How to create a temporary file with portable shell in a secure way?

Question

I want to create a temporary file in POSIX shell (/bin/sh).

I found out that mktemp(1) doens\'t exist on my AIX box, and according to How port

Answer 1

You didn't exactly define "secure", but one element of it is probably to clean up after yourself.

trap "rm -f \"$tmpfile\"" 0 1 2 3 15

You can probably man 3 signal to see if there are other signals that should cause your temp file to be erased. Signal zero means "on a clean exit".