$ cat test.tmpl
Hi ${USER}, this is a ${ENVIRONMENT} environment
USER=ruan ENVIRONMENT=test envsubst '${USER},${ENVIRONMENT}' < test.tmpl
Hi ruan, this is a test environment
$ cat test.tmpl
Hi ${USER}, this is a ${ENVIRONMENT} environment
USER=ruan ENVIRONMENT=test envsubst '${USER},${ENVIRONMENT}' < test.tmpl
Hi ruan, this is a test environment