matches.

    my $file = $inc->first_file('Path', 'ScanINC.pm' );

    # Find all possible versions of modules in @INC
    my ( @files ) = $inc->all_files('Path', 'ScanINC.pm');

    # Try to discover a File::ShareDir 'module' root.
    my $dir = $inc->first_dir('auto','share','module');

    # Should return the same as File::ShareDir::module_dir('Path::ScanINC')
    # ( assuming such a directory existed, which there is presently no plans of )
    my $dir = $inc->first_dir('auto','share','module','Path-ScanINC');


    # Find All File::ShareDir roots in @INC
    my ( @dirs ) = $inc->all_dirs('auto', 'share');

REF SUPPORT IN @INC

This module has elemental support for discovery of results in @INC using CODE/ARRAY/BLESSED entries in @INC. However, due to a limitation as to how perl itself implements this functionality, the best we can do at present is simply return what the above are expected to return. This means if you have any of the above ref-types in @INC, and one of those returns a true value, you'll get handed back an ARRAY reference instead of the file you were expecting.

Fortunately, @INC barely ever has refs in it. But in the event you need to work with refs in @INC and you expect that those refs will return true, you have to pick one of two options, either :

  • a. Write your code to work with the array-ref returned by the respective reference on a match
  • b. Use the all_ family of methods and try pretending that there are no array-refs in the list it returns.

Its possible in a future release we may have better choices how to handle this situation in future, but don't bet on it.

Given that the API as defined by Perl mandates code-ref's return lists containing file-handles or iterative code-ref's , not actual files, the best I can foresee at this time we'd be able to do to make life easier for you is creating a fake library somewhere in a tempdir and stuffing the result of the code-ref's into files in that directory prior to returning a path to the generated file.

( And it also tells me that they have to be "Real" file handles, not tied or blessed ones, so being able to ask a filehandle what file it represents is equally slim.... if that is of course what you require )

For more details, see perldoc perlfunc or perldoc -f require .

METHODS

new

    my $object = $class->new(
             inc => [ 'x', 'y', 'z' , ],
             immutable => 1 | undef
    );

immutable

    if( $inc->immutable ) {
            print "We're working with a snapshotted version of @INC";
    }

inc

    for my $i ( $inc->inc ) {
            say "Plain: $incer" if not ref $incer;
            say "Callback: $incer" if ref $incer;
    }

Returns a copy of the internal version of @INC it will be using.

If the object is immutable, then this method will continue to report the same value as c<@INC>, or will be updated every time the original array reference passed during construction gets updated:

    my $ref = [];
    my $a = Path::ScanINC->new( inc => $ref );
    my $b = Path::ScanINC->new( inc => $ref, immutable => 1 );

    push @{$ref} , 'a';

    is( [ $a->inc ]->[0] , 'a' , "non-immutable references keep tracking their original" );
    isnt( [ $b->inc ]->[0] , 'a' , "immutable references are shallow-copied at construction" );

Do note of course that is a SHALLOW copy, so if you have multiple @INC copies sharing the same array/bless references, changes to those references will be shared amongst all @INC's .

first_file

    if( defined ( my $file = $inc->first_file('Moose.pm') ) {
            print "Yep, Moose seems to be available in \@INC , its at $file, but its not loaded (yet)\n";
    }

This proves to be a handy little gem that replaces the oft used

    if( try { require Moose ; 1 } ){
            Yadayadayada
    }

And adds the benefit of not needing to actually source the file to see if it exists or not.

IMPORTANT: PORTABILITIY

For best system portability, where possible, its suggested you specify paths as arrays of strings, not slash-separated strings.

    $inc->first_file('MooseX' , 'Declare.pm')  # Good
    $inc->first_file('MooseX/Declare.pm')      # Bad.

This is for several reasons, all of which can be summarized as "Windows".

  • %INC keys all use Unix notation.
  • @INC callbacks expect Unix notation.
  • \ is a valid path part on Unix.
  • On Win32, we have to use \ Separation, not / for resolving physical files.

The sum of these means if you do this:

    $inc->first_file('MooseX/Declare.pm')

On win32, it might just end up doing:

    C:\some\path\here/MooseX/Declare.pm

Which may or may not work.

And additionally, if the above module is loaded, it will be loaded as

    "MooseX/Declare.pm"

in %INC, not what you'd expect, MooseX\Declare.pm

all_files

Returns all matches in all @INC paths.

    my $inc = Path::ScanINC->new();
    push @INC, 'lib';
    my ( @files ) = $inc->all_files('Something','Im','Working','On.pm');
    pp(\@files );

    # [
    #    '/something/........./lib/Something/Im/Working/On.pm',
    #    '/something/....../share/per5/lib/site_perl/5.15.9/Something/Im/Working/On.pm',
    # ]

Chances are if you understand how this can be useful, you'll do so immediately.

Useful for debugging what module is being loaded, and possibly introspecting information about multiple parallel installs of modules in %ENV, such as frequently the case with 'dual-life' modules.

    perl -MPath::ScanINC -E 'my $scanner = Path::ScanINC->new(); say for $scanner->all_files(qw( Scalar Util.pm ))'
    /usr/lib64/perl5/vendor_perl/5.12.4/x86_64-linux/Scalar/Util.pm
    /usr/lib64/perl5/5.12.4/x86_64-linux/Scalar/Util.pm

Sort-of like ye' olde' perldoc -l, but more like man -a

I might even be tempted to make a sub-module to make one-liners easier like

    perl -MPath::ScanINC::All=Scalar/Util.pm

REMINDER: If there are REFS in @INC that match, they'll return array-ref's, not strings.

first_dir

Just like first_file except for locating directories.

all_dirs

Just like all_dirs except for locating directories.

AUTHOR

Kent Fredric kentnl@cpan.org

COPYRIGHT AND LICENSE

This software is copyright (c) 2014 by Kent Fredric kentnl@cpan.org.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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