Master the Linux date Command: Formats, Options, and Real‑World Examples

Date is a versatile Linux command that can display the current date and time in many formats and also set the system clock.

<code>$ date
Mon May 20 22:02:24 PDT 2013</code>

1. Use the –date option to display a date from a string

When you provide a static date or time string, the -d or –date option parses the string and displays it, ignoring the current system time.

If you omit the time, 00:00:00 is used.

<code>$ date --date="12/2/2014"
Tue Dec  2 00:00:00 PST 2014

$ date --date="2 Feb 2014"
Sun Feb  2 00:00:00 PST 2014

$ date --date="Feb 2 2014"
Sun Feb  2 00:00:00 PST 2014</code>

You can also include a time component in the string:

<code>$ date --date="Feb 2 2014 13:12:10"
Sun Feb  2 13:12:10 PST 2014</code>

2. Use the –file option to read date patterns from a file

The -f/–file option works like –date but processes each line of a file as a separate date string.

<code>$ cat datefile
Sept 9 1986
Aug 23 1987

$ date --file=datefile
Tue Sep  9 00:00:00 PDT 1986
Sun Aug 23 00:00:00 PDT 1987</code>

3. Use –date for relative dates

You can obtain future or past dates by specifying relative expressions.

<code>$ date --date="next mon"
Mon May 27 00:00:00 PDT 2013</code>

Using the @ syntax, you can convert seconds since the Unix epoch to a date:

<code>$ date --date=@5
Wed Dec 31 16:00:05 PST 1969

$ date --date=@10
Wed Dec 31 16:00:10 PST 1969

$ date --date=@60
Wed Dec 31 16:01:00 PST 1969</code>

4. Display past dates

The –date option also accepts expressions like "3 seconds ago", "1 day ago", "yesterday", "1 month ago", or "1 year ago" to show past dates.

<code>$ date --date='3 seconds ago'
Mon May 20 21:59:20 PDT 2013

$ date --date='1 day ago'
Sun May 19 21:59:36 PDT 2013

$ date --date='yesterday'
Sun May 19 22:00:26 PDT 2013

$ date --date='1 month ago'
Sat Apr 20 21:59:58 PDT 2013

$ date --date='1 year ago'
Sun May 20 00:09:09 PDT 2012</code>

5. Use –set to change the system date and time

The -s or –set option lets you set the system clock.

<code>$ date
Sun May 20 09:31:00 PDT 2013

$ date -s "Sun May 20 21:00:00 PDT 2013"
Sun May 20 21:00:00 PDT 2013

$ date
Sun May 20 21:00:05 PDT 2013</code>

6. Use -u to display UTC

The -u, -utc, or -universal options show the date in Coordinated Universal Time.

<code>$ date
Mon May 20 07:53:00 PDT 2013

$ date -u
Tue May 21 07:55:00 UTC 2013</code>

7. Use -r to show a file's last modification time

After modifying a file's timestamp with touch, -r displays that timestamp.

<code>$ date
Sun May 20 25:48:00 PDT 2013

$ touch datefile

$ date
Sun May 20 26:12:00 PDT 2013

$ date -r datefile
Sun May 20 25:57:00 PDT 2013</code>

8. Various date format options

You can customize the output using format specifiers with the + option, such as %a for abbreviated weekday, %A for full weekday, %b for abbreviated month, %B for full month, %d for day of month, %D for MM/DD/YY, %F for YYYY‑MM‑DD, %H for 24‑hour, %I for 12‑hour, %j for day of year, %m for month number, %M for minute, %S for second, %N for nanoseconds, %T for HH:MM:SS, %u for ISO weekday number, %U for week number, %Y for full year, and %Z for time‑zone abbreviation.