如何在每行中提取含有关键词的字符串？

[nanxinda88]

richTextBox1中的数据：
---------------------------------------------
……
2010-01-01 01:01:01:5158=report
2010-01-01 01:03:03:5159=result
2010-01-01 01:08:08:5160=message
2010-01-01 01:11:11:5161=report
2010-01-01 01:12:12:5162=report
2010-01-01 01:13:13:5163=message
2010-01-01 01:16:16:5164=report
2010-01-01 01:18:18:5165=result
……
---------------------------------------------

想要把含有“report”的每行都提取出来，然后保留第三个冒号之前的字符串，并在richTextBox2中列出：
---------------------------------------------
……
2010-01-01 01:01:01
2010-01-01 01:11:11
2010-01-01 01:12:12
2010-01-01 01:16:16
……
---------------------------------------------
请问应该如何编写代码？
求助高手，感激不尽！

[nanxinda88]

都快沉了，顶出来！

[_autotest]

matchcollection mc=regex.matches(string,".*");
foreach (match m in mc)
{
string temp=m.value;
print temp.substring(0,temp.lastindexof(":"));
}

[huming_h]

string[] s = richTextBox1.Text.Split('\n');
foreach (string str in s)
{
if (str.Contains("report"))
{
int index = str.LastIndexOf(':');
this.richTextBox2.AppendText(str.Substring(0,index));
}
}

[_autotest]

string str = @"2010-01-01 01:01:01:5158=report 
                2010-01-01 01:03:03:5159=result 
            2010-01-01 01:08:08:5160=message 
            2010-01-01 01:11:11:5161=report 
            2010-01-01 01:12:12:5162=report 
            2010-01-01 01:13:13:5163=message 
            2010-01-01 01:16:16:5164=report 
            2010-01-01 01:18:18:5165=result";
            StringBuilder sb = new StringBuilder();
            MatchCollection mc = Regex.Matches(str, ".*");
            foreach (Match m in mc)
            {
                string temp = m.Value;
                if (temp != "")
                    sb.Append(temp.Substring(0, temp.LastIndexOf(":")));
            }
结果：
2010-01-01 01:01:01 
2010-01-01 01:11:11 
2010-01-01 01:12:12 
2010-01-01 01:16:16 
。。。。

[-过客-]

没必要搞那么麻烦

foreach(string s in richTextBox1.Lines)
{
    if (s.IndexOf("report")>0)
        richTextBox2.Text += s.Remove(s.LastIndexOf(":")) + "\r\n";
}