如何在正则表达式中使用变量？ [英] How to use variables with regex?

问题描述

这是输入字符串： 23x ^ 45 * y或2x ^ 2或y ^ 4 * x ^ 3 。

我在字母 x 后匹配 ^ [0-9] + 。换句话说，我匹配的是 x ，然后是 ^ ，然后是数字。问题是我不知道我是否匹配 x ，它可能是我作为变量存储在char数组中的任何字母。

I am matching ^[0-9]+ after letter x. In other words I am matching x followed by ^ followed by numbers. Problem is that I don't know that I am matching x, it could be any letter that I stored as variable in my char array.

例如：

foreach (char cEle in myarray) // cEle is letter in char array x, y, z, ...
{
    match CEle in regex(input) //PSEUDOCODE
}

我是regex的新手，并且我新定义了我可以通过定义regex变量来完成此操作，但是我不知道如何做。

I am new to regex and I new that this can be done if I define regex variables, but I don't know how.

推荐答案

您可以使用模式 @ [cEle] \ ^ \d + 字符数组：

You can use the pattern @"[cEle]\^\d+" which you can create dynamically from your character array:

string s = "23x^45*y or 2x^2 or y^4*x^3";
char[] letters = { 'e', 'x', 'L' };
string regex = string.Format(@"[{0}]\^\d+",
    Regex.Escape(new string(letters)));
foreach (Match match in Regex.Matches(s, regex))
    Console.WriteLine(match);

结果：

x^45
x^2
x^3

A需要注意的几件事：

A few things to note:

• 有必要将常规中的 ^ 转义


• 插入文字时使用 Regex.Escape 是个好主意。从用户到正则表达式的字符串，以避免他们键入的任何字符被误解为特殊字符。


• 这也将匹配长名称（如<$）的变量末尾的x c $ c> tax ^ 2 。可以通过使用单词边界（ \b ）来避免。


• 如果您写 x ^ 1 就像 x 一样，则此正则表达式将不匹配它。可以使用（\ ^ \d +）？来解决。

• It is necessary to escape the ^ inside the regular expression otherwise it has a special meaning "start of line".
• It is a good idea to use Regex.Escape when inserting literal strings from a user into a regular expression, to avoid that any characters they type get misinterpreted as special characters.
• This will also match the x from the end of variables with longer names like tax^2. This can be avoided by requiring a word boundary (\b).
• If you write x^1 as just x then this regular expression will not match it. This can be fixed by using (\^\d+)?.

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