Shell Programming and Scripting

a space is not null or empty, at least in perl its not considered to be. A space, as in " " or [^ ] is a space, it does contain a value, a space. With perl, false values are 0 (zero) and "". I think there is also one exception to that, a special false value in what is returned by one of perl functions but I can't remember which function. I don't think it has anything to do with the square brackets, but it would make no sense to use the square brackets (a character class) that contains no characters to match. I think it just boils down to the fact that spaces are not null or empty.

I agree. Basically, the way I've explained to myself why this character class regex does not match null or the empty string, was that it match _characters_ but nothing else.

Thanks a lot Kevin, especially for your Perl script - it helped me validate my understanding.

BTW, the language this question was about :
webMethods Flow - Wikipedia, the free encyclopedia

My guess would have been that the poster assumed that the regular expression would only match on a string which does not contain a space anywhere, i.e. expect it to only match on strings consisting of a single character other than space. But the way regular expressions are used in most tools is that they will regard a substring match anywhere in the input string as a success. So [^ ] matches 'foo bar' even though it includes a space, because there is a substring which matches the expression (and actually all possible substrings of length one will match except one, obviously; in practice, the matcher will be content with the first possible match, i.e. the substring "f").