Add some tips on shell scripts

README.coding_style

@@ -143,10 +143,30 @@ The old file will be copied to 'moonmelter.c.orig' as a back up.
       /* NOP unless x is true. */
       while (!x);
 
+3.1 Shell scripts
+
+Shell scripts should be written for POSIX portability as much as possible.
+Avoid using '/bin/bash' in the shebang line.  Use '/bin/sh' instead to allow
+for use of the system shell (some systems may not have Bash installed at all!)
+when the script is run.  The caveat is that some favorite Bash extensions are
+not POSIX portable so care is needed.  To help avoid the pitfalls, various
+tools exist such as 'checkbashisms' which will report syntax that is not
+portable.
+
+* Use four space indents as with the C style above.
+
+* Vertical space around conditional blocks can aid readability (newlines are
+  cheap!).
+
+* Try to keep line length between 80 and 100 characters if possible.
+  Backslashes (\) can sometimes be used to break up long lines.  Be careful as
+  the shell is often less forgiving than the C compiler with extra spaces.
+  Experiment.
+
 * Avoid the use of backticks (`) to invoke a subshell, also known as the grave
-  accent, in shell scripts, configure.ac, any Makefile.am, or .m4 files we
-  maintain.  While their use will likely be long supported, they do require
-  some care in use and can be difficult to read on the screen.
+  accent and backquote, in shell scripts, configure.ac, any Makefile.am, or
+  .m4 files we maintain.  While their use will likely be long supported, they
+  do require some care in use and can be difficult to read on the screen.
 
   The preferred construct is to use parentheses to invoke a subshell and the
   '$()' construct when the output of the command is intended to be captured in
@@ -167,6 +187,21 @@ The old file will be copied to 'moonmelter.c.orig' as a back up.
   don't usually maintain these files except to update them as needed, these
   rules are waived for those files.
 
+3.2 Python
+
+Python authors are already well aware of the classic PEP8 and need no further
+instruction on the matter.
+
+3.3 Perl
+
+Perl authors already know their code can resemble modem line noise and it will
+work flawlessly.  Somehow.
+
+3.4 Makefile
+
+When indenting a line in a Makefile.am (and the resulting Makefile) that a
+real Tab character (0x09) is required.  Spaces will cause 'make' errors.
+
 
 4. Use of code formatting tools