fs/skeleton/bin/is-interface-up

#!/bin/sh
#
# Returns 0 (true) if the provided interface is "up".
#
if [ -z "$1" ]; then
  echo "Usage: $0 interface" >&2
  exit 1
fi

if [ ! -e "/sys/class/net/$1" ]; then
  exit 1
fi

# Overrides for test.
#  interface_name=up|down semicolon separated.
#  Example: IIU_TEST_OVERRIDE="wan0=up;br0=down"
if [ ! -z "${IIU_TEST_OVERRIDE}" ]; then
  while [ "${IIU_TEST_OVERRIDE}" ]; do
    segment=${IIU_TEST_OVERRIDE%%;*}
    if [ "$segment" = "$1=up" ]; then
      exit 0
    elif [ "$segment" = "$1=down" ]; then
      exit 1
    fi

    if [ "$IIU_TEST_OVERRIDE" = "$segment" ]; then
        IIU_TEST_OVERRIDE=
    else
        IIU_TEST_OVERRIDE="${IIU_TEST_OVERRIDE#*;}"
    fi
  done
fi

ip link show dev "$1" | grep -q LOWER_UP