re = /(?<=\d)[^\d\n]+(?=\d)/
str = '555a555a5555
555%555(5555
5555555855
555a555~5555
555 555 5555
555.555.5555
555,555,5555
555(any special char or letter in keyboard here)555(again anything here special char or letter)5555
555y555-5555
555/555/5555
555\\555\\5555
555]555[5555
555~555~5555'
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