How to find the day of the week from timestamp - regex

Question

I have a timestamp 2015-11-01 21:45:25,296 like I mentioned above. is it possible to extract the the day of the week(Mon, Tue,etc) using any regular expression or grok pattern.
Thanks in advance

Answer 1

this is quite easy if you want to use the ruby filter. I am lazy so I am only doing this.
Here is my filter:
filter {
ruby {
code => "
p = Time.parse(event['message']);
event['day-of-week'] = p.strftime('%A');
"
}
}
The 'message' variable is the field that contains your timestamp
With stdin and stdout and your string, you get:
artur#pandaadb:~/dev/logstash$ ./logstash-2.3.2/bin/logstash -f conf2/
Settings: Default pipeline workers: 8
Pipeline main started
2015-11-01 21:45:25,296
{
"message" => "2015-11-01 21:45:25,296",
"#version" => "1",
"#timestamp" => "2016-08-03T13:07:31.377Z",
"host" => "pandaadb",
"day-of-week" => "Sunday"
}
Hope that is what you need,
Artur

Answer 2

What you want is:
Assuming your string is 2015-11-01 21:45:25,296
mydate='2015-11-01'
date +%a -d ${mydate% *}
Will give you what you want.

Answer 3

Short answer is not, you can't.
A regex, according to Wikipedia:
...is a sequence of characters that define a search pattern, mainly for use in pattern matching with strings, or string matching, i.e. "find and replace"-like operations.
So, a regex allow you to parse a String, it searches for information within the String, but it doesn't make calculations over it.
If you want to make such calculations you need help from a programming language (java, c#, or Ruby[like #pandaadb suggested] etc) or some other tool that makes those calculations (Epoch Converter).