To make a regex match all or nothing, you can use anchors to specify the start and end of the string. For example, if you want to match a string that contains only the characters 'abc', you can use the regex pattern "^abc$". The caret symbol (^) represents the start of the string, and the dollar sign ($) represents the end of the string. This ensures that the regex matches the entire string from start to finish, and nothing else.