子字符串的正则表达式，它的前面不应该有数字。

Question

我使用"[a-z][a-z0-9]*"查找子字符串：

" as4s“-找到as4s "s+sd4“- found s，sd4 “(4 asd悲伤)”-找到了asd，悲伤 "10asd“-发现asd

我需要改变这种体验，这样结果就会是：

" as4s“-找到as4s "s+sd4“- found s，sd4 “(4 4asd)”-发现悲伤 "10asd“-一无所获

可以使用此代码测试表达式：

using System.Text.RegularExpressions;

string input = "A*10+5.01E+10";
Regex r = new Regex("[a-zA-Z][a-zA-Z\d]*");
var identifiers = new Dictionary<string, string>();

MatchEvaluator me = delegate(Match m)
{
    Console.WriteLine(m);
    var variableName = m.ToString();

    if (identifiers.ContainsKey(variableName))
    {
        return identifiers[variableName];
    }
    else
    {
        i++;
        var newVariableName = "i" + i.ToString();
        identifiers[variableName] = newVariableName;
        return newVariableName;
    }
};

input = r.Replace(input, me);

Answer 1

您只需使用单词边界来避免匹配不需要的文本，例如前面有一个数字等等：

Regex r = new Regex("\b[a-zA-Z][a-zA-Z\d]*\b");

RegEx演示

Answer 2

(?<!\d)(\b[a-z][a-z0-9]*)

尝试this.Grab capture.See演示。

https://regex101.com/r/gX5qF3/7

NODE                     EXPLANATION
--------------------------------------------------------------------------------
  (?<!                     look behind to see if there is not:
--------------------------------------------------------------------------------
    \d                       digits (0-9)
--------------------------------------------------------------------------------
  )                        end of look-behind
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    \b                       the boundary between a word char (\w)
                         and something that is not a word char
--------------------------------------------------------------------------------
    [a-z]                    any character of: 'a' to 'z'
--------------------------------------------------------------------------------
    [a-z0-9]*                any character of: 'a' to 'z', '0' to '9'
                         (0 or more times (matching the most
                         amount possible))
--------------------------------------------------------------------------------
  )                        end of \1