Bash Source Command

Introduction

Before we start talking about Bash source command, let's first understand-What is Source Command ?

The source command in Bash is used to execute commands from a specified file within the current shell session. This command is particularly useful for running shell scripts or sourcing variables, functions, and aliases from external files.

In the current shell environment, the source command reads and executes commands from the file supplied as an input. Shell scripts can be used to load functions, variables, and configuration files.

In this tutorial, we will discuss Bash Source Command. We will also address a few FAQs on Bash Source Command.

Source Command Syntax

The source command has the following syntax:

source FILENAME [ARGUMENTS]
. FILENAME [ARGUMENTS]

• The commands source and . (a period) are the same.
• If the FILENAME parameter is not a complete path to a file, the command will look for it in the directories listed in the $PATH environment variable. If the file isn't in the $PATH, the command will search the current directory for it.
• If any ARGUMENTS are specified, they will be used as FILENAME positional parameters.
• The source command exit code is 0 if the FILENAME exists; otherwise, it returns 1 if the file is not found.

Source Command Examples

We'll look at some simple examples of how to utilize the source command in this section.

Sourcing Functions

If you have shell scripts that use the same routines, extract them into a separate file and use that file as a source in your scrips.

In this example, we'll make a file with a bash function that checks whether the user running the script is root and, if not, displays a notice before exiting the script.

check_root () {
  if [[ $EUID -ne 0 ]]; then
    echo "This script must be run as root" 
    exit 1
  fi
}

Simply source the functions.sh file and call the function: in any script that needs to be run solely by the root user.

#!/usr/bin/env bash

source functions.sh
check_root

echo "I am root"

If you run the script as a non-root user, it will quit with the message, "This script must be run as root."

The benefit of this technique is that your scripts will be smaller and easier to read, you'll be able to reuse the same function file many times, and you'll only have to edit one file if you need to change a function.

Bash Configuration file

You can also read variables from a file using the source command. The variables must be set using the VARIABLE=VALUE Bash syntax.

Create a test configuration file as follows:

VAR1="foo"
VAR2="bar"

To read the configuration file, use the source command in your bash script:

#!/usr/bin/env bash

source config.sh

echo "VAR1 is $VAR1"
echo "VAR2 is $VAR2"

If you run the script, the following is the result:

Output

VAR1 is foo
VAR2 is bar

FAQs on Bash Source Command

Conclusion

You learned how to use the source built-in command in your shell scripts in this tutorial.

If you have any queries, please leave a comment below and we’ll be happy to respond to them.