How to determine SSL cert expiration date from a PEM encoded certificate?

Question

If I have the actual file and a Bash shell in Mac or Linux, how can I query the cert file for when it will expire? Not a web site, but actually the certificate file itself,

Answer 1

One line checking on true/false if cert of domain will be expired in some time later(ex. 15 days):

openssl x509 -checkend $(( 24*3600*15 )) -noout -in <(openssl s_client -showcerts -connect my.domain.com:443 /dev/null | openssl x509 -outform PEM)
if [ $? -eq 0 ]; then
  echo 'good'
else
  echo 'bad'
fi