Source

The ‘source' command in Bash is used to execute the content of another script within the current script. It’s also commonly represented by the ‘.' (dot) operator. When you use ‘source' or ‘.' followed by a script file, the commands and variables defined in that script are made available in the current script’s context. It’s typically used for sourcing configuration files or reusing functions and variables.
The source command is generally safer in terms of security because it doesn’t execute arbitrary code; it merely includes the content of the specified script. However, you should still be cautious when sourcing scripts to ensure that the sourced script doesn’t contain any malicious code.

Example:

To begin, create a file named “constants.sh” where we will store constant values. In the following section, we will utilize the source command to incorporate this file.

Step 1: Create a “constants.sh” file on your system by opening a terminal using [Alt + Ctrl + T] or [Right Click -> Open in Terminal]

Step 2: Create a “constants.sh” file and open it using the nano editor.

‘nano’: The ‘nano' command is a text editor for Unix-like operating systems, including Linux. It is designed to be easy to use and is often preferred by those who are new to the command line or need a simple text editor for quick edits. To open a file with nano or create a new one, you can use the following command:

nano [filename]

Replace ‘[filename]' with the name of the file you want to open or create. If the file does not exist, ‘nano' will create a new one with that name.

Once you’re inside the ‘nano' text editor, you can use various keyboard shortcuts to perform actions like saving, quitting, searching, and more. Common shortcuts include:

• Ctrl + O: Save the current file.
• Ctrl + X: Exit ‘nano'.
• Ctrl + G: Open the help menu, which shows other available commands.
• Ctrl + W: Search for text within the file.
• Ctrl + K: Cut (delete) the current line.
• Ctrl + U: Uncut (paste) the previously cut text.

You can find more commands and options in the help menu by pressing Ctrl + G.

Keep in mind that ‘nano' is a basic text editor, and if you need more advanced features, you might want to consider using other text editors like ‘vim' or ‘emacs'.

Step 3: Write the following lines of script in the “constants.sh” file and save it using [Ctrl + S] and close the nano editor using [Ctrl + X]

constants.sh

# constants.sh
export PI="3.1415"
export A="Hello"

Step 4: Create and open “source.sh” file using nano editor, write the following script. Save and close the nano editor with same instruction present in step 3.

source.sh

#!/bin/bash
#Source the constants file
source constants.sh 
#Using echo to get values of constants.
echo "Value of PI: $PI"
echo "$A Geeks."

Note: You can use any name for the script, I used “source.sh”. Also here “source.sh” and “constants.sh” both are in the the same folder hence in execution of the the source command only file name is used but the syntax of the the source command is ” source /path/to/your/file”.

Step 5: Run the “source.sh” file using the following command and check the output

$ bash source.sh

The command “bash source.sh” is used to execute a Bash script called “source.sh.” When you run this command, it will execute the commands specified in the “source.sh” script.

The “source” command within the script is used to include and execute the contents of another script or file. In this case,“source.sh” is meant to include and run the “constants.sh” file.

So, running “bash source.sh” will execute the commands within “source.sh,” which, in turn, sources the “constants.sh” file and displays the values of variables.

The provided Bash script sources to the file named “constants.sh” to access variables and then uses the ‘echo' command to display the values of those variables. This assumes that “constants.sh” contains variable definitions for PI with the value of “3.14159” and A with the value “42.”

Shell scripting is a fundamental skill for anyone working with Unix-like operating systems, offering a powerful way to automate tasks and streamline workflows. Two key commands, “source” and “eval,” play distinct roles in the realm of shell scripting. In this article, we delve into the core concepts of both commands, providing clear explanations, practical examples, and essential considerations for using them effectively. By understanding the nuances of “source” and “eval,” you’ll gain a deeper insight into how they can simplify your scripting tasks and navigate potential security concerns when handling untrusted input. Let’s explore these essential tools for shell scripting and empower you to become a more proficient scripter.