#!/usr/bin/perl

use strict;
use warnings;
use File::Find;

my $dir = "/home/ivan/M1";

find(\&wanted, $dir);

sub wanted {
	my $file = $_; # storing unprocessed filename
	$_ =~ s/ /_/g; # replacing spaces with _
	rename "$File::Find::dir/$file", "$File::Find::dir/$_"; # renaming files
}

##</code><code>##

Can't cd to (/home/ivan/M1/) Some Dirname With Spaces: no such file or directory
 at ./1.pl line 16