mktemp/mktemp.1

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  31 .Dd December 30, 2005
  32 .Dt MKTEMP 1
  33 .Os
  34 .Sh NAME
  35 .Nm mktemp
  36 .Nd make temporary file name (unique)
  37 .Sh SYNOPSIS
  38 .Nm
  39 .Op Fl d
  40 .Op Fl q
  41 .Op Fl t Ar prefix
  42 .Op Fl u
  43 .Ar template ...
  44 .Nm
  45 .Op Fl d
  46 .Op Fl q
  47 .Op Fl u
  48 .Fl t Ar prefix
  49 .Sh DESCRIPTION
  50 The
  51 .Nm
  52 utility takes each of the given file name templates and overwrites a
  53 portion of it to create a file name.
  54 This file name is unique
  55 and suitable for use by the application.
  56 The template may be
  57 any file name with some number of
  58 .Ql X Ns s
  59 appended
  60 to it, for example
  61 .Pa /tmp/temp.XXXX .
  62 The trailing
  63 .Ql X Ns s
  64 are replaced with the current process number and/or a
  65 unique letter combination.
  66 The number of unique file names
  67 .Nm
  68 can return depends on the number of
  69 .Ql X Ns s
  70 provided; six
  71 .Ql X Ns s
  72 will
  73 result in
  74 .Nm
  75 selecting 1 of 56800235584 (62 ** 6) possible file names.
  76 On case-insensitive file systems, the effective number of unique
  77 names is significantly less; given six
  78 .Ql X Ns s ,
  79 .Nm
  80 will instead select 1 of 2176782336 (36 ** 6) possible unique file names.
  81 .Pp
  82 If
  83 .Nm
  84 can successfully generate a unique file name, the file
  85 is created with mode 0600 (unless the
  86 .Fl u
  87 flag is given) and the filename is printed
  88 to standard output.
  89 .Pp
  90 If the
  91 .Fl t Ar prefix
  92 option is given,
  93 .Nm
  94 will generate a template string based on the
  95 .Ar prefix
  96 and the
  97 .Dv _CS_DARWIN_USER_TEMP_DIR
  98 configuration variable if available.
  99 Fallback locations if
 100 .Dv _CS_DARWIN_USER_TEMP_DIR
 101 is not available are
 102 .Ev TMPDIR
 103 and
 104 .Pa /tmp .
 105 Care should
 106 be taken to ensure that it is appropriate to use an environment variable
 107 potentially supplied by the user.
 108 .Pp
 109 If no arguments are passed or if only the
 110 .Fl d
 111 flag is passed
 112 .Nm
 113 behaves as if
 114 .Fl t Li tmp
 115 was supplied.
 116 .Pp
 117 Any number of temporary files may be created in a single invocation,
 118 including one based on the internal template resulting from the
 119 .Fl t
 120 flag.
 121 .Pp
 122 The
 123 .Nm
 124 utility is provided to allow shell scripts to safely use temporary files.
 125 Traditionally, many shell scripts take the name of the program with
 126 the pid as a suffix and use that as a temporary file name.
 127 This
 128 kind of naming scheme is predictable and the race condition it creates
 129 is easy for an attacker to win.
 130 A safer, though still inferior, approach
 131 is to make a temporary directory using the same naming scheme.
 132 While
 133 this does allow one to guarantee that a temporary file will not be
 134 subverted, it still allows a simple denial of service attack.
 135 For these
 136 reasons it is suggested that
 137 .Nm
 138 be used instead.
 139 .Sh OPTIONS
 140 The available options are as follows:
 141 .Bl -tag -width indent
 142 .It Fl d
 143 Make a directory instead of a file.
 144 .It Fl q
 145 Fail silently if an error occurs.
 146 This is useful if
 147 a script does not want error output to go to standard error.
 148 .It Fl t Ar prefix
 149 Generate a template (using the supplied
 150 .Ar prefix
 151 and
 152 .Ev TMPDIR
 153 if set) to create a filename template.
 154 .It Fl u
 155 Operate in
 156 .Dq unsafe
 157 mode.
 158 The temp file will be unlinked before
 159 .Nm
 160 exits.
 161 This is slightly better than
 162 .Xr mktemp 3
 163 but still introduces a race condition.
 164 Use of this
 165 option is not encouraged.
 166 .El
 167 .Sh EXIT STATUS
 168 .Ex -std
 169 .Sh EXAMPLES
 170 The following
 171 .Xr sh 1
 172 fragment illustrates a simple use of
 173 .Nm
 174 where the script should quit if it cannot get a safe
 175 temporary file.
 176 .Bd -literal -offset indent
 177 tempfoo=`basename $0`
 178 TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1
 179 echo "program output" >> $TMPFILE
 180 .Ed
 181 .Pp
 182 To allow the use of $TMPDIR:
 183 .Bd -literal -offset indent
 184 tempfoo=`basename $0`
 185 TMPFILE=`mktemp -t ${tempfoo}` || exit 1
 186 echo "program output" >> $TMPFILE
 187 .Ed
 188 .Pp
 189 In this case, we want the script to catch the error itself.
 190 .Bd -literal -offset indent
 191 tempfoo=`basename $0`
 192 TMPFILE=`mktemp -q /tmp/${tempfoo}.XXXXXX`
 193 if [ $? -ne 0 ]; then
 194         echo "$0: Can't create temp file, exiting..."
 195         exit 1
 196 fi
 197 .Ed
 198 .Sh SEE ALSO
 199 .Xr mkdtemp 3 ,
 200 .Xr mkstemp 3 ,
 201 .Xr mktemp 3 ,
 202 .Xr confstr 3 ,
 203 .Xr environ 7
 204 .Sh HISTORY
 205 A
 206 .Nm
 207 utility appeared in
 208 .Ox 2.1 .
 209 This implementation was written independently based on the
 210 .Ox
 211 man page, and
 212 first appeared in
 213 .Fx 2.2.7 .
 214 This man page is taken from
 215 .Ox .