Taken from https://github.com/Noah-Huppert/scripts/blob/master/sslinfo

sslinfo.sh

#!/usr/bin/env bash
#?
# SSL Info - Displays information about the provided URL's SSL certificate.
#
# USAGE
#	sslinfo [OPTIONS] URL
#
# ARGUMENTS
# 	1. URL (string): URL to display SSL certificate information for. Should 
#			 not have a scheme components (ex., https://).
#
#			 Ex: www.noahh.io
#
#		 	 If a value matching the expression: /-*[Hh](?:elp)?$/
#			 is provided this help text will be printed.
# OPTIONS
# 	--trim,-t        Removes math garble (ex., 00:ae:86:12:f2:53:71:57:11) 
#			 from the output. Text that a human would most likely 
#			 not be able to make sense of.
#	
#	--page,-p        Page the potentially long output. The $PAGER
#			 environment variable must be configured.
#
# BEHAVIOR
#	Prints ssl certificate information to stdout
#?

# Options
while [ ! -z "$1" ]; do
	case "$1" in
		--trim|-t)
			trim=true
			;;
		--page|-p)
			# Check $PAGER environment variable is configured
			if [[ -z "$PAGER" ]]; then
				echo "Error: Page option provided but \$PAGER environment variable not set" >&2
				exit 1
			fi
			page=true
			;;
		--help|-h)
			show-help "$0"
			exit 1
			;;
		*)
			host="$1"
			;;
	esac

	shift
done

# Arguments
if [ -z "$host" ]; then
	echo "Error: host argument must be provided" >&2
	exit 1
elif ! [[ "$host" =~ ^([a-zA-Z0-9]+\.)+[a-zA-Z0-9]+$ ]]; then
	echo "Error: Invalid host \"$host\"" >&2
	exit 1
fi

# Openssl trick for getting cert info from SO: 
# https://serverfault.com/a/661982
info=$(echo | \
openssl s_client -showcerts -servername "$host" -connect "$host:443" 2>/dev/null | \
openssl x509 -inform pem -noout -text)

# Trim if requested
if [[ "$trim" ]]; then
	info=$(echo "$info" | sed -e '/\([0-9a-fA-F]\{2\}:\)\{2,\}/d')
fi

# Output info
# Page if requested
if [[ "$page" ]]; then
	echo "$info" | $PAGER
else
	echo "$info"
fi