Finding and replacing Stack Overflow style links within a string [duplicate]

Question

I have a user input string with Stack Overflow style links within the string like this:

The input string [foo](http://foo.com) with a link.

and I need to transform the string to include anchor tags like this:

The input string <a href="http://foo.com">foo</a> with a link.

So far, I've got (referenced from: PHP: Best way to extract text within parenthesis?):

$text = 'ignore everything except this (text)';
preg_match('#\((.*?)\)#', $text, $match);
print $match[1];

But I need to find a way to match both the element within parentheses and the element within brackets. And finally, replace the entire matched section with a the correctly formatted anchor tag.

Does anyone know the correct regex syntax to match [foo](http://foo.com) and further how to extract "foo" and "http://foo.com"?

Look for an existing MarkDown parser. They're usually using regex for this very case too. — mario
– mario, Commented Aug 20, 2014 at 0:24
Thank you for the suggestion on the markdown parser. There seems to be a really good one here: parsedown.org for my purposes it might be a bit too powerful. — stroz
– stroz, Commented Aug 20, 2014 at 0:40

Avinash Raj · Accepted Answer · 2014-08-20 00:34:52Z

2

The below regex would match the string which is in [blah](http://blah.blah) format. The characters inside the first [] braces are captured into the group 1 and the charcters inside the next () braces are captured into group 2. Later the charcetrs inside group 1 and 2 are referenced through back-referencing (ie, recalling it with \1 or \2)

Regex:

\[([^]]*)\]\(([^)]*)\)

Replacement string:

<a href="\2">\1</a>

DEMO

PHP code would be,

<?php
$mystring = "The input string [foo](http://foo.com) with a link";
echo preg_replace('~\[([^]]*)\]\(([^)]*)\)~', '<a href="\2">\1</a>', $mystring);
?>

Output:

The input string <a href="http://foo.com">foo</a> with a link

edited Aug 20, 2014 at 0:34

answered Aug 20, 2014 at 0:29

Avinash Raj

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2 Comments

mario Over a year ago

Look, that's a well-written regex, as always. But just providing code-dump answers is not very helpful. In particular when OP struggles with the syntax a little explanation would be appropriate. The DEMO link does not substitute that.

stroz Over a year ago

That's exactly what I've been trying to create. Thank you so much for this. I'll be accepting this answer in a minute.

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