mktemp/mktemp.1

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  32 .\" From: $OpenBSD: mktemp.1,v 1.8 1998/03/19 06:13:37 millert Exp $
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  35 .Dd November 20, 1996
  36 .Dt MKTEMP 1
  37 .Os
  38 .Sh NAME
  39 .Nm mktemp
  40 .Nd make temporary file name (unique)
  41 .Sh SYNOPSIS
  42 .Nm
  43 .Op Fl d
  44 .Op Fl q
  45 .Op Fl t Ar prefix
  46 .Op Fl u
  47 .Ar template ...
  48 .Nm
  49 .Op Fl d
  50 .Op Fl q
  51 .Op Fl u
  52 .Fl t Ar prefix
  53 .Sh DESCRIPTION
  54 The
  55 .Nm
  56 utility takes each of the given file name templates and overwrites a
  57 portion of it to create a file name.  This file name is unique
  58 and suitable for use by the application.  The template may be
  59 any file name with some number of
  60 .Ql X Ns s
  61 appended
  62 to it, for example
  63 .Pa /tmp/temp.XXXX .
  64 The trailing
  65 .Ql X Ns s
  66 are replaced with the current process number and/or a
  67 unique letter combination.
  68 The number of unique file names
  69 .Nm
  70 can return depends on the number of
  71 .Ql X Ns s
  72 provided; six
  73 .Ql X Ns s
  74 will
  75 result in
  76 .Nm
  77 testing roughly 26 ** 6 combinations.
  78 .Pp
  79 If
  80 .Nm
  81 can successfully generate a unique file name, the file
  82 is created with mode 0600 (unless the
  83 .Fl u
  84 flag is given) and the filename is printed
  85 to standard output.
  86 .Pp
  87 If the
  88 .Fl t Ar prefix
  89 option is given,
  90 .Nm
  91 will generate an template string based on the
  92 .Ar prefix
  93 and the
  94 .Ev TMPDIR
  95 environment variable if set.
  96 The default location if
  97 .Ev TMPDIR
  98 is not set is
  99 .Pa /tmp .
 100 Care should
 101 be taken to ensure that it is appropriate to use an environment variable
 102 potentially supplied by the user.
 103 .Pp
 104 Any number of temporary files may be created in a single invocation,
 105 including one based on the internal template resulting from the
 106 .Fl t
 107 flag.
 108 .Pp
 109 .Nm Mktemp
 110 is provided to allow shell scripts to safely use temporary files.
 111 Traditionally, many shell scripts take the name of the program with
 112 the pid as a suffix and use that as a temporary file name.  This
 113 kind of naming scheme is predictable and the race condition it creates
 114 is easy for an attacker to win.  A safer, though still inferior, approach
 115 is to make a temporary directory using the same naming scheme.  While
 116 this does allow one to guarantee that a temporary file will not be
 117 subverted, it still allows a simple denial of service attack.  For these
 118 reasons it is suggested that
 119 .Nm
 120 be used instead.
 121 .Sh OPTIONS
 122 The available options are as follows:
 123 .Bl -tag -width indent
 124 .It Fl d
 125 Make a directory instead of a file.
 126 .It Fl q
 127 Fail silently if an error occurs.  This is useful if
 128 a script does not want error output to go to standard error.
 129 .It Fl t Ar prefix
 130 Generate a template (using the supplied
 131 .Ar prefix
 132 and
 133 .Ev TMPDIR
 134 if set) to create a filename template.
 135 .It Fl u
 136 Operate in
 137 .Dq unsafe
 138 mode.  The temp file will be unlinked before
 139 .Nm
 140 exits.  This is slightly better than
 141 .Xr mktemp 3
 142 but still introduces a race condition.  Use of this
 143 option is not encouraged.
 144 .El
 145 .Sh DIAGNOSTICS
 146 The
 147 .Nm
 148 utility
 149 exits 0 on success, and 1 if an error occurs.
 150 .Sh EXAMPLES
 151 The following
 152 .Xr sh 1
 153 fragment illustrates a simple use of
 154 .Nm
 155 where the script should quit if it cannot get a safe
 156 temporary file.
 157 .Bd -literal -offset indent
 158 tempfoo=`basename $0`
 159 TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1
 160 echo "program output" >> $TMPFILE
 161 .Ed
 162 .Pp
 163 To allow the use of $TMPDIR:
 164 .Bd -literal -offset indent
 165 tempfoo=`basename $0`
 166 TMPFILE=`mktemp -t ${tempfoo}` || exit 1
 167 echo "program output" >> $TMPFILE
 168 .Ed
 169 .Pp
 170 In this case, we want the script to catch the error itself.
 171 .Bd -literal -offset indent
 172 tempfoo=`basename $0`
 173 TMPFILE=`mktemp -q /tmp/${tempfoo}.XXXXXX`
 174 if [ $? -ne 0 ]; then
 175         echo "$0: Can't create temp file, exiting..."
 176         exit 1
 177 fi
 178 .Ed
 179 .Sh SEE ALSO
 180 .Xr mkdtemp 3 ,
 181 .Xr mkstemp 3 ,
 182 .Xr mktemp 3 ,
 183 .Xr environ 7
 184 .Sh HISTORY
 185 A
 186 .Nm
 187 utility appeared in
 188 .Ox 2.1 .
 189 This implementation was written independently based on the
 190 .Ox
 191 man page, and
 192 first appeared in
 193 .Fx 2.2.7 .
 194 This man page is taken from
 195 .Ox