diff --git a/Library/Homebrew/brew.h.rb b/Library/Homebrew/brew.h.rb
index 7a5e55fea0..532e5b611d 100644
--- a/Library/Homebrew/brew.h.rb
+++ b/Library/Homebrew/brew.h.rb
@@ -95,7 +95,7 @@ def info name
   require 'formula'
 
   user=''
-  user=`git config --global github.user`.chomp if system "which git > /dev/null"
+  user=`git config --global github.user`.chomp if system "/usr/bin/which -s git"
   user='mxcl' if user.empty?
   # FIXME it would be nice if we didn't assume the default branch is master
   history="http://github.com/#{user}/homebrew/commits/master/Library/Formula/#{Formula.path(name).basename}"
diff --git a/Library/Homebrew/brewkit.rb b/Library/Homebrew/brewkit.rb
index 132bda851e..91ea9fa644 100644
--- a/Library/Homebrew/brewkit.rb
+++ b/Library/Homebrew/brewkit.rb
@@ -187,5 +187,5 @@ def inreplace(path, before, after)
   after.gsub! "$", "\\$"
 
   # FIXME use proper Ruby for teh exceptions!
-  safe_system "perl", "-pi", "-e", "s/#{before}/#{after}/g", path
+  safe_system "/usr/bin/perl", "-pi", "-e", "s/#{before}/#{after}/g", path
 end
diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 0c89c1f2b0..58e5b197b5 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -51,11 +51,11 @@ class HttpDownloadStrategy <AbstractDownloadStrategy
   def stage
     case `file -b #{@dl}`
       when /^Zip archive data/
-        safe_system 'unzip', '-qq', @dl
+        safe_system '/usr/bin/unzip', '-qq', @dl
         chdir
       when /^(gzip|bzip2) compressed data/
         # TODO do file -z now to see if it is in fact a tar
-        safe_system 'tar', 'xf', @dl
+        safe_system '/usr/bin/tar', 'xf', @dl
         chdir
       else
         # we are assuming it is not an archive, use original filename
@@ -94,7 +94,7 @@ class SubversionDownloadStrategy <AbstractDownloadStrategy
     ohai "Checking out #{@url}"
     @co=HOMEBREW_CACHE+@unique_token
     unless @co.exist?
-      safe_system 'svn', 'checkout', @url, @co
+      safe_system '/usr/bin/svn', 'checkout', @url, @co
     else
       # TODO svn up?
       puts "Repository already checked out"
@@ -102,7 +102,7 @@ class SubversionDownloadStrategy <AbstractDownloadStrategy
   end
   def stage
     # Force the export, since the target directory will already exist
-    safe_system 'svn', 'export', '--force', @co, Dir.pwd
+    safe_system '/usr/bin/svn', 'export', '--force', @co, Dir.pwd
   end
 end
 
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 099f2e6bbe..ed65e54260 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -217,7 +217,7 @@ private
     # I used /tmp rather than mktemp -td because that generates a directory
     # name with exotic characters like + in it, and these break badly written
     # scripts that don't escape strings before trying to regexp them :(
-    tmp=Pathname.new `mktemp -d /tmp/homebrew-#{name}-#{version}-XXXX`.strip
+    tmp=Pathname.new `/usr/bin/mktemp -d /tmp/homebrew-#{name}-#{version}-XXXX`.strip
     raise "Couldn't create build sandbox" if not tmp.directory? or $? != 0
     begin
       wd=Dir.pwd
@@ -311,12 +311,12 @@ private
 
     patch_list.each do |p|
       case p[:compression]
-        when :gzip  then safe_system "gunzip",  p[:filename]+'.gz'
-        when :bzip2 then safe_system "bunzip2", p[:filename]+'.bz2'
+        when :gzip  then safe_system "/usr/bin/gunzip",  p[:filename]+'.gz'
+        when :bzip2 then safe_system "/usr/bin/bunzip2", p[:filename]+'.bz2'
       end
       # -f means it doesn't prompt the user if there are errors, if just
       # exits with non-zero status
-      safe_system 'patch', '-f', *(p[:args])
+      safe_system '/usr/bin/patch', '-f', *(p[:args])
     end
   end
 
diff --git a/Library/Homebrew/unittest.rb b/Library/Homebrew/unittest.rb
index 41ebfb173c..6b24d30953 100755
--- a/Library/Homebrew/unittest.rb
+++ b/Library/Homebrew/unittest.rb
@@ -56,7 +56,7 @@ end
 class TestZip <Formula
   def initialize
     zip=HOMEBREW_CACHE.parent+'test-0.1.zip'
-    Kernel.system 'zip', '-0', zip, ABS__FILE__
+    Kernel.system '/usr/bin/zip', '-0', zip, ABS__FILE__
     @url="file://#{zip}"
     super 'testzip'
   end
diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index 3efeb99a6c..208a01e8ee 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -23,7 +23,7 @@
 
