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 December 30, 2005
  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.
  58 This file name is unique
  59 and suitable for use by the application.
  60 The template may be
  61 any file name with some number of
  62 .Ql X Ns s
  63 appended
  64 to it, for example
  65 .Pa /tmp/temp.XXXX .
  66 The trailing
  67 .Ql X Ns s
  68 are replaced with the current process number and/or a
  69 unique letter combination.
  70 The number of unique file names
  71 .Nm
  72 can return depends on the number of
  73 .Ql X Ns s
  74 provided; six
  75 .Ql X Ns s
  76 will
  77 result in
  78 .Nm
  79 selecting 1 of 56800235584 (62 ** 6) possible file names.
  80 .Pp
  81 If
  82 .Nm
  83 can successfully generate a unique file name, the file
  84 is created with mode 0600 (unless the
  85 .Fl u
  86 flag is given) and the filename is printed
  87 to standard output.
  88 .Pp
  89 If the
  90 .Fl t Ar prefix
  91 option is given,
  92 .Nm
  93 will generate a template string based on the
  94 .Ar prefix
  95 and the
  96 .Ev TMPDIR
  97 environment variable if set.
  98 The default location if
  99 .Ev TMPDIR
 100 is not set is
 101 .Pa /tmp .
 102 Care should
 103 be taken to ensure that it is appropriate to use an environment variable
 104 potentially supplied by the user.
 105 .Pp
 106 Any number of temporary files may be created in a single invocation,
 107 including one based on the internal template resulting from the
 108 .Fl t
 109 flag.
 110 .Pp
 111 The
 112 .Nm
 113 utility is provided to allow shell scripts to safely use temporary files.
 114 Traditionally, many shell scripts take the name of the program with
 115 the pid as a suffix and use that as a temporary file name.
 116 This
 117 kind of naming scheme is predictable and the race condition it creates
 118 is easy for an attacker to win.
 119 A safer, though still inferior, approach
 120 is to make a temporary directory using the same naming scheme.
 121 While
 122 this does allow one to guarantee that a temporary file will not be
 123 subverted, it still allows a simple denial of service attack.
 124 For these
 125 reasons it is suggested that
 126 .Nm
 127 be used instead.
 128 .Sh OPTIONS
 129 The available options are as follows:
 130 .Bl -tag -width indent
 131 .It Fl d
 132 Make a directory instead of a file.
 133 .It Fl q
 134 Fail silently if an error occurs.
 135 This is useful if
 136 a script does not want error output to go to standard error.
 137 .It Fl t Ar prefix
 138 Generate a template (using the supplied
 139 .Ar prefix
 140 and
 141 .Ev TMPDIR
 142 if set) to create a filename template.
 143 .It Fl u
 144 Operate in
 145 .Dq unsafe
 146 mode.
 147 The temp file will be unlinked before
 148 .Nm
 149 exits.
 150 This is slightly better than
 151 .Xr mktemp 3
 152 but still introduces a race condition.
 153 Use of this
 154 option is not encouraged.
 155 .El
 156 .Sh EXIT STATUS
 157 The
 158 .Nm
 159 utility
 160 exits 0 on success, and 1 if an error occurs.
 161 .Sh EXAMPLES
 162 The following
 163 .Xr sh 1
 164 fragment illustrates a simple use of
 165 .Nm
 166 where the script should quit if it cannot get a safe
 167 temporary file.
 168 .Bd -literal -offset indent
 169 tempfoo=`basename $0`
 170 TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1
 171 echo "program output" >> $TMPFILE
 172 .Ed
 173 .Pp
 174 To allow the use of $TMPDIR:
 175 .Bd -literal -offset indent
 176 tempfoo=`basename $0`
 177 TMPFILE=`mktemp -t ${tempfoo}` || exit 1
 178 echo "program output" >> $TMPFILE
 179 .Ed
 180 .Pp
 181 In this case, we want the script to catch the error itself.
 182 .Bd -literal -offset indent
 183 tempfoo=`basename $0`
 184 TMPFILE=`mktemp -q /tmp/${tempfoo}.XXXXXX`
 185 if [ $? -ne 0 ]; then
 186         echo "$0: Can't create temp file, exiting..."
 187         exit 1
 188 fi
 189 .Ed
 190 .Sh SEE ALSO
 191 .Xr mkdtemp 3 ,
 192 .Xr mkstemp 3 ,
 193 .Xr mktemp 3 ,
 194 .Xr environ 7
 195 .Sh HISTORY
 196 A
 197 .Nm
 198 utility appeared in
 199 .Ox 2.1 .
 200 This implementation was written independently based on the
 201 .Ox
 202 man page, and
 203 first appeared in
 204 .Fx 2.2.7 .
 205 This man page is taken from
 206 .Ox .