my $file = do { local $/; <DATA> };
$file =~ s/\n(?!A\d+\.)/ /g;
$file .= "\n";
print $file;

__DATA__
A6.8.5 This is
an example
sentence
A6.8.6 This is
an example
sentence

[download]
A6.8.5 This is an example sentence
A6.8.6 This is an example sentence

[download]

In reply to Re^3: How to remove extra line breaks (using regexp)? by ikegami
in thread How to remove extra line breaks (using regexp)? by larus

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