将记事本正则表达式转换为。净C#

Question

使用管道分隔的文件。目前，我使用记事本查找和替换REGEX模式^(?:[^|]*\|){5}\K[^|]*，它用第5和第6个|之间的空字符串替换所有行。我正在尝试以编程方式执行此过程，但是。NET不支持\K。我尝试了一些向后查找实例，但似乎无法理解它。

string[] lines = File.ReadAllLines(path);
foreach (string line in lines)
{
    string line2 = null;
    string finalLine = line;
    string[] col = line.Split('|');
    if (col[5] != null)
    {
        line2 = Regex.Replace(line, @"^(?:[^|]*\|){5}\K[^|]*", "");

Answer 1

无需使用lookbehinds，使用捕获组和反向引用：

line2 = Regex.Replace(line, @"^((?:[^|]*\|){5})[^|]*", "$1");

参见证明。

解释

--------------------------------------------------------------------------------
  ^                        the beginning of the string
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    (?:                      group, but do not capture (5 times):
--------------------------------------------------------------------------------
      [^|]*                    any character except: '|' (0 or more
                               times (matching the most amount
                               possible))
--------------------------------------------------------------------------------
      \|                       '|'
--------------------------------------------------------------------------------
    ){5}                     end of grouping
--------------------------------------------------------------------------------
  )                        end of \1
--------------------------------------------------------------------------------
  [^|]*                    any character except: '|' (0 or more times
                           (matching the most amount possible))

Answer 2

K是正则表达式语法/引擎的“变通方法”，不支持针对查找后断言的锚定。

. NET的正则表达式语法具有后视断言（使用语法（？

Regex.Replace(line, @"(?<=^(?:[^|]*\|){5})[^|]*", "")

在的上下文中。NET中，该模式现在描述：

(?<=               # begin (positive) look-behind assertion
    ^              # match start of string
    (?:            # begin non-capturing group
       [^|]*\|     # match (optional) field value + delimiter
    ){5}           # end of group, repeat 5 times
)                  # end of look-behind assertion
[^|]*              # match any non-delimiters (will only occur where the lookbehind is satisfied)