mktemp(1) - NetBSD Manual Pages

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


NAME

     mktemp -- make temporary file name (unique)


SYNOPSIS

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


DESCRIPTION

     The mktemp utility is provided to allow shell scripts to safely use tem-
     porary files.  It creates temporary files or directories using unique
     names, and prints the names.

     The name of each temporary file or directory is derived from a template
     that includes several trailing `X' characters, such as /tmp/prefix.XXXX.
     The trailing `X' characters in the template are replaced with a unique
     letter and number combination.  Any `X' characters other than at the end
     of the template are taken literally.  The number of unique file names
     mktemp can return depends on the number of trailing `Xs' in the template;
     six `Xs' will result in mktemp testing roughly 62 ** 6 (56800235584) com-
     binations.

     The templates used to create the unique names are derived from the -t
     prefix option, or the template arguments, possibly modified by other
     options.  Any number of temporary files or directories may be created in
     a single invocation using multiple template arguments.  It is possible to
     specify both a -t prefix option and one or more template arguments, but
     this is not usually done.

     If neither a -t prefix option, nor any template arguments are specified,
     then the default is equivalent to -t mktemp.

     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.


OPTIONS

     The available options are as follows:

     -d      Make a directory instead of a file.

     -p tmpdir
             Specifies a directory in which temporary files should be created.
             If this option is specified, then it applies to all temporary
             files, including those created as a result of a -t prefix option,
             and those created as a result of a template argument.

             If the -p tmpdir option is not specified, then temporary files
             created as a result of a -t prefix option will use a default tem-
             porary directory (as described under the -t option), but tempo-
             rary files created as a result of a template argument will not
             use a default temporary directory (so they will be created rela-
             tive to the current working directory, if the template does not
             begin with `/').

     -t prefix
             Generate a template using an appropriate directory name, followed
             by the supplied prefix, followed by `.XXXXXXXX'.  Any `X' charac-
             ters in the supplied prefix are taken literally, but the trailing
             `X' characters in the appended `.XXXXXXXX' are replaced by unique
             values.

             The directory name used for the template generated by the -t
             prefix option is taken from the -p tmpdir option, or from the
             TMPDIR environment variable, or /tmp as a default.

             If one or more template arguments are used in addition to the -t
             prefix option, then the prefix does not apply to the template
             arguments.

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

     -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.


NOTES

     mktemp takes care to create the files or directories in a way that is
     safe from race conditions (provided the -u option is not used).

     Traditionally, without mktemp, many shell scripts created temporary files
     using the name of the program with the pid as a suffix.  This kind of
     naming scheme is predictable and creates a race condition that allows an
     attacker to subvert the program by creating a different file, directory,
     or symbolic link under the same name.  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 recommended that mktemp be used instead of simpler schemes.

     Care should be taken to ensure that it is appropriate to use an environ-
     ment variable potentially supplied by the user.


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 was imported from FreeBSD,
     and the idea and the manual page were taken from OpenBSD.

NetBSD 10.0                      July 25, 2021                     NetBSD 10.0