即使匹配找到，preg_replace也只替换一次

Question

my HTML form code replaces some words with <-#word#-> using the code

$string = preg_replace("/($p)/i", '<-#$1#->', $string);

the problem is that if the form has some errors, upon resubmitting the form the word becomes <-#<-#<-#word#->#->#-> every time someone resubmits the form. Is it possible to replace but if it is already replaced then do not. This is what I tried using NOT operator but it is not working

$string = preg_replace("/^(<-#)($p)^(#->)/i", '<-#$1#->', $string);

Answer 1

You could use a negative lookarounds to assert what is directly on the left an on the right is not <-# and

(?<!<-#)(word)(?!#->)

Regex demo | Php demo

Your code could look like:

$string = preg_replace("/(?<!<-#)($p)(?!#->)/i", '<-#$1#->', $string);