A nested Bash script is a Bash script that is called or executed from within another Bash script.

To call or execute a Bash script from within another script, you can use the source command or the . operator followed by the path to the script file. For example:

Both of these commands will execute the script as if it were part of the current script. This means that any variables or functions defined in the script will be available in the current script after it is executed.

You can also execute a Bash script by specifying its path and filename as a command. For example:

This will run the script as a separate process, and any variables or functions defined in the script will not be available in the current script after it finishes executing.

It is also possible to nest scripts by calling one script from within another using the methods described above. For example, you might have a main script that calls several other scripts to perform different tasks.

There are many use cases for nested Bash scripts. Here are a few examples:

1. Automating tasks: You can use nested Bash scripts to automate tasks by defining a series of commands in a script and calling that script from another script or from the command line. For example, you might create a script to configure a new server, and then call that script from another script that sets up a whole network of servers.
2. Organizing code: Nested Bash scripts can be used to organize and modularize your code, making it easier to maintain and reuse. For example, you might create a script to perform a specific task and then call that script from other scripts as needed.
3. Providing command-line utilities: You can create command-line utilities using Bash scripts and make them available to users by adding them to the system path. For example, you might create a script to perform a specific task, such as backing up a database, and then make it available to users by adding it to the system path.

Here is an example of a simple nested Bash script that performs a task and then calls another script to perform another task:

In this example, the first script performs some task and then calls the second script using the . operator. The second script performs another task.

Startup scripts

In Linux, startup files are scripts that are executed when the system boots up or when a user logs in. These files are used to configure the system and perform tasks such as setting environment variables, starting system services, and running custom commands.

There are several types of startup files in Linux, including:

To execute a startup file, you can add the command to the file and then make the file executable by running the chmod command. For example:

You can also use the systemctl command to enable and disable system-wide startup files on systems that use the Systemd init system.