Say I have an interval with characters ['A'-'Z'], I want to match every of these characters except the letter 'F' and I need to do it through the ^ operator. Thus, I don't want to split it into two different intervals.
How can I do it the best way? I want to write something like ['A'-'Z']^'F' (All characters between A-Z except the letter F). This site can be used as reference: http://regexr.com/
EDIT: The relation to ocaml is that I want to define a regular expression of a string literal in ocamllex that starts/ends with a doublequote ( " ) and takes allowed characters in a certain range. Therefore I want to exclude the doublequotes because it obviously ends the string. (I am not considering escaped characters for the moment)
Since it is very rare to find two regular expressions libraries / processors with exactly the same regular expression syntax, it is important to always specify precisely which system you are using.
The tags in the question lead me to believe that you might be using ocamllex to build a scanner. In that case, according to the documentation for its regular expression syntax, you could use
['A'-'Z'] # 'F'
That's loosely based on the syntax used in flex:
[A-Z]{-}[F]
Java and Ruby regular expressions include a similar operator with very different syntax:
[A-Z&&[^F]]
If you are using a regular expression library which includes negative lookahead assertions (Perl, Python, Ecmascript/C++, and others), you could use one of those:
(?!F)[A-Z]
Or you could use a positive lookahead assertion combined with a negated character class:
(?=[A-Z])[^F]
In this simple case, both of those constructions effectively do a conjunction, but lookaround assertions are not really conjunctions. For a regular expression system which does implement a conjunction operator, see, for example, Ragel.