Determine how many days a certificate is still valid from within bash script - bash

Question

I want to check how many days the certificate of a website is valid from within a bash script which runs on a standard Ubuntu 14.04 server. openssl is available.
I already figured out that I can use openssl to get the target date
$ echo | openssl s_client -connect google.com:443 2>/dev/null|openssl x509 -noout -enddate
notAfter=Dec 22 16:37:00 2016 GMT
But how do I parse the resulting date and subtract the current one? Or might there be a better solution?

Answer 1

Just in single line
echo "(" $(date -d "`openssl x509 -in /etc/letsencrypt/live/d-herrmann.de/cert.pem -text -noout | grep "Not After" | cut -c 25-`" +%s) - $(date -d "now" +%s) ")" / 86400 | bc

Answer 2

With GNU date's %j to get day of the year and arithmetic expansion for subtraction:
$ echo $(( $(date -d "$(cut -d= -f2 <(echo 'notAfter=Dec 22 16:37:00 2016 GMT'))" '+%j') - $(date '+%j')))
73
$(date -d "$(cut -d= -f2 <(echo 'notAfter=Dec 22 16:37:00 2016 GMT'))" '+%j') gets us the day of the year from the date we have got, replace teh echo command inside process substitution, <(echo 'notAfter=Dec 22 16:37:00 2016 GMT') with the openssl command you have used initially
$(date '+%j') gets us today's date as day of the year
$(()) is used for subtracting the integers

Answer 3

date1="Dec 22 16:37:00 2016 GMT" # Future date
date2=$(date) # Current date
diff=$(($(date -d "$date1" +%j)-$(date -d "$date2" +%j))) #Diff between two date, %j is to show day of the year.
echo $diff #Display difference
73
Or just in one line:
echo $(($(date -d "Dec 22 16:37:00 2016 GMT" +%j)-$(date +%j)))
73

Answer 4

Here is a little script, which returns days, hours or minutes a cert is still valid, I just saved it in an executable file e.g. check_cert_age.sh
#!/bin/bash
# input domain as first parameter eg. ./heck_cert_age.sh stackoverflow.com
input="$1"
domain=$(echo "$input" | sed -e 's|^[^/]*//||' -e 's|/.*$||')
#domain=stackoverflow.com
echo
echo "Check the cert of Domain $domain"
datetime=$(timeout 5 openssl s_client -servername $domain -connect $domain:443 2>/dev/null | openssl x509 -noout -dates | sed 's/notAfter=\(.*\)$/\1/' | tail -n1)
if [ -z "$datetime" ]; then
echo
echo "ERROR"
echo
exit 0
fi
localtime=$(date -d "${datetime}" '+%R')
localdate=$(date -d "${datetime}" '+%Y-%m-%d')
timestamp=$(date -d "${datetime}" '+%s')
now=$(date '+%s')
diff=$((($timestamp-$now)/60))
if [ "$diff" -gt 3599 ] || [ "$diff" -lt 3599 ]; then
diffstr="$(expr $diff / 60 / 24) days"
elif [ "$diff" -gt 59 ] || [ "$diff" -lt 59 ] ; then
diffstr="$(expr $diff / 60) h"
else
diffstr="$diff min"
fi
echo
echo "The cert is valid until $localdate at $localtime ($diffstr)"
echo
The output will be:
Check the cert of Domain stackoverflow.com
The cert is valid until 2023-02-01 at 15:10 (50 days)
The output make a difference in days, hours, minutes and knows the difference to the local timezone. For minutes, it would look e.g. like that:
Check the cert of Domain ssl-cert-almost-expired.com
The cert is valid until 2022-12-13 at 15:39 (34 min)