man3/mktemp.3

   1 .\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" References consulted:
   6 .\"     Linux libc source code
   7 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
   8 .\"     386BSD man pages
   9 .\" Modified Sat Jul 24 18:48:06 1993 by Rik Faith (faith@cs.unc.edu)
  10 .\" Modified Fri Jun 23 01:26:34 1995 by Andries Brouwer (aeb@cwi.nl)
  11 .\" (prompted by Scott Burkett <scottb@IntNet.net>)
  12 .\" Modified Sun Mar 28 23:44:38 1999 by Andries Brouwer (aeb@cwi.nl)
  13 .\"
  14 .TH MKTEMP 3  2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
  15 .SH NAME
  16 mktemp \- make a unique temporary filename
  17 .SH LIBRARY
  18 Standard C library
  19 .RI ( libc ", " \-lc )
  20 .SH SYNOPSIS
  21 .nf
  22 .B #include <stdlib.h>
  23 .PP
  24 .BI "char *mktemp(char *" template );
  25 .fi
  26 .PP
  27 .RS -4
  28 Feature Test Macro Requirements for glibc (see
  29 .BR feature_test_macros (7)):
  30 .RE
  31 .PP
  32 .BR mktemp ():
  33 .nf
  34     Since glibc 2.12:
  35         (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200112L)
  36             || /* Glibc since 2.19: */ _DEFAULT_SOURCE
  37             || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
  38     Before glibc 2.12:
  39         _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
  40 .\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  41 .fi
  42 .SH DESCRIPTION
  43 .IR "Never use this function" ;
  44 see BUGS.
  45 .PP
  46 The
  47 .BR mktemp ()
  48 function generates a unique temporary filename
  49 from \fItemplate\fP.
  50 The last six characters of \fItemplate\fP must
  51 be XXXXXX and these are replaced with a string that makes the
  52 filename unique.
  53 Since it will be modified,
  54 .I template
  55 must not be a string constant, but should be declared as a character array.
  56 .SH RETURN VALUE
  57 The
  58 .BR mktemp ()
  59 function always returns \fItemplate\fP.
  60 If a unique name was created, the last six bytes of \fItemplate\fP will
  61 have been modified in such a way that the resulting name is unique
  62 (i.e., does not exist already)
  63 If a unique name could not be created,
  64 \fItemplate\fP is made an empty string, and
  65 .I errno
  66 is set to indicate the error.
  67 .SH ERRORS
  68 .TP
  69 .B EINVAL
  70 The last six characters of \fItemplate\fP were not XXXXXX.
  71 .SH ATTRIBUTES
  72 For an explanation of the terms used in this section, see
  73 .BR attributes (7).
  74 .ad l
  75 .nh
  76 .TS
  77 allbox;
  78 lbx lb lb
  79 l l l.
  80 Interface       Attribute       Value
  81 T{
  82 .BR mktemp ()
  83 T}      Thread safety   MT-Safe
  84 .TE
  85 .hy
  86 .ad
  87 .sp 1
  88 .SH STANDARDS
  89 4.3BSD, POSIX.1-2001.
  90 POSIX.1-2008 removes the specification of
  91 .BR mktemp ().
  92 .\" .SH NOTES
  93 .\" The prototype is in
  94 .\" .I <unistd.h>
  95 .\" for libc4, libc5, glibc1; glibc2 follows the Single UNIX Specification
  96 .\" and has the prototype in
  97 .\" .IR <stdlib.h> .
  98 .SH BUGS
  99 Never use
 100 .BR mktemp ().
 101 Some implementations follow 4.3BSD
 102 and replace XXXXXX by the current process ID and a single letter,
 103 so that at most 26 different names can be returned.
 104 Since on the one hand the names are easy to guess, and on the other
 105 hand there is a race between testing whether the name exists and
 106 opening the file, every use of
 107 .BR mktemp ()
 108 is a security risk.
 109 The race is avoided by
 110 .BR mkstemp (3)
 111 and
 112 .BR mkdtemp (3).
 113 .SH SEE ALSO
 114 .BR mktemp (1),
 115 .BR mkdtemp (3),
 116 .BR mkstemp (3),
 117 .BR tempnam (3),
 118 .BR tmpfile (3),
 119 .BR tmpnam (3)