How to show GUI dialog window from shell script on a Mac

When you run a shell script from a GUI app (from Alfred workflow, for example) you want to show an error and ask questions via GUI too. You can do it with AppleScript.

Show error message:

#!/usr/bin/env bash
 
# error "Message"
function error() {
  osascript <<EOT
    tell app "System Events"
      display dialog "$1" buttons {"OK"} default button 1 with icon caution with title "$(basename $0)"
      return  -- Suppress result
    end tell
EOT
}
 
error "Not enough cheese!"

AppleScript error message

(You can use note or stop instead of caution to show a different icon.)

Ask question:

#!/usr/bin/env bash
 
# prompt "Question" "Default value"
function prompt() {
  osascript <<EOT
    tell app "System Events"
      text returned of (display dialog "$1" default answer "$2" buttons {"OK"} default button 1 with title "$(basename $0)")
    end tell
EOT
}
 
value="$(prompt 'Enter:' '42')"

AppleScript prompt

Or you can download dlg-error and dlg-prompt and put them somewhere in $PATH:

#!/usr/bin/env bash
 
dlg-error "Not enough cheese!"
value="$(dlg-prompt 'Enter:' '42')"

P. S. You can show notifications in the Notification Center using terminal-notifier.