What happened to the TMP environment variable?

I always heard that the proper way to find the temporary folder on a UNIX machine was to look at the TMP environment variable. When writing code t开发者_Go百科hat worked on Windows as well as Linux, I would check for TEMP and TMP.

Today, I discovered that my Ubuntu install does not have that environment variable at all.

I know it seems you can always count on /tmp being there to put your temporary files in, but I understood that TMP was the way the user could tell you to put the temporary files someplace else.

Is that still the case?

You are probably thinking of TMPDIR.

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

A good way to create a temporary directory is using mktemp, e.g.

mktemp -d -t

This way, you can even make sure, that your file names won't collide with existing files.

POSIX/FHS says that /tmp is the root for temporary files, although some programs may choose to examine $TEMP or $TMP instead.

Similar to what @Chris Lercher said, I find that this works for me:

dirname $(mktemp -u -t tmp.XXXXXXXXXX)

That won't actually create a temp file (because of the -u flag to mktemp) but it'll give you the directory that temp files would be written to. This snippet works on OSX and Ubuntu (probably other *nix too).

If you want to set it into a variable, do something like this:

TMPDIR=`dirname $(mktemp -u -t tmp.XXXXXXXXXX)`

# Let's look at environment variable's
printenv | sort
# search for TMP var
printenv | grep TMP

## [ -d /tmp ] && echo 'is true' 
export TMP='/tmp' # In order to pass variables to a subshell.

Use $TMPDIR , this is the correct var name for Linux. Notice: the /tmp directory contents (files) will be deleted on Shutdown/REBOOT, This should be expected/desired.

FYI - ubuntu (and I assume other systemd based distros) does define the XDG_RUNTIME_DIR variable - which is a per-user temp space, so little more secure than just /tmp :

$ echo $XDG_RUNTIME_DIR

/run/user/1000
$ ls -ld $XDG_RUNTIME_DIR

drwx------ 2 ubuntu ubuntu 40 Dec 22 15:18 /run/user/1000

I think XDG_RUNTIME_DIR is maintained by systemd/pam, so it won't be set in Dockers or other non-systemd environments.

You can do something like this in ~/.bashrc if you like:

export TEMP="${XDG_RUNTIME_DIR:-/tmp}"

See: https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html https://www.freedesktop.org/wiki/

Also - there seems to me some caveats with XDG_RUNTIME_DIR and sudo: https://unix.stackexchange.com/questions/346841/why-does-sudo-i-not-set-xdg-runtime-dir-for-the-target-user