检查正则表达式是否包含捕获组

Question

I working on a routing system and i want to allow custom regex patterns. My question is how can i detect if a regex contains a capturing group?

So for example the pattern [0-9]+ would work, because it doesnt contain a capturing group. The pattern ([0-9]+) would not work.

It tried to ltrim and rtrim the pattern by the ( and ) character mask, this would work with patterns that start with a capturing group like ([A-Za-z]+) and ([0-9]+) . But with patterns that contain a capturing group elsewhere this would not work. So how could i check if the pattern contains a capturing group?

Answer 1

First you should match and omit any escaped characters from results then check if there is any opening bracket remained alone or is followed by ?P< , ?' or ?< . These are opening syntax of a named capturing group.

\\.(*SKIP)(?!)|\((?(?=\?)\?(P?['<]\w+['>]))

PHP:

if (preg_match("~\\\\.(*SKIP)(?!)|\((?(?=\?)\?(P?['<]\w+['>]))~", $regex)) {
    // Capturing group found
}

RegEx Explanation:

\\.                     # Match any escaped character
(*SKIP)(?!)             # Skip over and omit recent match
|                       # OR
\(                      # Match a single `(`
(?(?=\?)                # Which if is followed by `?`
    \?                      #
    P?['<]\w+['>]           # Next characters should be matched as ?P'name', ?<name> or ?'name'
)                       # End of conditional statement

Answer 2

I think you want to see if there are capturing groups eg (something) that are not at the start of the test pattern. This seems to work for me...

$pattern = '/^.+\(([^\)]+)\)/';

if (preg_match($pattern, $testpattern)) {
    // Capturing group found that is not at the start of the string
}