C# get text from file between two hashes

Question

In my C# program (at this point) I have two fields in my form. One is a word list using a listbox; the other is a textbox. I have been able to successfully load a large word list into the listbox from a text file. I can also display the selected item in the listbox into the textbox this way:

private void wordList_SelectedIndexChanged(object sender, EventArgs e)
     {
          string word = wordList.Text;
          concordanceDisplay.Text = word;
     }

I have another local file I need to get at to display some of its contents in the textbox. In this file each headword (as in a dictionary) is preceded by a #. So, I would like to take the variable 'word' and search in this local file to put the entries into the textbox, like so:

#headword1
    entry is here...
    ...
    ...
#headword2
    entry is here...
    ...
    ...
#headword3
    entry is here...
    ...
    ...

You get the format of the text file. I just need to search for the correct headword with # before that word, and copy all info from there until the next hash in the file, and place it in the text box.

Obviously, I am a newbie, so be gentle. Thanks much.

P.S. I used StreamReader to get at the word list and display it in the listbox like so:

StreamReader sr = new StreamReader("C:\\...\\list-final.txt");
       string line;
       while ((line = sr.ReadLine()) != null)
       {
           MyList.Add(line);
       }
       wordList.DataSource = MyList;

Answer 1

string getSection(string sectionName)
{
    StreamReader sr = new StreamReader(@"C:\Path\To\file.txt");
    string line;
    var MyList = new List<string>();
    bool inCorrectSection = false;
    while ((line = sr.ReadLine()) != null)
    {
        if (line.StartsWith("#"))
        {
            if (inCorrectSection)
                break;
            else
                inCorrectSection = Regex.IsMatch(line, @"^#" + sectionName + @"($| -)");
        }
        else if (inCorrectSection)
            MyList.Add(line);
    }
    return string.Join(Environment.NewLine, MyList);
}

// in another method
textBox.Text = getSection("headword1");

Here are a few alternate ways to check if the section matches, in rough order of how accurate they are in detecting the right section name:

// if the separator after the section name is always " -", this is the best way I've thought of, since it will work regardless of what's in the sectionName
inCorrectSection = Regex.IsMatch(line, @"^#" + sectionName + @"($| -)");
// as long as the section name can't contain # or spaces, this will work
inCorrectSection = line.Split('#', ' ')[1] == sectionName;
// as long as only alphanumeric characters can ever make up the section name, this is good
inCorrectSection = Regex.IsMatch(line, @"^#" + sectionName + @"\b");
// the problem with this is that if you are searching for "head", it will find "headOther" and think it's a match
inCorrectSection = line.StartsWith("#" + sectionName);

Answer 2

var sectionLines = File.ReadAllLines(fileName) // shortcut to read all lines from file
    .SkipWhile(l => l != "#headword2") // skip everything before the heading you want
    .Skip(1) // skip the heading itself
    .TakeWhile(l => !l.StartsWith("#")) // grab stuff until the next heading or the end
    .ToList(); // optional convert to list