Question

Expert

I swear I surf a lot of regular expression stuff to study but I find regular expression topic is too difficult to me understand. Any good suggestion for me?

Anyone can explain to me why this <p[^>]*> can simply remove the start <p> or <p attr="">?
And what could I do, if I want make it from

<div style="float: left; width: 350px; border: 1px solid #000000;" class="star1">abcdk</div>

to this

<div class="star1">abcdk</div>

Thanks in advance.

Answer 1

Suggestion: Play around with a regex tester to get the hang of what matches what.

Jason’s explanation was good, but maybe not in-depth enough for you if you’re just starting out with regexes. Let’s take <p[^>]*> a piece at a time:

• < has no special meaning to regex engines, so it means it just matches a single <
• p is the same: match a single p
• [ is a special character. Square braces in regex mean “any of these”. For instance, the regex [abc] would match any single character that is ‘a’, ‘b’, or ‘c’.
• ^ is a special character with two possible meanings. When inside of square brackets, like it is here, it’s a simple negation. Whereas [abc] would match any single character mentioned, [^abc] would match any single character not mentioned.
• > has no special meaning: just match a single >
• ] should be obvious to you by now: it closes the opening [
• * is a special character that says match 0 or more of what came before it; that means it could match nothing, or it could match a huge amount of stuff, as long as it all matches what comes before the *.
• > still no special meaning, like earlier

So we can break <p[^>]*> into three pieces, and we can say that it matches any series of characters:

• <p: that starts with a literal <p,
• [^>]*: which is followed by 0 or more characters that are not a >,
• >: and which ends with a literal >.

Oh, and http://www.regular-expressions.info is one of the best regex guides I’ve ever found online.