use strict;
my $str = '<product_11,product_12>=5,product_1,product_2,product_3=1,product_9=3,<product_5,product_6>=10,product_11,product_12,product_13,product_14=20';
my $regex = qr/(?<!\s*[=]\s*\d+)\,\s?(?![^\<]*\>)/p;
my $subst = '\\n';
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