SSL Cert Catalog with Expiry Checking

ssl_cert_expiry_check.sh

#!/usr/bin/bash

function monthnumber {
	month=$(echo ${1:0:3} | tr '[a-z]' '[A-Z]')
	MONTHS="JANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC"
	tmp=${MONTHS%%$month*}
	month=${#tmp}
	monthnumber=$((month/3+1))
	printf "%02d\n" $monthnumber
}

# Or at the expense of some flexibility and brevity, you get more readability:
function monthnumber2 {
	case $(echo ${1:0:3} | tr '[a-z]' '[A-Z]') in
		JAN) monthnumber="01" ;;
		FEB) monthnumber="02" ;;
		MAR) monthnumber="03" ;;
		APR) monthnumber="04" ;;
		MAY) monthnumber="05" ;;
		JUN) monthnumber="06" ;;
		JUL) monthnumber="07" ;;
		AUG) monthnumber="08" ;;
		SEP) monthnumber="09" ;;
		OCT) monthnumber="10" ;;
		NOV) monthnumber="11" ;;
		DEC) monthnumber="12" ;;
	esac
	printf "%02d\n" $monthnumber
}

TODAY=$( date "+%Y%m%d" )

echo "GET /" | openssl s_client -connect github.com:443 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > tmp.pem
cert_expiry_date=$(openssl x509 -in tmp.pem -noout -enddate | cut -d'=' -f2)
month_name=$(echo $cert_expiry_date | cut -d' ' -f1)
month_number=$( monthnumber $month_name )
cert_expiration_datestamp=$( echo $cert_expiry_date | awk "{printf \"%d%02d%02d\",\$4,\"${month_number}\",\$2}" )

echo "compare: [ $cert_expiration_datestamp -gt $TODAY ]"
if [ $cert_expiration_datestamp -gt $TODAY ] ; then
	echo "all ok, the cert expiration date is in the future."
else
	echo "WARNING: cert expiration date is in the past."
fi