remya:

You need only change your square brackets to curly brackets to turn it into valid perl code. Of course, you'll also need the appropriate constants and subroutines:

$ cat php_2_perl.pl 
#!/usr/bin/perl -w
use strict;
use warnings;
use constant {
    CURLOPT_URL         => 0,
    CURLOPT_POST        => 0,
    CURLOPT_POSTFIELDS  => 0,
};

sub curl_init   { print "Need to write curl_init\n"; }
sub curl_setopt { print "Need to write curl_setopt\n"; }
sub curl_exec   { print "Need to write curl_exec\n"; }

my ($ch, %_GET, $_POST);
$_GET{pap_custom} = 5;

# your code appears to be valid perl, given appropriate constant and
# subroutine definitions...

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,
    "http://affiliate.frankstrade.com/plugins/PayPal/paypal.php?pap_cu
+stom="
    . $_GET{'pap_custom'});
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $_POST);
curl_exec($ch);

$ perl php_2_perl.pl
Need to write curl_init
Need to write curl_setopt
Need to write curl_setopt
Need to write curl_setopt
Need to write curl_exec
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.