PHP Regex “Unknown modifier p” [duplicate]

Answer 1

$regex = "~^(/upload/temporary/)[0-9]{4}_[0-9]{2}_[0-9]{2}_[\w./-]+\.[a-z]{2,4}$~";

Change your delimiters to ~

When you use a delimiter for example /, you must escape all litteral / in your pattern otherwhise the regex engine believes that it is the end of the pattern.

Since u is a modifier and p isn't a modifier, you have this error because of the substring /^(/up....

Answer 2

In a regex string you have to escape your delimiters. Or better: use a character which doesn't appear in the regex itself as delimiter:

other delimiter (recommended):

$regex = "#^(/upload/temporary/)[0-9]{4}_[0-9]{2}_[0-9]{2}_[A-Za-z0-9._ /-]+.[A-z]{2,4}$#";

escaped delimiters:

$regex = "/^(\/upload\/temporary\/)[0-9]{4}_[0-9]{2}_[0-9]{2}_[A-Za-z0-9._ \/-]+.[A-z]{2,4}$/";

Answer 3

You need to escape the front slashes or just use another delimiter (I've used ! in this case):

$regex = "!^(/upload/temporary/)[0-9]{4}_[0-9]{2}_[0-9]{2}_[A-Za-z0-9._ /-]+.[A-z]{2,4}$!"