仅当没有第二组(包括变体)时,正则表达式提取第一组+第二组或第一组

Question

解释它的最好方法是准确显示我想要实现的目标:

• 案例1:"search for fenway park in boston"
  提取:组1 - > "fenway park",组2 - >"boston"

• 案例2:"search for fenway park"
  提取:组1 - >"fenway park"

请注意,在这两种情况下,我希望能够针对变化"search"("look for","find"以及,等...) ("in","at","around"等...).

我尝试了很多不同的变体,但最终都是"fenway park in boston"在第1组中提取而在第2组中没有任何内容,或者如果我得到第1个案例,则案例2将无效.

Answer 1

这应该适合你

^(?:search for|look for|find)\s*(.*?)(?:\s*(?:in|around|at)\s*(.*))?$

您可以添加更多子句,例如look for/in/at向非捕获组添加moer 或子句.

说明:

@"
^                   # Assert position at the beginning of a line (at beginning of the string or after a line break character)
(?:                 # Match the regular expression below
                       # Match either the regular expression below (attempting the next alternative only if this one fails)
      search\ for         # Match the characters “search for” literally
   |                   # Or match regular expression number 2 below (attempting the next alternative only if this one fails)
      look\ for           # Match the characters “look for” literally
   |                   # Or match regular expression number 3 below (the entire group fails if this one fails to match)
      find                # Match the characters “find” literally
)
\s                  # Match a single character that is a “whitespace character” (spaces, tabs, and line breaks)
   *                   # Between zero and unlimited times, as many times as possible, giving back as needed (greedy)
(                   # Match the regular expression below and capture its match into backreference number 1
   .                   # Match any single character that is not a line break character
      *?                  # Between zero and unlimited times, as few times as possible, expanding as needed (lazy)
)
(?:                 # Match the regular expression below
   \s                  # Match a single character that is a “whitespace character” (spaces, tabs, and line breaks)
      *                   # Between zero and unlimited times, as many times as possible, giving back as needed (greedy)
   (?:                 # Match the regular expression below
                          # Match either the regular expression below (attempting the next alternative only if this one fails)
         in                  # Match the characters “in” literally
      |                   # Or match regular expression number 2 below (attempting the next alternative only if this one fails)
         around              # Match the characters “around” literally
      |                   # Or match regular expression number 3 below (the entire group fails if this one fails to match)
         at                  # Match the characters “at” literally
   )
   \s                  # Match a single character that is a “whitespace character” (spaces, tabs, and line breaks)
      *                   # Between zero and unlimited times, as many times as possible, giving back as needed (greedy)
   (                   # Match the regular expression below and capture its match into backreference number 2
      .                   # Match any single character that is not a line break character
         *                   # Between zero and unlimited times, as many times as possible, giving back as needed (greedy)
   )
)?                  # Between zero and one times, as many times as possible, giving back as needed (greedy)
$                   # Assert position at the end of a line (at the end of the string or before a line break character)
"