Virtual Environments

Conan offer three special Conan generators to create virtual environments:

virtualenv: Declares the self.env_info variables of the requirements.
virtualbuildenv: Special build environment variables for autotools/visual studio.
virtualrunenv: Special environment variables to locate executables and shared libraries in the requirements.

These virtual environment generators create two executable script files (.sh or .bat depending on the current operating system), one to activate the virtual environment (set the environment variables) and one to deactivate it.

You can aggregate two or more virtual environments, that means that you can activate a virtualenv and then activate a virtualrunenv so you will have available the environment variables declared in the env_info object of the requirements plus the special environment variables to locate executables and shared libraries.

Virtualenv generator

Conan provides a virtualenv generator, able to read from each dependency the self.env_info variables declared in the package_info() method and generate two scripts “activate” and “deactivate”. These scripts set/unset all env variables in the current shell.

Example:

The recipe of cmake/3.16.3 appends to the PATH variable the package folder/bin.

You can check existing CMake conan package versions in conan-center with:

$ conan search cmake* -r=conan-center

In the bin folder there is a cmake executable:

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

Let’s prepare a virtual environment to have cmake available in the path. Open conanfile.txt and change (or add) virtualenv generator:

[requires]
cmake/3.16.3

[generators]
virtualenv

Run conan install:

$ conan install .

You can also avoid the creation of the conanfile.txt completely and directly do:

$ conan install cmake/3.16.3 -g=virtualenv

Activate the virtual environment, and now you can run cmake --version to check that you have the installed CMake in path.

$ source activate.sh # Windows: activate.bat without the source
$ cmake --version

Two sets of scripts are available for Windows - activate.bat/deactivate.bat and activate.ps1/deactivate.ps1 if you are using powershell. Deactivate the virtual environment (or close the console) to restore the environment variables:

$ source deactivate.sh # Windows: deactivate.bat without the source

Virtualbuildenv environment

Use the generator virtualbuildenv to activate an environment that will set the environment variables for Autotools and Visual Studio.

The generator will create activate_build and deactivate_build files.

Virtualrunenv generator

Use the generator virtualrunenv to activate an environment that will:

Append to PATH environment variable every bin folder of your requirements.
Append to LD_LIBRARY_PATH and DYLD_LIBRARY_PATH environment variables each lib folder of your requirements.

The generator will create activate_run and deactivate_run files. This generator is especially useful:

If you are requiring packages with shared libraries and you are running some executable that needs those libraries.
If you have a requirement with some tool (executable) and you need it in the path.

In the previous example of the cmake recipe, even if the cmake package doesn’t declare the self.env_info.path variable, using the virtualrunenv generator, the bin folder of the package will be available in the PATH. So after activating the virtual environment we could just run cmake in order to execute the package’s cmake.