diff --git a/Coding-Style.md b/Coding-Style.md
index 95dc468..501e358 100644
--- a/Coding-Style.md
+++ b/Coding-Style.md
@@ -25,8 +25,12 @@
 
 * especially with sed you need to be careful as GNU sed is only 80% compatible with BSD sed (`sed -i`,` \n`, `\t`, etc.). 
 
+* be careful with very advanced bash features. Mac OS X is still somewhat behind with bash -- it uses bash version 3
+  ([http://tldp.org/LDP/abs/html/bashver4.html](differences))
+
 * don't use additional binaries 
   * if you really, really need to use an additional one make sure it's available on the system before calling it
+  * don't use highly system depended binaries (rpm, ipconfig, ..) as it is not portable or requires lot's of efforts and ugly code to be portable.
 
 * every operation (string, etc.) which works with bash internall functions: use them whenever possible (replacing tr/sed/awk)