Best way get first word and rest of the words in a string in C#

you can store the split in a let clause

var parameters =
    from line in parameterTextBox.Lines
    let split = line.Split(' ')
    select new {name = split.First(), value = split.Skip(1)};

Sure.

var parameters = from line in parameterTextBox.Lines
                 let words = line.Split(' ')
                 select new { name = words.First(), words.skip(1) };

string Str= "one all of the rest";
Match m = Regex.match(Str,"(\w*) (\w.*)");
string wordone = m.Groups[1];
string wordtwo = m.Groups[2];