How to convert strings like "19-FEB-12" to epoch date in UNIX

Question

In UNIX how to convert to epoch milliseconds date strings like:

19-FEB-12
16-FEB-12
05-AUG-09

I need this to compare these dates with the current time on the server.

Answer 1

To convert a date to seconds since the epoch:

date --date="19-FEB-12" +%s

Current epoch:

date +%s

So, since your dates are in the past:

NOW=`date +%s`
THEN=`date --date="19-FEB-12" +%s`

let DIFF=$NOW-$THEN
echo "The difference is: $DIFF"

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Using BSD's date command, you would need

$ date -j -f "%d-%B-%y" 19-FEB-12 +%s

Differences from GNU date:

1. -j prevents date from trying to set the clock
2. The input format must be explicitly set with -f
3. The input date is a regular argument, not an option (viz. -d)
4. When no time is specified with the date, use the current time instead of midnight.