[RESOLVED] preg_replace warning

ajcether

Hi there, I'm getting this error:

Warning: preg_replace() [function.preg-replace]: Unknown modifier '<' in ....

for this code:

$pattern = '<title>title |';
$rep = '<title>title, '.date('F j, Y').' |';
$text = str_replace($pattern, $rep, $text);

#  <h2>...
$pattern = '<h2></h2>';
$rep = '<h2>'.date('F j, Y').'</h2>';
$text = preg_replace($pattern, $rep, $text); // line the warning refers to

Do I need to escape these or something to get rid of the warning? any help would be great!

laserlight

Use [man]preg_quote/man on $pattern, then remember to include the pattern delimiters.

ajcether

Thanks for the response, but what are the delimiters? Sorry, I'm new to php and someone else wrote this code before I got it >.<

bretticus

Delimiters mark the boundaries of your pattern. For example in the pattern "/^[a-z]+$/i" the forward slashes designate the actual pattern to match inside them "^[a-z]$". Notice the "i". That is a pattern modifier that tells the regexp function to ignore case (there are many kinds of pattern modifiers.) Thus we need delimiters "/" to show what the actual pattern is.

ajcether

so should I have $pattern = '/<h2></h2>/' instead then or something?

bretticus

ajcether wrote:
so should I have $pattern = '/<h2></h2>/' instead then or something?

Yep.

laserlight

so should I have $pattern = '/<h2></h2>/' instead then or something?

Not quite. I suggest that you first use preg_quote() on $pattern, and only then do you add the delimiters. If not, you could have problems. For example, your '/<h2></h2>/' actually is the pattern '/<h2></' with modifiers 'h2>/'.

bretticus

Yep laserlight. Sorry I was too hasty. You need to escape the delimiter and the pattern should be "/<h2><\/h2>/". And yes, preg_quote does the escaping for you.

"/" . preg_quote("<h2></h2>") . "/"

ajcether

Okay so I changed it to:

$pattern = '/'.preg_quote('<h2></h2>').'/';
$rep = '<h2>'.date('F j, Y').'</h2>';
$text = preg_replace($pattern, $rep, $text);

but now I'm getting:
Warning: preg_replace() [function.preg-replace]: Unknown modifier 'h' ...
preg_replace line again.

I tried doing:

$rep = '/'.preg_quote('<h2>'.date('F j, Y').'</h2>').'/';

But I still get the same warning.
What else do I need to fix?

laserlight

Oh dear, it looks like the forward slash is not itself one of the special characters in PCRE. As such, you need to use str_replace() appropriately:

$pattern = '/'. str_replace('/', '\\/', preg_quote('<h2></h2>')) .'/';
$rep = '<h2>'.date('F j, Y').'</h2>';
$text = preg_replace($pattern, $rep, $text);

ajcether

Awesome, no more warning 🙂 Thanks for your help!

bretticus

Oh dear, it looks like the forward slash is not itself one of the special characters in PCRE.

Strange, you'd think they would have included it in the PHP function because a delimiter does need to be escaped in a pattern. However, technically, i suppose it's not a PCRE special character.

Weedpacket

bretticus wrote:
i suppose it's not a PCRE special character.

Well, no: you can use any nonalphanumeric character for the delimiter. They can't all be special 🙂

laserlight wrote:
Oh dear, it looks like the forward slash is not itself one of the special characters in PCRE. As such, you need to use str_replace() appropriately:

Or you can tell preg_quote what the delimiter character is:

preg_quote($pattern, '/')