(6)正则表达式 组与非捕获组
以下提供一些简单的示例:
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Code
string x = "Live for nothing,die for something";
string y = "Live for nothing,die for somebody";
Regex r = new Regex(@"^Live ([a-z]{3}) no([a-z]{5}),die \1 some\2$");
Console.WriteLine("x match count:" + r.Matches(x).Count);//1
Console.WriteLine("y match count:" + r.Matches(y).Count);//0
//正则表达式引擎会记忆“()”中匹配到的内容,作为一个“组”,并且可以通过索引的方式进行引用。表达式中的“\1”,用于反向引用表达式中出现的第一个组,即粗体标识的第一个括号内容,“\2”则依此类推。
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string x = "Live for nothing,die for something";
Regex r = new Regex(@"^Live for no([a-z]{5}),die for some\1$");
if (r.IsMatch(x))
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{
Console.WriteLine("group1 value:" + r.Match(x).Groups[1].Value);//输出:thing
}
//获取组中的内容。注意,此处是Groups[1],因为Groups[0]是整个匹配的字符串,即整个变量x的内容。
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string x = "Live for nothing,die for something";
Regex r = new Regex(@"^Live for no(?<g1>[a-z]{5}),die for some\1$");
if (r.IsMatch(x))
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{
Console.WriteLine("group1 value:" + r.Match(x).Groups["g1"].Value);//输出:thing
}
//可根据组名进行索引。使用以下格式为标识一个组的名称(?<groupname>…)。
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string x = "Live for nothing nothing";
Regex r = new Regex(@"([a-z]+) \1");
if (r.IsMatch(x))
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{
x = r.Replace(x, "$1");
Console.WriteLine("var x:" + x);//输出:Live for nothing
}
//删除原字符串中重复出现的“nothing”。在表达式之外,使用“$1”来引用第一个组,下面则是通过组名来引用:
string x = "Live for nothing nothing";
Regex r = new Regex(@"(?<g1>[a-z]+) \1");
if (r.IsMatch(x))
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{
x = r.Replace(x, "${g1}");
Console.WriteLine("var x:" + x);//输出:Live for nothing
}
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string x = "Live for nothing";
Regex r = new Regex(@"^Live for no(?:[a-z]{5})$");
if (r.IsMatch(x))
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{
Console.WriteLine("group1 value:" + r.Match(x).Groups[1].Value);//输出:(空)
}
//在组前加上“?:”表示这是个“非捕获组”,即引擎将不保存该组的内容。
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