$time sed -i 's/sri/harry/' *
sed -i 's/sri/harry/' *  0.00s user 0.01s system 37% cpu 0.016 total

$time perl -pi -e 's/harry/sri/' 
perl -pi -e 's/harry/sri/' *  0.01s user 0.01s system 62% cpu 0.029 total