zenity

Display dialogs from the command-line/shell scripts. Return user-inserted values or 1 if error. More information: https://manned.org/zenity.

Display the default question dialog:

zenity --question
Display an info dialog displaying the text "Hello!":

zenity --info --text="{{Hello!}}"
Display a name/password form and output the data separated by ";":

zenity --forms --add-entry="{{Name}}" --add-password="{{Password}}" --separator="{{;}}"
Display a file selection form in which the user can only select directories:

zenity --file-selection --directory
Display a progress bar which updates its message every second and show a progress percent:

{{(echo "#1"; sleep 1; echo "50"; echo "#2"; sleep 1; echo "100")}} | zenity --progress