写作意图：

Linux系统自带的netstat在很多时候抓信息会发现耗CPU很高，特别是在做一些监控系统的时候，发现如果使用了netstat，监控系统本身会造成系统负载比较高，因此试着用perl写下，time测试比自带的netstat更快更节省资源，欢迎批评，呵呵。

#!/usr/bin/perl
# Written by FinalBSD at 2008-11-20.
# The netstat original written by C
# is expensive to me, so this born.
# As long as you retain this notice you
# can do whatever you want with this stuff.
# If we meet some day, and you think
# this stuff is worth it, you can
# buy me a beer in return.
use strict;
use warnings;
use Getopt::Std;
my $tcp     = "/proc/net/tcp";
my $tcp6     = "/proc/net/tcp6";
my $route    = "/proc/net/route";
my @tcpState     = (
"NULL",
"ESTABLISHED" ,
"SYN_SENT",
"SYN_RECV",
"FIN_WAIT1",
"FIN_WAIT2",
"TIME_WAIT",
"CLOSE",
"CLOSE_WAIT",
"LAST_ACK",
"LISTEN",
"CLOSING"
);
my @routeType   = (
"NULL",
"U",        # UP
"G",        # Gateway
"UG"        # UP & Gateway
);
my %opts;
getopts('nhatsrl', \%opts);
if($opts{h}) {
&usage();
}
if($opts{r}) {
&route_info($route);
exit;
}
&tcp_info($tcp);
&tcp_info($tcp6);
###################### FUNCTION DEFINITION ###########################
#############################
# Get statistics Information
############################
sub tcp_info($) {
my $file = shift;
open(FH, $file) or die("$!");
my $format = "%-30s  %-30s %-10s\n";
printf($format,"      Local Address","      Foreign Address","State");
while(<FH>) {
next if /local_address/;
my @data = split;
my $state = $tcpState[hex($data[3])];
# Show listening Sockets.
if($opts{l}){
printf($format, &hextoint($data[1]), &hextoint($data[2]), $state) if $state =~ /LIST/;
} else {
printf($format, &hextoint($data[1]), &hextoint($data[2]), $state);
}
}
close(FH);
}
#############################
# Convert hex to int
############################
sub hextoint($) {
my $tmp     = shift;
my @data;
my @ip;
my $int;
# if have ':', then it's  addr:port,else just port.
if( $tmp =~ /:/ ) {
if( $tmp =~ /FFFF/ ) {
@data = split /:/, $tmp;
# break it and do convert later.
@ip   = $data[0] =~ /\w{2}/g;
foreach my $index (12..15){
$ip[$index] = hex($ip[$index]);
}
$int  = sprintf("%-5s %d.%d.%d.%d:%d", "tcp6",$ip[15], $ip[14], $ip[13], $ip[12], hex($data[1]));
} else {
@data = split /:/, $tmp;
@ip   = $data[0] =~ /\w{2}/g;
foreach my $index (0..3){
$ip[$index] = hex($ip[$index]);
}
$int  = sprintf("%-s %d.%d.%d.%d:%d", "     ",$ip[3], $ip[2], $ip[1], $ip[0], hex($data[1]));
}
} else {
@ip   = $tmp =~ /\w{2}/g;
foreach my $index (0..3){
$ip[$index] = hex($ip[$index]);
}
$int  = sprintf("%d.%d.%d.%d", hex($ip[3]), hex($ip[2]), hex($ip[1]), hex($ip[0]));
}
return $int;
}
#############################
# Show Kernel route table
############################
sub route_info($) {
my $routefile = shift;美国云服务器
open(ROUTE, $routefile) or die ("Can't open route file!\n");
my $header = "Iface  Destination     Gateway      Flags   Genmask\n";
printf("%s", $header);
my $format = "%-5s %-15s %-15s %-5s %-15s\n";
while(<ROUTE>) {
next if /Iface/;
my @line = split;
my ($iface, $dest, $gw, $flags, $mask ) = ($line[0], &hextoint($line[1]), &hextoint($line[2]), hex($line[3]), &hextoint($line[7]));
printf($format, $iface, $dest, $gw, $routeType[$flags], $mask );
}
close(ROUTE);
}
#############################
# Show help information
############################
sub usage {
printf("%s\n\n%-30s\n%-30s\n%-30s\n%-30s\n%-30s\n%-30s\n",
"netstat written in Perl by FinalBSD.Copyright(c) 2008.",
"-n Show numeric ip and port address.",
"-r Display the kernel routing table.",
"-a Show both listening and non-listening socktes.",
"-t Show only TCP statistics.",
"-l Show only listening sockets.",
"-h Show help.",
);
exit;
}

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