Simple bash Script to Auto Connect Midi Devices, and use Linux Host (i.e. Raspberry) as a Midi Host.

auto-connect-midi.sh

#!/bin/bash

# This script will connect all masters to slaves
# So the communication is only unidirectional.
# Some midi devices can act as input and output, so differentiating them
# Helps to prevent unwanted communications between devices

# Identiy Master and Slaves using names

# Put here the masters (or devices that will act as inputs of other devices)
declare -a MASTERS=("Elektron Syntakt")

# Put here the slaves (or devices that will produce sound)
declare -a SLAVES=("NTS-1 digital kit")

# Erase all midi routes configured previously
printf "Cleanning existing midi connections...\n"
aconnect -x

IFS=""
for m in ${MASTERS[@]}; do
        ac_inputs=$(aconnect -i -l | grep "$m")
        m_client_id=$(printf "$ac_inputs\n" | awk -F ':' '{print $1;exit}' | sed 's/client\s//')
        m_client_port=$(printf "$ac_inputs\n" | awk '{getline;print}' | awk '{print $1}')

        m_client=$(printf "$m_client_id:$m_client_port")


        if [ ! -z "$m_client_id" ];
        then
                for s in ${SLAVES[@]}; do
                        ac_outputs=$(aconnect -o -l | grep "$s")
                        s_client_id=$(printf "$ac_outputs\n" | awk -F ':' '{print $1;exit}' | sed 's/client\s//')
                        if [ ! -z "$s_client_id" ];
                        then
                                s_client_port=$(printf "$ac_outputs\n" | awk '{getline;print}' | awk '{print $1}')
                                s_client=$(printf "$s_client_id:$s_client_port")

                                if [ "$m_client" != "$s_client" ];
                                then
                                        printf "Connecting devices. Input: $m. $m_client. Output: $s. $s_client\n"
                                        aconnect "$m_client" "$s_client"
                                fi
                        else
                                printf "Ignoring: $s. Output Device not found \n"
                        fi
                done
        else
                printf "Ignoring: $m. Input Device not found\n"
        fi
done

Before executing the script, you need to identify which devices will act as input (MASTERS) and which will act as output (SLAVES). In the above example I used as input "Elektron Syntakt" and output "NTS-1 Nutekt"

You can use it along with udev rules to execute it automatically when a new USB-MIDI interface is connected.

ACTION=="add|remove", SUBSYSTEM=="usb", DRIVER=="snd-usb-audio", RUN+="/usr/local/bin/auto-connect-midi.sh"

Don't forget to reload the udev rules:

sudo udevadm control --reload
sudo systemctl restar udev

You can also define a Systemd service descriptor to execute it automatically at boot.

[Unit]
Description=Auto Connect MIDI Devices

[Service]
ExecStart=/usr/local/bin/auto-connect-midi.sh

[Install]
WantedBy=multi-user.target