simple str replace question

[auxiv]

if im using:

$b = "topic-".<$number-variable>."html";
$a = str_replace($b, "topic_".<$number-variable>."php", $string);
echo $a;

I would like to know what the "<$number-variable>" <---- would be?

so if/when $string contains in this case: topic-23423.html (23423 is hypothetical) it will convert it over to: topic_23423.php. however the number string will change periodically, and I need php to expect a number range? whats the php code for <$number-variable> in this case?

[auxiv]

This would be a wildcard regular expression

[auxiv]

cant use regular expressions with str_replace

[rocknbil]

Sorry, I'm not sure what you're asking. :-)

I need php to expect a number range? whats the php code for <$number-variable> in this case?

Like this?

if ($number_variable > 0) { 
 $b = "topic-".$number_variable."html"; 
 $a = str_replace($b, "topic_".$number_variable."php", $string); 
} 

Unless you expect to have a file topic_0.html, use > 0 rather than is_numeric().
If you're doing what I **think** you're doing, Consider,

$request = 'example.com/products/12345'; // Etc., the page request 
$full_page = '/server/path/to/directory'; 
$dir = '/products'; // Or use explode below to parse 
$vars = explode('/',$request); 
$number_variable = array_pop($vars); // Last item in array 
if ($number_variable > 0) { 
 $page = 'topic_' . $number_variable . '.php'; 
 if (is_file("$full_path/$page")) { 
 header("Location:$dir/$page"); 
 } 
 else { "echo invalid file request"; exit; } 
} 
else { echo "Invalid page request"; } 

[auxiv]

Thanks for your response, and time you took to help rocknbil. Will try.