See the current Perl documentation for chmod.
Here is our local, out-dated (pre-5.6) version:
chmod - changes the permissions on a list of files
Changes the permissions of a list of files. The first element of the list
must be the numerical mode, which should probably be an octal number, and
which definitely should not a string of octal digits:
0644 is okay,
'0644' is not. Returns the number of files successfully changed. See also oct, if all you have is a string.
$cnt = chmod 0755, 'foo', 'bar'; chmod 0755, @executables; $mode = '0644'; chmod $mode, 'foo'; # !!! sets mode to # --w----r-T $mode = '0644'; chmod oct($mode), 'foo'; # this is better $mode = 0644; chmod $mode, 'foo'; # this is best