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Discover how to effectively filter and detect drifts in Terraform plans using shell scripts with practical solutions.
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How to Filter a Specific Line from Terraform Plan Output

Terraform is a powerful tool for managing infrastructure as code. However, sometimes, you may need to interface with its output in a more streamlined way. One common scenario is detecting drifts in your Terraform plans. If you’re working with shell scripts to automate this process, you might run into issues where the expected filtered output isn’t displayed correctly. This guide will guide you through the problem of filtering Terraform plan outputs and how to resolve it.

The Problem: Inconsistent Output in Terraform Drift Checks

When trying to check for drift in Terraform plans, you might find that the output isn't as expected. The primary objective is to filter through the output of terraform plan to identify if there are any changes, additions, or deletions. You can use tools like grep in your shell scripts for this purpose. However, without the correct syntax, you may end up with the entire output instead of a focused summary.

Here's the Scenario

You might set up a shell script that looks like this:

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

You might expect the output to only reflect the drift details, but instead, you receive the complete Terraform drift plan.

The Solution: Quoting Variables for Proper Filtering

The main issue here is related to how Bash handles variable expansion and newlines. When you don't quote the variable $tf_plan, Bash strips the newlines, treating the entire plan as one long string. This confusion results in grep processing the entire input rather than individual lines.

Here's How to Fix It

The solution is straightforward—add quotes around your variable when passing it to echo. Here's the corrected block of code:

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

Breakdown of Changes:

Quoting the Variable: By enclosing $tf_plan in quotes ("$tf_plan"), we ensure that grep can correctly identify and filter out the relevant lines by preserving the newline characters.

Expected Output

With this adjustment, the output should correctly reflect the drift state. For a scenario where a drift is detected, the output will resemble:

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

Conclusion

Filtering the output of Terraform plans in a shell script can initially seem challenging, especially when dealing with large outputs. By understanding how Bash handles variables and adjusting your syntax accordingly, you can effectively streamline your drift detection process with ease.

Final Thoughts

Shell scripting, combined with Terraform, can enhance your infrastructure management significantly. By paying attention to details like variable quoting, you can ensure that your scripts perform reliably. Happy scripting!