parsing the date to calculate days until cert expiry from a shell script

Question

I would like to get the days until a cert expires. Extracting the dates is easy with openssl

> cat cert | openssl x509 -noout -enddate
notAfter=Jun  8 17:07:09 2021 GMT

Unfortunately parsing the date Jun 8 17:07:09 2021 GMT and finding the days until today is not so straight forward. The goal would be to have

> cat cert | openssl x509 -noout -enddate | ...some commands...
15

Meaning 15 days until the cert expires.

I am aware of the openssl -checkend option, but that is just a boolean and I want the number of days.

If you would invest 10 seconds with searching via a search engine, then you wouldn't need to ask here. — Cyrus, Apr 02 '21 at 14:49

score 6 · Accepted Answer · answered Apr 02 '21 at 15:17

6

You may use this one liner shell script:

expiryDays=$(( ($(date -d "$(openssl x509 -in cert -enddate -noout | cut -d= -f2)" '+%s') - $(date '+%s')) / 86400 ))

Here is the breakup:

openssl ... command to print expiry date in notAfter=... format
cut -d= -f2 to get text after =
date -d ...'+%s'`: to get EPOCH seconds value for expiry date
date '+%s': to get EPOCH seconds value for today's date
(epochExpiry - epochToday) / 86400: to get difference of 2 EPOCH values as number of days

answered Apr 02 '21 at 15:17

anubhava

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This looks almost perfect. Unfortunately `date -d "Jun 8 17:07:09 2021 GMT" +%s` seems to only work on linux. On macOS -d sets the kernel's value for daylight saving time. – tcurdt Apr 02 '21 at 20:12
Yes of course but since you used `linux` tag in question this solution should work there. btw I also use mac but have gnu utilities installed using `home brew` to make it work – anubhava Apr 02 '21 at 20:15
1

Fair point. For that I should have asked for a POSIX solution. – tcurdt Apr 02 '21 at 20:21

score 1 · Answer 2 · answered Apr 02 '21 at 14:47

A quickie perl script using the Date::Parse module (Install through your OS package manager or favorite CPAN client):

#!/usr/bin/env perl
use strict;
use warnings;
use Date::Parse;
use feature qw/say/;

my $certdate = str2time($ARGV[0]);
my $now = time;
my $expiresecs = $certdate - $now;
say int(($expiresecs / (60 * 60 * 24)));

Example:

$ ./showdays "Jun  8 17:07:09 2021 GMT"
67

parsing the date to calculate days until cert expiry from a shell script

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