MKTEMP linux command manual

MKTEMP(1)                                                      MKTEMP(1)

       mktemp - make temporary filename (unique)

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

       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 pro-
       cess number and random letters.  The name chosen 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 read-
       able and writable by its owner (unless the -u flag is given)  and  the
       filename is printed to standard 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  reasons  it  is  suggested  that  mktemp be used

       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  generating  the
              temporary  filename.   The  directory will be overridden by the
              user's TMPDIR environment 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  direc-
              tory 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 specified direc-
                     tory is used.

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

       In this mode, the template (if specified) should be a directory compo-
       nent (as opposed to a full path) and thus should not contain any  for-
       ward 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.

       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  environment  vari-
       able 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  temporary  direc-
       tory other than /tmp.  In this example the temporary file will be cre-
       ated in /extra/tmp unless the user's TMPDIR environment variable spec-
       ifies 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

       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 -t example.XXXXXXXXXX' && {
                   # Safe to use $TMPFILE in this block
                   echo data > $TMPFILE
                   rm -f $TMPFILE

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

       mkdtemp(3), mkstemp(3), mktemp(3)

       The mktemp utility appeared in OpenBSD 2.1.

                              30 September 2001                     MKTEMP(1)