Writing portable bourne shell scripts

Many perl people like to go on and on about Bourne shell not being
portable.  However, for some reason, you don't really encounter that in
the python world.  Also, Bourne shell scripts actually are more easy to
write portably than C programs are...

Anyway, here's a list of things to do and/or not do, to come up with
a portable Bourne shell script, followed by a list of features that do
and do not work in various OS's Bourne shells.

For Bourne shell portability:

1) Use [ a = b ] && [ c = d ] instead of [ a = b -a c = d ],
and [ a = b ] || [ c = d] instead of [ a = b -o c = d].
-a and -o give inconsistent operator precedence across platforms.

2) Use echo foo | tr -d '\012' instead of echo -n foo or echo 'foo\c' to
suppress newline.

3) Use a big case statement on $1 and recursively call your script with
"$0" 'behavior', instead of using shell functions (but shell functions
are very common now anyway - the only /bin/sh I ever used that didn't
have them was on Ultrix, which is long gone now).  You can also do this
with symlinks to your program, and case'ing on $0.

4) If you set a variable inside of a loop, don't assume that it'll have
the same value when the loop is exited; Some /bin/sh's implement loops
by spawning subshells.  It's better to write the value to a temporary
file, and read it into a variable after the loop is exited.  Or
alternatively, echo your value to stdout, and then capture the result
with back quotes.  Yes, you can put back quotes around an entire series
of nested for loops or whatever.

5) Use awk to separate a variable on a delimiter instead of cut.  Some systems
have awk but not cut.

Specific features supported and not supported:

Shell functions work:
OSF1-4.0F no
SunOS-5.7 no
RHEL-3 yes
IRIX-6.5.20m yes
AIX-5.1-ML4 yes

Setting a variable within a loop and using the variable after the loop
ends works:
OSF1-4.0F yes
SunOS-5.7 yes
RHEL-3 yes
IRIX-6.5.20m yes
AIX-5.1-ML4 yes