OSX section to POSIX, moved to top

novice/teaching/02-shell.md

@@ -55,6 +55,15 @@ as long as learners using Windows do not run into roadblocks such as:
 
 #### Teaching Notes
 
+*  Command line utilities in OS X and Windows terminal emulators do include all the extensions beyond POSIX found in many Linux distributions. Avoid using these extensions, as they may not be available for students.  Some examples:
+
+    *   POSIX `ls` does not have an `--ignore=` or `-I` option
+    *   POSIX `head` takes `-n 10` or `-10`, but not the long form of `--lines=10`
+    *   Many Linux commands allow options to be specified after their arguments (e.g. `ls file1
+    file2 -l`), while most POSIX commands require options to come strictly first (`ls -l file1
+    file2`).
+
+
 *   Have learners open a shell
     and then do `whoami`,
     `pwd`,
@@ -157,15 +166,3 @@ Whatever you use,
 please *test it yourself* on a Windows machine *before* your bootcamp:
 things may always have changed behind your back since your last bootcamp.
 And please also make use of our Windows setup helper.
-
-#### OS X
-
-A number of the pre-installed versions of command line utilities in OS X are old compared
-to those in Linux distributions, or subtly different in their options. Avoid using options
-or constructions that may not work for learners.
-
--   `ls` does not have an `--ignore=` or `-I` option
--   `head` takes `-n 10` or `-10`, but not the long form of `--lines=10`
--   Many Linux commands allow options to be specified after their arguments (e.g. `ls file1
-    file2 -l`), while most OS X commands require options to come strictly first (`ls -l file1
-    file2`). ([Source](http://stackoverflow.com/a/8057405/1757441))