TMPDIR

TMPDIR is the canonical environment variable in Unix and POSIX that should be used to specify a temporary directory for scratch space. Most Unix programs will honor this setting and use its value to denote the scratch area for temporary files instead of the common default of or.
Other forms sometimes accepted are TEMP, TEMPDIR and TMP, but these alternatives are used more commonly by non-POSIX operating systems or non-conformant programs.
TMPDIR is specified in various Unix and similar standards, e.g. per the Single UNIX Specification.