c# replace string in a text file

Question

I am trying to replace string in a text file.

I use the following code:

string text = File.ReadAllText(@"c:\File1.txt");
text = text.Replace("play","123");
File.WriteAllText(@"c:\File1.txt", text);

It not only changes the word "play" to "123" but also change the word "display" to "dis123"

How to fix this problem?

Answer 1

You could take the advantage of "Regular expressions" here.

\b Matches the word boundary, This will solve your problem.

text = Regex.Replace(text, @"\bplay\b","123");

Read more about Regular expressions

Answer 2

You can use following snippets of code

var str = File.ReadAllText(@"c:\File1.txt");
                   var arr = str.Split(new[] { " " }, StringSplitOptions.RemoveEmptyEntries).ToList();

    for (int i = 0; i < arr.Count; i++)
    {
        if (arr[i].StartsWith("play"))
        {
            arr[i] = arr[i].Replace("play", "123");
        }
    }

    var res = string.Join(" ", arr);
File.WriteAllText(@"c:\File1.txt", result);

Also, this is case sensitive make sure this is what you want.