12.5 Reading a Directory Handle

After we have a directory handle open, we can read the list of names with readdir, which takes a single parameter: the directory handle. Each invocation of readdir in a scalar context returns the next filename (just the basename - you'll never get any slashes or backslashes in the return value) in a seemingly random order.[5] If no more names exist, readdir returns undef. Invoking readdir in a list context returns all of the remaining names as a list with one name per element. Here's an example of listing all of the names from your Windows directory:

[5] Specifically, this order is the one in which the filenames are kept in the directory - the same unordered order you get back from the dir command from the command prompt.

$windir = $ENV{"WINDIR"};
opendir(NT, $windir) || die "no $windir?: $!";
while ($name = readdir(NT)) { # scalar context, one per loop
        print "$name\n"; # prints ., .., system.ini, and so on
}
closedir(NT);

And here's a way of getting them all in alphabetical order with the assistance of sort:

$windir = $ENV{"WINDIR"};
opendir(NT, $windir) || die "no $windir?: $!";
foreach $name (sort readdir(NT)) { # list context, sorted
        print "$name\n"; # prints ., .., system.ini, and so on
}
closedir(NT);

The names include files that begin with a dot. This method is unlike globbing with <*>, which does not return names that begin with a dot. This method is a relic from Perl's UNIX heritage, where the standard filename expansion normally does not include any files that begin with a dot.

In the current version of Perl for Win32, and the current version of the standard distribution, opendir fails on UNC paths. You can work around this by mapping a drive to the UNC share before using directory handles, and then using the drive letter as the path instead of the UNC path. You can do this with the Win32::NetResource module extension (see the AddConnection function) or with the Windows NT net use command. For more information on modules and the Win32 extensions, see Appendix B, Libraries and Modules.