Source : Free On-Line Dictionary of Computing

Extensible Shell
     
         (es) A {Unix} {shell} written by Byron
        Rakitzis  and Paul Haahr ,
        derived from {rc}.  Es has real {functions}, {closures},
        {exceptions} and lets you redefine most internal shell
        operations.
     
        Version: 0.84.
     
        {(ftp://ftp.sys.utoronto.ca/pub/es/)}.
     
        ["Es - A Shell with Higher Order Functions", P. Haahr et al,
        Proc Winter 1993 Usenix Technical Conference].
     
        (1993-04-30)