Substitute environment variables in a string:
>>> import os
>>> from envsubst import envsubst
>>> del os.environ['PS1']
>>> print(envsubst('$USER@$HOST ${PS1:-$}:'))
[email protected] $:
>>> os.environ['PS1'] = ''
>>> print(envsubst('$USER@$HOST ${PS1:-$}:'))
[email protected] $:
>>> print(envsubst('$USER@$HOST ${PS1-foo}:'))
[email protected] :
>>> os.environ['DEFAULT_PROMPT'] = '$'
>>> print(envsubst('$USER@$HOST ${PS1:-$DEFAULT_PROMPT}:'))
Also supports $0, $1, etc. from argv.