Google Spreadsheets: - Validating cell contains only alphanumeric and underscore

Question

In Google Spreadsheets, how do I use a custom formula (with re2 regular expression) to only allow alphanumeric and underscore characters in cell content?

Answer 1

I needed a Validation which would detect this also. Here's my working solution.

=IF(REGEXMATCH(A1, "[^A-Za-z0-9_-]+"), FALSE, TRUE)

This Regex validation [^A-Za-z0-9_-]+ returns TRUE if anything is present in the string EXCEPT for letters, numbers, underscores and dashes (The ^ asserts a 'negated set')

Then we simply flip the boolean logic (using 'IF...FALSE,TRUE'). This results rejection of illegal characters.