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From: $OpenBSD: mktemp.1,v 1.8 1998/03/19 06:13:37 millert Exp $
$FreeBSD: releng/10.2/usr.bin/mktemp/mktemp.1 243240 2012-11-18 16:34:06Z eadler $
.Dd December 30, 2005 .Dt MKTEMP 1 .Os .Sh NAME .Nm mktemp .Nd make temporary file name (unique) .Sh SYNOPSIS .Nm .Op Fl d .Op Fl q .Op Fl t Ar prefix .Op Fl u .Ar template ... .Nm .Op Fl d .Op Fl q .Op Fl u .Fl t Ar prefix .Sh DESCRIPTION The .Nm utility takes each of the given file name templates and overwrites 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 .Ql X Ns s appended to it, for example
a /tmp/temp.XXXX . The trailing .Ql X Ns s are replaced with the current process number and/or a unique letter combination. The number of unique file names .Nm can return depends on the number of .Ql X Ns s provided; six .Ql X Ns s will result in .Nm selecting 1 of 56800235584 (62 ** 6) possible file names.
p If .Nm can successfully generate a unique file name, the file is created with mode 0600 (unless the .Fl u flag is given) and the filename is printed to standard output.
p If the .Fl t Ar prefix option is given, .Nm will generate a template string based on the .Ar prefix and the .Ev TMPDIR environment variable if set. The default location if .Ev TMPDIR is not set is
a /tmp . Care should be taken to ensure that it is appropriate to use an environment variable potentially supplied by the user.
p If no arguments are passed or if only the .Fl d flag is passed .Nm behaves as if .Fl t Li tmp was supplied.
p Any number of temporary files may be created in a single invocation, including one based on the internal template resulting from the .Fl t flag.
p The .Nm utility 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 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 .Nm be used instead. .Sh OPTIONS The available options are as follows: l -tag -width indent t Fl d Make a directory instead of a file. t Fl q Fail silently if an error occurs. This is useful if a script does not want error output to go to standard error. t Fl t Ar prefix Generate a template (using the supplied .Ar prefix and .Ev TMPDIR if set) to create a filename template. t Fl u Operate in .Dq unsafe mode. The temp file will be unlinked before .Nm exits. This is slightly better than .Xr mktemp 3 but still introduces a race condition. Use of this option is not encouraged. .El .Sh EXIT STATUS .Ex -std .Sh EXAMPLES The following .Xr sh 1 fragment illustrates a simple use of .Nm where the script should quit if it cannot get a safe temporary file. d -literal -offset indent tempfoo=`basename $0` TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1 echo "program output" >> $TMPFILE .Ed
p To allow the use of $TMPDIR: d -literal -offset indent tempfoo=`basename $0` TMPFILE=`mktemp -t ${tempfoo}` || exit 1 echo "program output" >> $TMPFILE .Ed
p In this case, we want the script to catch the error itself. d -literal -offset indent tempfoo=`basename $0` TMPFILE=`mktemp -q /tmp/${tempfoo}.XXXXXX` if [ $? -ne 0 ]; then echo "$0: Can't create temp file, exiting..." exit 1 fi .Ed .Sh SEE ALSO .Xr mkdtemp 3 , .Xr mkstemp 3 , .Xr mktemp 3 , .Xr environ 7 .Sh HISTORY A .Nm utility appeared in .Ox 2.1 . This implementation was written independently based on the .Ox man page, and first appeared in .Fx 2.2.7 . This man page is taken from .Ox .