Convert /proc/net/route IP from hex to quad-dotted representation

route-convert-to-ip.bash

#!/usr/bin/env bash
# not zsh portable

set -euxo pipefail

# Usage: ... | hex_to_ip
# Reads stdin and converts IPs from hex to quad-dotted representation.
function hex_to_ip {
    if [[ -n "$1" ]]; then echo "$0: Too many arguments">&2; return 1; fi
    # might break on big endian?
    sed -r 's/(..)(..)(..)(..)/0x\4 0x\3 0x\2 0x\1/;s/.*/printf "%d.%d.%d.%d" &/e'
}

# Usage: get_gateway_for_iface IFACE
# Prints the hex IP of the gateway associated with the interface IFACE.
# If there are multiple, picks the first.
function get_gateway_for_iface {
    if [[ -z "$1" ]]; then echo "Missing argument">&2; return 1; fi
    awk '$1 == "'"$1"'" && $3 != "00000000" { found=1; print $3 } END { exit !found }' /proc/net/route | head -n1
}

# Example: convert hex IP to quad-dotted IP
#     $ hex_to_ip <<< 4032A8C0
#     192.168.50.64
# Example: get gateway for eno1
#     $ get_gateway_for_iface eno1
#     0101A8C0
#     $ get_gateway_for_iface eno1 | hex_to_ip
#     192.168.1.1