Strip String of non-numeric characters

I’d like to turn any of these:
(123) 456-7890
(removing any special characters, spaces, etc.)

I figured it might start with placing the string in the system clipboard and then Set Variable to %CurrentClipboard%, then searching the variable, but haven’t gotten very far.

You could use a Regular Expression search and replace with [^\d] (not a numeral) as the search variable and with nothing as the replacement variable. If you had a list of numbers like that, you would probably need to add the line break as one of the characters not to replace–[^\d|\n] (not a number or a line break)–or you’ll end up with just one long line of numbers.