MKTEMP(1)                 BSD General Commands Manual                MKTEMP(1)

NAME
     mktemp -- make temporary filename (unique)

SYNOPSIS
     mktemp [-V] | [-dqtu] [-p directory] [template]

DESCRIPTION
     The mktemp utility takes the given filename template and
     overwrites a portion of it to create a unique filename.
     The template may be any filename with some number of `Xs'
     appended to it, for example /tmp/tfile.XXXXXXXXXX.  If no
     template is specified a default of tmp.XXXXXXXXXX is used
     and the -t flag is implied (see below).

     The trailing `Xs' are replaced with a combination of the
     current process number and random letters.  The name cho-
     sen depends both on the number of `Xs' in the template and
     the number of collisions with pre-existing files.  The
     number of unique filenames mktemp can return depends on
     the number of `Xs' provided; ten `Xs' will result in
     mktemp testing roughly 26 ** 10 combinations.

     If mktemp can successfully generate a unique filename, the
     file (or directory) is created with file permissions such
     that it is only readable and writable by its owner (unless
     the -u flag is given) and the filename is printed to stan-
     dard output.

     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 filename.  This kind of naming 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 rea-
     sons it is suggested that mktemp be used instead.

     The options are as follows:

     -V      Print the version and exit.

     -d      Make a directory instead of a file.

     -p directory
             Use the specified directory as a prefix when gen-
             erating the temporary filename.  The directory
             will be overridden by the user's TMPDIR environ-
             ment variable if it is set.  This option implies
             the -t flag (see below).

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

     -t      Generate a path rooted in a temporary directory.
             This directory is chosen as follows:

                If the user's TMPDIR environment variable is
                 set, the directory contained therein is used.

                Otherwise, if the -p flag was given the speci-
                 fied directory is used.

                If none of the above apply, /tmp is used.

             In this mode, the template (if specified) should
             be a directory component (as opposed to a full
             path) and thus should not contain any forward
             slashes.

     -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.

     The mktemp utility exits with a value of 0 on success or 1
     on failure.

ENVIRONMENT
     TMPDIR  directory in which to place the temporary file
             when in -t mode

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/example.XXXXXXXXXX` || exit 1
           echo "program output" >> $TMPFILE

     The same fragment with support for a user's TMPDIR envi-
     ronment variable can be written as follows.

           TMPFILE=`mktemp -t example.XXXXXXXXXX` || exit 1
           echo "program output" >> $TMPFILE

     This can be further simplified if we don't care about the
     actual name of the temporary file.  In this case the -t
     flag is implied.

           TMPFILE=`mktemp` || exit 1
           echo "program output" >> $TMPFILE

     In some cases, it may be desirable to use a default tempo-
     rary directory other than /tmp.  In this example the tem-
     porary file will be created in /extra/tmp unless the
     user's TMPDIR environment variable specifies otherwise.

           TMPFILE=`mktemp -p /extra/tmp example.XXXXXXXXXX` || exit 1
           echo "program output" >> $TMPFILE

     In some cases, we want the script to catch the error.  For
     instance, if we attempt to create two temporary files and
     the second one fails we need to remove the first before
     exiting.

           TMP1=`mktemp -t example.1.XXXXXXXXXX` || exit 1
           TMP2=`mktemp -t example.2.XXXXXXXXXX`
           if [ $? -ne 0 ]; then
                   rm -f $TMP1
                   exit 1
           fi

     Or perhaps you don't want to exit if mktemp is unable to
     create the file.  In this case you can protect that part
     of the script thusly.

           TMPFILE=`mktemp -q -t example.XXXXXXXXXX` && {
                   # Safe to use $TMPFILE in this block
                   echo data > $TMPFILE
                   ...
                   rm -f $TMPFILE
           }

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

HISTORY
     The mktemp utility appeared in OpenBSD 2.1.

BSD                           September 30, 2001                           BSD
