use strict;
my $str = '1070,"17",2,GN3-670,"COL,LA,R B, M STAY","2,60,6.45" ,",';
my $regex = qr/(?:\G(?!^)|([^"]*(?:"[^,"]*"[^"]*)*"))[^",]*\K,([^",]*+(?:"(?1)|$))?/p;
my $subst = '~$2';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html