1.\" Copyright (c) 1989, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 4. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" From: $OpenBSD: mktemp.1,v 1.8 1998/03/19 06:13:37 millert Exp $ 29.\" $FreeBSD$ 30.\" 31.Dd December 30, 2005 32.Dt MKTEMP 1 33.Os 34.Sh NAME 35.Nm mktemp 36.Nd make temporary file name (unique) 37.Sh SYNOPSIS 38.Nm 39.Op Fl d 40.Op Fl q 41.Op Fl t Ar prefix 42.Op Fl u 43.Ar template ... 44.Nm 45.Op Fl d 46.Op Fl q 47.Op Fl u 48.Fl t Ar prefix 49.Sh DESCRIPTION 50The 51.Nm 52utility takes each of the given file name templates and overwrites a 53portion of it to create a file name. 54This file name is unique 55and suitable for use by the application. 56The template may be 57any file name with some number of 58.Ql X Ns s 59appended 60to it, for example 61.Pa /tmp/temp.XXXX . 62The trailing 63.Ql X Ns s 64are replaced with the current process number and/or a 65unique letter combination. 66The number of unique file names 67.Nm 68can return depends on the number of 69.Ql X Ns s 70provided; six 71.Ql X Ns s 72will 73result in 74.Nm 75selecting 1 of 56800235584 (62 ** 6) possible file names. 76.Pp 77If 78.Nm 79can successfully generate a unique file name, the file 80is created with mode 0600 (unless the 81.Fl u 82flag is given) and the filename is printed 83to standard output. 84.Pp 85If the 86.Fl t Ar prefix 87option is given, 88.Nm 89will generate a template string based on the 90.Ar prefix 91and the 92.Ev TMPDIR 93environment variable if set. 94The default location if 95.Ev TMPDIR 96is not set is 97.Pa /tmp . 98Care should 99be taken to ensure that it is appropriate to use an environment variable 100potentially supplied by the user. 101.Pp 102If no arguments are passed or if only the 103.Fl d 104flag is passed 105.Nm 106behaves as if 107.Fl t Li tmp 108was supplied. 109.Pp 110Any number of temporary files may be created in a single invocation, 111including one based on the internal template resulting from the 112.Fl t 113flag. 114.Pp 115The 116.Nm 117utility is provided to allow shell scripts to safely use temporary files. 118Traditionally, many shell scripts take the name of the program with 119the pid as a suffix and use that as a temporary file name. 120This 121kind of naming scheme is predictable and the race condition it creates 122is easy for an attacker to win. 123A safer, though still inferior, approach 124is to make a temporary directory using the same naming scheme. 125While 126this does allow one to guarantee that a temporary file will not be 127subverted, it still allows a simple denial of service attack. 128For these 129reasons it is suggested that 130.Nm 131be used instead. 132.Sh OPTIONS 133The available options are as follows: 134.Bl -tag -width indent 135.It Fl d 136Make a directory instead of a file. 137.It Fl q 138Fail silently if an error occurs. 139This is useful if 140a script does not want error output to go to standard error. 141.It Fl t Ar prefix 142Generate a template (using the supplied 143.Ar prefix 144and 145.Ev TMPDIR 146if set) to create a filename template. 147.It Fl u 148Operate in 149.Dq unsafe 150mode. 151The temp file will be unlinked before 152.Nm 153exits. 154This is slightly better than 155.Xr mktemp 3 156but still introduces a race condition. 157Use of this 158option is not encouraged. 159.El 160.Sh EXIT STATUS 161.Ex -std 162.Sh EXAMPLES 163The following 164.Xr sh 1 165fragment illustrates a simple use of 166.Nm 167where the script should quit if it cannot get a safe 168temporary file. 169.Bd -literal -offset indent 170tempfoo=`basename $0` 171TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1 172echo "program output" >> $TMPFILE 173.Ed 174.Pp 175To allow the use of $TMPDIR: 176.Bd -literal -offset indent 177tempfoo=`basename $0` 178TMPFILE=`mktemp -t ${tempfoo}` || exit 1 179echo "program output" >> $TMPFILE 180.Ed 181.Pp 182In this case, we want the script to catch the error itself. 183.Bd -literal -offset indent 184tempfoo=`basename $0` 185TMPFILE=`mktemp -q /tmp/${tempfoo}.XXXXXX` 186if [ $? -ne 0 ]; then 187 echo "$0: Can't create temp file, exiting..." 188 exit 1 189fi 190.Ed 191.Sh SEE ALSO 192.Xr mkdtemp 3 , 193.Xr mkstemp 3 , 194.Xr mktemp 3 , 195.Xr environ 7 196.Sh HISTORY 197A 198.Nm 199utility appeared in 200.Ox 2.1 . 201This implementation was written independently based on the 202.Ox 203man page, and 204first appeared in 205.Fx 2.2.7 . 206This man page is taken from 207.Ox . 208