KornShell

KornShell, often abbreviated ksh, is a Unix shell and scripting language developed by David Korn at Bell Labs in the 1980s. It is designed as a superset of the Bourne shell (sh) with additional features inspired by the C shell (csh). Ksh is intended for interactive use and for writing portable scripts, and it has had a lasting influence on later shells while remaining available on many Unix-like systems.

Initial public release appeared as ksh88 in 1988, followed by ksh93 in the early 1990s, which added features such as improved scripting capabilities, associative arrays, extended built-in arithmetic, and enhanced programming constructs. Over the years, several open-source and commercial implementations produced variants such as pdksh and mksh, as well as compatible forks and extensions. The language has influenced other shells and remains a reference for forward-compatible scripting.

Key features include interactive command line editing, command history, job control, and a rich set of built-in commands. Scripting support includes arithmetic expansion, arrays and associative arrays (in later versions), functions, and the typeset keyword for declaring variables. The language provides pattern matching with [[ ... ]], arithmetic evaluation, robust I/O redirection, and support for subshells, functions, traps, and coprocesses.

Usage: ksh is typically invoked as /bin/ksh or /usr/bin/ksh on systems that provide it. While Bash has become the dominant shell on many systems, ksh remains in use for compatibility with legacy scripts and environments that rely on ksh-specific features.