re = /(?x) # Allow comments in regex (ignore whitespace)
(?: # Repeat *
[^(|)]*+ # Match every char except ( ) or |
( # 1. Group 1
\( # Opening paren
(?: # chars inside:
[^()]++ # a. everything inside parens except nested parens
| # or
(?1) # b. nested parens (recurse group 1)
) #
\) # Until closing paren.
)?+ # (end of group 1)
)*+ #
\K # Keep text out of match
\| # Match a pipe/
str = 'example|example (example(example))|example|example|example(example|example|example(example|example))|example'
subst = ''
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