use strict;
my $str = 'aaa,bbb,ccc,"ddd,eee","fff,ggg"
"aaa,bbb",ccc,ddd,"eee,fff"
"aaa,bbb","ccc,ddd","eee,fff",ggg
';
my $regex = qr/(?!\B"[^"]*),(?![^"]*"\B)/mp;
my $subst = '\\|';
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