How to Effectively Return Error Code When Using tee in Bash

Discover how to ensure the correct return code is passed in Bash when using the `tee` command with command piping.
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How to Effectively Return Error Code When Using tee in Bash

Using the tee command in Bash can sometimes lead to unexpected return codes, particularly when you’re piping the output of commands. This can be frustrating, especially when you need an accurate indication of whether your commands succeeded or failed. In this guide, we will explore a solution to ensure that you return the correct error code when using tee in your Bash scripts.

The Problem

When executing commands in Bash, it's important to obtain the right exit status. The exit status of a command can inform you if the command executed successfully or encountered an error. However, when you use tee in a pipeline, the exit status may not reflect the first command but instead may relate to tee.

Example 1: Expected Behavior

Consider the following command:

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Output:

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Here, the command fails as expected, and you receive the correct exit status of 1.

Example 2: Unexpected Behavior

Now, let’s look at a scenario where tee is involved:

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Output:

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In this example, you might expect the exit code to reflect the failure of the cp command. Instead, it returns 0, indicating success, which is misleading.

The Solution: Use set -o pipefail

You can solve this problem by utilizing the pipefail option in Bash. When activated, the pipefail option changes the behavior of the pipeline so that the return status is the value of the last command to exit with a non-zero status. If all commands in the pipeline succeed, then the exit status will be zero. To implement this solution, follow these steps:

Steps to Implement

Activate Pipefail: Use the set -o pipefail command at the beginning of your script or in the command line before executing your commands.

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Run Your Command with Tee: Execute your command with tee in the pipeline.

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Check the Exit Status: After executing the command, you can check the exit status using $?.

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Example Implementation

Here’s how your complete command should look:

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With this approach, you should now see the expected return code reflecting the status of the cp command, allowing you to handle errors more effectively.

Conclusion

Handling return codes when using tee in Bash can initially seem tricky, but by using the set -o pipefail option, you can ensure you are correctly capturing errors from your initial commands. This allows for more reliable scripts and easier debugging. Try implementing this solution in your Bash scripts to see the difference in how error statuses are managed.

Feel free to share your thoughts or any additional tips in the comments below!