Question

I’m simply trying to execute File.ReadAllLines against a specific file and, for every line, split on |. I have to use regex on this one.

This code below doesnt work, but you’ll see what i’m trying to do:

string[] contents = File.ReadAllLines(filename);
string[] splitlines = Regex.Split(contents, '|');
foreach (string split in splitlines)
{
    //Regex line = content.Split('|');
    //content.Split('|');
    string prefix = prefix = Regex.Match(line, @"(\S+)(\d+)").Groups[0].Value;
    File.AppendAllText(workingdirform2 + "configuration.txt", prefix+"\r\n");
}

Answer 1

It’s not entirely clear to me what you are trying to do, but there are a number of errors in your code. I have tried to guess what you are doing, but if this isn’t what you want, please explain what you do want preferably with some examples:

string inputFilename = "input.txt";
string outputFilename = "output.txt";

using (StreamWriter streamWriter = File.AppendText(outputFilename))
{
    using (StreamReader streamReader = File.OpenText(inputFilename))
    {
        while (true)
        {
            string line = streamReader.ReadLine();

            if (line == null)
            {
                break;
            }

            string[] splitlines = line.Split('|');
            foreach (string split in splitlines)
            {
                Match match = Regex.Match(split, @"\S+\d+");
                if (match.Success)
                {
                    string prefix = match.Groups[0].Value;
                    streamWriter.WriteLine(prefix);
                }
                else
                {
                    // Handle match failed...
                }
            }
        }
    }
}

Key points:

• You seem to want to perform an operation on each line, so you need to iterate over the lines.
• Use the simple string.Split method if you want to split on a single character. Regex.Split doesn’t accept a character and “|” has a special meaning in regular expressions so it wouldn’t have worked anyway unless you escaped it.
• You were opening and closing the output file multiple times. You should open it just once and keep it open until you have finished writing to it. The using keyword is useful here.
• Use WriteLine instead of appending “\r\n”.
• If the input file is large, use a StreamReader instead of ReadAllLines.
• If the match fails, your program will throw an exception. You probably should check match.Success before using the match and if this returns false, handle the error appropriately (skip the line, report a warning, throw an exception with an appropriate message, etc.)
• You aren’t actually using groups 1 and 2 in the regular expression, so you can remove the parentheses to save the regular expression engine from having to store results that you won’t use anyway.