Regex works in 'RegExr' but not with preg_replace?

Question

I'm new to regular expressions and I checked the following pattern using RegExr, but it fails in PHP with preg_replace.

I've tried adding an extra backslash to escape the first \ with no luck.

Any help pointing me in the right direction would be greatly appreciated.

Example:

   $output = preg_replace("\[if](.*)[/if/]*", ' ', $output);

I've also tried adding slashes:

    $output = preg_replace("/\[if](.*)[/if/]*/", ' ', $output);

The string I'm trying to modify is:

[if] <p>A statement goes here</p> [/if]

possible duplicate of PHP Regex for matching a UNC path - It might be insightful about what happens with those slashes in regular expression written in a PHP string. Most of these online tools don't give the PHP string, but just the regex. You need to encode it for PHP then in an extra step. — hakre
– hakre, Commented Mar 3, 2012 at 18:07
Please edit the question with a sample of the string you're trying to modify. I'm not sure if those square brackets are part of the regex logic or part of what you're trying to match. — p.g.l.hall
– p.g.l.hall, Commented Mar 3, 2012 at 18:15

Wrikken · Accepted Answer · 2012-03-03 20:05:29Z

3

Escape all ['s and ]'s if you want it to mean a literal
Delimiters are needed.
If a delimiter occurs in a pattern, is must be esaped, or choose another delimiter (I chose % because of the /).
The ending ]*, 0 or more times ].... are you sure?
I suspect using an ungreedy (.*?) is more likely needed, but I leave that up to you.

Gives:

"%\[if\](.*)\[/if\]%"

edited Mar 3, 2012 at 20:05

answered Mar 3, 2012 at 18:21

Wrikken

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3 Comments

jsuissa Over a year ago

Thanks. This makes sense -- appreciate the explanation. I replaced it and no errors -- but the string wasn't replaced? I've added the string to the question.

p.g.l.hall Over a year ago

The reason is that you need to remove the last / from the regex. It's trying to replace [if]whatever[/if/] there. Also, the last * can go too.

jsuissa Over a year ago

Working perfectly now. $output = preg_replace("%\[if\](.*?)\[/if\]%", '', $output);

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