my $line = do { local $/; <$fh> };
$line =~ s/\n*\n/ /g;

##</code><code>##

my $line = do { local $/; <$fh> };
$line =~ tr/\n/ /s;

##</code><code>##

( my $line = do { local $/; <$fh> } ) =~ tr/\n/ /s;