Software⏱️ 4 min read📅 2026-06-11

How to Fix: Bash script 'while read' loop causes 'broken pipe' error when run with GNU Parallel

GNU Parallel issue with while read loop causing broken pipe error.

Quick Answer: Turn off the SIGPIPE signal to prevent data corruption.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🚀 How to Resolve This Issue
  3. 💡 Conclusion

The 'broken pipe' error is a common issue that occurs when using bash scripts with GNU Parallel. This error happens when the input to the script exceeds the maximum allowed size, causing the pipe to become blocked and resulting in an error.

This problem is frustrating because it can be difficult to determine the cause of the issue, especially for users who are not familiar with bash scripting or GNU Parallel. However, by following the steps outlined in this guide, you should be able to resolve the issue and continue using your script without any issues.

🔍 Why This Happens

  • The primary reason why the 'broken pipe' error occurs when using a while read loop in bash scripts with GNU Parallel is due to the way that GNU Parallel handles input. When GNU Parallel receives a large amount of input, it will split the input into chunks and process them in parallel. However, if the script uses a while read loop to process each chunk individually, it can cause the pipe to become blocked and result in an error.
  • An alternative reason for this issue is that some systems may have limitations on the size of pipes or buffers, which can cause the 'broken pipe' error even when using a while read loop. In such cases, disabling the SIGPIPE signal may help resolve the issue.

🚀 How to Resolve This Issue

Disabling SIGPIPE Signal

  1. Step 1: To disable the SIGPIPE signal, you can add the following line to your bash script before using the while read loop: set -u. This will prevent the 'broken pipe' error from occurring.
  2. Step 2: Alternatively, you can use the following command to disable the SIGPIPE signal on a per-command basis: bash -c 'set -u; ./linkcheck.sh'. However, this method is not recommended as it can have side effects such as data corruption if not used carefully.
  3. Step 3: It's also worth noting that some systems may have different default settings for SIGPIPE handling. In such cases, disabling the signal may require additional configuration or tweaking of system settings.

Modifying Script to Process Chunks Individually

  1. Step 1: To avoid using a while read loop altogether, you can modify your script to process each chunk individually. This can be done by replacing the while read loop with a for loop that processes each line of input separately.
  2. Step 2: For example, you can use the following code: domain=$(cat); host $domain. This will process each line of input individually and avoid the 'broken pipe' error.

💡 Conclusion

In conclusion, the 'broken pipe' error in bash scripts with GNU Parallel can be caused by a variety of factors. By disabling the SIGPIPE signal or modifying your script to process chunks individually, you should be able to resolve the issue and continue using your script without any issues.

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