Which regular expression operator means 'Don't' match this character?
RegexRegex Problem Overview
*, ?, + characters all mean match this character. Which character means 'don't' match this? Examples would help.
Regex Solutions
Solution 1 - Regex
You can use negated character classes to exclude certain characters: for example [^abcde] will match anything but a,b,c,d,e characters.
Instead of specifying all the characters literally, you can use shorthands inside character classes: [\w] (lowercase) will match any "word character" (letter, numbers and underscore), [\W] (uppercase) will match anything but word characters; similarly, [\d] will match the 0-9 digits while [\D] matches anything but the 0-9 digits, and so on.
If you use PHP you can take a look at the regex character classes documentation.
Solution 2 - Regex
There's two ways to say "don't match": character ranges, and zero-width negative lookahead/lookbehind.
The former: don't match a, b, c or 0: [^a-c0]
The latter: match any three-letter string except foo and bar:
(?!foo|bar).{3}
or
.{3}(?<!foo|bar)
Also, a correction for you: *, ? and + do not actually match anything. They are repetition operators, and always follow a matching operator. Thus, a+ means match one or more of a, [a-c0]+ means match one or more of a, b, c or 0, while [^a-c0]+ would match one or more of anything that wasn't a, b, c or 0.
Solution 3 - Regex
[^] ( within [ ] ) is negation in regular expression whereas ^ is "begining of string"
[^a-z] matches any single character that is not from "a" to "z"
^[a-z] means string starts with from "a" to "z"
Solution 4 - Regex
^ used at the beginning of a character range, or negative lookahead/lookbehind assertions.
>>> re.match('[^f]', 'foo')
>>> re.match('[^f]', 'bar')
<_sre.SRE_Match object at 0x7f8b102ad6b0>
>>> re.match('(?!foo)...', 'foo')
>>> re.match('(?!foo)...', 'bar')
<_sre.SRE_Match object at 0x7f8b0fe70780>