now before you prepare to right a speech about the perils of HTML parsing with regex, I already know it. This is more just a curiosity question, than actually wanting to know the question for practical usage.
Basically, given a file of HTML in some random, but perfectly valid format, can you parse out the content of <p> tags using a half-sane number of regular expressions? (and also pretending that <p> tags can not be nested or some other minor limitation)
Yes, under restrictions like valid HTML and non-nesting, you can use regular expressions for certain uses.
It's certainly possible to extract all the text between {insert character sequence 1 here} and {insert character sequence 2 here} with regular expressions, so long as those sequences aren't overlapping. For example:
/(?<{insert character sequence 1 here}).*?(?={insert character sequence 2 here})/
Of course, it's terribly brittle and will break horribly if what you're running it on is even slightly malformed, or contains either character sequence outside the context where it's meaningful, or any number of other ways. If you oversimplify the problem, then yes you can get away with an oversimplified solution.
It depends on what you limitations you'd consider minor. XHTML, for one obvious example, is somewhat more amenable to simple parsing. A great deal depends on whether you're thinking in terms of parsing existing HTML, or generating new HTML that could be parsed relatively easily. For the former case, I'd say the restrictions were major -- i.e., you'd need to know a great deal about the specific HTML in question to parse it. For the latter case, I'd say the restrictions were fairly trivial -- i.e., would only involve how you write the HTML, but would not affect what you could express in HTML.
` contains any nested tags, then it's relatively simple. Just have to strip all comments, script and such like, then find matching `
` tags. If the HTML is not valid, then it can be very difficult.
– Orbling Jan 07 '11 at 02:01