bash shell计算时间差

function getTiming() {
start=$1
end=$2
start_s=$(echo $start | cut -d '.' -f 1)
start_ns=$(echo $start | cut -d '.' -f 2)
end_s=$(echo $end | cut -d '.' -f 1)
end_ns=$(echo $end | cut -d '.' -f 2)
time=$(( ( 10#$end_s - 10#$start_s ) * 1000 + ( 10#$end_ns / 1000000 - 10#$start_ns / 1000000 ) ))
echo "$time ms"

}

start=$(date +%s.%N) end=$(date +%s.%N) runtime=$(getTiming $start $end) echo "runtime: "$runtime