Sun was so into keeping backward compatibility intact they would not update the default /bin/sh because of some compatibility issues that could affect customers

Sun was so into keeping backward compatibility intact they would not update the default /bin/sh because of some compatibility issues that could affect customers. So they included the newer XPG4 sh in a different location (it is a POSIX-compliant ksh88): /usr/xpg4/bin/sh. So you can write: #!/usr/bin/env sh So that users who have setup PATH=/usr/xpg4/bin:$PATH get the correct shell and everything works fine.