Regex: How to match a string that is not only numbers

Question

Is it possible to write a regular expression that matches all strings that does not only contain numbers? If we have these strings:

• abc
• a4c
• 4bc
• ab4
• 123

It should match the four first, but not the last one. I have tried fiddling around in RegexBuddy with lookaheads and stuff, but I can't seem to figure it out.

Answer 1

(?!^d+$)^.+$

This says lookahead for lines that do not contain all digits and match the entire line.