Determines range of ephemeral ports and number of unused ports.

findUnusedPorts.pl

#!/usr/bin/perl

#################################################################################
# Author: NQPC
# Description: determines range of ephemeral ports and number of unused ports 
# OS: CentOS
##################################################################################  

use strict;
use warnings;

my ($minport, $maxport) = split /\s+/, `cat /proc/sys/net/ipv4/ip_local_port_range`;
print "minport=$minport, maxport=$maxport, number=", ($maxport - $minport + 1). "\n";
my @portrange = ($minport..$maxport);
my @freeflag = (1) x scalar @portrange;

my %free;
@free{@portrange} = @freeflag;

my @out = `netstat -ant`;
my @ports;
for my $line (@out) {
  if ( $line !~ /^tcp/ ) { next; }
  my (@f) = split /\s+/, $line;
  my ($ip, $port) = split ':', $f[3];
  $free{$port} = 0;
}


my @freeports;
while ( my ($k, $v) = each %free ) {
  if ( $v ) {
    push @freeports, $k;
  }
}

print "free ports: ", scalar @freeports, "\n";