Resolving the command substitution: syntax error near unexpected token in Bash Scripts

A guide on fixing the `command substitution: syntax error near unexpected token` in Bash scripts by understanding process substitution and POSIX mode. --- This video is based on the question https://stackoverflow.com/q/68035754/ asked by the user 'Joe_Informatics' ( https://stackoverflow.com/u/15895559/ ) and on the answer https://stackoverflow.com/a/68036146/ provided by the user 'John Bollinger' ( https://stackoverflow.com/u/2402272/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: command substitution: line 72: syntax error near unexpected token `(' Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Understanding and Fixing Bash Script Errors: Handling command substitution: syntax error near unexpected token When working with Bash scripting, encountering syntax errors can be a frustrating experience, especially if you are still getting familiar with the nuances of the language. One common error that may arise is: command substitution: line 72: syntax error near unexpected token ('`. This guide will help you understand what causes this error and how to fix it effectively. The Problem This specific error message typically points to issues with command substitution, particularly when using process substitutions in Bash scripts. Here is an example of the offending code: [[See Video to Reveal this Text or Code Snippet]] The error likely occurs at line 72, which uses process substitutions, indicated by the <(command) syntax, alongside attempting to execute it in a situation where Bash may not be properly recognizing it. The Cause of the Error The root cause of this syntax error lies in how Bash handles process substitutions and its POSIX compliance. Here are the key points to understand: Process Substitution in Bash: This feature is a Bash extension and not universally available in all shell environments. Running in POSIX Mode: When Bash is ran using the sh command, it may invoke a less feature-rich shell, often in POSIX mode, which does not recognize Bash-specific extensions like process substitution. How to Identify Your Shell Environment When running your script, you might use this command: [[See Video to Reveal this Text or Code Snippet]] In this case, Bash runs as sh, and thus, it defaults to POSIX mode, leading to unrecognized syntax, such as your process substitutions. The Solution To fix this error, you can adopt one of the following approaches: 1. Run the Script Directly Instead of invoking your script with sh, run it directly by marking it as executable and executing it by name. Here’s how to do it: Make your script executable by running: [[See Video to Reveal this Text or Code Snippet]] Execute the script directly: [[See Video to Reveal this Text or Code Snippet]] When launched this way, the shebang (the first line of the script) will dictate the behavior of the script and allow the use of Bash features like process substitution. 2. Check the Shebang Line Ensure your script starts with an appropriate shebang line for Bash. It should read something like this: [[See Video to Reveal this Text or Code Snippet]] This specifies that the script should always run using Bash, regardless of how it’s invoked. 3. Avoid Running with sh As a best practice, avoid executing the script using sh if your script relies on Bash-specific features, as this limits the syntax available to you and leads to potential errors like the one you encountered. Conclusion Debugging Bash scripts can come with its challenges, particularly when transitioning to using advanced features like process substitutions. By understanding how Bash interacts with these features and ensuring you run your scripts correctly, you can overcome common syntax errors effectively. Implement the above solutions, and you should be able to modify scripts without running into the command substitution syntax error again. If you've found this guide useful or have any questions or further topics you want to cover regarding Bash scripting, please leave a comment below!