Shell Programming and Scripting

startsec=$(date +%s)

 endsec=$(date +%s)
 duration=$(expr $endsec - $startsec)
 echo $duration

DIR=/your/directory

first_ts=$(ls -lt $DIR | tail -1 | awk '{print $8}')
last_ts=$(ls -ltr $DIR | tail -1 | awk '{print $8}')

first_mm=$(echo $first_ts | cut -d":" -f 1)
first_ss=$(echo $first_ts | cut -d":" -f 2)
last_mm=$(echo $last_ts | cut -d":" -f 1)
last_ss=$(echo $last_ts | cut -d":" -f 2)

first_totsec=$(expr $first_mm \* 60 + $first_ss)
last_totsec=$(expr $last_mm \* 60 + $last_ss)

duration=$(expr $last_totsec - $first_totsec)

if [ $duration -gt 60 ]
then
  echo "\n" Diff between first and last file mtime: $(echo $duration | awk '{printf("%2d min %2d sec",$1/60,$1%60)}') "\n"
else
  echo "\n Diff between first and last file mtime: $duration seconds.\n"
fi