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

Try awk. As a bonus, you can keep the split seconds.

echo "00:20:40.25" | awk -F: '{ print ($1 * 3600) + ($2 * 60) + $3 }'

Try this:

T='00:20:40.28'
SavedIFS="$IFS"
IFS=":."
Time=($T)
Seconds=$((${Time[0]}*3600 + ${Time[1]}*60 + ${Time[2]})).${Time[3]}
IFS="$SavedIFS"

echo $Seconds

($<string>) splits <string> based on the splitter (IFS).

${<array>[<index>]} returns the element of the <array> at the <index>.

$((<arithmetic expression>)) performs the arithmetic expression.

Hope this helps.

This would work even if you don't specify hours or minutes: echo "04:20:40" | sed -E 's/(.*):(.+):(.+)/\1*3600+\2*60+\3/;s/(.+):(.+)/\1*60+\2/' | bc