Question

I want to split a requested url filename chunks of up to 2 characters and then rewrite to a directory structure:

Input (line-by-line):

a.txt
ba.txt
cba.txt
dcba.txt
edcba.txt
fedcba.txt
gfedcba.txt
hgfedcba.txt

Desired Output:

a/file.txt
ba/file.txt
c/ba/file.txt
dc/ba/file.txt
e/dc/ba/file.txt
fe/dc/ba/file.txt
g/ef/dc/ba/file.txt
hg/ef/dc/ba/file.txt

Achived output (with regex following):

///a/file.txt
///ba/file.txt
//c/ba/file.txt
//dc/ba/file.txt
/e/dc/ba/file.txt
/fe/dc/ba/file.txt
g/fe/dc/ba/file.txt
hg/fe/dc/ba/file.txt

RegEx:

([a-z]{1,2}?)??([a-z]{1,2}?)??([a-z]{1,2}?)??([a-z]{1,2})??\.txt

Replacement:

$1/$2/$3/$4/file.txt

I found no way to repeat a match and capture each iteration.

Unfortunately even if a match $1 – $3 is not found a slash will be written by this replacement text.

Answer 1

found a way using .NET Group.Captures Property

LinqPad snippet:

string inputUrl= "/gfedcba.txt";
string pattern = @"/([a-z]{1,2})+\.txt";
string rewrittenUrl = inputUrl;

Match match = Regex.Match(inputUrl, pattern, RegexOptions.RightToLeft);

if(match.Success){
    var captures = match.Groups[1].Captures;
    rewrittenUrl="";
    for(int i = captures.Count; i > 0; i--) {
        rewrittenUrl += "/" + captures[i-1].Value;
    }
    rewrittenUrl += ".txt";
}

"inputUrl:".Dump();
inputUrl.Dump();
"rewrittenUrl:".Dump();
rewrittenUrl.Dump();

LinqPad output:

inputUrl:

/gfedcba.txt

rewrittenUrl:

/g/fe/dc/ba.txt

now i’m going to write an custom IIS Url Rewrite Provider