如何从多个txt文件中裁剪字符串

我有数千个.log文件，我需要在所有文件中找到一些字符串。

我将举个例子来解释：在所有的.log文件上，我都有一个名为"AAA"的字符串，在这个字符串之后，我有一个可以从一个日志文件到其他日志文件的不同编号。我知道如何搜索AAA字符串。我不知道的是如何只裁剪AAA字符串之后的字符串编号。

更新：.log文件包含很多行。在.log文件中，我只有一行包含字符串"A12A"。在那行之后，我有一个号码（例如：5465）。我需要的是提取A12A后面的数字。注意：A12A和5465字符串编号之间有一个间隔。

示例：.log文件："assddsf dfdfsd dfd A12A 5465 dffdsfsdf dfdfdf"我需要提取的是：5465。

到目前为止我拥有的是：

// Modify this path as necessary.
string startFolder = @"c:'program files'Microsoft Visual Studio 9.0'";
// Take a snapshot of the file system.
System.IO.DirectoryInfo dir = new System.IO.DirectoryInfo(startFolder);
// This method assumes that the application has discovery permissions
// for all folders under the specified path.
IEnumerable<System.IO.FileInfo> fileList = dir.GetFiles("*.*", System.IO.SearchOption.AllDirectories);
string searchTerm = @"Visual Studio";
// Search the contents of each file.
// A regular expression created with the RegEx class
// could be used instead of the Contains method.
// queryMatchingFiles is an IEnumerable<string>.
var queryMatchingFiles =
    from file in fileList
    where file.Extension == ".htm"
    let fileText = GetFileText(file.FullName)
    where fileText.Contains(searchTerm)
    select file.FullName;
// Execute the query.
Console.WriteLine("The term '"{0}'" was found in:", searchTerm);
foreach (string filename in queryMatchingFiles)
{
    Console.WriteLine(filename);
}
// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
// Read the contents of the file.
static string GetFileText(string name)
{
    string fileContents = String.Empty;
// If the file has been deleted since we took 
// the snapshot, ignore it and return the empty string.
if (System.IO.File.Exists(name))
{
    fileContents = System.IO.File.ReadAllText(name);
}
return fileContents;

}

private static readonly string _SearchPattern = "A12A";
private static readonly Regex _NumberExtractor = new Regex(@"'d+");
private static IEnumerable<Tuple<String, int>> FindMatches()
{
    var startFolder = @"D:'";
    var filePattern = @"*.htm";
    var matchingFiles = Directory.EnumerateFiles(startFolder, filePattern, SearchOption.AllDirectories);
    foreach (var file in matchingFiles)
    {
        // What encoding do your files use?
        var lines = File.ReadLines(file, Encoding.UTF8);
        foreach (var line in lines)
        {
            int number;
            if (TryGetNumber(line, out number))
            {
                yield return Tuple.Create(file, number);
                // Stop searching that file and continue with the next one.
                break;
            }
        }
    }
}
private static bool TryGetNumber(string line, out int number)
{
    number = 0;
    // Should casing be ignored??
    var index = line.IndexOf(_SearchPattern, StringComparison.InvariantCultureIgnoreCase);
    if (index >= 0)
    {
        var numberRaw = line.Substring(index + _SearchPattern.Length);
        var match = _NumberExtractor.Match(numberRaw);
        return Int32.TryParse(match.Value, out number);
    }
    return false;
}