$ template -h
usage: template [-h] [-o OUTPUT] [filename]

A CLI tool for generating files from Jinja2 templates and environment
variables.

positional arguments:
  filename              Input filename

  optional arguments:
    -h, --help            show this help message and exit
      -o OUTPUT, --output OUTPUT
                              Output to filename
$ export name='John'
$ echo 'Hello {{ name if name is defined else 'world' }}. | template
Hello John.
$ echo '{{ USER }}' > username.j2
$ template --output username.txt username.j2
$ cat username.txt
John