SSH ProxyCommand to connect to UTM guest on shared network.

proxy-utm-guest.sh

#!/bin/bash
#
# Determine current IP address of the UTM guest VM and nc to it.
# Jason White (jdwhite@menelos.com)
# 2024-06-05
#
# Note: VMs must be named the same as the SSH hostname.
#
# ~/.ssh/config entry for host as follows:
#
# Host utmguest-1 utmguest-2 utmtest-3
#     ProxyCommand proxy-utm-guest %h %p
#

# NetCat path.
NC=/usr/bin/nc

VM_NAME=$1
VM_PORT=${2:-22}
VM_BASEPATH="${HOME}/Library/Containers/com.utmapp.UTM/Data/Documents"
VM_CONFIG="${VM_BASEPATH}/${VM_NAME}.utm/config.plist"

if [ ! -r "${VM_CONFIG}" ]; then
    echo "No VM with that name - exiting." >&2
    exit 1
fi

# This will not handle VMs with multiple network interfaces well.
MACADDR=$(grep -Eio '(([0-9A-F]{2}:){5}[0-9A-F]{2})' ${VM_CONFIG} | tr 'A-Z' 'a-z')

if [ ! -n "${MACADDR}" ]; then
    echo "Unable to obtain MACADDR -- exiting" >&2
    exit 1
fi

# Scan ARP cache on bridge interfaces to find matching IP address.
for bridge in $(ifconfig -l -X bridge\*); do
    IPADDR=$(arp -ani ${bridge} | awk -v mac="${MACADDR}" ' $4==mac {print $2}' | tr -d '()')
    if [ -n "$IPADDR" ]; then
        exec ${NC} -4n ${IPADDR} ${VM_PORT}
        break
    fi
done

exit