brew list --versions --multiple

With --multiple, only list formulae with multiple versions installed.

Library/Contributions/manpages/brew.1.md

@@ -227,7 +227,7 @@ Note that these flags should only appear after a command.
     If provided, `--local` will move them into the user's `~/Applications`
     folder instead of the system folder. It may need to be created, first.
 
-  * `ls, list [--unbrewed] [--versions] [--pinned]` [<formulae>]:
+  * `ls, list [--unbrewed] [--versions [--multiple]] [--pinned]` [<formulae>]:
     Without any arguments, list all installed formulae.
 
     If <formulae> are given, list the installed files for <formulae>.
@@ -238,7 +238,8 @@ Note that these flags should only appear after a command.
     by Homebrew.
 
     If `--versions` is passed, show the version number for installed formulae,
-    or only the specified formulae if <formulae> are given.
+    or only the specified formulae if <formulae> are given. With `--multiple`,
+    only show formulae with multiple versions installed.
 
     If `--pinned` is passed, show the versions of pinned formulae, or only the
     specified (pinned) formulae if <formulae> are given.

Library/Homebrew/cmd/list.rb

@@ -63,6 +63,7 @@ module Homebrew extend self
       ARGV.named.map{ |n| HOMEBREW_CELLAR+n }.select{ |pn| pn.exist? }
     end.each do |d|
       versions = d.children.select{ |pn| pn.directory? }.map{ |pn| pn.basename.to_s }
+      next if ARGV.include?('--multiple') && versions.count < 2
       puts "#{d.basename} #{versions*' '}"
     end
   end

share/man/man1/brew.1

 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BREW" "1" "March 2014" "Homebrew" "brew"
+.TH "BREW" "1" "April 2014" "Homebrew" "brew"
 .
 .SH "NAME"
 \fBbrew\fR \- The missing package manager for OS X
@@ -242,7 +242,7 @@ Find all installed formulae that have compiled \fB\.app\fR\-style "application"
 If provided, \fB\-\-local\fR will move them into the user\'s \fB~/Applications\fR folder instead of the system folder\. It may need to be created, first\.
 .
 .TP
-\fBls, list [\-\-unbrewed] [\-\-versions] [\-\-pinned]\fR [\fIformulae\fR]
+\fBls, list [\-\-unbrewed] [\-\-versions [\-\-multiple]] [\-\-pinned]\fR [\fIformulae\fR]
 Without any arguments, list all installed formulae\.
 .
 .IP
@@ -252,7 +252,7 @@ If \fIformulae\fR are given, list the installed files for \fIformulae\fR\. Combi
 If \fB\-\-unbrewed\fR is passed, list all files in the Homebrew prefix not installed by Homebrew\.
 .
 .IP
-If \fB\-\-versions\fR is passed, show the version number for installed formulae, or only the specified formulae if \fIformulae\fR are given\.
+If \fB\-\-versions\fR is passed, show the version number for installed formulae, or only the specified formulae if \fIformulae\fR are given\. With \fB\-\-multiple\fR, only show formulae with multiple versions installed\.
 .
 .IP
 If \fB\-\-pinned\fR is passed, show the versions of pinned formulae, or only the specified (pinned) formulae if \fIformulae\fR are given\. See also \fBpin\fR, \fBunpin\fR\.