$TMPPREFIX is not an environment variable?

[Agent-E11]

(I am not entirely sure this is the right place to ask this question, but this is the best place I have found so far)
I am trying to access the temporary directory using an environment variable (for compatibility), so, I run echo $TMPPREFIX this prints /tmp/zsh that is good. I then try it in a bash script, and it is undefined. I then (in the shell) type export TMPPREFIX=${TMPPREFIX} and run the bash script again and it works. Why is TMPPREFIX a shell variable and not an environment variable? Is there any way to access it from a bash script? Is there a better way of getting the path to the temporary directory? (Don't know why, but the TMP and TMPDIR environment variables are not defined either)

[ErrrorMaxx]

TMPPREFIX is zsh-specific variable

[Agent-E11]

yes, I know. Is there a way to access it from a script? If not, is there a better way of getting the path to the temporary directory?

[carlosala]

You can both execute the script with zsh (if is POSIX-compliant) or, in case it's bash/sh, you can always execute the script with TMPPREFIX=$TMPPREFIX ./script.sh.