Writing beautiful terminal GUI on Linux with dialog and jq

I wrapped Free RDP inside a nice script

I connect from time to time from my home computer to a remote PC, using Linux and FreeRPD. After a while it was irritating to be repeating the same commands over and over.

Having an bash function like this was my lazy solution:

export REMOTE_RDP_USER="myremoteuser"
function remote_machine() {
  /usr/bin/xfreerdp /cert-ignore /sound:sys:alsa /f /u:$REMOTE_RDP_USER /v:$1 /p:$2
}

And then I was constantly doing this:

remote_pass=(/bin/cat/.mypassfile)
remote_machine $remote_machine $remote_pass

That was annoying. Not to mention that I had my password on clear text on my machine (I have an encrypted drive but still…)

So I decided to spend a little bit of time and came up with a nice script to handle my basic needs.

What information I need to connect to my remote desktop?

Not much (remote machine and remote user + domain), I just need it to be structured so a simple JSON file will do:

"machines": [
        {
            "name": "machine1.domain.com",
            "description": "Personal-PC"
        },
        {
            "name": "machine2.domain.com",
            "description": "Virtual-Machine"
        }
    ],
    "remote_user": "MYUSER@DOMAIN",
    "title" : "MY COMPANY RDP connection"
}

Obviously JSON is not the best format for configuration files (as it doesn’t support comments for example) but it has plenty of tools on Linux parse its contents from the command line. A very useful tool that stands over the top is ‘jq’. Let me show you how I can extract the list of machines:

/usr/bin/jq --compact-output --raw-output '.machines[]| .name' $HOME/.config/scripts/kodegeek_rdp.json)
"machine1.domain.com"
"machine2.domain.com"

You can try your expressions at jq play just by copying and pasting your JSON files there and then use the expression on your scripts.

So now that I have all the data I need to connect to my remote computer, let’s build a nice UI for it.

Dialog to the rescue

You can handle the workflow entirely from the script, using several chained dialog calls

Dialog is one of these underrated Linux tools that you wish you knew long time ago. You can build very nice and simple UI that will work perfectly on your terminal.

For example, to create a simple checkbox list with my favorite languages, selecting Python by default:

dialog --clear --checklist "Favorite programming languages:" 10 30 7 1 Python on 2 Java off 3 Bash off 4 Perl off 5 Ruby off

And this is how it looks like

Look ma, a ncurses menu!

Putting everything together: Writing an GUI with Dialog and JQ

At the end I wrote an GUI together that used jq to extract my configuration details from my JSON file and organized the flow with dialog. I ask the password every single time and I save it on a temporary file that gets removed after the script is done using it (or if is interrupted, etc.).

The script is pretty basic but is secure and also let me focus on more serious tasks :-)

So how the script looks like?

