正则表达式:匹配到可选单词

有几种方法可以做到这一点。你可以这样做:

^(.*?)(with|$)

with 或者在队伍的尽头 $ anchor .

I have a sentence with a clause I don't want.
I have a sentence and I like it.

as seen on rubular.com ):

• • 第1组: "I have a sentence "
  • 第2组: "with"
• • 第1组: "I have a sentence and I like it" .
  • "" (空字符串)

您可以使用 (?:with|$) 如果你不需要区分这两种情况。

相关问题

• Difference between .*? and .* for regex

如果我正确理解你的需要,你想把句子和单词“with”匹配起来,或者,如果没有,把整个句子都匹配起来?为什么不编写regexp来显式地查找这两种情况呢?

/(.*) with |(.*)/

这不是两个案子都有吗?

string optional = "with a clause I don't want" 
string rx = "^(.*?)" + Regex.Escape(optional) + ".*$";

// displays "I have a sentence"
string foo = "I have a sentence with a clause I don't want.";
Console.WriteLine(Regex.Replace(foo, rx, "$1"));

// displays "I have a sentence and I like it."
string bar = "I have a sentence and I like it.";
Console.WriteLine(Regex.Replace(bar, rx, "$1"))

如果您不需要regex提供的复杂匹配,那么可以使用 IndexOf Remove . (显然,您可以将逻辑抽象为助手和/或扩展方法或类似方法):

string optional = "with a clause I don't want" 

// displays "I have a sentence"
string foo = "I have a sentence with a clause I don't want.";
int idxFoo = foo.IndexOf(optional);
Console.WriteLine(idxFoo < 0 ? foo : foo.Remove(idxFoo));

// displays "I have a sentence and I like it."
string bar = "I have a sentence and I like it.";
int idxBar = bar.IndexOf(optional);
Console.WriteLine(idxBar < 0 ? bar : bar.Remove(idxBar));