.net - Escaping mid-string percent signs, is a regex the best option? -

i need escape % characters in string entered user - replacing them [%] unless @ start or end of string.

for example %foo%foo[%]foo% should become %foo[%]foo[%]foo%. whitespace isn't concern: escaping mid-string percent signs.

a regular expression of [^[]%[^\]] match mid-string percentages, adjacent characters (so o%f in example).

is there reasonable regular expression match mid-string non-escaped percentage characters?

i wondering if non-regex solution preferable, such as

iterating through characters in string, , building replacement string percentages escaped

const string test = "%foo%foo[%]foo%";  stringbuilder escaped = new stringbuilder(); escaped.append(test[0]);  (int = 1; < test.length - 1; i++) {     if (test[i] != '%' || (test[i - 1] == '[' && test[i] == '%' && test[i + 1] == ']'))     {         escaped.append(test[i]);     }     else     {         escaped.append("[%]");     } }  escaped.append(test[test.length - 1]); 

-or-

doing three-pass token-based replacement such as

const string token = "!percent!"; // string hope(!) never encounter in string we're escaping const string test = "%foo%foo[%]foo%";  string escaped = test.replace("[%]", token); escaped = replaced.replace("%", token); escaped = replaced.replace(token, "[%]"); 

(although escape first or last character percentages, isn't want)

as why need - escaping like filter expression values entered user being applied datatable.

you might try:

(?<!^)((?<!\[)|(?!.\]))%(?!$) 

it's bit ugly because wanted match cases foo[%foo , foo%]foo.

(?<!^) - prevents match @ start of string (negative behind) (?!$) - prevents match @ end of string (negative ahead) (?<!\[)|(?!.\]) - prevents match if previous '[' , ']' next.   

you use regex command like:

regex.replace(input, @"(?<!^)((?<!\[)|(?!.\]))%(?!$)", x => "[" + x + "]")