Regex with exception of particular words

Question

I have problem with regex. I need to make regex with an exception of a set of specified words, for example: apple, orange, juice. and given these words, it will match everything except those words above.

applejuice (match)
yummyjuice (match)
yummy-apple-juice (match)
orangeapplejuice (match)
orange-apple-juice (match)
apple-orange-aple (match)
juice-juice-juice (match)
orange-juice (match)

apple (should not match)
orange (should not match)
juice (should not match)

Answer 1

If you really want to do this with a single regular expression, you might find lookaround helpful (especially negative lookahead in this example). Regex written for Ruby (some implementations have different syntax for lookarounds):

rx = /^(?!apple$|orange$|juice$)/

Answer 2

I noticed that apple-juice should match according to your parameters, but what about apple juice? I'm assuming that if you are validating apple juice you still want it to fail.

So - lets build a set of characters that count as a "boundary":

/[^-a-z0-9A-Z_]/        // Will match any character that is <NOT> - _ or 
                        // between a-z 0-9 A-Z 

/(?:^|[^-a-z0-9A-Z_])/  // Matches the beginning of the string, or one of those 
                        // non-word characters.

/(?:[^-a-z0-9A-Z_]|$)/  // Matches a non-word or the end of string

/(?:^|[^-a-z0-9A-Z_])(apple|orange|juice)(?:[^-a-z0-9A-Z_]|$)/ 
   // This should >match< apple/orange/juice ONLY when not preceded/followed by another
   // 'non-word' character just negate the result of the test to obtain your desired
   // result.

In most regexp flavors \b counts as a "word boundary" but the standard list of "word characters" doesn't include - so you need to create a custom one. It could match with /\b(apple|orange|juice)\b/ if you weren't trying to catch - as well...

If you are only testing 'single word' tests you can go with a much simpler:

/^(apple|orange|juice)$/ // and take the negation of this...