date

POSIX 7 http://pubs.opengroup.org/onlinepubs/9699919799/utilities/date.html

Get system date:

date

Sample output:

Sun Feb  1 12:21:15 CET 2015

Format current time and output it:

date '+%Y-%m-%d_%H:%M:%S'

Sample output:

2015-02-01 12:21:52

GNU extensions

Saner RFC-3339 format:

date --rfc-3339=seconds

Sample output:

2015-02-08 15:42:37+01:00

Set the system date:

sudo date -s "1 JUN 2012 09:30:00"