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Learn how to write your first ZSH Auto-completion function

In this post, I’ll guide you in writing few, very basic Zsh autocompletion functions. Everything will be used at its minimal level.

I’m assuming that you’ve a basic knowledge of bash.

You need activate completion system first if you’re not using something like oh-my-zsh. Just run(or add to .zshrc):

autoload -U compinit compinit

Let’s say our program is called hello.

Here’s what will happen:

• You write a completion function. It usually starts with _(underscore) :

• Bind your function to a command

• Whenever you press <Tab> after hello, _hello will be called.

Whenever you want to throw out possible completions, you’ll use one of the following utility functions(in this post):

compadd

To get:

You’ll write:

compadd cmd1 cmd2 cmd3

_describe

To get:

You’ll write:

Note: In both of above commands, we didn’t consider which argument no. it is, means even hello cmd1 <Tab> will give same output. Next command will solve this problem.

_arguments

Now this is a powerful one. You can control multiple arguments.

By multiple arguments I mean hello arg1 arg2 not hello arg1|arg2

Here’s the basic syntax: _arguments <something> <something> ... where <something> can either be:

• '-o[description]' for an option
• '<argument number>:<message>:<what to do>' for an argument

First one is self-explanatory, whenever called it’ll give

For the second one:

• <argument number> is self-explanatory
• I’ll leave message empty to demonstrate a minimal example.
• <what to do> can be quite a few things, we’ll discuss only two:

1. List of arguments possible at given argument number. For example, if two arguments(world and universe) are possible at argument one(hello world|universe), we can write:

2. Set variable state to an identifier. For example, if we want to call another function at argument no. 2, we can write:

That might be confusing, lets sum up _arguments by an example:

Lets say, our program has possible args like:

Its completion function can be:

What Next?

I hope you were able to successfully write your first autocompletion function. I recommed to visit:

• Mads’ Blog
• Zsh Autocompletions Howto

Originally published at mrigank11.github.io.