$cnt = chown $uid, $gid, 'foo', 'bar';
chown $uid, $gid, @filenames;
Here's an example that looks up non-numeric uids in the passwd file:
print "User: ";
chop($user = <STDIN>);
print "Files: "
chop($pattern = <STDIN>);
($login,$pass,$uid,$gid) = getpwnam($user) or die "$user not in passwd file";
@ary = <${pattern}>; # expand filenames
chown $uid, $gid, @ary;
On most systems, you are not allowed to change the ownership of the file unless you're the superuser, although you should be able to change the group to any of your secondary groups. On insecure systems, these restrictions may be relaxed, but this is not a portable assumption.