optimize command with or and pipe to parse the output of ifconfig

Question

I have this command line, but it's doubling the grep and awk

ifconfig eth1 2> /dev/null | grep "inet " | awk '{gsub("addr:","",$2);  print $2 }' ||
ifconfig eth0 2> /dev/null | grep "inet " | awk '{gsub("addr:","",$2);  print $2 }'`

I have being trying to shorten this by doing something like,

echo $(ifconfig eth1 2> /dev/null || ifconfig eth0 2> /dev/null) &>  grep "inet " |
awk '{gsub("addr:","",$2);  print $2 }'

but it returns nothing at all when I am looking to get the IP of server. What is the best way to say get info if on error try this and then pipe it to grep

Answer 1

Another more modular approach: not bash-specific

get_ifconfig () { 
    for iface do 
        ifconfig "$iface" 2>/dev/null && return
    done
}
get_ifconfig eth1 eth2 eth3 | sed -n 's/.*inet addr:\([0-9.]\+\).*/\1/p'

Answer 2

Try this:

$ ( ifconfig eth2 2>/dev/null || ifconfig eth0 2>/dev/null ) | grep ...

It has the same logic, but it does the || inside the parens so it only passes the output of the successful command to grep.

Answer 3

How about this approach

$ echo eth1 eth0 | xargs -n 1 ifconfig 2>/dev/null | awk '/inet/{gsub("addr:","",$2);print $2;exit}'
192.168.124.132
$

Answer 4

If you want to grab the first interface that has an IPv4 address, you can run ifconfig just once to display all the interfaces and extract the first entry with an IPv4 address. You can also optimize the extraction by combining what you're doing with grep and awk.

ifconfig -a | awk '/^[^ ]/ {iface=$1}
                  iface ~ /^eth/ && sub(/inet addr:/,"") {print $1; exit}'

The newline is optional, I included it for clarity. This is a more elaborate version of

ifconfig -a | awk 'sub(/inet addr:/,"") {print $1; exit}'

which might print something like 127.0.0.1 (from the loopback interface) that you presumably don't want.

If you prefer to use ip, parsing is about equally awkward.

ip addr | awk '/^[0-9]/ {iface=$2}
               iface ~ /^eth/ && $1 == "inet" {sub(/\/.*/, "", $2); print $2}'