zsh

Zsh, or the Z shell, is a Unix shell designed for interactive use and scripting. It extends traditional shells such as sh, ksh, and tcsh with a rich set of features that improve usability. Zsh was developed by Paul Falstad in the early 1990s and is distributed as free, open-source software under a BSD-style license.

Its features include a programmable completion system that can provide context-aware suggestions for commands, options, file names, and more. It also offers spell correction and approximate completion, allowing users to type with fewer errors. Zsh supports extended globbing for advanced file matching, powerful parameter expansion, arrays and associative arrays, and extensive prompt customization. The built-in Zsh Line Editor (zle) provides a configurable editing experience, and the history mechanism supports persistent history across sessions.

For configuration, Zsh reads several startup files, including ~/.zshrc for interactive shells and ~/.zprofile for login shells. It is largely compatible with POSIX sh but supplies many extensions that enhance scripting and interactive use. Scripts written for zsh can use features such as arrays, associative arrays, and improved test constructs, while still remaining executable as standalone programs via a shebang like #!/usr/bin/env zsh.

Zsh has grown a sizable ecosystem, with popular frameworks such as Oh My Zsh and Prezto that organize themes and plugins. It remains a common alternative to Bash in many environments and is the default shell on macOS since Catalina (2019).