#!/bin/bash
# author Jose Vicente Nunez
# Do not use this script on a public computer. It is not secure...
# https://invisible-island.net/dialog/
: ${DIALOG_OK=0}
: ${DIALOG_CANCEL=1}
: ${DIALOG_HELP=2}
: ${DIALOG_EXTRA=3}
: ${DIALOG_ITEM_HELP=4}
: ${DIALOG_ESC=255}
declare tmp_file=$(/usr/bin/mktemp 2>/dev/null) || declare tmp_file=/tmp/test$$
trap "/bin/rm -f $tmp_file" 0 1 2 5 15 EXIT INT
/bin/chmod go-wrx ${tmp_file} > /dev/null 2>&1
declare TITLE=$(/usr/bin/jq --compact-output --raw-output '.title' $HOME/.config/scripts/kodegeek_rdp.json)|| exit 100
declare REMOTE_USER=$(/usr/bin/jq --compact-output --raw-output '.remote_user' $HOME/.config/scripts/kodegeek_rdp.json)|| exit 100
declare MACHINES=$(
    declare tmp_file2=$(/usr/bin/mktemp 2>/dev/null) || declare tmp_file2=/tmp/test$$
    # trap "/bin/rm -f $tmp_file2" 0 1 2 5 15 EXIT INT
    declare -a MACHINE_INFO=$(/usr/bin/jq --compact-output --raw-output '.machines[]| join(",")' $HOME/.config/scripts/kodegeek_rdp.json > $tmp_file2)
    declare -i i=0
    while read line; do
        declare machine=$(echo $line| /usr/bin/cut -d',' -f1)
        declare desc=$(echo $line| /usr/bin/cut -d',' -f2)
        declare toggle=off
        if [ $i -eq 0 ]; then
            toggle=on
            ((i=i+1))
        fi
        echo $machine $desc $toggle
    done < $tmp_file2
    /bin/cp /dev/null $tmp_file2
) || exit 100
/usr/bin/dialog \
    --clear \
    --title "$TITLE" \
    --radiolist "Which machine do you want to use?" 20 61 2 \
    $MACHINES 2> ${tmp_file}
return_value=$?
export remote_machine=""
case $return_value in
  $DIALOG_OK)
    export remote_machine=$(/bin/cat ${tmp_file})
    ;;
  $DIALOG_CANCEL)
    echo "Cancel pressed.";;
  $DIALOG_HELP)
    echo "Help pressed.";;
  $DIALOG_EXTRA)
    echo "Extra button pressed.";;
  $DIALOG_ITEM_HELP)
    echo "Item-help button pressed.";;
  $DIALOG_ESC)
    if test -s $tmp_file ; then
      /bin/rm -f $tmp_file
    else
      echo "ESC pressed."
    fi
    ;;
esac
if [ -z "${remote_machine}" ]; then
  /usr/bin/dialog \
  	--clear  \
	--title "Error, no machine selected?" --clear "$@" \
       	--msgbox "No machine was selected!. Will exit now..." 15 30
  exit 100
fi
/bin/ping -c 4 ${remote_machine} >/dev/null 2>&1
if [ $? -ne 0 ]; then
  /usr/bin/dialog \
  	--clear  \
	--title "VPN issues or machine is off?" --clear "$@" \
       	--msgbox "Could not ping ${remote_machine}. Time to troubleshoot..." 15 50
  exit 100
fi
/bin/rm -f ${tmp_file}
/usr/bin/dialog \
  --title "$TITLE" \
  --clear  \
  --insecure \
  --passwordbox "Please enter your Windows password for ${remote_machine}\n" 16 51 2> $tmp_file
return_value=$?
case $return_value in
  $DIALOG_OK)
    /usr/bin/mkdir -p -v $HOME/logs
    /usr/bin/xfreerdp /cert-ignore /sound:sys:alsa /f /u:$REMOTE_USER /v:${remote_machine} /p:$(/bin/cat ${tmp_file})| \
    /usr/bin/tee $HOME/logs/$(/usr/bin/basename $0)-$remote_machine.log
    ;;
  $DIALOG_CANCEL)
    echo "Cancel pressed.";;
  $DIALOG_HELP)
    echo "Help pressed.";;
  $DIALOG_EXTRA)
    echo "Extra button pressed.";;
  $DIALOG_ITEM_HELP)
    echo "Item-help button pressed.";;
  $DIALOG_ESC)
    if test -s $tmp_file ; then
      /bin/rm -f $tmp_file
    else
      echo "ESC pressed."
    fi
    ;;
esac

Are dialog and JQ the best options?

You can skin this rabbit in many ways (JavaFX, Gnome Zenity, Python TKinter, etc.) I just wanted to show you one nice way to acomplish this in short time, 100 lines of code.

It is not perfect. Specially integration with Bash makes the code very verbose but it is still easy to debug and maintain. I spent 30 minutes writing it down, so imagine what you can do to write more easy to use programs for you and your users.

Please clap if you like this article! I also want to know what you think, so please leave me a message in the comments section.