Certificate Report Bash Script - Expiring within 30days

I'm using the below for now, but it aint so useful.

cat Certificate_script

rm Certificate_Report.txt
tmsh list sys crypto recursive cert | grep '^sys\|expiration\|common-name' > Certificate_Report.txt

So I thought of going with for loop condition on a new script by using the below,

delete files if already exists
rm /var/tmp/Certificate_mgmt/Certificate_validity-report.txt
rm /var/tmp/Certificate_mgmt/validity-report.txt
pushd /config/filestore/files_d/Common_d/certificate_d/
for x in *.crt_*; do
  echo -n $x
 remove the file type .crt
  y=${x%.crt_*}
  echo -e $y >> /var/tmp/Certificate_mgmt/validity-report.txt
openssl x509 -noout -in /config/filestore/files_d/Common_d/certificate_d/$y.* -dates -serial -subject >> /var/tmp/Certificate_mgmt/validity-report.txt
  echo -e "\n----------" >> /var/tmp/Certificate_mgmt/validity-report.txt
done
cat /var/tmp/Certificate_mgmt/validity-report.txt |  grep -B4 subject > /var/tmp/Certificate_mgmt/Certificate_validity-report.txt
popd

But the point is I'm just getting the required parameters, how do I manage to create a report which could get me [Cert name, Common Name, Expiry Date, Serial] expiring in 30 days.