diff --git a/Library/ENV/4.3/xcrun b/Library/ENV/4.3/xcrun
index 7443cec179..128f40ba2a 100755
--- a/Library/ENV/4.3/xcrun
+++ b/Library/ENV/4.3/xcrun
@@ -1,50 +1,57 @@
-#!/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby -W0
-
+#!/bin/sh
 # Historically, xcrun has had various bugs, and in some cases it didn't
 # work at all (e.g. CLT-only in the Xcode 4.3 era). This script emulates
 # it and attempts to avoid these issues.
 
 # Some build tools set DEVELOPER_DIR, so discard it
-ENV.delete "DEVELOPER_DIR"
+unset DEVELOPER_DIR
 
-if ARGV.empty? || ARGV[0][0..0] == "-"
-  exec "/usr/bin/xcrun", *ARGV
-end
+if [ $# -eq 0 ]; then
+  exec /usr/bin/xcrun "$@"
+fi
 
-arg0 = ARGV.shift
+case "$1" in
+  -*) exec /usr/bin/xcrun "$@" ;;
+esac
 
-exe = "/usr/bin/#{arg0}"
-if File.executable?(exe)
-  exec(exe, *ARGV) if ENV["HOMEBREW_PREFER_CLT_PROXIES"]
-  sdkroot = ENV["HOMEBREW_SDKROOT"]
-  exec(exe, *ARGV) unless sdkroot && File.directory?(sdkroot)
-end
+arg0=$1
+shift
 
-$:.unshift "/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8"
-require "pathname"
+exe="/usr/bin/${arg0}"
+if [ -x "$exe" ]; then
+  if [ -n "$HOMEBREW_PREFER_CLT_PROXIES" ]; then
+    exec "$exe" "$@"
+  elif [ -z "$HOMEBREW_SDKROOT" -o ! -d "$HOMEBREW_SDKROOT" ]; then
+    exec "$exe" "$@"
+  fi
+fi
 
-def canonical_dirname path
-  Pathname.new(path).dirname.realpath.to_s
-end
+SUPERBIN=$(cd "${0%/*}" && pwd -P)
 
-SUPERBIN = canonical_dirname(__FILE__)
+exe=$(/usr/bin/xcrun --find "$arg0" 2>/dev/null)
+if [ -x "$exe" -a "${exe%/*}" != "$SUPERBIN" ]; then
+  exec "$exe" "$@"
+fi
 
-exe = `/usr/bin/xcrun --find #{arg0} 2>/dev/null`.chomp
-if File.executable?(exe) && canonical_dirname(exe) != SUPERBIN
-  exec(exe, *ARGV)
-end
+old_IFS=$IFS
+IFS=:
+for path in $PATH; do
+  if [ "$path" = "$SUPERBIN" ]; then
+    continue
+  fi
 
-paths = ENV["PATH"].split(File::PATH_SEPARATOR)
-paths.delete(SUPERBIN)
-paths.each do |path|
-  exe = File.join(path, arg0)
-  exec(exe, *ARGV) if File.executable?(exe)
-end
+  exe="${path}/${arg0}"
+  if [ -x "$exe" ]; then
+    exec "$exe" "$@"
+  fi
+done
+IFS=$old_IFS
 
-abort <<-EOS
-Failed to execute: #{arg0} #{ARGV.join(" ")}
+echo >&2 "
+Failed to execute $arg0 $@
 
 Xcode and/or the CLT appear to be misconfigured. Try one or both of the following:
   xcodebuild -license
   sudo xcode-select -switch /path/to/Xcode.app
-EOS
+"
+exit 1