Simple way to convert HH:MM:SS (hours:minutes:seconds.split seconds) to seconds

Question

What\'s an easy way to convert 00:20:40.28 (HH:MM:SS) to seconds with a Bash script?

Split seconds can be cut out, it’s not essential.

Answer 1

With GNU date, you can perform the conversion if the duration is less than 24 hours, by treating it as a time of day on the epoch:

to_seconds() {
    local epoch=$(date --utc -d @0 +%F)
    date --utc -d "$epoch $1" +%s.%09N
}

Running it with the example from the question:

$ to_seconds 00:20:40.29
1240.290000000

Note that --utc, @, %s and %N are all GNU extensions not necessarily supported by other implementations.