FindLib(3)

NAME
File::FindLib - Find and use a file/dir from a directory above your script file

SYNOPSIS
    use File::FindLib 'lib';

Or

    use File::FindLib 'lib/MyCorp/Setup.pm';

DESCRIPTION
File::FindLib starts in the directory where your script (or library) is located and looks for the file or directory whose name you pass in. If it isn't found, then FindLib looks in the parent directory and continues moving up parent directories until it finds it or until there is not another parent directory.

If it finds the named path and it is a directory, then it prepends it to @INC. That is,

    use File::FindLib 'lib';

is roughly equivalent to:

    use File::Basename qw< dirname >;
    use lib dirname(__FILE__) . '/../../../lib';

except you don't have to know how many '../'s to include and it adjusts if __FILE__ is a symbolic link.

If it finds the named path and it is a file, then it loads the Perl code stored in that file. That is,

    use File::FindLib 'lib/MyCorp/Setup.pm';

is roughly equivalent to:

    use File::Basename qw< dirname >;
    BEGIN {
        require dirname(__FILE__) . '/../../../lib/MyCorp/Setup.pm';
    }

except you don't have to know how many '../'s to include (and it adjusts if __FILE__ is a symbolic link).

  MOTIVATION
It is common to have a software product that gets deployed as a tree of directories containing commands (scripts) and/or test scripts in the deployment that need to find Perl libraries that are part of the deployment.

By including File::FindLib in your standard Perl deployment, you can include one or more custom initialization or boot-strap modules in each of your software deployments and easily load one by pasting one short line into each script. The custom module would likely add some directories to @INC so that the script can then just load any modules that were included in the deployment.

For example, you might have a deployment structure that looks like:

    bin/init
    ...
    db/bin/dump
    ...
    lib/MyCorp/Setup.pm
    lib/MyCorp/Widget.pm
    lib/MyCorp/Widget/Connect.pm
    ...
    t/TestEnv.pm
    t/itPing.t
    t/itTimeOut.t
    t/MyCorp/Widget/basic.t
    ...
    t/MyCorp/Widget/Connect/retry.t
    ...
    t/testlib/MyTest.pm
    ...

And your various Perl scripts like bin/init and db/bin/dump might start with:

    use File::FindLib 'lib/MyCorp/Setup.pm';
    use MyCorp::Widget;

And Setup.pm might start with:

    package MyCorp::Setup;
    use File::FindLib 'lib';

While your various test scripts might start with:

    use File::FindLib 't/TestEnv.pm';
    use MyTest qw< plan ok >;

where TestEnv.pm might start with:

    package TestEnv;
    use File::FindLib 'testlib';    # Find modules in $repo/t/testlib/
    use File::FindLib 'lib';        # Find modules in $repo/lib/

And you don't have to worry about having to update a script if it gets moved to a different point in the deployment directory tree.

  SYMBOLIC LINKS
If the calling script/library was loaded via a symbolic link (if "-l __FILE__" is true inside the calling code), then File::FindLib will start looking from where that symbolic link points. If it points at another symbolic link or if any of the parent directories are symbolic links, then File::FindLib will ignore this fact.

So, if we have the following symbolic links:

    /etc/init.d/widget -> /site/mycorp/widget/bin/init-main
    /site/mycorp/widget/bin/init-main -> ../util/admin/init
    /site/mycorp/widget/ -> ../dist/widget/current/
    /site/mycorp/dist/widget/current/ -> 2011-12-01/
    /site/mycorp/dist/widget/2011-12-01 -> v1.042_037/
    /site/mycorp/ -> /export/site/mycorp/
    /site -> /export/var/site

And the following command produces the following output:

    $ head -2 /etc/init.d/widget
    #!/usr/bin/perl
    use File::FindLib 'lib/Setup.pm';
    $

Then File::FindLib will do:

    See that it was called from /etc/init.d/widget.
    See that this is a symbolic link.
    Act like it was called from /site/mycorp/widget/bin/init-main.
    (Ignore that this is another symbolic link.)
    Search for:
        /site/mycorp/widget/bin/lib/Setup.pm
        /site/mycorp/widget/lib/Setup.pm
        /site/mycorp/lib/Setup.pm
        /site/lib/Setup.pm
        /lib/Setup.pm

Only the first symbolic link that we mentioned is noticed.

This would be unfortunate if you also have the symbolic link:

    /etc/rc2.d/S99widget -> ../init.d/widget

Since running that command would cause the following searches:

    /etc/init.d/lib/Setup.pm
    /etc/lib/Setup.pm
    /lib/Setup.pm

If you instead made a hard link:

    # ln /etc/init.d/widget /etc/rc2.d/S99widget

then /etc/init.d/widget would also be a symbolic link to /site/mycorp/widget/bin/init-main which would surely work better.

So future versions of File::FindLib may notice more cases of symbolic links or provide options for controlling which symbolic links to notice.

  %INC
The code:

    use File::FindLib 'lib/MyCorp/Setup.pm';

is more accurately approximated as:

    use File::Basename qw< dirname >;
    BEGIN {
        my $path= dirname(__FILE__) . '/../../../lib/MyCorp/Setup.pm';
        require $path;
        $INC{'MyCorp/Setup.pm'} ||= $INC{$path};
    }

The setting of $INC{'MyCorp/Setup.pm'} is so that:

    use File::FindLib 'lib/MyCorp/Setup.pm';
    ...
    use MyCorp::Setup;

doesn't try to load the MyCorp::Setup module twice.

Though, this is only done if lib/MyCorp/Setup.pm defines a MyCorp::Setup package... and $INC{'MyCorp/Setup.pm'} isn't already set and there is no lib::MyCorp::Setup package defined. See the source code if you have to know every detail of the heuristics used, though misfires are unlikely (especially since module names are usually capitalized while library subdirectory names usually are not).

Even this problem case is unlikely and the consequences of loading the same module twice are often just harmless warnings, if that.

So this detail will not matter most of the time.

PLANS
I'd like to support a more powerful interface. For example:

    use File::FindLib(
        -from           => __FILE__,
        -upto           => 'ReleaseVersion.txt',
        -inc            => 'custom/lib',    # Like: use lib ...
        +inc            => 'lib',           # Like: push @INC, ...
        -load           => 'initEnv.pl',    # Like: require ...
        \my $DataDir    => 'custom/data',   # Sets $DataDir to full path
    );

But adding such an interface should not interfere with the one-argument interface already implemented.

CONTRIBUTORS
Author: Tye McQueen, http://perlmonks.org/?node=tye

ALSO SEE
Lake Missoula