use strict;
no warnings;

my @data = (1,2,3,undef,4,5);

for (@data) {
   /(\d+)/;
   print $1 if $1;
}
print "\n";

for (@data) {
   my ($numb) = $_ =~ /(\d+)/;
   print $numb if $numb;
}
print "\n";