Running a Shell Script That Executes Another Shell Script

Mastering the techniques of running a shell script that invokes another shell script is a fundamental skill in efficient and modular scripting. In this guide, we'll explore the steps and provide a detailed, step-by-step example to help you achieve this. Whether you're a beginner or an experienced developer, this comprehensive guide will provide you with the necessary knowledge.

Steps to Run a Shell Script That Calls Another Script

Create the First Shell Script: This script will call the secondary script. Create the Second Shell Script: This is the script that you wish to execute from the first. Make Both Scripts Executable: Ensuring both scripts have the executable permission is crucial. Run the First Script: Execute the first script, which will then run the second script.

Step-by-Step Example

Create the Second Shell Script

bash #!/bin/bash echo 'This is the second script.'

Create the First Shell Script

bash #!/bin/bash echo 'This is the first script.' call the second script

Make Both Scripts Executable

chmod x first_ chmod x second_

Run the First Script

./first_

Output

When you run the command ./first_, you should see the following output: This is the first script. This is the second script.

Key Points

Ensure the path to the second script is correct. If second_ is in a different directory, you might need to provide the full path or change to that directory first. You can also run the second script using an absolute path or relative path, depending on your current working directory. This approach enables you to organize your scripts and modularize your code effectively.

Further Techniques for Running Shell Scripts

Running Another Shell Script with Arguments

If the other script requires arguments, you can pass variables from the first script as argument values to the second script. foo'inputfile' bar'outputfile' script2 $foo $bar

Capturing the Output of Another Script in a Variable

If you need to capture the output of another script in a variable in the first script, you can use the 'backtick' or `$` form. baz`script2 foo bar` bar will contain the STDOUT stream produced by script2

Running the Second Script in Parallel with the First

To run the second script in parallel with the first, run it in the background and wait for it to finish before exiting. script2 foo bar # do more stuff in script1 wait exit

Running a Script in the Background

If script2 produces output or throws errors, it can get confusing because both script1 and script2 output to STDOUT, which is your shell session. If you want to have script2 output to a file and not have to wait for it to finish, use the nohup command. nohup script2 foo bar n nohup: ignoring input and backgrounding

For more advanced usage, you can redirect output to a file using the following command:

nohup script2 foo bar script2.out

The system will notify the calling session that output is being written to a file, defaulting to nohup.out, or otherwise specify a file name. The system will announce when the job has completed at the next command prompt after completion.