rc (Unix shell)

[1] A port of the original rc to Unix is part of Plan 9 from User Space.

A rewrite of rc for Unix-like operating systems by Byron Rakitzis is also available but includes some incompatible changes.

[7] It does so by introducing "program fragments" in braces as a new datatype, lexical scoping via let, and some more minor improvements.

The bulk of es development occurred in the early 1990s, after the shell was introduced at the Winter 1993 USENIX conference in San Diego.

[8] Official releases appear to have ceased after 0.9-beta-1 in 1997,[9] and es lacks features present in more popular shells, such as zsh and bash.