List Network Adaptors

ifconfig

Is Network Interface Connected

cat /sys/class/net/wlan0/operstate

Indicates the interface operational state, possible values are: “unknown”, “notpresent”, “down”, “lowerlayerdown”, “testing”,”dormant”, “up”.”no such file or directory”

You can test for “up”.

cat /sys/class/net/wlan0/carrier

Will give a result of 0, 1 or a ‘no such file or directory’ error message.

NOTE – we have seen this commant return a ‘1’ when the WiFi adaptor is not actually connected (‘ip addr’ returns “wlan0: <NO-CARRIER,…”. In this instance cat /sys/class/net/wlan0/operstate returned “dormant”

Other commands

See https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-net

Restarting After Changes

See here.