External command "brew missing"

This will print installed brews that are missing deps.

Library/Contributions/examples/brew-missing.rb

+require "formula"
+require 'formula_installer'
+
+def main
+  # Names of outdated brews; they count as installed.
+  outdated = outdated_brews.select {|b| b[1] }
+
+  HOMEBREW_CELLAR.subdirs.each do |keg|
+    next unless keg.subdirs
+    if ((f = Formula.factory(keg.basename.to_s)).installed? rescue false)
+      f_deps = FormulaInstaller.expand_deps(f).collect{|g| g.name}.uniq
+      next if f_deps.empty?
+
+      missing_deps = []
+      f_deps.each do |dep_name|
+        unless Formula.factory(dep_name).installed? or outdated.include?(dep_name)
+          missing_deps << dep_name
+        end
+      end
+
+      puts "#{f.name}: #{missing_deps.join(', ')}" unless missing_deps.empty?
+    end
+  end
+end
+
+main()