Re: Why does this preg_replace function not work?

Dave M G wrote:

PHP List, In the code below, I want to take the text within $content, and change every instance of [h3] into <h3>, and every instance of [/h3] into </h3>. And then do the same for [em], [/em], [strong], and so on. However, this code does absolutely nothing to the text stored in content: $tags = array ("h3", "em", "strong", "hr"); $content = preg_replace("[" . $tags . "]", "<" . $tags . ">", $content); $content = preg_replace("[/" . $tags . "]", "</" . $tags . ">", $content); Clearly I've either misunderstood the use of preg_replace(), or regular expressions, or arrays, despite having looked them up in the PHP online manual. I also tried str_replace(), but predictably that did not help. As far as I understand it, it does not accept arrays. What am I doing wrong in the above code? And can the two preg_replace() commands be achieved in one line? Thank you for any advice. -- Dave M G

First of all, why the hell are you using preg_* functions for this? You're feeding static content to it, no modifiers *at all* (not even case-insensitivity). I recommend you go back to str_replace() as that is what you need. You'd also be wise to read up on arrays and regular expressions (a lot). preg_replace() uses regular-expressions. Regular expressions require (in php) 2 delimiters, one at the start of the expression and one at the end, followed by optional modifiers/flags. Eg: /regexpGoesHere/i this would match "regexpGoesHere" and be case-insensitive. You don't use delimiters (first problem). Second problem with your code is that you're assuming that [, ], < and > are not meta-characters. Unfortunately, [ and ] ARE meta-characters. This means that when you would pass it "[h3]" it would see that as "any character which is an 'h' or '3' is a valid candidate for this expression". You would either need to escape it so it becomes \[h3\] which would mean "any string looking like '[h3]' is a valid candidate". Right, well, first let's go and fix the mess you've made of your arrays. Here's a lesson for you: Say you have $array = array('a','b','c'); print($array); print($array); What do you expect to see? a b ? Because looking at your code it seems like you're expecting something very strange. The thing you'll see is: Array Array Your correct version would be to either loop over it using a construct such as foreach(), while() or the like, OR use the special case of preg_replace and str_replace functions, which may also take 2 arrays as their parameters. Remember though, you CAN NOT MIX ARRAYS WITH STRINGS just like that. So, a more correct version for you would be (using str_replace because i's faster and easier and more appropriate): $tagsOld = array ("[h3]", "[em]", "[strong]", "[hr]","[/h3]", "[/em]", "[/strong]", "[/hr]"); $tagsNew = array ("<h3>", "<em>", "<strong>", "<hr>","</h3>", "</em>", "</strong>", "</hr>"); $content = str_replace($tagsOld, $tagsNew, $content); What I've done here is made an array with what is to be replaced and a second one with what it is to be replaced with. Internally, str_replace goes over the whole list of $tagsOld and replaces each value with the corresponding value from $tagsNew (based on position in the array, meansing the 2nd value from $tagsOld will be replaced with the 2nd value from $tagsNew). hope you understand what you did (wrong) now, - tul