pip install lawyerup

$ lawyerup --help
usage: lawyerup [-h] [--vars | --context [KEY=VALUE [KEY=VALUE ...]]] LICENSE

Add license headers to files passed in on stdin

positional arguments:
  LICENSE               the license to add, one of GPR, GRR, generic

optional arguments:
  -h, --help            show this help message and exit
  --vars                list template variables for specified license
  --context [KEY=VALUE [KEY=VALUE ...]]
                        KEY=VALUE formatted variables to generate the license

$ cat list-of-files | lawyerup <license> --context KEY1=VAL1 KEY2=VAL2 ...