What is a shell script?

A shell script is much like a Windows batch file: it is a file that contains commands to be run as if they were being executed on the command-line. It is similar to a program, where you can define variables and use control logic to automate certain tasks and commands. Common reasons for writing shell scripts include simplifying complex actions into a single simple command and reducing the possibility of human error. Shell scripts are an essential skill for UNIX system administrators and also very valuable for programmers in UNIX environments.