commandliners

The following chunk of code

sub traverse {
    my ($dir, $callback) = @_;
    my $present;

    opendir $present, $dir or return();

    for (grep { ! /^(\.|\.\.)$/ } readdir $present) {
        my $path = "$dir/$_";

        &$callback($path);
        traverse($path, $callback) if -d $path;
    }

    closedir $present;
    return();
}

is an easy implementation (without error-checking) of a generic directory-traversing function in Perl. It should be called

traverse(dir, sub)

where dir is a directory name and sub is a reference to a subroutine. A trivial example:

sub textP {
  my $file = shift;
  if (-T $file) {
    print "[$file] is a text file\n";
  } else {
    print "[$file] is NOT a text file\n";
  }
  return;
}

traverse(".", \&textP);

All the above is well-known and common functional-programming practice, but quite useful.