at first glance this commands records the pid of su itself rather than the binary it starts  a more careful analysis shows that the string in the single quotes is a part of command which  bin sh  c runs  consider explaining the trick  it is not obvious at all  also a space before the leading single quote character totally changes the meaning of the command  and breaks the script greeting  hello sh  c  echo  greeting world  hello  world sh  c  echo  greeting world hello