use charnames ":full";

$string =~ s{ 
              \N{LEFT SINGLE QUOTATION MARK} | \N{RIGHT SINGLE QUOTATION MARK} 
            }
            {
              \N{APOSTROPHE} 
            }xg;

##</code><code>##

    Pi          InitialPunctuation
                (may behave like Ps or Pe depending on usage)
    Pf          FinalPunctuation
                (may behave like Ps or Pe depending on usage)