Chapter 2: Date Manipulation
__Linux 101 Hacks
Hack 7. Set System Date and Time
To change the system date use:
# date {mmddhhmiyyyy.ss}
o mm – Month
o dd – Date
o hh – 24 hour format
o mi – Minutes
o yyyy – Year
o ss – seconds
For example, to set system date to Jan 31st 2009, 10:19 p.m, 53 seconds
# date 013122192009.53
You can also change system date using set argument as shown below.
# date 013122192009.53
# date +%Y%m%d -s "20090131"
# date -s "01/31/2009 22:19:53"
# date -s "31 JAN 2009 22:19:53"
# date set="31 JAN 2009 22:19:53"
To set the time only:
# date +%T -s "22:19:53"
# date +%T%p -s "10:19:53PM"
Hack 8. Set Hardware Date and Time
Before setting the hardware date and time, make sure the OS date and timeis set appropriately as shown in the hack#7.
Set the hardware date and time based on the system date as shown below:
# hwclock –systohc
# hwclock --systohc –utc
Use hwclock without any parameter, to view the current hardware date andtime:
# maybe sudo hwclock
Check the clock file to verify whether the system is set for UTC:
# cat /etc/sysconfig/clock
ZONE="America/Los_Angeles"
UTC=false
ARC=false
Hack 9. Display Current Date and Time in a SpecificFormat
Following are different ways of displaying the current date and time invarious formats:
代码
$ date
Thu Jan 1 08:19:23 PST 2009
$ date --date="now"
Thu Jan 1 08:20:05 PST 2009
$ date --date="today"
Thu Jan 1 08:20:12 PST 2009
$ date --date='1970-01-01 00:00:01 UTC +5 hours' +%s
18001
$ date '+Current Date: %m/%d/%y%nCurrent Time:%H:%M:%S'
Current Date: 01/01/09
Current Time:08:21:41
$ date +"%d-%m-%Y"
01-01-2009
$ date +"%d/%m/%Y"
01/01/2009
$ date +"%A,%B %d %Y"
Thursday,January 01 2009
Following are the different format options you can pass to the datecommand:
代码
o %D date (mm/dd/yy)
o %d day of month (01..31)
o %m month (01..12)
o %y last two digits of year (00..99)
o %a locale’s abbreviated weekday name (Sun..Sat)
o %A locale’s full weekday name, variable length
(Sunday..Saturday)
o %b locale’s abbreviated month name (Jan..Dec)
o %B locale’s full month name, variable length
(January..December)
o %H hour (00..23)
o %I hour (01..12)
o %Y year (1970...)
Hack 10. Display Past Date and Time
Following are various ways to display a past date and time:
代码
$ date --date='3 seconds ago'
Thu Jan 1 08:27:00 PST 2009
$ date --date="1 day ago"
Wed Dec 31 08:27:13 PST 2008
$ date --date="1 days ago"
Wed Dec 31 08:27:18 PST 2008
$ date --date="1 month ago"
Mon Dec 1 08:27:23 PST 2008
$ date --date="1 year ago"
Tue Jan 1 08:27:28 PST 2008
$ date --date="yesterday"
Wed Dec 31 08:27:34 PST 2008
$ date --date="10 months 2 day ago"
Thu Feb 28 08:27:41 PST 2008
Hack 11. Display Future Date and Time
Following examples shows how to display a future date and time.
代码
$ date
Thu Jan 1 08:30:07 PST 2009
$ date --date='3 seconds'
Thu Jan 1 08:30:12 PST 2009
$ date --date='4 hours'
Thu Jan 1 12:30:17 PST 2009
$ date --date='tomorrow'
Fri Jan 2 08:30:25 PST 2009
$ date --date="1 day"
Fri Jan 2 08:30:31 PST 2009
$ date --date="1 days"
Fri Jan 2 08:30:38 PST 2009
$ date --date="2 days"
Sat Jan 3 08:30:43 PST 2009
$ date --date='1 month'
Sun Feb 1 08:30:48 PST 2009
$ date --date='1 week'
Thu Jan 8 08:30:53 PST 2009
$ date --date="2 months"
Sun Mar 1 08:30:58 PST 2009
$ date --date="2 years"
Sat Jan 1 08:31:03 PST 2011
$ date --date="next day"
Fri Jan 2 08:31:10 PST 2009
$ date --date="-1 days ago"
Fri Jan 2 08:31:15 PST 2009
$ date --date="this Wednesday"
Wed Jan 7 00:00:00 PST 2009
