How do I replace only strings NOT in HTML tags?

DonkaWechico

I'm writing a php file that will search through a web page's source code, replacing a user-given string with another user-given string. The problem is, if a user were to replace all occurences of "href" (or "a" for that matter) it would alter the HTML code and, in this case, all hyperlinks would cease to function. I'm trying to find a way to replace only the occurences of the string that are not within HTML tags. I've tried using ereg_replace by making a regular expression something like this:

ereg_replace("(>[^{<]*)".$stringtoreplace,} "\1".$stringreplacewith, $string);

As you can see it looks for a closing tag followed by 0 or more non-opening tags and the string, then replaces with the original stuff and the new string.

This kind of works, but for some reason it will only replace one occurence of the string between > and <. Anyway, I figured there must be a better way to do this. What would be nice is a "is_string_in_tags()" function in PHP, but the closest I've found is strip_tags() and I can't see how that would help me as I want to keep the HTML in the string. Any ideas?

Weedpacket

Four approaches (all assuming that the < and > characters only appear as the start and end of tags):

preg_split on [<>]to get an array of strings - even-numbered pieces are from outside tags, odd-numbered pieces are from inside tags. Alter the even-numbered pieces and then reassemble the array (by putting '<' and '>' on the ends of the odd-numbered pieces and [man]join[/man]ing the entire array with an empty string as glue.
preg_replace() using assertions; A string is outside a tag if in what follows there is a < before there is a >: $stringtosearchfor."(?=[^>](<|$))"; since the content of the assertion isn't included as part of the match, the next attempt at matching picks up where $stringtosearchfor left off.
preg_replace_callback: just use >([^<])< as the search regexp and a separate callback function to actually do the replace.
Something like what I did in a similar situation and wrote up here.

DonkaWechico

Excellent! I used the protect_from_borking function, which is quite nifty I would like to add. It worked beautifully.

So, problem solved. I may soon be posting another similar thread so be on the lookout 🙂. What I'm trying to do is alter a user-given page's source code so that relative path locations of the form:

where there is no "./" or "../" or "/" etc, just the dir name, will be converted to absolute path locations. The reason I specified "user-given" above is because that makes PHP's built in realpath() function irrelevant, as I'm pretty sure that only works for the current server. My regular expression is a real mess so I'm probably going to post for some better suggestions.

Thanks for your help!