Regular expression to replace relative link with root relative link

Question

I have a line of text containing html with all types of links (relative, absolute, root). I need a regular expression that PHP preg_replace can execute to replace all relative links to root links without affecting any of the other links. I already have a root path.

Substituted links:

 <tag ... href="path/to_file.ext" ... > ---> <tag ... href="/basepath/path/to_file.ext" ... > <tag ... href="path/to_file.ext" ... /> ---> <tag ... href="/basepath/path/to_file.ext" ... /> 

Untouched links:

 <tag ... href="/any/path" ... > <tag ... href="/any/path" ... /> <tag ... href="protocol://domain.com/any/path" ... > <tag ... href="protocol://domain.com/any/path" ... /> 

Answer 1

If you just want to change the base URI, you can try the BASE element :

 <base href="/basepath/"> 

But note that changing the base URI affects all relative URIs, not just relative URI paths.

Otherwise, if you really want to use a regular expression, consider that the relative path, as you want, should be of type path-noscheme (see RFC 3986 ):

 path-noscheme = segment-nz-nc *( "/" segment ) segment = *pchar segment-nz-nc = 1*( unreserved / pct-encoded / sub-delims / "@" ) ; non-zero-length segment without any colon ":" pchar = unreserved / pct-encoded / sub-delims / ":" / "@" pct-encoded = "%" HEXDIG HEXDIG unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "=" 

So, the beginning of the URI should match:

 ^([a-zA-Z0-9-._~!$&'()*+,; =@ ]|%[0-9a-fA-F]{2})+($|/) 

But please use the correct HTML parser for HTML parsing. You can then query the DOM to get the href attributes and check the value using the regular expression above.

Answer 2

I came up with this:

 preg_replace('#href=["\']([^/][^\':"]*)["\']#', $root_path.'$1', $html); 

This may be too simplistic. The obvious drawback that I see is that it will also match href="something" when it is outside the tag, but hopefully it can launch you.