 # args are additional inputs to puts until a nil arg is encountered
 def ohai title, *sput
-  title = title[0, `tput cols`.strip.to_i-4] unless ARGV.verbose?
+  title = title[0, `/usr/bin/tput cols`.strip.to_i-4] unless ARGV.verbose?
   puts "\033[0;34m==>\033[0;0;1m #{title}\033[0;0m"
   puts *sput unless sput.empty?
 end
@@ -59,12 +59,12 @@ end
 # Kernel.system but with exceptions
 def safe_system cmd, *args
   puts "#{cmd} #{args*' '}" if ARGV.verbose?
-  exec_success=Kernel.system cmd, *args
+  exec_success = Kernel.system cmd, *args
   # some tools, eg. tar seem to confuse ruby and it doesn't propogate the
   # CTRL-C interrupt to us too, so execution continues, but the exit code os
   # still 2 so we raise our own interrupt
   raise Interrupt, cmd if $?.termsig == 2
-  unless exec_success and $?.success?
+  unless exec_success
     puts "Exit code: #{$?}"
     raise ExecutionError.new(cmd, args)
   end 
@@ -75,23 +75,23 @@ def curl *args
 end
 
 def puts_columns items, cols = 4
-  items = items.join("\n") if items.is_a?(Array)
-  items.concat("\n") unless items.empty?
   if $stdout.tty?
-    width=`stty size`.chomp.split(" ").last
-    IO.popen("pr -#{cols} -t", "w"){|io| io.write(items) }
+    items = items.join("\n") if items.is_a?(Array)
+    items.concat("\n") unless items.empty?
+    width=`/bin/stty size`.chomp.split(" ").last
+    IO.popen("/usr/bin/pr -#{cols} -t", "w"){|io| io.write(items) }
   else
-    items.each { |i| $stdout.write(i) }
+    puts *items
   end
 end
 
 def exec_editor *args
   editor=ENV['EDITOR']
   if editor.nil?
-    if system "which -s mate" and $?.success?
+    if system "/usr/bin/which -s mate"
       editor='mate'
     else
-      editor='vim'
+      editor='/usr/bin/vim'
     end
   end
   # we split the editor because especially on mac "mate -w" is common
@@ -103,9 +103,9 @@ end
 # provide an absolute path to a command or this function will search the PATH
 def arch_for_command cmd
     archs = []
-    cmd = `which #{cmd}` if not Pathname.new(cmd).absolute?
+    cmd = `/usr/bin/which #{cmd}` if not Pathname.new(cmd).absolute?
 
-    IO.popen("file #{cmd}").readlines.each do |line|
+    IO.popen("/usr/bin/file #{cmd}").readlines.each do |line|
       case line
       when /Mach-O executable ppc/
         archs << :ppc7400
diff --git a/bin/brew b/bin/brew
index 5664ee5a74..465d928c75 100755
--- a/bin/brew
+++ b/bin/brew
@@ -11,20 +11,20 @@ if %w[/ /usr].include? HOMEBREW_PREFIX.to_s then abort <<-EOS
   #{HOMEBREW_WWW}
   EOS
 end
-if `sw_vers -productVersion` =~ /10\.(\d)\.(\d+)/ and $1.to_i < 5
 
 # remove MacPorts and Fink from the PATH, this prevents issues like:
 # http://github.com/mxcl/homebrew/issues/#issue/13
 # http://github.com/mxcl/homebrew/issues/#issue/48
 fix_PATH
 
+if `/usr/bin/sw_vers -productVersion` =~ /10\.(\d)\.(\d+)/ and $1.to_i < 5
   onoe "Homebrew requires Leopard or higher"
   abort "But thanks for your interest anyway!"
 end
 if Hardware.cpu_type == :ppc or Hardware.cpu_type == :dunno
   abort "Sorry, Homebrew does not support your computer's CPU architecture."
 end
-unless system "which -s gcc-4.2" and $?.success?
+unless system "/usr/bin/which -s gcc-4.2"
   abort "Sorry, Homebrew requires gcc 4.2, which is provided by Xcode 3.1"
 end
 
@@ -94,7 +94,7 @@ begin
       end
 
       unless ARGV.force?
-        unless system "which #{ENV['CC'] or 'cc'} &> /dev/null" and $?.success?
+        unless system "/usr/bin/which -s #{ENV.cc}"
           raise "We cannot find a c compiler, have you installed the latest Xcode?"
         end
         formulae = ARGV.formulae.reject do |f|