if( $string =~ m/(?<!\d)(\d{4,5})(?!\d)/ ) {
  print "$1\n";
}

##</code><code>##

my( @found ) = $string =~ m/(?<!\d)(\d{4,5})(?!\d)/g;

##</code><code>##

$string =~ s/(?<!\d)\d{4,5}(?!\d)//g;