While there might be a chgrp command in your OS, Perl does not have a chgrp() function. Perl only has a chown() function, which is used to set both the user and the group id of a file. This is because many Perl functions mimic the C library, and not the programs from /usr/bin.

Also, there are 12 protection bits, not 9. You are forgetting the "set user id", "set group id" and the "sticky bit".

Abigail