es

Es is an extensible shell. The language was derived from the Plan 9 shell, rc, and was influenced by functional programming languages, such as Scheme, and the Tcl embeddable programming language.

"Es is an extensible Unix shell with first class functions, lexical scope, exceptions, and rich return values (i.e., functions can return values other than just numbers). Es's extensibility comes from the ability to modify and extend the shell's builtin services, such as path searching and redirection. Like the Plan 9 shell rc, it is great for both interactive use and for scripting, particularly since its quoting rules are much less baroque than the C or Bourne shells." -- Paul Haahr