4. External Commands

cabal-install provides a system for external commands, akin to the ones used by tools like git or cargo.

If you execute cabal <cmd>, cabal-install will search the path for an executable named cabal-<cmd> and execute it. The name of the command is passed as the first argument and the remaining arguments are passed afterwards. An error will be thrown in case the custom command is not found.

The $CABAL environment variable is set to the path of the cabal-install executable which invoked the subcommand.

It is strongly recommended that you implement your custom commands by calling the CLI via the $CABAL variable rather than linking against the Cabal library. There is no guarantee that the subcommand will link against the same version of the Cabal library as cabal-install so it would lead to unexpected results and incompatibilities.

cabal-install can also display the help message of the external command. When cabal help <cmd> is invoked, then cabal-<cmd> <cmd> --help will be called so your external command can display a help message.

For ideas or existing external commands, visit this Discourse thread.