Bash - convert time interval string to nr. of seconds

Question

I'm trying to convert strings, describing a time interval, to the corresponding number of seconds.

After some experimenting I figured out that I can use date like this:

soon=$(date -d '5 minutes 10 seconds' +%s); now=$(date +%s)
echo $(( $soon-$now ))

but I think there should be an easier way to convert strings like "5 minutes 10 seconds" to the corresponding number of seconds, in this example 310. Is there a way to do this in one command?

Note: although portability would be useful, it isn't my top priority.

Answer 1

You could start at epoch

date -d"1970-01-01 00:00:00 UTC 5 minutes 10 seconds" "+%s"
310

You could also easily sub in times

Time="1 day"
date -d"1970-01-01 00:00:00 UTC $Time" "+%s"
86400

Answer 2

There is one way to do it, without using date command in pure bash (for portability)

Assuming you just have an input string to convert "5 minutes 10 seconds" in a bash variable with a : de-limiter as below.

$ convertString="00:05:10"
$ IFS=: read -r hour minute second <<< "$convertString"
$ secondsValue=$(((hour * 60 + minute) * 60 + second))
$ printf "%s\n" "$secondsValue"
310

You can run the above commands directly on the command-line without the $ mark.