OK, but in this case, for the sake of readability and maintainability, better stick with one approach 
DB<105> p $str =~ s/ (?<=[^"\n]) \t (?=[^"\n]) /***/gxr
    start***middle1    "quote1***quote2"    middle2***end    
    start***middle1    "quote1***quote2"    middle2***end

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Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

In reply to Re^4: Regex for replacing a character "not next to" another character by LanX
in thread Regex for replacing a character "not next to" another character by flightdm

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