How to do arithmetic operation in .rewriteRule function? - .htaccess

Question

Is this possible to do arithmetic operation in .rewriteRule function?I want to rewrite my url.
From this
/view.php?id=2
To
/?p=6 (id*2+2)

Answer 1

You can use a rewrite map to call an external program, it's going to be a bit slower under heavy load though. The rewrite map can only be defined in the server's config or vhost config, not in an htaccess file. But it can be used in an htaccess file.
So you have a simple script that reads from stdin and does your math:
#!/usr/bin/perl
$| = 1; # Turn off I/O buffering
while (true) {
print <STDIN> * 2 + 2;
}
Then declare the mapping:
RewriteMap math prg:/path/to/script.pl
Then use the mapping in the htaccess file in your document root:
RewriteEngine On
RewriteCond %{QUERY_STRING} ^id=([0-9]+)
RewriteRule ^view\.php$ /?p=${math:%1} [L]

Answer 2

To redirect http://example.com/view.php?id=2 to http://example.com/?p=6 you would do this:
in .htaccess:
RewriteEngine On
RewriteCond %{QUERY_STRING} id=([0-9]*)
RewriteRule view.php calc.php?id=%1 [L]
And in calc.php:
<?php
$base_url = 'http://example.com/?p=';
$id = $_GET['id'];
$new_id = $id * 2 + 2;
$url = $base_url.$new_id;
header("Location: $url");
exit();