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？

Question

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

Answer 1

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.