Tad more complicated: 

$_ = do{ local $/; <DATA> };
s[("[^\n"]*?")|("[^\n"]+?\n[^"]+?")][ ##"
    $1 || do{ (my $x = $2) =~ s[\s+][ ]g; $x }
]ge;
print;
"boom"
hello "" bill
hello "  " bill
"baz hello jock"
"boom2"
 abc "baz2 hello2 jock2 "

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Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

In reply to Re^3: Changing quoted strings spanning more than one line by BrowserUk
in thread Changing quoted strings spanning more than one line by eyepopslikeamosquito

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