You can use date to get time and date of a day:
[pengyu@GLaDOS ~]$date
Tue Aug 27 15:01:27 CST 2013
Also hwclock would do:
[pengyu@GLaDOS ~]$hwclock
Tue 27 Aug 2013 03:01:29 PM CST -0.516080 seconds
For customized output, you can either redirect the output of date to something like awk, or write your own program to do that.
Remember to put your own executable scripts/binary into your PATH (e.g. /usr/bin) to make it invokable anywhere.