Hi Team, Can you help me to understand the logic behind the below script. ===========

#!/usr/bin/perl
use lib "/opt/proxypac";
#
# Use mod_perl and Net::Netmask

# Strict and warnings are recommended.
#use strict;
use warnings;
use Net::Netmask;

print "Content-type: application/x-ns-proxy-autoconfig\n\n";

# initialisation - only need to do it once. Skip it if the data is alr
+eady resident in memory
if (!$specialRoutingFile) {

$base            = "/opt/proxypac/";
#ln either cross-use-n.txt or cross-use-a.txt to cross-use.txt based o
+n which side this runs on
$crossusefile         = $base."cross-use.txt";
$defaultfile            = $base."default.txt";
$specialRoutingFile     = $base."special-routing.txt";
$netRoutingFile         = $base."net-routing.txt";
$dataXFile              = $base."data-x.txt";
$proxyXFile             = $base."proxy-x.txt";

$version                = "2.1"; 
#loading and parsing default.txt
open($file, "< $defaultfile")
  or die "Could not open file default.txt $!";
  $DefaultProxy=<$file>;
  chomp $DefaultProxy;
#  $block = new Net::Netmask ("0.0.0.0/0");
#  $block->tag("region1", $DefaultProxy);
#  $block->storeNetblock();
close($file);

#loading and parsing proxy-x.txt
open($file, "< $proxyXFile")
  or die "Could not open file proxy-x.txt $!";
while (<$file>){
  chomp;
  chop if (m/\r$/);
  (my $region, my $proxy, my $proxy2) = split("#");
  if ($proxy2) {$Proxies{"$region"}=$proxy.";PROXY ".$proxy2;}
  else {$Proxies{"$region"}=$proxy;}
} #while
close($file);

#loading and parsing data-x.txt
open($file, "< $dataXFile")
  or die "Could not open file data-x.txt $!";
while (<$file>){
  chomp;
  chop if (m/\r$/);
  (my $dataXNet, my $region1, my $region2) = split("#");
  # use default if a proxy reference is invalid
  $region1 = $DefaultProxy unless ($Proxies{"$region1"});
  if ($region2 && !$Proxies{"$region2"}) {$region2 = $DefaultProxy;}
  $block = new Net::Netmask ($dataXNet);
  $block->tag("region1", $region1);
  $block->tag("region2", $region2);
  $block->storeNetblock();
} #while
close($file);

# build the exception header
$pac = <<"EOF";
 if ( shExpMatch(host, "localhost") ) { return "DIRECT"; }
 if ( shExpMatch(host, "localhost.*") ) { return "DIRECT"; }
 if ( shExpMatch(host, "127.0.0.*") ) { return "DIRECT"; }
 if ( isPlainHostName(host) ) { return "DIRECT"; }
 if ( isInNet(myIpAddress(), "10.255.32.0", "255.255.240.0")) { return
+ "DIRECT"; }

EOF
{
open(my $file, "< $crossusefile")
  or die "Could not open file $crossusefile $!";
local $/;
$pac.=<$file>;
}

#loading and parsing special-routing.txt
open($file, "< $specialRoutingFile")
  or die "Could not open file special-routing.txt $!";
while (<$file>){
  chomp;
  chop if /\r$/;
  (my $webServer, my $dnsq, my $proxy, my $proxy2) = split(" ");
  if(!($proxy eq "DIRECT")){
        if ($proxy eq "PROXY") { $proxy="proxy";}
        else {
            if ($proxy2) { $proxy="\"PROXY $proxy;PROXY $proxy2\"";}
            else { $proxy="\"PROXY $proxy\"";}
        }
  }
 else {$proxy="\"".$proxy."\"";}
if ($dnsq eq "Y") {
 $dnsq="dnsResolve(host+'.prx.nsn-intra.net');";
}
else {
 $dnsq="";
}
if ( $webServer =~ /^\..*/) {
  $pac .= <<EOF;
 if ( dnsDomainIs(host, "$webServer") ) { $dnsq return $proxy; }
EOF
}
elsif ( $webServer =~ /.*\*.*/) {
  $pac .= <<EOF;
 if (shExpMatch(host,"$webServer") ) { $dnsq return $proxy; }
EOF
}
else{
  $pac .= <<EOF;
 if (host == "$webServer") { $dnsq return $proxy; }
EOF
}
}
close($file);

$pac .= "\n";

#----------------------------------
#loading and parsing net-routing.txt
open($file, "< $netRoutingFile")
  or die "Could not open file net-routing.txt $!";
$pac .= <<EOF;



 if (isResolvable(host)) {
 resolved_host = dnsResolve(host);
EOF

while (<$file>){
  chomp;
  chop if /\r$/;
  (my $webHost, my $webHostMask, my $proxy) = split(";");
  if ($proxy eq "PROXY") { $proxy="proxy";}
  elsif(!($proxy eq "DIRECT")){ $proxy= "\"PROXY ".$proxy."\""; }
  else {$proxy="\"DIRECT\"";}
 $pac .= <<EOF;
 if ( isInNet(resolved_host, "$webHost","$webHostMask") ) { return $pr
+oxy; }
EOF

}
close($file);

} #if - end of initialisation

### main code ###

$ipAddr = $ENV{'REMOTE_ADDR'};

# Check for test IP in query
if ( $ENV{'QUERY_STRING'} =~ /^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/ ) 
+{
  $ipAddr = $ENV{'QUERY_STRING'};
}
# expire headers are handled by Apache
#print "Cache-Control: max-age=1800\n";

#------------------
# print out the PAC
print <<EOF;
/*
** automatic proxy configuration V$version for $ipAddr from $ENV{'SERV
+ER_NAME'} ($ENV{'SERVER_ADDR'})
*/
EOF


print "function FindProxyForURL(url, host) {\n var proxy=\"";

$block = findNetblock($ipAddr);
if ($block->base() eq "0.0.0.0") {
    print STDERR "IPAM:$ENV{'REMOTE_ADDR'}\n";
}
if ($block->tag("region1") eq "DIRECT") {
  print "DIRECT";
} else {
$proxy1 = $Proxies{$block->tag("region1")};

print "PROXY $proxy1;";
if (!($block->tag("region1") =~ /^GLB /) && ($block->tag("region2"))){
  $proxy2 = $Proxies{$block->tag("region2")};
  print " PROXY $proxy2;";
}
}
print "\";\n$pac}\n return proxy;\n}\n";

#for pilot only
print STDERR "PILOT:$ENV{'REMOTE_ADDR'},$proxy1\n";

#close($file);

exit 0;
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