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 /tmp or /var/tmp.

Other forms sometimes accepted are,   and  , but these alternatives are used more commonly by non-POSIX operating systems or non-conformant programs.

is specified in various Unix and similar standards, e.g. per the Single UNIX Specification.