Environment variables

There are several use cases for environment variables:

  • Conan global configuration environment variables (e.g. CONAN_COMPRESSION_LEVEL). They can be configured in conan.conf or as system environment variables, and control Conan behavior.

  • Package recipes can access environment variables to determine their behavior. A typical example would be when launching CMake. It will check for CC and CXX environment variables to define the compiler to use. These variables are mostly transparent for Conan, and just used by the package recipes.

  • Environment variables can be set in different ways:

    • global, at the OS level, with export VAR=Value or in Windows SET VAR=Value.

    • In the Conan command line: conan install -e VAR=Value.

    • In profile files.

    • In package recipes in the self.env_info field, so they are activated for dependent recipes.

Defining environment variables

You can use profiles to define environment variables that will apply to your recipes. You can also use -e parameter in conan install, conan info and conan create commands.

[env]
CC=/usr/bin/clang
CXX=/usr/bin/clang++

If you want to override an environment variable that a package has inherited from its requirements, you can use either profiles or -e to do it:

conan install . -e mypkg:PATH=/other/path

If you want to define an environment variable, but you want to append the variables declared in your requirements, you can use the [] syntax:

$ conan install . -e PATH=[/other/path]

This way the first entry in the PATH variable will be /other/path, but the PATH values declared in the requirements of the project will be appended at the end using the system path separator.

Automatic environment variables inheritance

If your dependencies define some env_info variables in the package_info() method, they will be automatically applied before calling the consumer conanfile.py methods source(), build(), package() and imports(). You can read more about env_info object here.

For example, if you are creating a package for a tool, you can define the variable PATH:

class ToolExampleConan(ConanFile):
   name = "my_tool_installer"
   ...

   def package_info(self):
       self.env_info.path.append(os.path.join(self.package_folder, "bin"))

If another Conan recipe requires the my_tool_installer in the source(), build(), package() and imports(), the bin folder of the my_tool_installer package will be automatically appended to the system PATH. If my_tool_installer packages an executable called my_tool_executable in the bin of the package folder, we can directly call the tool because it will be available in the path:

class MyLibExample(ConanFile):
   name = "my_lib_example"
   ...

   def build(self):
       self.run(["my_tool_executable", "some_arguments"])

You could also set CC, CXX variables if we are packing a compiler to define what compiler to use or any other environment variable. Read more about tool packages here.