PHP preg_replace removes the whitespace

Question

I have a string:

$test = "Test string<i> hello world</i>."

Then I am running

$test = preg_replace('/(<i>{1}\s*)([\w*\d*\D*\W*\x*\O*\S*\s*]*?)(<\/i>{1})/', '<italic>$2</italic>', $test);

And the result is

Test string<italic>hello world</italic>.

Why is the whitespace before the hello world lost?

Here is an example http://pastebin.com/SXFhsCGK.

Thank you.

[\w*\d*\D*\W*\x*\O*\S*\s*] Ouch. What are you trying to do here? — Robin
– Robin, Commented Apr 3, 2014 at 8:39
I am trying to match everything between and . The goal is to replace tags by <italic> tags — Milos Cuculovic
– Milos Cuculovic, Commented Apr 3, 2014 at 8:40
Sure, this can be done, but the question is not how to do it differently, but why this happens. — Milos Cuculovic
– Milos Cuculovic, Commented Apr 3, 2014 at 8:44
This consumes Your whitespace after : ({1}\s*). BTW I guess {1} isn't what You intend, it says "match the <, then match the i and then match (exactly one, which is default) >". — Roman Hocke
– Roman Hocke, Commented Apr 3, 2014 at 8:45

Robin · Accepted Answer · 2014-04-03 09:05:04Z

2

Solution

As @Reeno puts it in the comments, replacing the  tags by <italic> ones directly is the way to go (assuming they're all tags you want to replace):

preg_replace('%<(/?)i>%', '<$1italic>', $test)

What was wrong with your regex

The space is lost because it is matched by the \s* in {1}\s*, so it's not in the capturing group.

Also, writing [\w\W...] means "match any character that is either alphanumeric OR any character that is not alphanumeric"... So basically, match everything.

And the {1} quantifier is (always?) useless (>{1} is equivalent to >).

Heuristically, what you wanted to do was use this regex (s is so that the dot matches newline too):

~<i>(.*?)</i>~s

edited Apr 3, 2014 at 9:05

answered Apr 3, 2014 at 8:47

Robin

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