re = /^(\+\b33|\b0)[67][0-9]{8}$/m
str = '+33611223344+33611223344
0611223344 0744332211
0744332211+33611223344
0744332211 +33611223344
0611223344
0744332211
+33611223344
+33744332211
06112233440744332211'
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