How to Properly Pass Command Line Arguments in Self-Invoking Bash Scripts

Описание: Learn how to correctly pass all command line arguments to a self-invoking bash script within a Docker container using simple quoting methods.
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This video is based on the question https://stackoverflow.com/q/63294130/ asked by the user 'hallvors' ( https://stackoverflow.com/u/163549/ ) and on the answer https://stackoverflow.com/a/63297640/ provided by the user 'Philippe' ( https://stackoverflow.com/u/2125671/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering Command Line Arguments in Bash: Self-Invoking Scripts

When working with bash scripts, especially for those looking to run scripts in a containerized environment like Docker, you might face challenges in passing command line arguments correctly. One common issue arises when invoking a script that calls itself while attempting to forward any provided arguments, particularly with different quoting mechanics. This guide will walk you through the correct way to handle passing command line arguments in a self-invoking bash script, ensuring that everything functions smoothly.

The Problem

Suppose you have a bash script like the one below, intended to invoke itself in a new context. For example, you may need it to be run inside a Docker container. You attempt to pass all command line arguments as follows:

[[See Video to Reveal this Text or Code Snippet]]

When saved as test.sh, and if you run it with ./test.sh 1 2 "3 4", you might notice unexpected behavior where only the first argument appears as output. If you run the script with set -x, you may see the command expands oddly, leading to errors in argument handling.

The Solution

To correctly pass all command line arguments while self-invoking, one should avoid using bash -c due to its poor handling of arguments with spaces or special characters. Instead, the key is to directly call the script with ./test.sh "$@ ". Below is the revised code:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made

Use of ./test.sh "$@ ": This modification will ensure all arguments, including those with spaces, are passed correctly.

Elimination of bash -c: This is essential, as bash -c can insert unwanted quoting that disrupts the expected behavior.

Benefits of the Revised Script

Simpler Logic: The script is now more straightforward without complexities introduced by the bash -c command.

Proper Handling of Arguments: Using "$@ " ensures all variations of input arguments are respected and echoed as intended.

Conclusion

When dealing with self-invoking bash scripts, especially in complex environments like Docker, remember to handle your command line arguments with care. Avoid unnecessary complexities by using straightforward solutions that respect bash's handling of arguments. By implementing the suggested changes, you’ll ensure your script invocations work flawlessly, allowing you to focus on developing robust applications without hiccups caused by command line issues.

If you follow the recommendations in this post, you’ll be well on your way to mastering command line argument handling in bash scripts. Happy scripting!