cleanup: add an option to perform a 'dry run'

Sometimes you want to know what `brew cleanup` will do before it
actually removes anything. Introduce a '-n' option (chosen to match
other UNIX tools) to do this.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

2 files changed, 5 insertions, 3 deletions

diff --git a/Library/Contributions/manpages/brew.1.md b/Library/Contributions/manpages/brew.1.md
index a15fbfeb7..806762a94 100644
--- a/Library/Contributions/manpages/brew.1.md
+++ b/Library/Contributions/manpages/brew.1.md
@@ -54,13 +54,15 @@ For the full command list, see the COMMANDS section.
   * `cat` <formula>:
     Display the source to <formula>.
 
-  * `cleanup [--force]` [<formula>]:
+  * `cleanup [--force] [-n]` [<formula>]:
     For all installed or specific formulae, remove any older versions from the
     cellar. By default, does not remove out-of-date keg-only brews, as other
     software may link directly to specific versions.
 
     If `--force` is passed, remove out-of-date keg-only brews as well.
 
+    If `-n` is passed, show what would be removed, but do not actually remove anything.
+
   * `create [--autotools|--cmake] [--no-fetch]` <URL>:
     Generate a formula for the downloadable file at <URL> and open it in
     $EDITOR. Homebrew will attempt to automatically derive the formula name
diff --git a/Library/Homebrew/cmd/cleanup.rb b/Library/Homebrew/cmd/cleanup.rb
index 0f9f2c3cb..0aec10f56 100644
--- a/Library/Homebrew/cmd/cleanup.rb
+++ b/Library/Homebrew/cmd/cleanup.rb
@@ -13,7 +13,7 @@ module Homebrew extend self
         end
       end
       # seems like a good time to do some additional cleanup
-      Homebrew.prune
+      Homebrew.prune unless ARGV.include? '-n'
     else
       ARGV.formulae.each do |f|
         cleanup_formula f
@@ -36,7 +36,7 @@ module Homebrew extend self
       f.rack.children.each do |keg|
         if f.installed_prefix != keg
           print "Removing #{keg}..."
-          rm_rf keg
+          rm_rf keg unless ARGV.include? '-n'
           puts
         end
       end