시간측정 shell script time date

#!/bin/sh

fname=$1

atime=$(date '+%s')

#./ffmpeg -i $fname -codec:v libx264 -s 640x480 -aspect 4:3 -b:v 4000k -an -y ${fname%.mp4}_00.mp4

btime=$(date '+%s')

echo $atime

echo $btime

total=$(expr $btime - $atime)

echo $total