I'm trying to get the default gateway, using the destination 0.0.0.0
I used this command: netstat -rn | grep 0.0.0.0
And it returned this list:
**Destination Gateway Genmask Flags MSS Window irtt Iface<br>
10.9.9.17 0.0.0.0 255.255.255.255 UH 0 0 0 tun0<br>
133.88.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0<br>
0.0.0.0 133.88.31.70 0.0.0.0 UG 0 0 0 eth0**<br>
My goal here is to ping the default gateway using destination 0.0.0.0;
thus, that is 133.88.31.70; but this one returns a list because of using grep.
How do i get the default gateway only? I will need it for my bash script to identify if net connection is up or not.
You can get the default gateway using ip command like this:
IP=$(/sbin/ip route | awk '/default/ { print $3 }')
echo $IP
The ip route command from the iproute2 package can select routes without needing to use awk/grep, etc to do the selection.
To select the default route (from possibly many)
$ ip -4 route list 0/0 # use -6 instead of -4 for ipv6 selection.
default via 172.28.206.254 dev wlan0 proto static
To select the next hop for a particular interface
$ ip -4 route list type unicast dev eth0 exact 0/0 # Exact specificity
default via 172.29.19.1 dev eth0
In the case of multiple default gateways, you can select which one gets chosen as the next-hop to a particular destination address.
$ ip route get $(dig +short google.com | tail -1)
173.194.34.134 via 172.28.206.254 dev wlan0 src 172.28.206.66
cache
You can then extract the value using sed/awk/grep, etc. Here is one example using bash's read builtin.
$ read _ _ gateway _ < <(ip route list match 0/0); echo "$gateway"
172.28.206.254
works on any linux:
route -n|grep "UG"|grep -v "UGH"|cut -f 10 -d " "
This simple perl script will do it for you.
#!/usr/bin/perl
$ns = `netstat -nr`;
$ns =~ m/0.0.0.0\s+([0-9]+.[0-9]+.[0-9]+.[0-9]+)/g;
print $1
Basically, we run netstat, save it to $ns. Then find the line that starts off with 0.0.0.0. Then the parentheses in the regex saves everything inside it into $1. After that, simply print it out.
If it was called null-gw.pl, just run it on the command like:
perl null-gw.pl
or if you need it inside a bash expression:
echo $(perl null-gw.pl)
Good luck.
This is how I do it:
#!/bin/sh
GATEWAY_DEFAULT=$(ip route list | sed -n -e "s/^default.*[[:space:]]\([[:digit:]]\+\.[[:digit:]]\+\.[[:digit:]]\+\.[[:digit:]]\+\).*/\1/p")
echo ${GATEWAY_DEFAULT}
Another perl thing:
$return = (split(" ", `ip route | grep default`))[2];<br>
Note: use these backticks before ip and after default
netstat -rn | grep 0.0.0.0 | awk '{print $2}' | grep -v "0.0.0.0"
#!/bin/bash
##################################################################3
# Alex Lucard
# June 13 2013
#
# Get the gateway IP address from the router and store it in the variable $gatewayIP
# Get the Router mac address and store it in the variable gatewayRouter
# Store your routers mac address in the variable homeRouterMacAddress
#
# If you need the gateway IP uncomment the next line to get the gateway address and store it in the variable gateWayIP
# gatewayIP=`sudo route -n | awk '/^0.0.0.0/ {print $2}'`
homeRouterMacAddress="20:aa:4b:8d:cb:7e" # Store my home routers mac address in homeRouterMac.
gatewayRouter=`/usr/sbin/arp -a`
# This if statement will search your gateway router for the mac address you have in the variable homeRouterMacAddress
if `echo ${gatewayRouter} | grep "${homeRouterMacAddress}" 1>/dev/null 2>&1`
then
echo "You are home"
else
echo "You are away"
fi
There are a lot of answers here already. Some of these are pretty distro specific. For those who found this post looking for a way to find the gateway, but not needing to use it in code/batch utilization (as I did)... try:
traceroute www.google.com
the first hop is your default gateway.
For a list of all default gateways, use mezgani's answer, duplicated (and slightly simplified) here:
/sbin/ip route | awk '/^default/ { print $3 }'
If you have multiple network interfaces configured simultaneously, this will print multiple gateways. If you want to select a single known network interface by name (e.g. eth1), simply search for that in addition to filtering for the ^default lines:
/sbin/ip route |grep '^default' | awk '/eth1/ {print $3}'
You can make a script that takes a single network-interface name as an argument and prints the associated gateway:
#!/bin/bash
if [[ $# -ne 1 ]]; then
echo "ERROR: must specify network interface name!" >&2
exit 1
fi
# The third argument of the 'default' line associated with the specified
# network interface is the Gateway.
# By default, awk does not set the exit-code to a nonzero status if a
# specified search string is not found, so we must do so manually.
/sbin/ip route | grep '^default' | awk "/$1/ {print \$3; found=1} END{exit !found}"
As noted in the comments, this has the advantage of setting a sensible exit-code, which may be useful in a broader programmatic context.
If you know that 0.0.0.0 is your expected output, and will be at the beginning of the line, you could use the following in your script:
IP=`netstat -rn | grep -e '^0\.0\.0\.0' | cut -d' ' -f2`
then reference the variable ${IP}.
It would be better to use awk instead of cut here... i.e.:
IP=`netstat -rn | grep -e '^0\.0\.0\.0' | awk '{print $2}'`
use command below:
route -n | grep '^0\.0\.\0\.0[ \t]\+[1-9][0-9]*\.[1-9][0-9]*\.[1-9][0-9]*\.[1-9][0-9]*[ \t]\+0\.0\.0\.0[ \t]\+[^ \t]*G[^ \t]*[ \t]' | awk '{print $2}'
/sbin/route |egrep "^default" |cut -d' ' -f2-12 #and 'cut' to taste...
The following command returns the default route gateway IP on a Linux host using only bash and awk:
printf "%d.%d.%d.%d" $(awk '$2 == 00000000 && $7 == 00000000 { for (i = 8; i >= 2; i=i-2) { print "0x" substr($3, i-1, 2) } }' /proc/net/route)
This should even work if you have more than one default gateway as long as their metrics are different (and they should be..).
来源：https://stackoverflow.com/questions/1204629/how-do-i-get-the-default-gateway-in-linux-given-the-destination