re = /(\d)([() -]*)(\d)([() -]*)(\d)([() -]*)(\d)([() -]*)(\d)([() -]*)(\d)([() -]*)(\d+)/
str = 'Input
PhoneNumber> (123) 556-7890 PhoneNumber>
Output PhoneNumber>(XXX) XXX-7890 PhoneNumber>
Input
PhoneNumber> 123 556 7890 PhoneNumber>
Output PhoneNumber>XXX XXX 7890 PhoneNumber>
Input
PhoneNumber> (123) 556- 7890 PhoneNumber>
Output PhoneNumber>(XXX) XXX- 7890 PhoneNumber>'
subst = 'x\\2x\\4x\\6x\\8x\\10x\\12\\13'
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