openssl s_client -showcerts -connect example.com:443
openssl s_client -verify 0 -showcerts -connect example.com:443
openssl s_client -tls1 -showcerts -connect example.com:443
openssl x509 -noout -in example.com.crt -text | less
openssl rsa -in example.com.key -noout -text
openssl req -in example.com.csr -noout -text | less
openssl s_client -connect example.com:443 (then issue some HTTP commands interactively)
openssl s_client -starttls smtp -connect example.com:25 (then issue SMTP commands interactively)
openssl req -newkey rsa:2048 -keyout key.pem -out req.pem
openssl req -new -key key.pem -out req.pem