Determine if SSL cert is about to expire

is_cert_expiring.sh

#!/usr/bin/env sh
# http://stackoverflow.com/questions/21297853/how-to-determine-ssl-cert-expiration-date-from-a-pem-encoded-certificate
# Usage: is_cert_expiring.sh [/path/to/cert/file.pem [seconds]]
1=${1:file.pem} # File path
2=${2:-86400}   # Seconds to expiry
if openssl x509 -checkend $2 -noout -in $1; then
  echo "Certificate is good for another day!"
else
  echo "Certificate has expired or will do so within 24 hours!"
  echo "(or is invalid/not found)"
fi