preg_match() error trying to match variable

Question

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)

Well, tell us the content of `$statement`, but chances are, you are looking for `preg_quote`. — Wrikken, Jul 03 '13 at 19:37
@Wrikken I have edited the post so you see what is the $statement is. — Bryce, Jul 03 '13 at 19:43

score 3 · Accepted Answer · answered Jul 03 '13 at 19:38

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.

preg_match() error trying to match variable

1 Answers1