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Top Forums Shell Programming and Scripting Bash- Determine what interface is online Post 302852659 by Jotne on Thursday 12th of September 2013 05:19:28 AM
Old 09-12-2013
Code:
ip route get 8.8.8.8
8.8.8.8 via 192.168.10.1 dev eth0  src 192.168.10.33
    cache

This tests what route is used to connect to a public IP, like this Google DNS IP

gawk version (rs limitation)
Code:
ip route get 8.8.8.8 | awk 'NR==2 {print $1}' RS="dev"
eth0

You need to find the word after dev, and this can vary on the line, depending if computer is behind a firewall/router, or connected directly on the net.

EDIT: a more portable version
Code:
ip route get 8.8.8.8 | awk -F"dev " 'NR==1 {split($2,a," ");print a[1]}'

 

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SYSTEMD-NETWORKD-WAIT-ONLINE.SERVICE(8) 		     systemd-networkd.service			   SYSTEMD-NETWORKD-WAIT-ONLINE.SERVICE(8)

NAME
systemd-networkd-wait-online.service, systemd-networkd-wait-online - Wait for network to come online SYNOPSIS
systemd-networkd-wait-online.service /lib/systemd/systemd-networkd-wait-online DESCRIPTION
systemd-networkd-wait-online is a one-shot system service that waits for the network to be configured. By default, it will wait for all links it is aware of and which are managed by systemd-networkd.service(8) to be fully configured or failed, and for at least one link to gain a carrier. OPTIONS
The following options are understood: -i, --interface= Network interface to wait for before deciding if the system is online. This is useful when a system has several interfaces which will be configured, but a particular one is necessary to access some network resources. This option may be used more than once to wait for multiple network interfaces. When used, all other interfaces are ignored. --ignore= Network interfaces to be ignored when deciding if the system is online. By default, only the loopback interface is ignored. This option may be used more than once to ignore multiple network interfaces. --timeout= Fail the service if the network is not online by the time the timeout elapses. A timeout of 0 disables the timeout. Defaults to 120 seconds. SEE ALSO
systemd(1), systemd-networkd.service(8) systemd 237 SYSTEMD-NETWORKD-WAIT-ONLINE.SERVICE(8)
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