Q:

how to get a different time-clock on CLI apart from your time-zone?

Is there a way to invoke or know a different clock or time on the CLI. The thing is I'm on UTC+5:30 time but at times need to know time in different time-zones. If there is a CLI way in which this can be known would be helpful.  

A:

As several others have mentioned, the TZ environment variable is what affects the output of date.  However, in most cases you won't want to leave TZ changed; you will just want to see the time in that timezone, leaving your environment unaffected afterwards.
For that purpose, the best tool to use is env.  From the env man page:
NAME
    env - run a program in a modified environment
SYNOPSIS
    env [OPTION]... [-] [NAME=VALUE]... [COMMAND [ARG]...]

So in this case, the command you want would look something like:
env TZ='EST' date

There are other formats acceptable for the timezone—many of them.  If you have particular requirements, it's a good idea to read man timezone which explains the valid timezone formats.

