#!/usr/bin/perl -w

use strict;
use File::Find;

my $dir = '.'; # or wherever

finddepth(\&myrename, $dir);

sub myrename {

	return unless -d; # if you only care about dirs
	return unless / /;
	my $oldname=$_;
	s/ /_/g;
	return if ($oldname eq $_);

        if (rename $oldname,$_) {
          	print "renamed  $File::Find::name to $_\n";
        } else {
              warn "Couldn't rename $File::Find::name to $_: $!";
        }
}