这个php / regex查询出了什么问题？

Question

preg_replace("/(/s|^)(php|ajax|c\+\+|javascript|c#)(/s|$)/i", '$1#$2$3', $somevar);

例如，它打算将PHP变成#PHP。

Warning: preg_replace(): Unknown modifier '|'

Answer 1

It's because you are using the forward slash ( / ) as your delimiter. When the regex engine gets to /s (3rd character) it thinks the regex is over and the rest of it are modifiers. But no such modifier ( | ) exists, thus the error.

Next time, you can either:

• Change your delimiters to something you won't use in your regex, ie:

  preg_replace("!(/s|^)(php|ajax|c\\+\\+|javascript|c#)(/s|$)!i", '$1#$2$3', $somevar);

• Or escape those characters with a backslash, ie: "/something\\/else/" *

I also suspect you didn't intend to use /s , but the escape character \\s that matches whitespace characters.

Answer 2

The first character in the regular expression is the delimiter. If you need to use this inside your regular expression then you need to escape it:

"/(\/s|^)...
   ^

Or alternatively, choose another delimiter that isn't used anywhere in your regular expression so that you don't need to escape:

"~(/s|^)...(/s|$)~i"

I prefer to do the latter as it makes the regular expression more readable.

(Although as NullUserException points out, the actual error is that you should have used a backslash instead of a slash).