正则表达式替换：仅替换 "or" 条件中的第一次出现

Question

我需要将\d+和a+替换为x，我想将所有\d+替换为x，但是对于a+, 如果有的话，我只想替换第一次出现的。

是否可以只使用一个正则表达式来实现这一点？

Input	Desired Output
`123,456,789`	`x,x,x`
`123,456,a,789`	`x,x,x,x`
`aaa,aa,aaa`	`x,aa,aaa`
`aa,123,456,aaaa,789`	`x,x,x,aaaa,x`
`aaa,123,456,aa,789,aaaa`	`x,x,x,aa,x,aaaa`

This 肯定不行:

/\d+|a+/gm

我正在使用 PCRE 正则表达式引擎，或者是否有任何模式修饰符或控制动词可以做到这一点？提前致谢。

Answer 1

经过认真的斗争，我想出了这个主意：

(?:(\G|^)|)(?(1)(?:a+|\d+([^a\d]+))|\d+)

替换为

(?:(\G|^)|)

Testing last anchor \G or the start of the string ^ before every match optionally, and put the caught anchor in group 1

(?(1)(?:a+|\d+([^a\d]+))|\d+)

If cause, if the anchor has been detected, matching a+ or \d+

If the sequence detected is \d+, also matches the ([^a\d]+) to keep the anchor for next match.

If the sequence detected is a+, only matches a+, so the anchor will be broken for the next test.

While the anchor \G is not detected in group 1, that means a+ has already been detected, after that only matches \d+, and the \G will never be detected anymore.

这是proof

好像只在这个场景有用，不知道对真题有没有用。

Answer 2

抱歉，我忘记了答案必须 post 放在一边，post 首先在评论中。

现在是：

正则表达式：\d+|((?<!a|(?!(?1)).))a+

替换：x

https://regex101.com/r/v24o7B/1

正则表达式替换：仅替换 "or" 条件中的第一次出现

Regex Substitution: only replace the first occurance from a "or" condition

regex

pcre

substitution