Look for container extraction programs in PATH.

Library/Homebrew/cask/lib/hbc/container/cab.rb

@@ -6,17 +6,15 @@ module Hbc
   class Container
     class Cab < Base
       def self.me?(criteria)
-        cabextract = Hbc.homebrew_prefix.join("bin", "cabextract")
+        cabextract = which("cabextract")
 
         criteria.magic_number(%r{^MSCF}n) &&
-          cabextract.exist? &&
+          !cabextract.nil? &&
           criteria.command.run(cabextract, args: ["-t", "--", criteria.path.to_s]).stderr.empty?
       end
 
       def extract
-        cabextract = Hbc.homebrew_prefix.join("bin", "cabextract")
-
-        unless cabextract.exist?
+        if (cabextract = which("cabextract")).nil?
           raise CaskError, "Expected to find cabextract executable. Cask '#{@cask}' must add: depends_on formula: 'cabextract'"
         end
 

Library/Homebrew/cask/lib/hbc/container/generic_unar.rb

@@ -14,9 +14,7 @@ module Hbc
       end
 
       def extract
-        unar = Hbc.homebrew_prefix.join("bin", "unar")
-
-        unless unar.exist?
+        if (unar = which("unar")).nil?
           raise CaskError, "Expected to find unar executable. Cask #{@cask} must add: depends_on formula: 'unar'"
         end
 

Library/Homebrew/cask/lib/hbc/container/lzma.rb

@@ -10,9 +10,7 @@ module Hbc
       end
 
       def extract
-        unlzma = Hbc.homebrew_prefix.join("bin", "unlzma")
-
-        unless unlzma.exist?
+        if (unlzma = which("unlzma")).nil?
           raise CaskError, "Expected to find unlzma executable. Cask '#{@cask}' must add: depends_on formula: 'lzma'"
         end
 

Library/Homebrew/cask/lib/hbc/container/xz.rb

@@ -10,9 +10,7 @@ module Hbc
       end
 
       def extract
-        unxz = Hbc.homebrew_prefix.join("bin", "unxz")
-
-        unless unxz.exist?
+        if (unxz = which("unxz")).nil?
           raise CaskError, "Expected to find unxz executable. Cask '#{@cask}' must add: depends_on formula: 'xz'"
         end
 

Library/Homebrew/cask/test/cask/installer_test.rb

@@ -42,7 +42,7 @@ describe Hbc::Installer do
     end
 
     it "works with cab-based Casks" do
-      skip("cabextract not installed") unless Hbc.homebrew_prefix.join("bin", "cabextract").exist?
+      skip("cabextract not installed") if which("cabextract").nil?
       asset = Hbc.load("container-cab")
       empty = stub(formula: [], cask: [], macos: nil, arch: nil, x11: nil)
       asset.stubs(:depends_on).returns(empty)
@@ -72,7 +72,7 @@ describe Hbc::Installer do
     end
 
     it "works with 7z-based Casks" do
-      skip("unar not installed") unless Hbc.homebrew_prefix.join("bin", "unar").exist?
+      skip("unar not installed") if which("unar").nil?
       asset = Hbc.load("container-7z")
       empty = stub(formula: [], cask: [], macos: nil, arch: nil, x11: nil)
       asset.stubs(:depends_on).returns(empty)
@@ -101,7 +101,7 @@ describe Hbc::Installer do
     end
 
     it "works with Stuffit-based Casks" do
-      skip("unar not installed") unless Hbc.homebrew_prefix.join("bin", "unar").exist?
+      skip("unar not installed") if which("unar").nil?
       asset = Hbc.load("container-sit")
       empty = stub(formula: [], cask: [], macos: nil, arch: nil, x11: nil)
       asset.stubs(:depends_on).returns(empty)
@@ -117,7 +117,7 @@ describe Hbc::Installer do
     end
 
     it "works with RAR-based Casks" do
-      skip("unar not installed") unless Hbc.homebrew_prefix.join("bin", "unar").exist?
+      skip("unar not installed") if which("unar").nil?
       asset = Hbc.load("container-rar")
       empty = stub(formula: [], cask: [], macos: nil, arch: nil, x11: nil)
       asset.stubs(:depends_on).returns(empty)
@@ -159,7 +159,7 @@ describe Hbc::Installer do
     end
 
     it "works with pure xz-based Casks" do
-      skip("unxz not installed") unless Hbc.homebrew_prefix.join("bin", "unxz").exist?
+      skip("unxz not installed") if which("unxz").nil?
       asset = Hbc.load("container-xz")
       empty = stub(formula: [], cask: [], macos: nil, arch: nil, x11: nil)
       asset.stubs(:depends_on).returns(empty)
@@ -175,7 +175,7 @@ describe Hbc::Installer do
     end
 
     it "works with lzma-based Casks" do
-      skip("unlzma not installed") unless Hbc.homebrew_prefix.join("bin", "unlzma").exist?
+      skip("unlzma not installed") if which("unlzma").nil?
       asset = Hbc.load("container-lzma")
       empty = stub(formula: [], cask: [], macos: nil, arch: nil, x11: nil)
       asset.stubs(:depends_on).returns(empty)

Library/Homebrew/cask/test/test_helper.rb

@@ -151,17 +151,7 @@ require "support/never_sudo_system_command"
 require "tmpdir"
 require "tempfile"
 
-# create directories
-FileUtils.mkdir_p Hbc.homebrew_prefix.join("bin")
-
 # Common superclass for test Casks for when we need to filter them out
 module Hbc
   class TestCask < Cask; end
 end
-
-# jack in some optional utilities
-FileUtils.ln_s "/usr/local/bin/cabextract", Hbc.homebrew_prefix.join("bin/cabextract")
-FileUtils.ln_s "/usr/local/bin/unar", Hbc.homebrew_prefix.join("bin/unar")
-FileUtils.ln_s "/usr/local/bin/unlzma", Hbc.homebrew_prefix.join("bin/unlzma")
-FileUtils.ln_s "/usr/local/bin/unxz", Hbc.homebrew_prefix.join("bin/unxz")
-FileUtils.ln_s "/usr/local/bin/lsar", Hbc.homebrew_prefix.join("bin/lsar")