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 portable is mktemp(1)?, it isn't that portable and/or secure anyway.

So, what should I use instead ?

Answer 1

Why not use /dev/random?

It could be neater with perl but od and awk will do, something like:

tempfile=XXX-$(od -N4 -tu /dev/random | awk 'NR==1 {print $2} {}')

Answer 2

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".

Answer 3

Got here from google for portable mktemp. My needs are less secure than OP's, so I ended up just using the script's PID:

tempx=/tmp/mytemp.$$