decision on regular expression length - regex

Question

I want to accomplish the following requirements using Regex only (no C# code can be used )
• BTN length is 12 and BTN starts with 0[123456789] then it should remove one digit from left and one digit from right.
WORKING CORRECTLY
• BTN length is 12 and it’s not the case stated above then it should always return 10 right digits by removing 2 from the start. (e.g. 491234567891 should be changed to 1234567891)
NOT WORKING CORRECTLY
• BTN length is 11 and it should remove one digit from left. WORKING CORRECTLY
for length <=10 BTNs , nothing is required to be done , they would remain as it is or Regex may get failed too on them , thats acceptable .
USING SQL this can be achieved like this
case when len(BTN) = 12 and BTN like '0[123456789]%' then SUBSTRING(BTN,2,10) else RIGHT(BTN,10) end
but how to do this using Regex .
So far I have used and able to get some result correct using this regex
[0*|\d\d]*(.{10}) but by this regex I am not able to correctly remove 1st and last character of a BTN like this 015732888810 to 1573288881 as this regex returns me this 5732888810 which is wrong
code is
string s = "111112573288881,0573288881000,057328888105,005732888810,15732888815,344956345335,004171511326,01777203102,1772576210,015732888810,494956345335";
string[] arr = s.Split(',');
foreach (string ss in arr)
{
// Match mm = Regex.Match(ss, #"\b(?:00(\d{10})|0(\d{10})\d?|(\d{10}))\b");
// Match mm = Regex.Match(ss, "0*(.{10})");
// ([0*|\\d\\d]*(.{10}))|
Match mm = Regex.Match(ss, "[0*|\\d\\d]*(.{10})");
// Match mm = Regex.Match(ss, "(?(^\\d{12}$)(.^{12}$)|(.^{10}$))");
// Match mm = Regex.Match(ss, "(info)[0*|\\d\\d]*(.{10}) (?(1)[0*|\\d\\d]*(.{10})|[0*|\\d\\d]*(.{10}))");
string m = mm.Groups[1].Value;
Console.WriteLine("Original BTN :"+ ss + "\t\tModified::" + m);
}

Answer 1

This should work:
(0(\d{10})0|\d\d(\d{10}))
UPDATE:
(0(\d{10})0|\d{1,2}(\d{10}))
1st alternate will match 12-digits with 0 on left and 0 on right and give you only 10 in between.
2nd alternate will match 11 or 12 digits and give you the right 10.
EDIT:
The regex matches the spec, but your code doesn't read the results correctly. Try this:
Match mm = Regex.Match(ss, "(0(\\d{10})0|\\d{1,2}(\\d{10}))");
string m = mm.Groups[2].Value;
if (string.IsNullOrEmpty(m))
m = mm.Groups[3].Value;
Groups are as follows:
index 0: returns full string
index 1: returns everything inside the outer closure
index 2: returns only what matches in the closure inside the first alternate
index 3: returns only what matches in the closure inside the second alternate
NOTE: This does not deal with anything greater than 12 digits or less than 11. Those entries will either fail or return 10 digits from somewhere. If you want results for those use this:
"(0(\\d{10})0|\\d*(\\d{10}))"
You'll get rightmost 10 digits for more than 12 digits, 10 digits for 10 digits, nothing for less than 10 digits.
EDIT:
This one should cover your additional requirements from the comments:
"^(?:0|\\d*)(\\d{10})0?$"
The (?:) makes a grouping excluded from the Groups returned.
EDIT:
This one might work:
"^(?:0?|\\d*)(\\d{10})\\d?$"

Answer 2

(?(^\d{12}$)(?(^0[1-9])0?(?<digit>.{10})|\d*(?<digit>.{10}))|\d*(?<digit>.{10}))
which does the exact same thing as sql query + giving result in Group[1] all the time so i didn't had to change the code a bit :)