Trying to extract the IP address of the default gateway

dixon464 · 12-09-2014, 11:34 AM

Hope you can help.

I am doing a FD in applied networking and having trouble with this line

DG= netstat -rn | grep 0.0.0.0 | awk '{print $2}' | grep -v "0.0.0.0"

ping -c 3 $DG

I am trying to extract the DG from netstat so I can ping to check it responds to ping command.

the result looks right when echo'd to the screen but when i try to ping the DG it errors, i can only think the the data in the $DG variable contains the wrong data, it there a way to clean this up?

Error message =

Usage: ping [-aAbBdDfhLnOqrRUvV] [-c count] [-i interval] [-I interface]
[-m mark] [-M pmtudisc_option] [-l preload] [-p pattern] [-Q tos]
[-s packetsize] [-S sndbuf] [-t ttl] [-T timestamp_option]
[-w deadline] [-W timeout] [hop1 ...] destination

I must be doing something daft

Hope you can help

Regards
Stuart

smallpond · 12-09-2014, 12:14 PM

Where does this "grep | awk" thing come from? I see that all the time. awk is much more powerful than grep. No need to use both.

You forgot to capture the output of the commands:

Code:

 DG=$(netstat -rn |awk '$4 ~ /G/ {print $2}')

dixon464 · 12-09-2014, 12:25 PM

Thank you smallpond, works a treat.

pingu · 12-09-2014, 12:25 PM

When you assign a variable with result of command, use "$()"
So try:

Code:

 DG=$(netstat -rn | grep 0.0.0.0 | awk '{print $2}' | grep -v "0.0.0.0") ; ping $DG

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Edit: Solved 10 minutes ago by smallpond, didn't notice that.