Get current time in seconds since the Epoch on Linux, Bash

This should work:

date +%s

Just to add.

Get the seconds since epoch(Jan 1 1970) for any given date(e.g Oct 21 1973).

date -d "Oct 21 1973" +%s

Convert the number of seconds back to date

date --date @120024000

The command date is pretty versatile. Another cool thing you can do with date(shamelessly copied from date --help). Show the local time for 9AM next Friday on the west coast of the US

date --date='TZ="America/Los_Angeles" 09:00 next Fri'

Better yet, take some time to read the man page http://man7.org/linux/man-pages/man1/date.1.html