Save Remote SSL Certificate via Linux Command Line

Something like:

openssl s_client -servername remote.server.net -connect remote.server.net:443 </dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' >/path/to/certificate.pem

That's what I use with fetchmail to retrieve the certificate of an SSL capable IMAP or POP3 server (except obviously I don't use port 443)

(Note that "redundant" -servername parameter is necessary to make openssl do a request with SNI support.)

From http://www.madboa.com/geek/openssl/#cert-retrieve

#!/bin/sh
#
# usage: retrieve-cert.sh remote.host.name [port]
#
REMHOST=$1
REMPORT=${2:-443}

echo |\
openssl s_client -connect ${REMHOST}:${REMPORT} 2>&1 |\
sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p'