md5 -s "test string"
MD5 ("test string") = 6f8db599de986fab7a21625b7916589c
MD5 hash using pipe:
echo -n test string | md5
6f8db599de986fab7a21625b7916589c
MD5 hash using pipe, but echo without n option:
echo test string | md5
f299060e0383392ebeac64b714eca7e3