You want to do something to each file in a particular directory.

Use opendir to open the directory and readdir to retrieve every filename:

In scalar context, readdir returns the next filename in the directory until it reaches the end of the directory, when it returns undef. In list context it returns the rest of the filenames in the directory or an empty list if there were no files left. As explained in this chapter's Introduction, the filenames returned by readdir do not include the directory name. When you work with the filenames returned by readdir, you must either move to the right directory first or prepend the directory to the filename.

This shows one way of prepending:

$dir = "/usr/local/bin";
print "Text files in $dir are:\n";
opendir(BIN, $dir) or die "Can't open $dir: $!";
while( $file = readdir BIN) {
    print "$file\n" if -T "$dir/$file";
}
closedir(BIN);

The readdir function will return the special directories "." (the directory itself) and ".." (the parent of the directory). Most people skip those files with code like:

while ( defined ($file = readdir BIN) ) {
    next if $file =~ /^\.\.?$/;     # skip . and ..
    # ...
}

Like filehandles, bareword directory handles are per-package constructs. You can use the local *DIRHANDLE syntax to get a new bareword directory handle. Alternatively, pass an undefined scalar as the first argument to opendir and Perl will put a new indirect directory handle into that scalar:

opendir my $dh, $directory or die;
while (defined ($filename = readdir($dh))) {
  # ...
}
closedir $dh;

Or, finally, you can use DirHandle to get an object-oriented view of a directory handle. The following code uses DirHandle and produces a sorted list of plain files that aren't dotfiles (that is, their names don't begin with a "."):

use DirHandle;

sub plainfiles {
   my $dir = shift;
   my $dh = DirHandle->new($dir)   or die "can't opendir $dir: $!";
   return sort                       # sort pathnames
          grep {    -f     }         # choose only "plain" files
          map  { "$dir/$_" }         # create full paths
          grep {  !/^\./   }         # filter out dot files
          $dh->read( );             # read all entries
}

DirHandle's read method behaves just like readdir, returning all remaining filenames. The bottom grep returns only those that don't begin with a period. The map turns the filenames returned by read into fully qualified filenames, and the top grep filters out directories, links, etc. The resulting list is then sort ed and returned.

In addition to readdir, there's also rewinddir (to move the directory handle back to the start of the filename list), seekdir (to move to a specific offset in the list), and telldir (to find out how far from the start of the list you are).

The closedir, opendir, readdir, rewinddir, seekdir, and telldir functions in perlfunc(1) and in Chapter 29 of Programming Perl; documentation for the standard DirHandle module (also in Chapter 32 of Programming Perl)