re = /,(?=(((?!\)).)*\()|[^\(\)]*$)/
str = 'off_sls_total numeric(12, 2), off_sls_profit numeric(12, 2), off_sls_profit_percent numeric(12, 2), off_profit numeric(12, 2), off_profit_percent numeric(12, 2)'
subst = ',\\n\\t'
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
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 Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html