Bash Script to change WLan SSID

I'm new to Linux, and I'm looking for a simple way to update the SSID and associated password on the wlan0 interface at a set time. I need to copy file from a device on Network 'A' to a device on Network 'B' and only have a single Wireless interface.

I've manually been able to follow the process by;

Update - /etc/netplan/50-cloud-init.yaml

Apply - sudo netplan apply

Restart - sudo systemctl restart systemd-networkd

Status - sudo systemctl status systemd-networkd

But now, I'd like to automate it via Bash or other method. I'm running Ubuntu on a RasperryPi Zero 2W, hence only single WiFi interface. I have tried to get a Netgear A6150 connected also, but not yet achieved this.

Make a copy of your /etc/netplan/50-cloud-init.yaml at any location you choose - here referenced as /path/to/50-cloud-init.yaml (at the same time this file serves as a backup).

The content of this file should be along the lines of:

version: 2
wifis:
  renderer: networkd
  wlan0:
    dhcp4: true
    optional: true
    access-points:
      SSID:
        password: PASS

The important thing here is that the SSID and PASS are given as stated here. Adjust the contents to match your specific network config.

Then make a text file for your bash script, also anywhere you like and make it executable - here referenced as /path/to/bash-script.

The content of this file should then be:

#!/bin/bash

# check if script is run as root
if [[ "$EUID" -ne 0 ]]; then
    echo "Please run this script as root / with sudo."
    exit 1
fi

# assign values to $SSID and $PASS variables - you can add additional SSID and password pairs if you like.
case "$1" in
  <SSID1>)
    SSID=<SSID1>
    PASS=<PASS1>
    ;;

  <SSID2>)
    SSID=<SSID2>
    PASS=<PASS2>
    ;;
esac

# only do something if $SSID variable has been set
if [[ -n "$SSID" ]]; then

  # copy your template file into the netplan folder
  cp -f /path/to/50-cloud-init.yaml /etc/netplan/50-cloud-init.yaml

  # replace the "variables" in the netplan config file with the actual values
  sed -i "s/SSID/$SSID/;s/PASS/$PASS/" /etc/netplan/50-cloud-init.yaml

  # apply netplan config
  netplan apply

  # restart networkd
  systemctl restart systemd-networkd

else
  echo "Invalid SSID given".
  exit 1
fi

Replace all instances of <SSIDx> and <PASSx> with your actual SSID and passwords.

Now run your script /path/to/bash-script with your chosen SSID as the first parameter, like:

/path/to/bash-script <SSIDx>

And this will do what you're after.