Shell scripts are a fundamental part of the OS X programming environment. As a ubiquitous feature of UNIX and UNIX-like operating systems, they represent a way of writing certain types of command-line tools in a way that works on a fairly broad spectrum of computing platforms.
Because shell scripts are written in an interpreted language whose power comes from executing external programs to perform processing tasks, their performance can be somewhat limited. However, because they can execute without any additional effort on nearly any modern operating system, they represent a powerful tool for bootstrapping other technologies. For example, the autoconf tool, used for configuring software prior to compilation, is a series of shell scripts.