re = /(?<=[^x]|^)(x{3}|x{5})(?:[^x]|$)/m
str = 'xxx
xxxxx
xxxx xxx x xxxxx
xx xxxxx xxx
xxxxxx
xxx
xxxx'
# Print the match result
str.scan(re) do |match|
puts match.to_s
end
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