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What Does $Env Mean In Cmake?

2 minutes read

In CMake, $ENV is a variable that provides access to environment variables set on the system where CMake is running. These variables can be accessed and used within the CMakeLists.txt files to pass information or configure the build process based on the values of these environment variables. This can be useful for dynamically adjusting build settings or paths based on the system environment.


How to use $env in cmake?

In CMake, the $env command is used to access environment variables within the CMake script. Here's how you can use $env in CMake:

  1. To access the value of an environment variable, use the following syntax:
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$ENV{VARIABLE_NAME}


For example, if you want to access the value of the PATH environment variable, you can use:

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message($ENV{PATH})


  1. You can also use environment variables in CMake commands. For example, if you want to set a variable based on the value of an environment variable, you can do so like this:
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set(MY_VAR $ENV{MY_ENV_VAR})


  1. You can use environment variables in various parts of your CMake script, such as setting variables, conditionals, and commands.


Overall, using $env in CMake allows you to access and utilize environment variables in your CMake scripts, making it easier to customize build configurations and behavior based on the environment.


How does $env contribute to the maintainability of cmake scripts?

The $env variable in CMake allows for the use of environment variables in scripts, which can help make the scripts more maintainable by allowing for easier configuration and customization. This can be particularly useful in scenarios where different systems or environments require different settings or paths, as it allows these values to be easily changed without having to modify the script itself. By using $env, scripts can be made more flexible and adaptable, reducing the need for hardcoding values and making them easier to maintain and update in the long run.


How does $env help with environmental variables in cmake?

$env is a special syntax used in CMake to access and manipulate environmental variables within a CMake script. This can be useful when specifying paths or settings that are dependent on the user's environment.


For example, if you want to set a specific include directory based on an environmental variable, you can use $env to access that variable and set the include directory accordingly:

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include_directories($env{MY_INCLUDE_DIR})


This will include the directory specified in the MY_INCLUDE_DIR environmental variable.


$env can also be used to set environmental variables within a CMake script, allowing you to customize the build process based on the user's environment:

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set(ENV{MY_ENV_VAR} "/path/to/some/directory")


This will set the MY_ENV_VAR environmental variable to the specified directory for the duration of the CMake script execution.


Overall, $env in CMake provides a flexible way to work with environmental variables, making it easier to customize build configurations based on the user's environment.

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