This function attempts to change a file’s user group. With the exception of the superuser, You must be the owner of the file in question and you must be a member of the group you’re changing it to.

Specify the group as either the group name or number. You’ll get a return value of false if it’s unsuccessful.

chgrp( '/home/admin/test/one_file.txt',
       'my_group' );
chgrp( '/home/admin/test/nother_file.php',
       17 );