Question

How to construct a regex not to contain a set of strings within.

For this example, I want to validate the Address Line 1 text box so that it wont contain any secondary address parts such ‘Apt’, ‘Bldg’,’Ste’,’Unit’ etc.

Answer 1

A regex can be used to verify that a string does not contain a set of words. Here is a tested Java code snippet with a commented regex which does precisely this:

if (s.matches("(?sxi)" +
    "# Match string containing no 'bad' words.\n" +
    "^                # Anchor to start of string.\n" +
    "(?:              # Step through string one char at a time.\n" +
    "  (?!            # Negative lookahead to exclude words.\n" +
    "    \\b          # All bad words begin on a word boundary\n" +
    "    (?:          # List of 'bad' words NOT to be matched.\n" +
    "      Apt        # Cannot be 'Apt',\n" +
    "    | Bldg       # or 'Bldg',\n" +
    "    | Ste        # or 'Ste',\n" +
    "    | Unit       # or 'Unit'.\n" +
    "    )            # End list of words NOT to be matched.\n" +
    "    \\b          # All bad words end on a word boundary\n" +
    "  )              # Not at the beginning of bad word.\n" +
    "  .              # Ok. Safe to match this character.\n" +
    ")*               # Zero or more 'not-start-of-bad-word' chars.\n" +
    "$                # Anchor to end of string.")
    ) {
    // String has no bad words.
    System.out.print("OK: String has no bad words.\n");
} else {
    // String has bad words.
    System.out.print("ERR: String has bad words.\n");
} 

This assumes that the words must be “whole” words and that the “bad” words should be recognized regardless of case. Note also, (as others have correctly stated), that this is not as efficient as simply checking for the presence of bad words and then taking the logical NOT.