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.Dd August 7, 2020 33.Dt TMPFILE 3 34.Os 35.Sh NAME 36.Nm tempnam , 37.Nm tmpfile , 38.Nm tmpnam 39.Nd temporary file routines 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In stdio.h 44.Ft FILE * 45.Fn tmpfile void 46.Ft char * 47.Fn tmpnam "char *str" 48.Ft char * 49.Fn tempnam "const char *tmpdir" "const char *prefix" 50.Sh DESCRIPTION 51The 52.Fn tmpfile 53function 54returns a pointer to a stream associated with a file descriptor returned 55by the routine 56.Xr mkstemp 3 . 57The created file is unlinked before 58.Fn tmpfile 59returns, causing the file to be automatically deleted when the last 60reference to it is closed. 61The file is opened with the access value 62.Ql w+ . 63The file is created in the directory determined by the environment variable 64.Ev TMPDIR 65if set. 66The default location if 67.Ev TMPDIR 68is not set is 69.Pa /tmp . 70.Pp 71The 72.Fn tmpnam 73function 74returns a pointer to a file name, in the 75.Dv P_tmpdir 76directory, which 77did not reference an existing file at some indeterminate point in the 78past. 79.Dv P_tmpdir 80is defined in the include file 81.In stdio.h . 82If the argument 83.Fa str 84is 85.Pf non- Dv NULL , 86the file name is copied to the buffer it references. 87Otherwise, the file name is copied to a static buffer. 88In either case, 89.Fn tmpnam 90returns a pointer to the file name. 91.Pp 92The buffer referenced by 93.Fa str 94is expected to be at least 95.Dv L_tmpnam 96bytes in length. 97.Dv L_tmpnam 98is defined in the include file 99.In stdio.h . 100.Pp 101The 102.Fn tempnam 103function 104is similar to 105.Fn tmpnam , 106but provides the ability to specify the directory which will 107contain the temporary file and the file name prefix. 108.Pp 109The environment variable 110.Ev TMPDIR 111(if set), the argument 112.Fa tmpdir 113(if 114.Pf non- Dv NULL ) , 115the directory 116.Dv P_tmpdir , 117and the directory 118.Pa /tmp 119are tried, in the listed order, as directories in which to store the 120temporary file. 121.Pp 122The argument 123.Fa prefix , 124if 125.Pf non- Dv NULL , 126is used to specify a file name prefix, which will be the 127first part of the created file name. 128The 129.Fn tempnam 130function 131allocates memory in which to store the file name; the returned pointer 132may be used as a subsequent argument to 133.Xr free 3 . 134.Sh RETURN VALUES 135The 136.Fn tmpfile 137function 138returns a pointer to an open file stream on success, and a 139.Dv NULL 140pointer 141on error. 142.Pp 143The 144.Fn tmpnam 145and 146.Fn tempfile 147functions 148return a pointer to a file name on success, and a 149.Dv NULL 150pointer 151on error. 152.Sh ENVIRONMENT 153.Bl -tag -width Ds 154.It Ev TMPDIR 155.Pf [ Fn tempnam 156and 157.Fn tmpfile 158only] 159If set, 160the directory in which the temporary file is stored. 161.Ev TMPDIR 162is ignored for processes 163for which 164.Xr issetugid 2 165is true. 166.El 167.Sh COMPATIBILITY 168These interfaces are provided from System V and 169.Tn ANSI 170compatibility only. 171.Pp 172Most historic implementations of these functions provide 173only a limited number of possible temporary file names 174(usually 26) 175before file names will start being recycled. 176System V implementations of these functions 177(and of 178.Xr mktemp 3 ) 179use the 180.Xr access 2 181system call to determine whether or not the temporary file 182may be created. 183This has obvious ramifications for setuid or setgid programs, 184complicating the portable use of these interfaces in such programs. 185.Pp 186The 187.Fn tmpfile 188interface should not be used in software expected to be used on other systems 189if there is any possibility that the user does not wish the temporary file to 190be publicly readable and writable. 191.Sh ERRORS 192The 193.Fn tmpfile 194function 195may fail and set the global variable 196.Va errno 197for any of the errors specified for the library functions 198.Xr fdopen 3 199or 200.Xr mkstemp 3 . 201.Pp 202The 203.Fn tmpnam 204function 205may fail and set 206.Va errno 207for any of the errors specified for the library function 208.Xr mktemp 3 . 209.Pp 210The 211.Fn tempnam 212function 213may fail and set 214.Va errno 215for any of the errors specified for the library functions 216.Xr malloc 3 217or 218.Xr mktemp 3 . 219.Sh SEE ALSO 220.Xr mkstemp 3 , 221.Xr mktemp 3 222.Sh STANDARDS 223The 224.Fn tmpfile 225and 226.Fn tmpnam 227functions 228conform to 229.St -isoC . 230.Sh SECURITY CONSIDERATIONS 231The 232.Fn tmpnam 233and 234.Fn tempnam 235functions are susceptible to a race condition 236occurring between the selection of the file name 237and the creation of the file, 238which allows malicious users 239to potentially overwrite arbitrary files in the system, 240depending on the level of privilege of the running program. 241Additionally, there is no means by which 242file permissions may be specified. 243It is strongly suggested that 244.Xr mkstemp 3 245be used in place of these functions. 246