A shell script is a script written for the shell, or command line interpreter, of an operating system. The shell is often considered a simple domain-specific programming language. Typical operations performed by shell scripts include file manipulation, program execution, and printing text.

Many shell script interpreters double as command line interface, such as the various Unix shells, Windows PowerShell or the MS-DOS COMMAND.COM. Others, such as AppleScript or the graphical Windows Script Host (WScript.exe), add scripting capability to computing environments without requiring a command line interface. Other examples of programming languages primarily intended for shell scripting include DCL and JCL.

In its most basic form, a shell script can provide a convenient variation of a system command where special environment settings, command options, or post-processing is applied automatically, but in a way that allows the new script to still act as a fully normal Unix command.

One example would be to create a version of ls, the command to list files, giving it a shorter command name of l, which would be normally saved in a user's bin directory as /home/username/bin/l, and a default set of command options pre-supplied.