Es (Unix shell)

It is a Unix shell. The name, it stands for extensible shell, extensible shell.

Features

The it has the core features of the Unix shell:

  • Command or filter chains ( Pipes, " piping " )
  • Redirection of program inputs and outputs
  • Summaries of commands and command chains in command files ( shell scripts )

Unlike other Unix shells basic shell constructs can be semantically manipulated ( extended) in it. Thus, for example, the pipe symbol | Define so that it not only means that the output of a program is connected to the input of a second program, but also that it produces an output that indicates how long it takes to connect in claim ( Profiler ).

It is of common Unix shells is different, that their language inventory is implemented as a set of function calls. This " superficiality " of the symbolism makes the semantic extensibility possible.

It has some properties that are typical of functional programming. Syntactically similar to the shell largely the Plan 9 shell rc.

History

It was written by Paul Haahr and Byron Rakitzis. After Rakitzis had re-implemented in the early 1990s by the rc shell for Unix, the idea of syntactic innovation, rc meant compared to other shells, to be followed by a semantic innovation emerged. In contrast to the development of the common shells, which mainly increased the oriented habits usability, in terms of the shell language but remained conservative, the shell language should it be adapted to developments in the field of programming languages, without attending by many concessions the user-friendliness to affect the performance of the shell.

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