use strict;

my %hash;
my $entry;
my $line;
my $key;
open(INFILE, "data") || die;
while ($line = <INFILE>) {
    chomp($line);
    if ($line) {   # in an entry
        if (!$entry) {    # this is the first line
            $entry .= $line . "\n";
            ($key = $line) =~ s/\D//g;
        } else {
            $entry .= $line . "\n";
        }
    } else {       # left the entry
        $hash{$key} = $entry;
        $entry = "";
    }
}
close(INFILE);

open(OUTFILE, ">datax") || die;
foreach $key (sort(keys(%hash))) {
    print OUTFILE $hash{$key} . "\n";
}
close(OUTFILE);