c# search string in txt file

Question

I want to find a string in a txt file if string compares, it should go on reading lines till another string which I'm using as parameter.

Example:

CustomerEN //search for this string
...
some text which has details about the customer
id "123456"
username "rootuser"
...
CustomerCh //get text till this string

I need the details to work with them otherwise.

I'm using linq to search for "CustomerEN" like this:

File.ReadLines(pathToTextFile).Any(line => line.Contains("CustomerEN"))

But now I'm stuck with reading lines (data) till "CustomerCh" to extract details.

Rawling · Accepted Answer · 2012-10-12T10:07:55.570

If your pair of lines will only appear once in your file, you could use

File.ReadLines(pathToTextFile)
    .SkipWhile(line => !line.Contains("CustomerEN"))
    .Skip(1) // optional
    .TakeWhile(line => !line.Contains("CustomerCh"));

If you could have multiple occurrences in one file, you're probably better off using a regular foreach loop - reading lines, keeping track of whether you're currently inside or outside a customer etc:

List<List<string>> groups = new List<List<string>>();
List<string> current = null;
foreach (var line in File.ReadAllLines(pathToFile))
{
    if (line.Contains("CustomerEN") && current == null)
        current = new List<string>();
    else if (line.Contains("CustomerCh") && current != null)
    {
        groups.Add(current);
        current = null;
    }
    if (current != null)
        current.Add(line);
}

If you need case insensitive search check out http://stackoverflow.com/questions/444798/case-insensitive-containsstring — Alexei Levenkov, Nov 30 '15 at 02:03

score 14 · Answer 2 · answered Oct 12 '12 at 10:05

14

You have to use while since foreach does not know about index. Below is an example code.

int counter = 0;
string line;

Console.Write("Input your search text: ");
var text = Console.ReadLine();

System.IO.StreamReader file =
    new System.IO.StreamReader("SampleInput1.txt");

while ((line = file.ReadLine()) != null)
{
    if (line.Contains(text))
    {
        break;
    }

    counter++;
}

Console.WriteLine("Line number: {0}", counter);

file.Close();

Console.ReadLine();

answered Oct 12 '12 at 10:05

Ekk

5,627
19
27

You don't really need to know the index. – Rawling Oct 12 '12 at 10:09
He need to find first string, wich appears only after other keyword. – Anton Sizikov Oct 12 '12 at 10:11
And there is no reason you couldn't put the counter in a foreach as well if you wanted to. – Chris Oct 12 '12 at 10:18
1

Every other solution proposed reads the entire file into memory and holds it there until the search is complete. This is the only one that carefully manages memory with a stream while performing the search. – Cdaragorn May 17 '18 at 22:15

score 4 · Answer 3 · answered Oct 12 '12 at 10:02

4

With LINQ, you could use the SkipWhile / TakeWhile methods, like this:

var importantLines = 
    File.ReadLines(pathToTextFile)
    .SkipWhile(line => !line.Contains("CustomerEN"))
    .TakeWhile(line => !line.Contains("CustomerCh"));

answered Oct 12 '12 at 10:02

Cristian Lupascu

39,078
16
100
137

Anton Sizikov · Answer 4 · 2012-10-12T10:08:25.647

If you whant only one first string, you can use simple for-loop.

var lines = File.ReadAllLines(pathToTextFile);

var firstFound = false;
for(int index = 0; index < lines.Count; index++)
{
   if(!firstFound && lines[index].Contains("CustomerEN"))
   {
      firstFound = true;
   }
   if(firstFound && lines[index].Contains("CustomerCh"))
   {
      //do, what you want, and exit the loop
      // return lines[index];
   }
}

score 0 · Answer 5 · answered Jun 09 '17 at 19:01

I worked a little bit the method that Rawling posted here to find more than one line in the same file until the end. This is what worked for me:

                foreach (var line in File.ReadLines(pathToFile))
                {
                    if (line.Contains("CustomerEN") && current == null)
                    {
                        current = new List<string>();
                        current.Add(line);
                    }
                    else if (line.Contains("CustomerEN") && current != null)
                    {
                        current.Add(line);
                    }
                }
                string s = String.Join(",", current);
                MessageBox.Show(s);

c# search string in txt file

5 Answers5

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