create a pair of veth for use with netns

nsrun.sh

#!/bin/bash

netns0="{$1}"
addr0="{$2}"
ip0() { ip -n $netns0 "$@"; }
n0() { ip netns exec $netns0 "$@"; }
waitiface() { bash -c "while [[ \$(< \"/sys/class/net/$1/operstate\") != up ]]; do read -t .1 -N 0 || true; done;"; }

ip netns del $netns0 2>/dev/null || true
ip link del vin-"$netns0"
ip netns add $netns0
ip link add vout-"$netns0" type veth peer name vin-"$netns0"
ip link set vout-"$netns0" netns "$netns0"
ip link set up vin-"$netns0"
ip0 link set up dev vout-"$netns0"
waitiface vin-"$netns0"
ip0 addr add "$addr0" dev lo
ip0 route add default dev vout-"$netns0"
ip route add $addr0 dev vin-"$netns0"

n0 sudo -unobody /usr/local/bin/script --options

sudo is unnecessary in the last line.