MKTEMP(1)               NetBSD General Commands Manual               MKTEMP(1)

     mktemp -- make temporary file name (unique)

     mktemp [-dqu] [-p tmpdir] {-t prefix | template ...}

     The mktemp utility takes each of the given file name templates and over-
     writes a portion of it to create a file name.  This file name is unique
     and suitable for use by the application.  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 testing roughly 26 ** 6 combinations.

     If mktemp can successfully generate a unique file name, the file is cre-
     ated with mode 0600 (unless the -u flag is given) and the filename is
     printed to standard output.

     If the -t prefix option is given, mktemp will generate a template string
     based on the prefix and the TMPDIR environment variable, if set.  The
     default location if TMPDIR is not set is /tmp.  The default location of
     the temporary directory can be overridden with the -p tmpdir option.  The
     template string created will consist of the prefix followed by a `.' and
     an eight character unique letter combination.  `Xs' in the prefix string
     will be treated as literal.  If an additional template argument is
     passed, a second file will be created.  Care should be taken to ensure
     that it is appropriate to use an environment variable potentially sup-
     plied by the user.

     Any number of temporary files may be created in a single invocation using
     multiple template arguments, also a single one based on the internal tem-
     plate with the -t option value as filename prefix.

     At least one template argument or the -t option must be present.

     mktemp is provided to allow shell scripts to safely use temporary files.
     Traditionally, many shell scripts take the name of the program with the
     pid as a suffix and use that as a temporary file name.  This kind of nam-
     ing scheme is predictable and the race condition it creates is easy for
     an attacker to win.  A safer, though still inferior, approach is to make
     a temporary directory using the same naming scheme.  While this does
     allow one to guarantee that a temporary file will not be subverted, it
     still allows a simple denial of service attack.  For these reasons it is
     suggested that mktemp be used instead.

     The available options are as follows:

     -d      Make a directory instead of a file.

     -q      Fail silently if an error occurs.  This is useful if a script
             does not want error output to go to standard error.

     -t prefix
             Generate a template (using the supplied prefix and TMPDIR if set)
             to create a filename template.  If -t prefix and template are
             both given, prefix will not apply to template.

     -u      Operate in ``unsafe'' mode.  The temp file will be unlinked
             before mktemp exits.  This is slightly better than mktemp(3) but
             still introduces a race condition.  Use of this option is not

     The mktemp utility exits with a value of 0 on success, and 1 on any fail-

     The following sh(1) fragment illustrates a simple use of mktemp where the
     script should quit if it cannot get a safe temporary file.

           TMPFILE=`mktemp /tmp/${0##*/}.XXXXXX` || exit 1
           echo "program output" >> $TMPFILE

     To allow the use of $TMPDIR:

           TMPFILE=`mktemp -t ${0##*/}` || exit 1
           echo "program output" >> $TMPFILE

     In this case, we want the script to catch the error itself.

           TMPFILE=`mktemp -q /tmp/${0##*/}.XXXXXX`
           if [ $? -ne 0 ]; then
                   echo "$0: Can't create temp file, exiting..."
                   exit 1

     mkdtemp(3), mkstemp(3), mktemp(3), environ(7)

     The mktemp utility appeared in NetBSD 1.5.  It has been imported from
     FreeBSD, the idea and the manual page were taken from OpenBSD.

NetBSD 6.0                      August 15, 2009                     NetBSD 6.0

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