Originally, zsh offered a completion system called 'compctl'. This allowed users to program the shell to produce arguments other than filenames for interactive Tab-completion. It was powerful, but not powerful enough for some.

In 1998, Sven Wischnowsky introduced an "experimental new-style completion" system to zsh. This system made it possible to use Z-Shell functions to describe possibilities for Tab-completing programs.

This new system matured, and is often seen as the primary reason why users are currently drawn to zsh.

This talk will describe how to write a function for the zsh completion system. This will be accomplished by introducing a program that lacks completion support, and demonstrating, step-by-step, how to instruct zsh regarding proper Tab-completion for that program.

A basic knowledge of shell syntax will be assumed.

Clint Adams is the maintainer of the zsh package, and has written a few completion functions.