c# regex pattern position and last 3 chars

Question

I am trying to create a new string based on a file name. Part of the name contains irrelevant information like the current year. For example D2015987.txt . For me the important part of the regex is to extract D987 from the part of the file name.

I started off by using Regex.Match(@"D\\d{4}|\\d{3}\\b+") , this seems to trim off the last digit when I get the values. In reality I am attempting to create a new string from this value, so I may also be able to use string newStr = Regex.Replace(pattern).value ...

I also need assistance with creating a new value that will match a pattern similar to this D11Q1987.txt ... from this I need the DQ987 part as well.

Thanks in advance for your help. Dan

Answer 1

try this : pattern is ^(\\w)\\d+(\\d{3})\\.txt$ replace with $1$2

now u use this code in your code according your (C#) syntax. i hope this work. c# code

using System.IO;
using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
    // This is the input string we are replacing parts from.
    string input = "D2015987.txt";

    // Use Regex.Replace to replace the pattern in the input.
    string output = Regex.Replace(input, @"^(\w)\d+(\d{3})\.txt$", "$1$2");

    // Write the output.
    Console.WriteLine(input);
    Console.WriteLine(output);
    }
}

output c#

D2015987.txt
D987

another php solution

$str = "D2015987.txt";

preg_match($re, $str, $matches);
$r=$matches[1].$matches[2];
var_dump($r );

output for php

string 'D987' (length=4)

Answer 2

1. (.) grabs the first, capture group 1
2. \\d+ matches any number of digits (but at least one)
3. ([A-Za-z]) matches a single character, and captures it as group 1.
4. \\d matches a single digit.
5. (\\d{3}) matches three digits.
6. \\. escapes the period.
7. txt finishes it off looking for the literal characters txt

Regex:

    (.)\d+([A-Za-z])\d(\d{3})\.txt

Now, if the last digits are variable length, but always preceded by a digit, we simply change the {3} to + .

    (.)\d+([A-Za-z])\d(\d+)\.txt

$1 contains D (by your example), `$2' contains Q (by your example) and $3 contains 987, but both examples depend on being preceded by a digit that we can use as a marker but throw away.