cmd.sh anywhere

git diff cmd.sh

diff --git a/cmd.sh b/cmd.sh
index 0b0f9b6..9f0d8cf 100755
--- a/cmd.sh
+++ b/cmd.sh
@@ -1,8 +1,9 @@
 #!/bin/bash
-cmd=$1
+[[ $# -eq 0 ]] && echo "error: need to specify what command to run" >&2 && exit 1
+cmd="$1"
 shift
 
-topdir=`pwd`
+topdir="$(/usr/bin/python -c "import os,sys; print os.path.dirname(os.path.realpath(sys.argv[1]))" "$0")"
 for lib in nvpair uutil zpool zfs zfs_core; do
 	export DYLD_LIBRARY_PATH=$topdir/lib/lib${lib}/.libs:$DYLD_LIBRARY_PATH
 done
@@ -12,4 +13,4 @@ done
 
 #echo PATH=$PATH
 #echo DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH
-exec ./cmd/$cmd/.libs/$cmd "$@"
+exec "$topdir"/cmd/$cmd/.libs/$cmd "$@"