Applescript to display real date of selected timestamp

TimestampToDate.scpt

on run {input, parameters}

    tell application "System Events"
        set activeApp to name of first process whose frontmost is true
    end tell

    set _timestamp to (input as string)

    tell application activeApp
        set realDate to ((do shell script "date -r " & _timestamp) as string)
        display dialog realDate
    end tell

    return realDate

end run

To use with a keyboard shortcut:

1. Open Automator
2. Create a new 'Service', which "receives selected text in any application"
3. Drag 'Run Applescript' into the Workflow window, paste in the code
4. Save as 'Unix Timestamp' (or something else unique)
5. System Preferences > Keyboard > Keyboard Shortcuts > Services
6. Find the service in the list (under 'Text') and add a shortcut for it