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 102Any number of temporary files may be created in a single invocation, 103including one based on the internal template resulting from the 104.Fl t 105flag. 106.Pp 107The 108.Nm 109utility is provided to allow shell scripts to safely use temporary files. 110Traditionally, many shell scripts take the name of the program with 111the pid as a suffix and use that as a temporary file name. 112This 113kind of naming scheme is predictable and the race condition it creates 114is easy for an attacker to win. 115A safer, though still inferior, approach 116is to make a temporary directory using the same naming scheme. 117While 118this does allow one to guarantee that a temporary file will not be 119subverted, it still allows a simple denial of service attack. 120For these 121reasons it is suggested that 122.Nm 123be used instead. 124.Sh OPTIONS 125The available options are as follows: 126.Bl -tag -width indent 127.It Fl d 128Make a directory instead of a file. 129.It Fl q 130Fail silently if an error occurs. 131This is useful if 132a script does not want error output to go to standard error. 133.It Fl t Ar prefix 134Generate a template (using the supplied 135.Ar prefix 136and 137.Ev TMPDIR 138if set) to create a filename template. 139.It Fl u 140Operate in 141.Dq unsafe 142mode. 143The temp file will be unlinked before 144.Nm 145exits. 146This is slightly better than 147.Xr mktemp 3 148but still introduces a race condition. 149Use of this 150option is not encouraged. 151.El 152.Sh EXIT STATUS 153The 154.Nm 155utility 156exits 0 on success, and 1 if an error occurs. 157.Sh EXAMPLES 158The following 159.Xr sh 1 160fragment illustrates a simple use of 161.Nm 162where the script should quit if it cannot get a safe 163temporary file. 164.Bd -literal -offset indent 165tempfoo=`basename $0` 166TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1 167echo "program output" >> $TMPFILE 168.Ed 169.Pp 170To allow the use of $TMPDIR: 171.Bd -literal -offset indent 172tempfoo=`basename $0` 173TMPFILE=`mktemp -t ${tempfoo}` || exit 1 174echo "program output" >> $TMPFILE 175.Ed 176.Pp 177In this case, we want the script to catch the error itself. 178.Bd -literal -offset indent 179tempfoo=`basename $0` 180TMPFILE=`mktemp -q /tmp/${tempfoo}.XXXXXX` 181if [ $? -ne 0 ]; then 182 echo "$0: Can't create temp file, exiting..." 183 exit 1 184fi 185.Ed 186.Sh SEE ALSO 187.Xr mkdtemp 3 , 188.Xr mkstemp 3 , 189.Xr mktemp 3 , 190.Xr environ 7 191.Sh HISTORY 192A 193.Nm 194utility appeared in 195.Ox 2.1 . 196This implementation was written independently based on the 197.Ox 198man page, and 199first appeared in 200.Fx 2.2.7 . 201This man page is taken from 202.Ox . 203