Create a veth using dummy module without setting an IP

create_veth.sh

#!/usr/bin/env bash

# Create a dummy veth. 
# To add an addr:
#   ip addr add $addr/24 brd + dev $veth label $veth:0
# To remove $veth:
#   if addr set:
#     ip addr del $addr/24 brd + dev eth10 label veth5:0
#   ip link delete $veth type dummy
#   rmmod dummy

set -o nounset
set -o pipefail
#set -o errexit

# Report and die. If called from within a function/subshell, this will only
# exit the function/subshell, not the script.
function die {
    local msg="$1"
    (>&2 echo Fatal: "$msg")  # Subshell avoids interactions with other redirections
    kill -SIGPIPE "$$"  # exit code: 141
}

# Report. Override leader with an optional replacement.
function info {
    local msg="$1"
    local leader="${2:-==}"
    (echo "$leader" "$msg")  # Subshell avoids interactions with other redirections
}

function create_veth {
    local veth="$1"
    local dum="dummy0"

    # load dummy mod
    mod=$(lsmod | grep dummy)
    if [ -z "$mod" ]; then
        modprobe dummy || die "cannot modprobe dummy"
    fi

    # Create $veth unless found
    veth_show=$(2>&1 ip link show "$veth")
    if [[ "$veth_show" =~ "does not exist" ]]; then
        info "Creating veth [$veth]"
        ip link add "$dum" type dummy       || die "cannot add dummy0"
        ip link set name "$veth" dev "$dum" || die "cannot add $veth name to $dum"
        ip link set dev "$veth" up          || die "cannot bring $veth up"
    else
        info "$veth already exists"
    fi

    ip link show "$veth"                || die "cannot show link $veth"
}

create_veth "veth5"