perl -l -0777 -pe 's/\n+(\D)/\1/g' file
[download]

Or if the lines shouldn't be joined across the blank lines then this:

    perl -l -00 -pe 's/\n(\D)/\1/g' file
[download]

--
John.

use strict;
use warnings;

$_=<DATA>;
chomp;
print;
while (<DATA>) {
    chomp;
    s/^\s*$// or /^\D/ or print "\n";
    print;
}
print "\n";

__DATA__
4374564735|fegfg|sfffsg|QDFWFWwefwe

cty|Sd|45|445|35
7345634785|24756|4864586|2356
845245|2347624|264|2376274|2846242
|sfh|Sgfdg|EFgefg|434590|563456
|9345890345|84|3457|345|wdfdhiwdfh
324523|24562|248|2048|2323480|2923472
|3568245|34057|23|43057345734|2472
[download]

my $buffer = "";
while (<FH>) {
    next unless /\S/;   # Skip blank lines.
    if (/^\D/) {        # A bar is a non-digit as well.
        chomp $buffer;
        $buffer .= $_;
        next;
    }
    print $buffer;
    $buffer = $_;
}
print $buffer;
[download]

my $nl = "";
while (<FH>) {
    next unless /\S/;
    $nl = chomp;
    print $nl unless /^\d/ || $. == 1;
    print;
}
print $nl;  # Prints newline if we saw at least one non-blank file.
[download]

Not to me; the specific problem is too detailed.

It does however smell strongly of "I'm over my head with this perl stuff and my script doesn't work - fix it for me".

--


@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/;
map{y/X_/\n /;print}map{pop@$_}@/for@/
[download]