use strict;
my $str = "abc dddd     10 ";
my $number;
if ($str =~ /^.*?(\d+)\s*$/) {
  $number = $1;
}
else {
  # do something with unexpected record
}

##</code><code>##

if ($str =~ /^(\w+\s+){2,3}(\d+)/) {
  $number = $2;
}