Getting matching result using Regex

Question

I need to find the matching result i.e a string using Regex. Let me demonstrate the scenario using sample inputs.

string input= "xb-cv_107_20190608_032214_006";          // <-1st case
string input = "yb-ha_107_20190608_032214_006__foobar"; // <-2nd case
string input= "fv_vgf_ka01mq3286__20190426_084135_039"; // <-3rd case
string input="fv_vgf_ka01mq3286__2090426_084135_039"; //<-4th case

For 1st case input, output required= "xb-cv_107_20190608_032214_006".
For 2nd case input, output required= "yb-ha_107_20190608_032214_006".
For 3rd case input, output required= "fv_vgf_ka01mq3286__20190426_084135_039".
For 4th case input, output required= null since the pattern does not match.

The procedure to get the output is:

• Check using regex if pattern ends with _ followed by 8 decimals followed by '_' followed by 6 decimals followed by 3 decimals
• Or check using regex if pattern ends with _ followed by 8 decimals followed by _ followed by 6 decimals followed by 3 decimals exists followed by __ exists followed by anything random.

Till now, I have come up with this Regex expression:

string pattern = @".+[_][0-9]{8}[_][0-9]{6}[_][0-9]{3}([_]{2})?";
var result = Regex.Match(input, pattern)?.Groups[0].Value ;

Answer 1

You may use

var result = Regex.Match(input, @"^(.+_[0-9]{8}_[0-9]{6}_[0-9]{3})__")?.Groups[1].Value;

Regex details:

• ^ - start of string
• ( - Group 1 start:
  • .+ - any 1+ chars other than LF, as many as possible
  • _[0-9]{8}_[0-9]{6}_[0-9]{3} - _, 8 digits, _, 6 digits, _, 3 digits
• ) - end of Group 1
• __ - two underscores.

If there is a match, the result holds the value that resides in Group 1.

If there is no match, result is null.