Скачать или смотреть Overcoming CMake Command Line Option Issues in zsh

Discover why `CMake` options fail to split in `zsh` and learn how to remedy this common issue efficiently.
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This video is based on the question https://stackoverflow.com/q/68754400/ asked by the user 'Tom de Geus' ( https://stackoverflow.com/u/2646505/ ) and on the answer https://stackoverflow.com/a/68755452/ provided by the user 'Alex Reinking' ( https://stackoverflow.com/u/2137996/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Overcoming CMake Command Line Option Issues in zsh

When working with CMake, an essential tool for building software, you may encounter a frustrating scenario where command line options do not split as expected, particularly when using the zsh shell. This issue can lead to confusion and delays in your development process, especially if you're accustomed to the behavior in bash. In this guide, we’ll explore the root of the problem and provide a straightforward solution to avoid such pitfalls in the future.

The Initial Problem: Command Line Options Not Splitting

Consider a scenario where you have the following simple CMakeLists.txt file:

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When your command line call looks like this:

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You see the expected output:

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However, things take a wrong turn when you attempt to use an intermediate variable in zsh. For example:

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The output becomes a mix of the expected and unexpected:

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Why does this happen? Why does CMake fail to correctly parse the options?

Understanding the Cause: Shell Behavior Differences

The key to understanding this issue lies not in CMake itself, but in how different shells, specifically bash and zsh, handle variable expansion and word-splitting:

Bash: By default, when you expand a variable, it automatically splits words based on spaces, correctly passing options to CMake.

Zsh: Unlike bash, zsh does not perform word-splitting by default during variable expansion. This means that when you use ${CMAKE_ARGS}, the entire string is treated as one single argument, leading to incorrect behavior in CMake.

For instance, while bash would correctly identify and split -DUSE_ASSERT=1 and -DUSE_DEBUG=0 as two separate flags, zsh sees it all as one massive string, causing the confusion.

The Solution: Correct Variable Expansion

To overcome this issue in zsh, you need to restore the expected behavior of word-splitting during variable expansion. This can be done by modifying the way you expand your variable in the command line. Specifically, use the following syntax:

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The =${CMAKE_ARGS} syntax instructs zsh to perform word-splitting on the variable, effectively transforming it back into the expected individual command line options.

Conclusion

Understanding the differences in how shells handle variable expansion can significantly reduce the frustration when working in various environments. By following the solutions outlined in this post, you can overcome the command line option splitting issues you may encounter while using CMake in zsh. Remember, simply adjusting how you expand your variables can save you considerable time and effort in your development cycle.

Feel free to share your experiences or any additional tips you might have for working with CMake, zsh, or any other shell-related concerns in the comments below!