Regex.Replace("a b c a b c", "a", "*")
returns
"* b c * b c"
Is there a simple way to replace only the first occurence, such that the result is
"* b c a b c"
Cannot find a RegExOption that would limit the replacement. In particular
Regex.Replace("a b c a b c", "a", "*", RegexOptions.Multiline)
Regex.Replace("a b c a b c", "a", "*", RegexOptions.Singleline)
do not make any difference - obviously. There are not much more options however.
Use the appropriate overload
Regex rgx = new Regex("a");
string result = rgx.Replace("a b c a b c", "*", 1); // * b c a b c
Use capturing group along with the starting anchor.
Regex.Replace("a b c a b c", "^([^a]*)a", "$1*")
^([^a]*) captures all the characters which exists before the first a. And the following a on the above regex matches only the first a. So by replacing the matched chars with the characters present inside the group index 1 plus * will give you the desired output.
