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

NAME
     mktemp -- make temporary file name (unique)

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

DESCRIPTION
     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 template string cre-
     ated 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 supplied 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.

OPTIONS
     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
             encouraged.

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

EXAMPLES
     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
           fi

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

HISTORY
     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 5.1                     January 12, 2006                     NetBSD 5.1

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