while ($string =~ /(\s+\|)/)
{
        $string =~ s/$1/\|/;
}
[download]

There's no point in first doing a match, and then a substitution. If it doesn't match, the substitution won't happen, and if it match, the substitution happens as well. Furthermore, because your match includes a |, that pipe symbol will be in $1, and it will be unescaped. But you interpolate $1 in your substitution, so there the pipe symbol will be seen as an alternation.

What you want is:

$string =~ s/\s+\|/|/g;
[download]

No while necessary.

Abigail