bash Cookbook

Converting Dates and Times to Epoch Seconds

Problem

You want to convert a date and time to Epoch seconds to make it easier to do date and time arithmetic.

Solution

Use the GNU date command with the nonstandard -d option and a standard %s format:

# "Now" is easy
$ date '+%s'
1131172934

# Some other time needs the non-standard -d
$ date -d '2005-11-05 12:00:00 +0000' '+%s'
1131192000

Discussion

If you do not have the GNU date command available, this is a harder problem to solve. Our advice is to obtain and use the GNU date command if at all possible. If that is not possible you might be able to use Perl. Here are three ways to print the time right now in Epoch seconds:

$ perl -e 'print time, qq(\n);'
1154158997

# Same as above
$ perl -e 'use Time::Local; print timelocal(localtime()) . qq(\n);'
1154158997

$ perl -e 'use POSIX qw(strftime); print strftime("%s", localtime()) . qq(\n);'
1154159097

Using Perl to convert a specific day and time instead of right now is even harder due to Perl’s date/time data structure. Years start at 1900 and months (but not days) start at zero instead of one. The format of the command is: timelocal (sec, min, hour, day, month-1, year-1900). So to convert 2005-11-05 06:59:49 to Epoch seconds:

# The given time is in local time
$ perl -e 'use Time::Local; printtimelocal("49", "59", "06", "05", "10", "105") .
.qq(\n);'
1131191989

# The given time is in UTC time
$ perl -e 'use Time::Local; print timegm("49", "59", "06", "05", "10", "105") .
qq(\n);'
1131173989

See Also ...