Finding the correct tmp dir on multiple platforms

Question

I have a script that needs to create temporary files for its work, and clean up after itself. My question is about finding the right base directory for the temporary files.

The script needs to work on multiple platforms: Git Bash (Windows), Solaris, Linux, OSX. On each platform, the preferred temp directory is expressed differently:

• Windows: %TMP% (and possibly %TEMP%)
• OSX: $TMPDIR
• Linux, UNIX: supposed to be $TMPDIR but appears to be unset on multiple systems I tried

So in my script I added this boilerplate:

if test -d "$TMPDIR"; then
    :
elif test -d "$TMP"; then
    TMPDIR=$TMP
elif test -d /var/tmp; then
    TMPDIR=/var/tmp
else
    TMPDIR=/tmp
fi

This seems too tedious. Is there a better way?

Answer 1

A slightly more portable way to handle temporary files is to use mktemp. It'll create temporary files and return their paths for you. For instance:

$ mktemp
/tmp/tmp.zVNygt4o7P
$ ls /tmp/tmp.zVNygt4o7P
/tmp/tmp.zVNygt4o7P

You could use it in a script quite easily:

tmpfile=$(mktemp)
echo "Some temp. data..." > $tmpfile
rm $tmpfile

Reading the man page, you should be able to set options according to your needs. For instance:

• -d creates a directory instead of a file.
• -u generates a name, but does not create anything.

Using -u you could retrieve the temporary directory quite easily with...

$ tmpdir=$(dirname $(mktemp -u))

More information about mktemp is available here.

Edit regarding Mac OS X: I have never used a Mac OSX system, but according to a comment by Tyilo below, it seems like Mac OSX's mktemp requires you to provide a template (which is an optional argument on Linux). Quoting:

The template may be any file name with some number of "Xs" appended to it, for example /tmp/temp.XXXX. The trailing "Xs" are replaced with the current process number and/or a unique letter combination. The number of unique file names mktemp can return depends on the number of "Xs" provided; six "Xs" will result in mktemp selecting 1 of 56800235584 (62 ** 6) possible file names.

The man page also says that this implementation is inspired by the OpenBSD man page for mktemp. A similar divergence might therefore be observed by OpenBSD and FreeBSD users as well (see the History section).

Now, as you probably noticed, this requires you to specify a complete file path, including the temporary directory you are looking for in your question. This little problem can be handled using the -t switch. While this option seems to require an argument (prefix), it would appear that mktemp relies on $TMPDIR when necessary.

All in all, you should be able to get the same result as above using...

$ tmpdir=$(dirname $(mktemp tmp.XXXXXXXXXX -ut))

_{Any feedback from Mac OS X users would be greatly appreciated, as I am unable to test this solution myself.}

Answer 2

If you're looking for the same thing in fewer lines...

for TMPDIR in "$TMPDIR" "$TMP" /var/tmp /tmp
do
    test -d "$TMPDIR" && break
done

You could write this in one.

Answer 3

You might do:

: "${TMPDIR:=${TMP:-$(CDPATH=/var:/; cd -P tmp)}}"
cd -- "${TMPDIR:?NO TEMP DIRECTORY FOUND!}" || exit

The shell should either find an executable directory in one of the 4 alternatives or exit with a meaningful error. Still, POSIX defines the $TMPDIR variable (for XCU systems):

TMPDIR This variable shall represent a pathname of a directory made available for programs that need a place to create temporary files.

It also requires the /tmp path.