A shell script is a text file that contains a sequence of commands for a UNIX-based operating system. It is called a shell script because it combines a sequence of commands, that would otherwise have to be typed into the keyboard one at a time, into a single script. The shell is the operating system's command-line interface (CLI) and interpreter for the set of commands that are used to communicate with the system.
A shell script is usually created for command sequences in which a user has a need to use repeatedly in order to save time. Like other programs, the shell script can contain parameters, comments and subcommands that the shell must follow. Users initiate the sequence of commands in the shell script by simply entering the file name on a command line.
Shell scripting is meant to be simple and efficient. It uses the same syntax in the script as it would on the shell command line, removing any interpretation issues. Writing code for a shell script is also faster and requires less of learning curve than other programming languages.
However, if there is an error in a shell script, this can prove to be extremely costly if left unnoticed. Additionally, differing platforms associated with shell scripting may not be compatible. Shell scripts can also be slower to execute than individual commands.