Retrieves values from Docker environment variables
The primary use case for this was inspecting TLS certificates in Docker environment variables, which looks something like this:
Verify a TLS cert in a container abc123 with PEM data in MYAPP_TLS_CRT and MYAPP_TLS_KEY:
$ ./dockerenv --container-id abc123 tls verify --cert MYAPP_TLS_CRT --key MYAPP_TLS_KEY
YYYY/MM/DD HH:MM:SS Loaded X509KeyPair with 1 certs
YYYY/MM/DD HH:MM:SS Certificate 0 (CA: false)
YYYY/MM/DD HH:MM:SS =========================
YYYY/MM/DD HH:MM:SS Subject : CN=myapp-tls-certificate-subject
YYYY/MM/DD HH:MM:SS Subject Key Id :
YYYY/MM/DD HH:MM:SS
YYYY/MM/DD HH:MM:SS Issuer : CN=myapp-selfsigned-ca
YYYY/MM/DD HH:MM:SS Authority Key Id :
YYYY/MM/DD HH:MM:SS
YYYY/MM/DD HH:MM:SS Not Before : YYYY-MM-DD HH:MM:SS +0000 UTC (1 month ago)
YYYY/MM/DD HH:MM:SS Not After : YYYY-MM-DD HH:MM:SS +0000 UTC (5 months from now)
YYYY/MM/DD HH:MM:SS
...
To save the value of MYAPP_DATABASE_PASS in container abc123 to the local var DB_PASSWORD:
$ DB_PASSWORD=$(dockerenv -c abc123 -v MYAPP_DATABASE_PASS)