DOMAIN=example.com
openssl req -new -newkey rsa:2048 -nodes -keyout $DOMAIN.key -out $DOMAIN.csr
cat STAR_$DOMAIN.crt COMODORSADomainValidationSecureServerCA.crt COMODORSAAddTrustCA.crt AddTrustExternalCARoot.crt > $DOMAIN.crt
openssl rsa -in $DOMAIN.key -text > $DOMAIN.pem
Ref: https://gist.github.com/bradmontgomery/6487319
openssl s_client -servername example.com -connect example.com:443 </dev/null 2>/dev/null | openssl x509 -text