BASH SCRIPT QUESTION: Determine which NIC out of multiple NICs the server hostname runs on.

I need to script finding which of the NICS on the server is the one the IP the hostname of the server runs on my Redhat 5 and Redhat 6 x86 servers. This is only part of the script since I'll use the variable for comparison later on in the script but below is how I'm going to do it. Do you think there is a better way to do it or do you think this is good enough? What I'm relying on is that $(hostname) actually matches the entry in /etc/hosts but sometimes hostname has FQDN and sometimes not.

host=$(hostname)

HOSTIP=$(cat /etc/hosts | grep ${host} | awk ‘{print $1}’)
 
if [  ! -z ${HOSTIP} ]; then
          HOSTNIC=$(/sbin/ifconfig -a | grep -B2  ${HOSTIP} )
   else
         printf “HOST NIC IS UNKNOWN”
         exit 1
fi
lolaferrariAsked:
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David FavorLinux/LXD/WordPress/Hosting SavantCommented:
Depends on what you mean by hostname.

If you're talking about the random/useless/anything string returned from the hostname command, then usually the first IPV4 listed in ifconfig will be what you're looking to identify.

If you're talking about a true DNS lookup (far better), then use something like...

dig +short FQDN

Open in new window


Where FQDN is some domain running on machine.

Likely better to grep /etc/netplan/* or /etc/network/interfaces.d/* for first IPV4 address to pickup address which will be config'ed first during reboot.
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lolaferrariAuthor Commented:
Great! Thanks again David!
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