Programming Perl, 4th Edition

chmod

chmod LIST

This function changes the permissions of a list of files. The first element of the list must be the numerical mode, as in the chmod(2) syscall. The function returns the number of files successfully changed. For example:

$cnt = chmod 0755, "file1", "file2";

will set $cnt to 0, 1, or 2, depending on how many files were changed. Success is measured by lack of error, not by an actual change, because a file may have had the same mode before the operation. An error probably means you lacked sufficient privileges to change its mode because you were neither the file’s owner nor the superuser. Check $! to find the actual reason for failure.

Here’s a more typical usage:

chmod(0755, @executables) == @executables
        || die "couldn't chmod some of @executables: $!";

If you need to know which files didn’t allow the change, use something like this:

@cannot = grep {not chmod(0755, $_) } "file1", "file2", "file3";
die "$0: could not chmod @cannot" if @cannot;

This idiom uses the grep function to select only those elements of the list for which the chmod function failed.

On systems that support fchmod(2), you may also pass filehandles in the argument list. On systems without fchmod(2) support, passing filehandles raises a runtime exception. To be recognized, filehandles must be passed as typeglobs ...