preg_match（）错误尝试匹配变量[重复]

Question

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• Replace string only once with php preg_replace 2 answers

I keep getting an error when using this and I am not sure why. Any help would be amazing. I have Googled it and found examples but I get the error even with other peoples examples.

$statement = $list[$i];
echo $statement;
preg_match("/$statement/i", $q)

I also tried this and neither work:

$statement = '/' . $list[$i] . '/i';
echo $statement;
preg_match($statement, $q)

The error I get is:

Warning: preg_match() [function.preg-match]: Compilation failed: nothing to repeat at offset 0

When I echo out the $statement I get: "/Who/i" (without the quotes)

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Answer 1

Make sure that whatever's in $statement will actually produce a VALID regex, e.g.

$statement = '(a|'; // note lack of closing )
preg_match("/$statement/", $text);

will actually produce the regex

/(a|/

which is invalid, because there's no closing ) to finish off the capture group. You can get around this with:

$statement = preg_quote('(a|');
             ^^^^^^^^^^

which will escape any regex metacharacters so you produce a valid regex in the end.

Essentially, you're probably suffering from the regex equivalent of an SQL injection attack.