Extract certificate chain from a URL you visit

extract_certs.sh

#!/bin/bash

# Derived from https://unix.stackexchange.com/a/487546/378468

URL=www.google.com

openssl s_client -showcerts -verify 5 -servername "$URL" -connect "$URL":443 < /dev/null | \
    awk '/BEGIN CERTIFICATE/,/END CERTIFICATE/{ if(/BEGIN CERTIFICATE/){a++}; out="cert"a".pem"; print >out}'

for cert in *.pem; do
    newname=$(openssl x509 -noout -subject -in $cert | sed -nE 's/.*CN ?= ?([^,]*).*/\1/; s/[ ,.*]/_/g; s/__/_/g; s/_-_/-/; s/^_//g;p' | tr '[:upper:]' '[:lower:]').pem
    echo "${newname}";
    mv "${cert}" "${newname}"
done