

MKTEMP(1)                                               MKTEMP(1)


NNAAMMEE
       mmkktteemmpp - make temporary filename (unique)

SSYYNNOOPPSSIISS
       mmkktteemmpp [--VV] | [--ddqqTTttuu] [--pp _d_i_r_e_c_t_o_r_y] [_t_e_m_p_l_a_t_e]

DDEESSCCRRIIPPTTIIOONN
       The  mmkktteemmpp  utility takes the given filename _t_e_m_p_l_a_t_e and
       overwrites a portion of it to create  a  unique  filename.
       The  _t_e_m_p_l_a_t_e may be any filename with some number of `Xs'
       appended to it, for example _/_t_m_p_/_t_f_i_l_e_._X_X_X_X_X_X_X_X_X_X_.  If  no
       _t_e_m_p_l_a_t_e  is  specified a default of _t_m_p_._X_X_X_X_X_X_X_X_X_X if LFN
       support is available, and _t_p_X_X_X_X_X_X_._X_X_X if LFN  support  is
       not  available  is  used  and  the --t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 _t_e_m_p_l_a_t_e and
       the  number of collisions with pre-existing files.  If LFN
       support is not available, like on plain DOS, the number of
       `Xs'  in  the  _t_e_m_p_l_a_t_e is restricted to 6 in the filename
       and 3 more in the extension.  The number of  unique  file-
       names mmkktteemmpp can return depends on the number of `Xs' pro-
       vided; ten `Xs' will result in mmkktteemmpp testing  roughly  26
       ** 10 combinations.

       If mmkktteemmpp 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u flag is given) and the filename is printed to stan-
       dard output.

       mmkktteemmpp  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 mmkktteemmpp be used instead.

       The options are as follows:

       --VV     Print the version and exit.

       --dd     Make a directory instead of a file.

       --pp _d_i_r_e_c_t_o_r_y
              Use the specified _d_i_r_e_c_t_o_r_y as a prefix when gener-
              ating the temporary filename.  The  _d_i_r_e_c_t_o_r_y  will


                        30 September 2001                       1


MKTEMP(1)                                               MKTEMP(1)


              be  overridden  by  the  user's  TMPDIR environment
              variable if it is set.  If the environment variable
              has  been  set, it will be checked if the directory
              contained therein can be accessed.  If this is  not
              possible then the current working directory will be
              used as prefix when generating the temporary  file-
              name.  This option implies the --tt flag (see below).

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

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

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

              +o      Otherwise,  if  the  --pp  flag  was given the
                     specified directory is used.

              +o      If none of the above apply, _/_t_m_p  (on  MSDOS
                     and clones _._/ ) is used.

       --TT     Generate  a path rooted in a temporary directory on
              MSDOS and clones.  This directory is chosen as fol-
              lows:

              +o      If the user's TMPDIR environment variable is
                     set,  the  directory  contained  therein  is
                     used.  On MSDOS and clones also the environ-
                     ment variables TMP and TEMP will be  checked
                     in that order.

              +o      Otherwise,  if  the  --pp  flag  was given the
                     specified directory is used.

              +o      If none of the above apply, _/_t_m_p  (on  MSDOS
                     and clones _._/ ) is used.

       In  these  modes,  the _t_e_m_p_l_a_t_e (if specified) should be a
       directory component (as opposed to a full path)  and  thus
       should  not  contain  any  forward  slashes.  On MSDOS and
       clones also neither backslashes nor  drive  letter  prefix
       are allowed.

       --uu     Operate  in  "unsafe"  mode.  The temp file will be
              unlinked before mmkktteemmpp  exits.   This  is  slightly
              better  than  mktemp(3) but still introduces a race
              condition.  Use of this option is not encouraged.

       The mmkktteemmpp utility exits with a value of 0 on success or 1
       on failure.


                        30 September 2001                       2


MKTEMP(1)                                               MKTEMP(1)


EENNVVIIRROONNMMEENNTT
       TMPDIR  directory  in  which  to  place the temporary file
               when in --tt mode

       TMPDIR  or

       TMP     and

       TEMP    on MSDOS and clones directory in  which  to  place
               the temporary file when in --TT mode

EEXXAAMMPPLLEESS
       The  following  sh(1) fragment illustrates a simple use of
       mmkktteemmpp 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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 _/_t_m_p_.  In this example the tem-
       porary file will  be  created  in  _/_e_x_t_r_a_/_t_m_p  unless  the
       user's  TMPDIR (or TMP and TEMP on MSDOS and clones) envi-
       ronment 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 mmkktteemmpp is unable to


                        30 September 2001                       3


MKTEMP(1)                                               MKTEMP(1)


       create the file.  In this case you can protect  that  part
       of the script thusly.

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


SSEEEE AALLSSOO
       mmkkddtteemmpp(3), mmkksstteemmpp(3), mmkktteemmpp(3)

HHIISSTTOORRYY
       The mmkktteemmpp utility appeared in OpenBSD 2.1.


                        30 September 2001                       4