如何复制文本文件的特定部分

Question

My goal is to copy specific contents of .txt files into 1 big text file. I've searched through the website and found a way to merge my files.

using (var output = File.Create("output"))
{
    foreach (var file in new[] { "file1", "file2" })
    {
        using (var input = File.OpenRead(file))
        {
            input.CopyTo(output);
        }
    }
}

This answer was posted by: n8wrl

The structure of my text looks like this:

...

Sentence A

Important stuff

Sentence B

...

So I would need a way to search for "Sentence A" and "Sentence B" in the document and copy the lines between these two.

Thanks for your help!

Answer 1

Consider the options from this post: Fastest way to search string in large text file to locate what you want for the start and end sentence, use those positions (start of first and end of second) in a substring.

Make sure you test for the situations where the second sentence appears before the first, where it appears twice (do you want the text between the first sentence and the second occurrence of the second sentence?) and where there is no second sentence. Then consider similar scenarios for the first sentence (eg if it appears after the second sentence, if it appears more than once, and if it doesn't appear at all while the second sentence is present).

Answer 2

Assuming that both "Sentence A" and "Sentence B" are in whole lines you can try a simple Linq . Let's extract the "important stuff" first:

private static IEnumerable<string> Staff(string file) 
{
    return File
        .ReadLines(file)
        .SkipWhile(line => line != "Sentence A")  // Skip until Sentence A found 
        .Skip(1)                                  // Skip Sentence A itself
        .TakeWhile(line => line != "Sentence B"); // Take until Sentence B found 
}

Then combine all the files into one:

string[] files = new[] 
{
    "file1", "file2", "file3"
};

var extracts = files.SelectMany(file => Staff(file));

finally, let's write all the extracts into the file:

File.WriteAllLines("output", extracts);

Edit: In case you have merged files ("important stuff" can appear several times) we have to implement FSM (Finite State Machine):

private static IEnumerable<string> Staff(string file) 
{
    bool important = false;

    foreach (string line in file.ReadLines(file)) 
    {
        if (important) 
            if (line == "Sentence B")
                important = false;
            else
                yield return line;
        else 
            important = line == "Sentence B"; 
    }
} 

Please, notice that we have to scan the entire file, that's why we should avoid file merging.

Answer 3

You need something like this:

var sentenceA = "Sentence A";
var sentenceB = "Sentence B";
using (var output = System.IO.File.Create("output"))
{
    foreach (var file in new[] { "file1", "file2" })
    {
        using (var input = File.OpenRead(file))
        {
            var reader = new System.IO.StreamReader(input);
            var text = reader.ReadToEnd().Split(new string[] { Environment.NewLine }, StringSplitOptions.None).ToString();
            if (text.Contains(sentenceA) && text.Contains(sentenceB)) {
                output.Write(text.Substring(text.IndexOf(sentenceA), text.IndexOf(sentenceB) + sentenceB.Length));
            }
        }
    }
}