如何在Golang中的正则表达式中的第一个匹配项之前插入子字符串？

问题描述：

I have a regex as following (ORDER\s+BY)|(LIMIT)|$. I want to insert a substring before the first match of the regex. I am looking for a pure regexp solution in Golang not finding the index and then adding a substring. Since Golang only has regexp.ReplaceAll func which replaces all the matches, not the first one.

exp := regexp.MustCompile(`(ORDER\s+BY)|(LIMIT)|$`)
fmt.Println(exp.ReplaceAllString(str, "..."))

Example

Input: abcd ORDER BY LIMIT substring=GROUP BY

Expected output: abcd GROUP BY ORDER BY LIMIT

Input: abcd LIMIT

Expected output: abcd GROUP BY LIMIT

我有一个正则表达式，如下所示（ORDER \ s + BY）|（LIMIT）| $ 代码>。我想在正则表达式的第一个匹配项之前插入一个子字符串。我在Golang中寻找纯正则表达式解决方案，但没有找到索引，然后添加了子字符串。由于Golang仅具有regexp.ReplaceAll函数，它将替换所有匹配项，而不是第一个匹配项。 p>

  exp：= regexp.MustCompile（`（ORDER \ s + BY）|（  LIMIT）| $`）
fmt.Println（exp.ReplaceAllString（str，“ ...”））
  code>  pre> 
 
 示例 p> 
 
  
输入： abcd ORDER BY LIMIT  code> substring =  GROUP BY  code>  p> 
 
 
预期输出： abcd GROUP BY ORDER BY LIMIT   code>  p> 
 
 
输入： abcd LIMIT  code>  p> 
 
 
预期的输出： abcd GROUP BY LIMIT  code  >  p> 
  div>

答

You may use

str := "abcd ORDER BY LIMIT"
exp := regexp.MustCompile(`^(.*?)(ORDER\s+BY|LIMIT|$)`)
fmt.Println(exp.ReplaceAllString(str, "${1}GROUP BY ${2}"))

If there can be line breaks before the pattern use (?s) in front: (?s)^(.*?)(ORDER\s+BY|LIMIT|$).

See the Go demo and the regex graph:

Details

^ - start of string
(.*?) - Group 1 (${1}): any 0+ chars, as few as possible
(ORDER\s+BY|LIMIT|$) - Group 2 (${2}): any of the three alternatives, whichever comes first:
- ORDER\s+BY - ORDER, 1+ whitespaces, BY
- LIMIT - a LIMIT substring
- $ - end of string.

答

My guess is that this expression might work here:

(ORDER\s+BY\s+LIMIT|LIMIT)$

Demo

Test

package main

import (
    "regexp"
    "fmt"
)

func main() {
    var re = regexp.MustCompile(`(?m)(ORDER\s+BY\s+LIMIT|LIMIT)$`)
    var str = `abcd ORDER BY LIMIT
abcd LIMIT`
    var substitution = "GROUP BY $1"

    fmt.Println(re.ReplaceAllString(str, substitution))
}

如何在Golang中的正则表达式中的第一个匹配项之前插入子字符串？

Demo

Test

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