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Real-Time Output Flushing in Bash Scripts

Learn how to achieve real-time output flushing in bash scripts and avoid waiting for commands to finish before seeing their results. --- This video is based on the question https://stackoverflow.com/q/76552745/ asked by the user 'vaso123' ( https://stackoverflow.com/u/1087195/ ) and on the answer https://stackoverflow.com/a/76552797/ provided by the user 'Barmar' ( https://stackoverflow.com/u/1491895/ ) 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: Flushing output while program runs from bash Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Real-Time Output Flushing in Bash Scripts: A Simple Guide Bash scripting can sometimes be a tricky experience, especially when you're dealing with commands whose outputs you want to see immediately while they are running. If you’ve ever run a command in a bash script and noticed that the output is only produced after the command has finished executing, then you’re not alone! This article will guide you on how to modify your bash script so that output is flushed real-time, allowing you to see results as they come in. Understanding the Problem Let’s take a look at your initial script: [[See Video to Reveal this Text or Code Snippet]] The issue here is that readarray collects all output from the command into an array, which means you won't see anything printed to the standard output (STDOUT) until $COMMAND has finished executing. This can be frustrating if you're running potentially long commands, such as ls -la or unzip, and you want to monitor their progress. The Solution: Stream Output with a While Loop Instead of storing all outputs in an array before printing them, we can modify the script to read from the command output in real-time. Here’s how you can do it: Step 1: Using the While Loop You can replace the readarray command with a while loop. Here’s an example of how to do this: [[See Video to Reveal this Text or Code Snippet]] What This Does: The while loop will read each line from the command as it runs. It prints each line immediately to STDOUT using echo. Meanwhile, it appends each line to theLines variable, allowing you to keep a record if needed. Step 2: Keeping Output in an Array (Optional) If you want to keep outputs in an array for any reason, you can further extend the script as follows: [[See Video to Reveal this Text or Code Snippet]] Important Note About Newlines: It's essential to notice how we use $'
' when adding new lines to the theLines variable. Bash doesn’t handle escape sequences inside double quotes, so the $'
' notation is necessary to correctly add new lines. Conclusion Now you know how to modify your bash scripts to achieve real-time output flushing! This method allows you to monitor the output of commands as they run, making your scripts more interactive and informative. Whether you're executing file listing commands or decompressing files, watching their output in real-time can improve your scripting experience significantly. Happy scripting! If you have any further questions or need additional help with bash scripts, feel free to ask.