Varsubst is a rewrite of envsubst.

Varsubst render templates from a string with a given resolver.

Currently varsubst support shell-like variables.

Entry-point has currently been removed. It may be added in the future.

Resolvers provided are :

• EnvResolver : provide value based on environnement variables.
• DictResolver : provide value based on a given python dictionary.

Supported template variables

Varsubst support shell-like variables which are defined as follows:

• $MY_SIMPLE_VAR or ${MY_SIMPLE_VAR}: will resolve the variable MY_SIMPLE_VAR
• ${USER-default} : will resolve the variable USER. If variable is unset then default string is returned.
• ${USER-$DEFAULT_USER} : will resolve the variable USER. If variable is unset, resolve the variable DEFAULT_USER.
• ${USER:-default} : will resolve the variable USER. If variable is unset or empty then default string is returned.
• ${USER-$DEFAULT_USER} : will resolve the variable USER. If variable is unset or empty, resolve the variable DEFAULT_USER.

Usage

from varsubst import varsubst
from varsubst.resolvers import DictResolver
from varsubst.interpolators.jinja_interpolator import JinjaInterpolator

print(varsubst('$USER')) # result : 'tiboun'

print(varsubst('$UNDEFINED')) # result : KeyUnresolvedException('UNDEFINED')

print(varsubst('$UNDEFINED', fail_on_unresolved=False)) # result : ''

print(varsubst('$UNDEFINED', fail_on_unresolved=False)) # result : ''

print(varsubst('$USER', resolver=DictResolver({'USER': 'tiboun'})))

print(varsubst('{{ USER }}', interpolator=JinjaInterpolator()))

Extras

You may install varsubst[jinja2] as well if you intend to interpolate template with Jinja. If you plan to use jinja2 only, you may install it yourself in your project instead of using this one.