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CLI Arguments with Environment Variables

You can also configure a CLI argument to read a value from an environment variable if it is not provided in the command line as a CLI argument.

To do that, use the envvar parameter for typer.Argument():

import typer


def main(name: str = typer.Argument("World", envvar="AWESOME_NAME")):
    typer.echo(f"Hello Mr. {name}")


if __name__ == "__main__":
    typer.run(main)

In this case, the CLI argument name will have a default value of "World", but will also read any value passed to the environment variable AWESOME_NAME if no value is provided in the command line:

// Check the help
$ python main.py --help

Usage: main.py [OPTIONS] [NAME]

Arguments:
  [NAME]  [env var: AWESOME_NAME;default: World]

Options:
  --install-completion  Install completion for the current shell.
  --show-completion     Show completion for the current shell, to copy it or customize the installation.
  --help                Show this message and exit.

// Call it without a CLI argument
$ python main.py

Hello Mr. World

// Now pass a value for the CLI argument
$ python main.py Czernobog

Hello Mr. Czernobog

// And now use the environment variable
$ AWESOME_NAME=Wednesday python main.py

Hello Mr. Wednesday

// CLI arguments take precedence over env vars
$ AWESOME_NAME=Wednesday python main.py Czernobog

Hello Mr. Czernobog

Multiple environment variables

You are not restricted to a single environment variable, you can declare a list of environment variables that could be used to get a value if it was not passed in the command line:

import typer


def main(name: str = typer.Argument("World", envvar=["AWESOME_NAME", "GOD_NAME"])):
    typer.echo(f"Hello Mr. {name}")


if __name__ == "__main__":
    typer.run(main)

Check it:

// Check the help
$ python main.py --help

Usage: main.py [OPTIONS] [NAME]

Arguments:
  [NAME]  [env var: AWESOME_NAME, GOD_NAME;default: World]

Options:
  --install-completion  Install completion for the current shell.
  --show-completion     Show completion for the current shell, to copy it or customize the installation.
  --help                Show this message and exit.

// Try the first env var
$ AWESOME_NAME=Wednesday python main.py

Hello Mr. Wednesday

// Try the second env var
$ GOD_NAME=Anubis python main.py

Hello Mr. Anubis

Hide an env var from the help text

By default, environment variables used will be shown in the help text, but you can disable them with show_envvar=False:

import typer


def main(name: str = typer.Argument("World", envvar="AWESOME_NAME", show_envvar=False)):
    typer.echo(f"Hello Mr. {name}")


if __name__ == "__main__":
    typer.run(main)

Check it:

//Check the help
$ python main.py --help

// It won't show the env var
Usage: main.py [OPTIONS] [NAME]

Arguments:
  [NAME]  [default: World]

Options:
  --install-completion  Install completion for the current shell.
  --show-completion     Show completion for the current shell, to copy it or customize the installation.
  --help                Show this message and exit.

// But it will still be able to use it
$ AWESOME_NAME=Wednesday python main.py

Hello Mr. Wednesday

Technical Details

In Click applications the env vars are hidden by default. 🙈

In Typer these env vars are shown by default. 👀