es (extensible shell) is a command line interpreter developed by Byron Rakitzis and Paul Haahr, that uses a scripting language syntactically similar to the rc shell of the Plan 9 operating system and was originally based on code from Byron Rakitzis's clone of rc for Unix. It is intended to provide a fully functional programming language as a Unix shell. The bulk of es development occurred in the early 1990s, after the shell was introduced at the Winter 1993 USENIX conference in San Diego.
Official releases appear to have ceased after 0.9-beta1 in 1997, and standard es lacks some features compared to more popular shells such as zsh and bash, but unofficial development has been continued with job control and history patches and a more ambitious renamed fork, Xs (including syntax changes and C++ code).
See also 
External links