You also need to be careful that the tests are portable from one platform

to another.  You're probably working on Linux, where the GNU toolchain has

more (or different) functionality than on MacOS, *BSD, Solaris, AIX, etc.

While testing on all platforms is the only sure-fire way to make sure that

you've written portable code, here's a list of problems that have been

found and fixed in the tests.  Another, more comprehensive list may be

found in the GNU Autoconf manual, online here:

    http://www.gnu.org/software/autoconf/manual/html_node/Portable-Shell.html

sh:

The Bourne shell is a very basic shell.  /bin/sh on Linux is typically

bash, which even in Bourne-shell mode has many features that Bourne shells

on other Unix systems don't have (and even on Linux /bin/sh isn't

guaranteed to be bash).  You'll need to be careful about constructs that

seem ubiquitous, but are actually not available in the least common

denominator.  While using another shell (ksh, bash explicitly, posix shell,

etc.) explicitly may seem like another option, these may not exist in a

portable location, and so are generally probably not a good idea.  You may

find that rewriting the test in python will be easier.

- don't use pushd/popd; save the output of "pwd" and use "cd" in place of

  the pushd, and cd back to the saved pwd instead of popd.

- don't use math expressions like let, (( ... )), or $(( ... )); use "expr"

  instead.

grep:

- don't use the -q option; redirect stdout to /dev/null instead.

- don't use extended regular expressions with grep; use egrep instead, and

  don't escape any regex operators.

sed:

- make sure that the beginning-of-line matcher ("^") is at the very

  beginning of the expression -- it may not be supported inside parens.

echo:

- echo may interpret "\n" and print a newline; use printf instead if you

  want a literal "\n" (backslash + n).

false:

- false is guaranteed only to return a non-zero value; you cannot depend on

  it being 1.  On Solaris in particular, /bin/false returns 255.  Rewrite

  your test to not depend on a particular return value, or create a

  temporary "false" executable, and call that instead.

diff:

- don't use the -N option.  There's no particularly good workaround short

  of writing a reasonably complicated replacement script, but substituting

  gdiff for diff if you can't rewrite the test not to need -N will probably

  do.