In programming, a script is a text file that contains a series of instructions written in a scripting language that can be executed by a computer or shell interpreter to produce a desired result.

These scripts are primarily used to regroup multiple instructions together to automate repetitive or complex tasks that would be time-consuming or error-prone if done manually, one command at a time.

Common tasks often include custom CLI tools creation, data processing, file manipulation, software installation, automated testing, program compilation, and so on.

An overview of Bash scripts

In the context of Bash, a Bash script is a regular file that contains instructions written in the Bash scripting language and is executed by the Bash shell.

Bash scripts are easily distinguishable from other files and scripts, as they usually have a .sh file extension, for example script.sh, although it is not mandatory.

The shebang directive

Bash scripts always start with an interpreter directive called a shebang #! that indicates to the system that the script should be interpreted and executed using the Bash shell specified at the absolute /bin/bash path:

#!/bin/bash

This directive is essential as it ensures that the correct interpreter is used to execute the script, regardless of the shell it is executed from or the user's default shell settings.

Commands and execution order

A Bash script consists of a series of Bash commands that are read and executed by the Bash interpreter, from top to bottom.

More specifically, Bash executes the first command in the script after the shebang, then moves to the next line, and repeats the process until it reaches the end of the script or encounters an exit condition, such as an explicit exit command or an error.

#!/bin/bashcommand_1command_2...