Like cargo and git, ion offers a variety of built-in commands that are baked into the same executable. However, cargo and git allow users to invoke "external" commands; programs that live on the user's $PATH and which are named in the format cargo-<command> or git-<command> respectively. ion should support this functionality as well, allowing developers to add their own commands without needing to merge them into this repo.

Resources:

• clap support for external commands
• cargo searching the PATH
• cargo running a possibly external command
• The which crate, which will search the PATH for you.