Unix Command Shells

Abstract

The Unix operating system contains many software components. Two hold particularly privileged positions: the kernel and the shell. The kernel is the operating system in the narrowest sense of that word, the supervisory program which schedules all processes and executes them in the proper way at the right time. Which programs to execute, how to run them, what to do with the output, and similar matters are communicated to the kernel through the Unix command decoder program, the shell. In this chapter, the external appearance of the shell is described in sufficient detail to allow reasonably complete use of its main facilities. However, the shell is a complex program and many of its more esoteric features can only be hinted at here.