use strict;
use warnings;
use Data::Dumper;
use utf8;

my $str = " 1 i á \x{3C3} _ ";          # \x{3C3} = small sigma 
warn Dumper $str;

$str =~ s/\w+//g;                       # delete all alpha-nums
warn Dumper $str;

warn "WORKS!" if $str =~ m/^ +$/;