osascript of course: it lets you control the UI of Cocoa applications, and even more for scriptable ones: osascript -e 'tell application "Safari" to close

osascript of course: it lets you control the UI of Cocoa applications, and even more for scriptable ones: osascript -e 'tell application "Safari" to close every document ¬ whose url contains "news.ycombinator.com"' (¬, option-(lowercase L), is the AppleScript line continuation character)