App::Dispatch - Tool to have #! dispatch to the best executable for the job.


App::Dispatch is an alternative to /usr/bin/env. Unlike /usr/bin/env, it does not rely on your environment to tell it which program to use. You can set system-wide, and user level configurations for which program to use. You can also specify a cascade of aliases and/or paths to search.

Lately it has been a trend to avoid the system install of programming languages, Perl, Ruby, Python, etc, in most cases it is recommended that you do not use the system installation of the language. A result of this is heavy use of #!/usr/bin/env to lookup the correct binary to execute based on your $PATH. The problem with /usr/bin/env is that you may not always have control over the environment. For example if you have a script that you must run with sudo, your $PATH will be reset.

With App::Dispatch you can specify multiple locations to try when looking for the program. You can also configure aliases at the system or user level. This is useful when you have multiple versions of the program installed and wish different things to use different ones by a label. In this way the versions need not be in the same location on each machine that can run the script.



The following #! line will cause the script to be run by perl, it will try each path listed in order.

    #!/usr/local/bin/dispatch perl /path/to/perl /alternate/path/to/perl /another/perl

This tells the script to use the specified path if available, otherwise fall back to whichever perl is in the environment.

    #!/usr/local/bin/dispatch perl /path/to/perl ENV

You can also pass arguments to the program by putting them after --:

    #!/usr/local/bin/dispatch perl /path/to/perl ENV -- -w



        SYSTEM     = /usr/bin/perl
        DEFAULT    = /opt/ACME/current/bin/perl
        production = /opt/ACME/stable/bin/perl

This #! line will run perl, it will find the 'production' perl, if no production perl is found it will try 'DEFAULT'. Anything after the -- is passed as arguments to perl.

    #!/usr/local/bin/dispatch perl production DEFAULT -- -w

This will run the default perl.

    #!/usr/local/bin/dispatch perl



Locations are loaded in this order. All locations that exist are loaded. Later files can override earlier ones.


The system wide configuration


System wide config dir, to have app specific config files for easier management with system packages.


User specific overrides or additions.


        SYSTEM     = /usr/bin/perl
        DEFAULT    = /opt/ACME/current/bin/perl
        production = /opt/ACME/stable/bin/perl

        SYSTEM  = /usr/bin/gcc
        DEFAULT = /usr/bin/gcc
        old     = /opt/legacy/bin/gcc


This tool is very useful for perl shops in their own scripts. However it most likely should not be used in any scripts that will be installed with a cpan distribution. Distributions should use a normal #! line that will be rewritten by the build tools to use the perl for which the dist was installed. This is important because of dependency chains and XS modules.


Chad Granum


Copyright (C) 2013 Chad Granum

App-Dispatch is free software; Standard perl licence.

App-Dispatch is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the license for more details.