1.\" Copyright (c) 1988, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)tmpnam.3 8.2 (Berkeley) 11/17/93 33.\" 34.Dd August 7, 2020 35.Dt TMPFILE 3 36.Os 37.Sh NAME 38.Nm tempnam , 39.Nm tmpfile , 40.Nm tmpnam 41.Nd temporary file routines 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In stdio.h 46.Ft FILE * 47.Fn tmpfile void 48.Ft char * 49.Fn tmpnam "char *str" 50.Ft char * 51.Fn tempnam "const char *tmpdir" "const char *prefix" 52.Sh DESCRIPTION 53The 54.Fn tmpfile 55function 56returns a pointer to a stream associated with a file descriptor returned 57by the routine 58.Xr mkstemp 3 . 59The created file is unlinked before 60.Fn tmpfile 61returns, causing the file to be automatically deleted when the last 62reference to it is closed. 63The file is opened with the access value 64.Ql w+ . 65The file is created in the directory determined by the environment variable 66.Ev TMPDIR 67if set. 68The default location if 69.Ev TMPDIR 70is not set is 71.Pa /tmp . 72.Pp 73The 74.Fn tmpnam 75function 76returns a pointer to a file name, in the 77.Dv P_tmpdir 78directory, which 79did not reference an existing file at some indeterminate point in the 80past. 81.Dv P_tmpdir 82is defined in the include file 83.In stdio.h . 84If the argument 85.Fa str 86is 87.Pf non- Dv NULL , 88the file name is copied to the buffer it references. 89Otherwise, the file name is copied to a static buffer. 90In either case, 91.Fn tmpnam 92returns a pointer to the file name. 93.Pp 94The buffer referenced by 95.Fa str 96is expected to be at least 97.Dv L_tmpnam 98bytes in length. 99.Dv L_tmpnam 100is defined in the include file 101.In stdio.h . 102.Pp 103The 104.Fn tempnam 105function 106is similar to 107.Fn tmpnam , 108but provides the ability to specify the directory which will 109contain the temporary file and the file name prefix. 110.Pp 111The environment variable 112.Ev TMPDIR 113(if set), the argument 114.Fa tmpdir 115(if 116.Pf non- Dv NULL ) , 117the directory 118.Dv P_tmpdir , 119and the directory 120.Pa /tmp 121are tried, in the listed order, as directories in which to store the 122temporary file. 123.Pp 124The argument 125.Fa prefix , 126if 127.Pf non- Dv NULL , 128is used to specify a file name prefix, which will be the 129first part of the created file name. 130The 131.Fn tempnam 132function 133allocates memory in which to store the file name; the returned pointer 134may be used as a subsequent argument to 135.Xr free 3 . 136.Sh RETURN VALUES 137The 138.Fn tmpfile 139function 140returns a pointer to an open file stream on success, and a 141.Dv NULL 142pointer 143on error. 144.Pp 145The 146.Fn tmpnam 147and 148.Fn tempfile 149functions 150return a pointer to a file name on success, and a 151.Dv NULL 152pointer 153on error. 154.Sh ENVIRONMENT 155.Bl -tag -width Ds 156.It Ev TMPDIR 157.Pf [ Fn tempnam 158and 159.Fn tmpfile 160only] 161If set, 162the directory in which the temporary file is stored. 163.Ev TMPDIR 164is ignored for processes 165for which 166.Xr issetugid 2 167is true. 168.El 169.Sh COMPATIBILITY 170These interfaces are provided from System V and 171.Tn ANSI 172compatibility only. 173.Pp 174Most historic implementations of these functions provide 175only a limited number of possible temporary file names 176(usually 26) 177before file names will start being recycled. 178System V implementations of these functions 179(and of 180.Xr mktemp 3 ) 181use the 182.Xr access 2 183system call to determine whether or not the temporary file 184may be created. 185This has obvious ramifications for setuid or setgid programs, 186complicating the portable use of these interfaces in such programs. 187.Pp 188The 189.Fn tmpfile 190interface should not be used in software expected to be used on other systems 191if there is any possibility that the user does not wish the temporary file to 192be publicly readable and writable. 193.Sh ERRORS 194The 195.Fn tmpfile 196function 197may fail and set the global variable 198.Va errno 199for any of the errors specified for the library functions 200.Xr fdopen 3 201or 202.Xr mkstemp 3 . 203.Pp 204The 205.Fn tmpnam 206function 207may fail and set 208.Va errno 209for any of the errors specified for the library function 210.Xr mktemp 3 . 211.Pp 212The 213.Fn tempnam 214function 215may fail and set 216.Va errno 217for any of the errors specified for the library functions 218.Xr malloc 3 219or 220.Xr mktemp 3 . 221.Sh SEE ALSO 222.Xr mkstemp 3 , 223.Xr mktemp 3 224.Sh STANDARDS 225The 226.Fn tmpfile 227and 228.Fn tmpnam 229functions 230conform to 231.St -isoC . 232.Sh SECURITY CONSIDERATIONS 233The 234.Fn tmpnam 235and 236.Fn tempnam 237functions are susceptible to a race condition 238occurring between the selection of the file name 239and the creation of the file, 240which allows malicious users 241to potentially overwrite arbitrary files in the system, 242depending on the level of privilege of the running program. 243Additionally, there is no means by which 244file permissions may be specified. 245It is strongly suggested that 246.Xr mkstemp 3 247be used in place of these functions. 248