preg_replace and numeric literals

[zollies]

Gurus / Experts

I'm going quietly insane trying to figure this out.

On the manual page for preg_replace it mentions that you should use the following notation to avoid problems:

In this case the solution is to use \${1}1. This creates an isolated $1 backreference, leaving the 1 as a literal.

It also gives a full scripts Example 1 on the man page.

IT DOESN'T WORK !!!!

It does not even seem to recognise the ${1} notation at all.

I have been struggling with this for days.

I've tried the example script on 4-5 PHP systems, windows and linux, versions 4.04 to 4.2.2.

I've tried slashes until they fill the screen, brackets, braces, quotes, splitting the replace string, using a function on the numeric append .... aaarrrgggh !

What am I missing ?

I basically want to match a value and then append some numeric values straight to it.

Thanks in advance

[matt_4013]

You're right, it doesn't work, and it's been submitted as a bug 🙂

There's a couple of work arounds for it. Last time, I used this one.

$result = preg_replace("/()()()()()()()()()\\[url\\](.*?)\[\\/url\\]/i", "\\\\101", "\[url\]blah\[/url\]"); 
echo $result;

And the result outputs: blah1

This works because you can only have 99 matches, so, the first 10 are empty, and \10 holds the one you want, and the 3rd number is treated as a literal. It sucks to do.

Then there's this method:

$result = preg_replace("/\\[url\\](.*?)\[\\/url\\]/i", "\\\\1_", "\[url\]blah\[/url\]"); 
$result = str_replace("_", "1", $result);
echo $result;

And once again the output is blah1. This method uses a non special character, then replaces it using the str_replace function with the number you want.

Doing this gets really messy. Ugh.

Hope that helps,
Matt

[matt_4013]

Actually, it looks like it HASN'T been submitted as a bug. I am unable to test it on the latest CVS, as I don't have access to a server running it at the moment (Everything is a production server, ARGH!), but if you can test this code on the latest CVS, and see if it works, you can submit it 🙂

<?php

// Example from PHP Manual
$string = "April 15, 2003";
$pattern = "/(\\w+) (\\d+), (\\d+)/i";
$replacement = "\\${1}1,\\$3";
print preg_replace($pattern, $replacement, $string);
/*

   Expected Output
   ===============

April1,2003

   Output
   ======

${1}1,2003

*/

// Personal test
$string = "[url]test[/url]";
$pattern = "/\\\\[url\\\\](.*?)\\\\[\\/url\\\\]/i";
$replacement = "\\${1}1";
echo preg_replace($pattern, $replacement, $string);

/*

   Expected Output
   ===============

test1

   Output
   ======

${1}1

*/
?>

[Weedpacket]

FWIW, the example code given

$string = "April 15, 2003";
$pattern = "/(\w+) (\d+), (\d+)/i";
$replacement = "\${1}1,\$3";
print preg_replace($pattern, $replacement, $string);

produces the "expected output" (April1,2003) on PHP 4.3.0 (at least, it Works For Me).

[svan_rv]

I am also getting the same result as

${1}1,2003.

I am using php 4.1. Is it a bug?.Any work around for this problem?

svan

[zollies]

Peeps

Thanks for the replies.

It does seem to be a bug BUT why wasn't it fixed earlier?? I'm sure I read that this was fixed in 4.2.x. It is, however, confirmed to be fixed in the NEWS file for 4.3.2.

I have tried it on 4.3.2 and it DOES work now (thx Weedpacket).

For reference the bug is "Bug #18442 Numbered backreferences don't work properly" - http://bugs.php.net/bug.php?id=18442

What a pain ! Now I have to wait ages for my hosting companies to update to this version of PHP ... aaargghhh.

I found a workaround similar to matt_4013's suggestion.

As there can be no more that 99 backreferences you can do the following:

<?php
$string = "April 15, 2003";
$pattern = "/(\w+) (\d+), (\d+)/i";
$replacement = "\$1$991,\$3";
print preg_replace($pattern, $replacement, $string);

/* Output
   ======

April1,2003

 */
?>

Assuming you haven't got a value for backreference 99, it resolves to blank but provides a partition between the $1 and the 1. What a fudge though !

Thanks all.

[svan_rv]

thanks zollies. it works with your method.
Also many thanks for all for the help.

svan