use strict;
use warnings;

my $data = <<DATA;
0       ASDF
        ASEE
        ASEE

13      DERG
        DREG

28      QWER
        QWER

42      WERT
        WERT
        WERT

55      QWEASD
        QWEASD
        QWEASD
        QWEASD

DATA

open my $inFile, '<', \$data;

$/ = "\n\n";

while (<$inFile>) {
    if (my ($number) = m/(\d+)/) {
        s/\b\p{Alpha}+\b/$number/g;
    } else {
        warn "Malformed record in input line $.\n$_\nContinuing.\n";
    }
    print;
}