Regular expression replacement

Question

Hi,

I ve got the following reg exp

(-[^\w+])|([\w+]-[\w+])

I want to use it to replace dashes with a whitespace

test -test             should not be replaced
test - test            should be replaced
test-test              should be replaced

So only if test -test the dash should NOT be replaced.

Currently ([\w+]-[\w+]) is replacing the t's around the dash.

        var specialCharsExcept = new Regex(@"([\w+]-[\w+])", RegexOptions.IgnoreCase);

        if (string.IsNullOrEmpty(term))
            return "";

        return specialCharsExcept.Replace(term, " ");

Any help? Thanks in advance

PS: I am using C#.

Update

I'm trying to use your reg exp for the following case now.

some - test "some test"   - everything within the quotes the expression should not be applied

Is this possible?

Answer 1

Ok, changed according to comment.

>>> r = ' +(-) +|(?<=\w)-(?=\w)'
>>> re.sub(r, ' ', 'test - test')
'test test'
>>> re.sub(r, ' ', 'test-test')
'test test'
>>> re.sub(r, ' ', 'test -test')
'test -test'

EDIT Corrected according to comment. The trick is to add the 'lookahead assertion' with ?= and the lookbehind with ?<=, which not be part of the match, but will be checked.

Answer 2

Try this crazy one:

-(?!\w(?<=\s-\w))

This regex:

• Searches for a dash that isn't followed by a (letter with a space two characters before it).
• Takes care of test- test and -test, which you don't have in your test cases.
• Selects only the dash, so you can replace it (this really what made the definition so complicated).

By the way - you don't need RegexOptions.IgnoreCase because your regex has no literal parts, you aren't tryting to captrue /test/ from "Test TEST". This will do:

Regex specialCharsExcept = new Regex(@"-(?!\w(?<=\s-\w))");
return specialCharsExcept.Replace(term, " ");