A Perl script to convert Nagios/Unix epoch time to a human readable format

By Alvin Alexander. Last updated: July 16, 2016

I had to work with Nagios a lot this morning, in particular reading through the nagios.log log file. If you're ever read that log file, or looked at some other Linux/Unix log files, you've seen records that display the time in an epoch time format, which looks like this:

1219822177

If you can read the epoch time format and know the actual human readable date and time, you're a better person than I am (or you've been looking at Nagios, Linux, or Unix log files too long).

To help me read these date/time records I created a simple Perl date-conversion program I named epochtime.pl. In short, you run the program like this:

epochtime.pl 1219822177

and it produces output like this:

2008/08/27 03:29:37

(Maybe a computer can't read that time format very well, but a human can read it pretty easily.)

My epoch time converting Perl script

Given that introduction, here is the source code for my epochtime.pl Perl script:

#!/usr/bin/perl

# ------------------------------------------------------------
# epochtime.pl
# ------------
# from devdaily.com
# a perl script to convert Nagios "epoch time" (epoch seconds)
# into a human-readable format.
# ------------------------------------------------------------

$num_args = $#ARGV + 1;
die "Usage: this-program epochtime (something like '1219822177')" if
($num_args != 1);

$epoch_time = $ARGV[0];

($sec,$min,$hour,$day,$month,$year) = localtime($epoch_time);

# correct the date and month for humans
$year = 1900 + $year;
$month++;

printf "%02d/%02d/%02d %02d:%02d:%02d\n", $year, $month, $day, $hour, $min, $sec;

Discussion

If you're an experienced Perl programmer this script isn't too hard to decipher. Here's an explanation of how it works:

I use the special Perl $#ARGV variable to determine how many command line arguments there are.
Since there must be only one command line argument, the next thing I do is die if the number of arguments does not equal 1.
To make the program a little easier to understand I create the variable $epoch_time.
I use the localtime method to convert the epoch time into six separate variables.
I make adjust the $year and $month to again make them more human readable.
I use printf to print the output in a nice format.