SkipWhile TakeWhile, then take also lines above until a match

Question

I'm using SkipWhile and TakeWhile to gather lines from a large file using Linq .

var foundLines = File.ReadLines(filePath).SkipWhile(line => !line.Contains("pattern1")).TakeWhile(line => !line.Contains("pattern2"));

But I also want the text above the lines I gathered until another string match. Is this possible?

I'll try to show this visually. I only have pattern1 , this variable is given. pattern2 and pattern3 are static data.

...
...
...pattern3...
...
...
...pattern1...
...
...
...pattern2...
...
...

The text between pattern1 and pattern2 is what I can simply catch by doing SkipWhile and TakeWhile on File.ReadLines . After this is catched, I need to go up and catch all data until pattern3 .

So the whole data I want to catch is from pattern3 until pattern2 . But my starting point must be pattern1 because that info (ID) is given and data changes based on that.

For example:

Pattern1 is an ID, or a GUID: KFK284NSKQLOFIE8.

Pattern2 is "end processing"

Pattern3 is "start processing"

And I need all lines between "start processing" and "end processing"

If this is not possible with Linq , how can I solve this problem? Would FileStream.Seek be an option?

Answer 1

Try following code. Used code like this for a very long time and I feel is the best method. Each capture is a single string in the List object data. I can modify code to change the format of Data if required.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        const string FILENAME = @"c:\temp\test.txt";
        static void Main(string[] args)
        {
            List<string> data = new List<string>();
            StreamReader reader = new StreamReader(FILENAME);

            string line = "";
            Boolean foundPattern3 = false;
            while((line = reader.ReadLine()) != null)
            {
                if (line.Contains("pattern3"))
                {
                    data.Add(line);
                    foundPattern3 = true;
                }
                else
                {
                    if (line.Contains("pattern2"))
                    {
                        foundPattern3 = false;
                    }
                    else
                    {
                        if (foundPattern3)
                        {
                            data[data.Count() - 1] += "\n" + line;
                        }
                    }
                }
            }
        }
    }
}