This is a very experimental feature and it will have breaking changes in future releases.

Environment is a class that helps defining modifications to the environment variables. This class is used by other tools like the conan.tools.gnu autotools helpers and the VirtualBuildEnv and VirtualRunEnv generator.


def __init__(self, conanfile):
  • conanfile: the current recipe object. Always use self.

Variable declaration

from conan.tools.env import Environment

env = Environment(self)
env.define("MYVAR1", "MyValue1")  # Overwrite previously existing MYVAR1 with new value
env.append("MYVAR2", "MyValue2")  # Append to existing MYVAR2 the new value
env.prepend("MYVAR3", "MyValue3") # Prepend to existing MYVAR3 the new value
env.remove("MYVAR3", "MyValue3")  # Remove the MyValue3 from MYVAR3
env.unset("MYVAR4")               # Remove MYVAR4 definition from environment

# And the equivalent with paths
env.define_path("MYPATH1", "path/one")  # Overwrite previously existing MYPATH1 with new value
env.append_path("MYPATH2", "path/two")  # Append to existing MYPATH2 the new value
env.prepend_path("MYPATH3", "path/three") # Prepend to existing MYPATH3 the new value

The “normal” variables (the ones declared with define, append and prepend) will be appended with a space, by default, but the separator argument can be provided to define a custom one.

The “path” variables (the ones declared with define_path, append_path and prepend_path) will be appended with the default system path separator, either : or ;, but it also allows defining which one.


Environments can be composed:

from conan.tools.env import Environment

env1 = Environment(self)
env2 = Environment(self)

env1.compose(env2) # env1 has priority, and its modifications will prevail

Creating launcher files

Environments can generate launcher files:

env1 = Environment(self)
env1.define("foo", "var")

It will generate automatically a my_launcher.bat for Windows systems or my_launcher.sh otherwise.

Also, by default, Conan will automatically append that launcher file path to a list that will be used to create a conan_env.bat/sh file aggregating all the launchers in order. The conan_env.sh/bat launcher will be created after the execution of the generate() method.

The conan_env.bat/sh launcher will be executed by default before calling every self.run command. You can change the default launcher with the env argument:

# This will automatically wrap the "foo" command with the correct launcher:
# my_launcher.sh && foo
self.run("foo", env=["my_launcher"])

You can also use auto_activate=False argument to avoid appending the script to the aggregated conan_env.bat/sh:

env1 = Environment(self)
env1.define("foo", "var")
env1.save_script("my_launcher", auto_activate=False)

Applying the environment

As an alternative to a launcher, environments can be applied in the python environment, but the usage of the launchers is recommended if possible:

from conan.tools.env import Environment

env1 = Environment(self)
env1.define("foo", "var")
with env1.apply():
   # Here os.getenv("foo") == "var"

Iterating the Environment object

You can iterate an Environment object like this:

env1 = Environment()
env1.append("foo", "var")
env1.append("foo", "var2")
for name, value in env.items():
    assert name == "foo":
    assert value == "var var2"

Other Environment usage

There are some other places where this Environment is used internally by Conan:

  • In recipes package_info() method, in new self.buildenv_info and self.runenv_info.

  • In generators like AutootoolsDeps, AutotoolsToolchain, that need to define environment.

  • In profiles new [buildenv] and [runenv] sections.

The definition in package_info() is as follow, taking into account that both self.buildenv_info and self.runenv_info are objects of Environment() class.

from conans import ConanFile

class App(ConanFile):
    name = "mypkg"
    version = "1.0"
    settings = "os", "arch", "compiler", "build_type"

    def package_info(self):
        # This is information needed by consumers to build using this package
        self.buildenv_info.append("MYVAR", "MyValue")
        self.buildenv_info.prepend_path("MYPATH", "some/path/folder")

        # This is information needed by consumers to run apps that depends on this package
        # at runtime
        self.runenv_info.define("MYPKG_DATA_DIR", os.path.join(self.package_folder,