The '''es shell''' is a [[command line interpreter]] developed by Byron Rakitzis and Paul Haahr, that uses a [[scripting language]] similar to the [[rc shell]] of the [[Plan 9 from Bell Labs|Plan 9]] [[operating system]]<ref>http://foldoc.org/Extensible+Shell</ref>, and was originally based on code from Byron Rakitzis's clone of [[rc shell|rc]] for Unix<ref>http://luv.asn.au/overheads/shells-talk.html</ref>. It is intended to provide a fully [[functional programming|functional]] [[programming language]] as a [[Unix shell]]<ref>http://nnc3.com/lj/LJ/LJ12/0062.html</ref>. The bulk of es' development occurred in the early 1990s, after the shell was introduced at the Winter 1993 [[USENIX]] conference in [[San Diego]].<ref>[http://www.webcom.com/~haahr/es/es-usenix-winter93.html Es: A shell with higher-order functions] by Byron Rakitzis, [[NetApp|NetApp, Inc]], and Paul Haahr, [[Adobe Systems Incorporated]]</ref>
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Current official releases appear to have ceased with the release of 0.9-beta1 in 1997 <ref>ftp://ftp.sys.utoronto.ca/pub/es/</ref>, and standard es lacks some features compared to more popular shells such as zsh and bash <ref>http://www.faqs.org/faqs/unix-faq/shell/shell-differences/</ref> but unofficial development has been continued with [http://web.archive.org/web/20070626160532/http://theorie1.physik.uni-erlangen.de/rogalsky/es/es.html job control and history patches] and a more ambitious fork, [http://github.com/frytvm/XS Xs] (including syntax changes and C++ code).
