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We have one quite complex regular expression which checks for string structure.
I wonder if there is an easy way to find out which character in the string that is causing reg expression not to match.
For example,
string.match(reg_exp).get_position_which_fails
Basically, the idea is how to get "position" of state machine when it gave up.
Here is an example of regular expression:
%q^[^\p{Cc}\p{Z}]([^\p{Cc}\p{Zl}\p{Zp}]{0,253}[^\p{Cc}\p{Z}])?$
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Similarly, the negation variant of the character class is defined as "[^ ]" (with ^ within the square braces), it matches a single character which is not in the specified or set of possible characters. For example the regular expression [^abc] matches a single character except a or, b or, c.
Basically (0+1)* mathes any sequence of ones and zeroes. So, in your example (0+1)*1(0+1)* should match any sequence that has 1. It would not match 000 , but it would match 010 , 1 , 111 etc. (0+1) means 0 OR 1.
If you add a * after it – /^[^abc]*/ – the regular expression will continue to add each subsequent character to the result, until it meets either an a , or b , or c . For example, with the source string "qwerty qwerty whatever abc hello" , the expression will match up to "qwerty qwerty wh" .
There is a method for matching specific characters using regular expressions, by defining them inside square brackets. For example, the pattern [abc] will only match a single a, b, or c letter and nothing else.
The short answer is: No.
The long answer is that a regular expression is a complicated finite state machine that may be in a state trying to match several different possible paths simultaneously. There's no way of getting a partial match out of a regular expression without constructing a regular expression that allows partial matches.
If you want to allow partial matches, either re-engineer your expression to support them, or write a parser that steps through the string using a more manual method.
You could try generating one of these automatically with Ragel if you have a particularly difficult expression to solve.
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