bash script. if I invoke it directly, like ./myscript it should enter a subshell, change PS1 to something, and source current file to make all functions available in the new shell.

bash script subshell change PS1 source current file functions available

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1
Changing the PS1 on an interactive bash subshell easily
I would like to change the prompt to remind the user that they are in a special subshell and haven't gone through the rest of the process yet.
Unix
2
Update variable in bash function and use it in prompt (PS1)
I want to do is to call a function in PS1 to update a variable inside the function. Then I like to use that variable to add another line to PS1.
Stack Overflow

To create a Bash script that enters a subshell, changes the command prompt (PS1), and sources the current file to make all functions available, you can follow the steps outlined below. This guide will provide a detailed explanation along with a sample script you can use.

Creating the Bash Script

Step 1: Open a Terminal

Begin by opening your terminal on a Unix-like operating system (Linux, macOS, etc.).

Step 2: Create a New Bash Script

You can use any text editor to create a new script file. For this example, we’ll create a file called myscript.sh.

touch myscript.sh
chmod +x myscript.sh  # Make the script executable

Step 3: Edit the Script

Next, open the file in your favorite text editor:

nano myscript.sh

Step 4: Write the Script

Copy and paste the following code into myscript.sh. This script sets the new PS1 prompt, enters a subshell, and sources the current file:

#!/bin/bash

# Change the prompt for the subshell
export PS1="(mysubshell) \$ "

# Source the current file to make all functions available
source "${BASH_SOURCE[0]}"

# Start a new interactive bash shell
bash --rcfile <(echo "export PS1='(mysubshell) \$ '")

Step 5: Save and Exit

If you are using nano, save the changes by pressing CTRL + O, then exit with CTRL + X.

Explanation of the Script

  • Shebang (#!/bin/bash): This line tells the system to execute the script using Bash.

  • Changing PS1: The export PS1="(mysubshell) \$ " command modifies the command prompt to indicate that you are inside a subshell.

  • Sourcing the Current Script: The line source "${BASH_SOURCE[0]}" ensures all functions defined in the current script are loaded into the subshell. ${BASH_SOURCE[0]} refers to the path of the script being executed.

  • Starting a New Interactive Shell: The command bash --rcfile <(echo "export PS1='(mysubshell) \$ '") starts a new interactive Bash shell with the modified PS1 prompt. The <(echo ...) syntax creates a temporary file containing the command you want to run, allowing the new shell to use it.

Step 6: Running the Script

Now, you can run your script directly from the terminal with the following command:

./myscript.sh

You should see the prompt change to (mysubshell) $, indicating that you are in a new subshell. Any functions defined in the script will be available in this subshell.

Tips and Additional Information

  • Exiting the Subshell: To exit the subshell, simply type exit or press Ctrl + D. This action will take you back to the original shell.

  • Use Cases: This script can be useful for testing changes in an isolated environment without affecting the main shell session.

  • Modification and Customization: You can modify the PS1 variable further to include colors or additional information, such as the current working directory. For example, you could set export PS1="\[\e[32m\](mysubshell) \[\e[0m\]\$ " to add color.

By following these steps, you will successfully create a Bash script that facilitates entering a subshell with a modified prompt and access to all defined functions. This technique enhances your scripting capabilities and provides a controlled testing environment.

Sources

10
1
Changing the PS1 on an interactive bash subshell easily
Unix

I would like to change the prompt to remind the user that they are in a special subshell and haven't gone through the rest of the process yet.

2
Update variable in bash function and use it in prompt (PS1)
Stack Overflow

I want to do is to call a function in PS1 to update a variable inside the function. Then I like to use that variable to add another line to PS1.

3
How to use source within a bash script to change the terminal prompt?
Superuser

First off, you don't need to write and source a file to change an environment variable--you can set PS1 just by executing PS1='$\ '.

4
[SOLVED] PS1: not working in .sh files, and why use 'export'?
Linuxquestions

The only purpose of export is to make the value available to sub-processes. Without it they are generally limited to the current shell environment.

5
Run an interactive bash subshell with initial commands without ...
Serverfault

If you simply pass an --init-file option, your script would replace the default, rather than augment it. The solution is to pass, using the <(..

6
Subshells and Functions – BASH Programming for Workflow ...
Uomresearchit

Subshells are separate instances of the command process, run as a new process, and defined within your scripts using () .

7
What's so special about PS1? Fun with customizing Bash command ...
Warp

Discover how to customize the PS1 prompt in Bash and how Warp integrates it to enhance your terminal experience.

8
Extending the Bash Prompt | Linux Journal
Linuxjournal

To change the way the prompt appears, change the PS1 variable. For experimentation purposes, the PS1 string can be entered at the prompt to show ...

9
how to export VARs from a subshell to a parent shell? - Server Fault
Serverfault

The answer is sourcing. Sourcing allows you to include variables in a script in the current shell, but never a parent of that.

10
GNU Bash Reference Manual
Gnu

This manual is meant as a brief introduction to features found in Bash. The Bash manual page should be used as the definitive reference on shell behavior.