Annotation of src/usr.bin/mktemp/mktemp.1, Revision 1.18
1.18 ! aaron 1: .\" $OpenBSD: mktemp.1,v 1.17 2000/06/26 02:43:31 pjanzen Exp $
1.1 millert 2: .\"
1.13 millert 3: .\" Copyright (c) 1996, 2000 Todd C. Miller <Todd.Miller@courtesan.com>
4: .\" All rights reserved.
1.1 millert 5: .\"
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7: .\" modification, are permitted provided that the following conditions
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9: .\" 1. Redistributions of source code must retain the above copyright
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11: .\" 2. Redistributions in binary form must reproduce the above copyright
12: .\" notice, this list of conditions and the following disclaimer in the
13: .\" documentation and/or other materials provided with the distribution.
1.13 millert 14: .\" 3. The name of the author may not be used to endorse or promote products
15: .\" derived from this software without specific prior written permission.
1.1 millert 16: .\"
1.13 millert 17: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
18: .\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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1.1 millert 27: .\"
1.11 aaron 28: .Dd November 20, 1996
1.1 millert 29: .Dt MKTEMP 1
30: .Os
31: .Sh NAME
32: .Nm mktemp
33: .Nd make temporary file name (unique)
34: .Sh SYNOPSIS
35: .Nm mktemp
1.5 millert 36: .Op Fl d
37: .Op Fl q
1.1 millert 38: .Op Fl u
39: .Ar template
40: .Sh DESCRIPTION
41: The
42: .Nm mktemp
43: utility takes the given file name template and overwrites a
1.15 aaron 44: portion of it to create a unique file name.
45: The template may be any file name with some number of
1.1 millert 46: .Ql X Ns s
47: appended
48: to it, for example
1.12 millert 49: .Pa /tmp/temp.XXXXXXXXXX .
1.15 aaron 50: .Pp
1.1 millert 51: The trailing
52: .Ql X Ns s
1.16 aaron 53: are replaced with a combination of the current process number and
1.15 aaron 54: random letters.
55: The name chosen depends both on the number of
1.13 millert 56: .Ql X Ns s
57: in the template and the number of collisions with pre-existing files.
1.1 millert 58: The number of unique file names
59: .Nm
60: can return depends on the number of
61: .Ql X Ns s
1.13 millert 62: provided; ten
1.1 millert 63: .Ql X Ns s
64: will
65: result in
66: .Nm
1.13 millert 67: testing roughly 26 ** 10 combinations.
1.1 millert 68: .Pp
69: If
70: .Nm
1.13 millert 71: can successfully generate a unique file name, the file (or directory)
72: is created with file permissions such that it is only readable and writable
73: by its owner (unless the
1.1 millert 74: .Fl u
1.13 millert 75: flag is given) and the filename is printed to standard output.
1.8 millert 76: .Pp
1.10 aaron 77: .Nm mktemp
1.8 millert 78: is provided to allow shell scripts to safely use temporary files.
79: Traditionally, many shell scripts take the name of the program with
1.15 aaron 80: the PID as a suffix and use that as a temporary file name.
81: This kind of naming scheme is predictable and the race condition it creates
82: is easy for an attacker to win.
83: A safer, though still inferior approach
84: is to make a temporary directory using the same naming scheme.
85: While this does allow one to guarantee that a temporary file will not be
86: subverted, it still allows a simple denial of service attack.
87: For these reasons it is suggested that
1.8 millert 88: .Nm
89: be used instead.
1.14 aaron 90: .Pp
91: The options are as follows:
1.18 ! aaron 92: .Bl -tag -width Ds
1.5 millert 93: .It Fl d
94: Make a directory instead of a file.
95: .It Fl q
1.15 aaron 96: Fail silently if an error occurs.
97: This is useful if
1.5 millert 98: a script does not want error output to go to standard error.
1.1 millert 99: .It Fl u
100: Operate in
101: .Dq unsafe
1.15 aaron 102: mode.
103: The temp file will be unlinked before
1.1 millert 104: .Nm
1.15 aaron 105: exits.
106: This is slightly better than
1.1 millert 107: .Fn mktemp 3
1.15 aaron 108: but still introduces a race condition.
109: Use of this option is not encouraged.
1.6 millert 110: .El
1.15 aaron 111: .Pp
1.1 millert 112: The
113: .Nm
114: utility
1.10 aaron 115: exits with a value of 0 on success or 1 on failure.
1.1 millert 116: .Sh EXAMPLES
117: The following
118: .Xr sh 1
119: fragment illustrates a simple use of
120: .Nm
121: where the script should quit if it cannot get a safe
122: temporary file.
123: .Bd -literal -offset indent
1.17 pjanzen 124: CMD=`basename $0`
125: TMPFILE=`mktemp /tmp/$CMD.XXXXXXXXXX` || exit 1
1.1 millert 126: echo "program output" >> $TMPFILE
127: .Ed
128: .Pp
1.12 millert 129: In this case, we want the script to catch the error ourselves.
1.1 millert 130: .Bd -literal -offset indent
1.17 pjanzen 131: CMD=`basename $0`
132: TMPFILE=`mktemp -q /tmp/$CMD.XXXXXXXXXX`
1.2 millert 133: if [ $? -ne 0 ]; then
1.17 pjanzen 134: echo "$CMD: Can't create temp file, exiting..."
1.1 millert 135: exit 1
136: fi
1.12 millert 137: .Ed
138: .Pp
139: Or perhaps you don't want to exit if
140: .Nm
1.15 aaron 141: is unable to create the file.
142: In this case you can protect the part of the script thusly.
1.12 millert 143: .Bd -literal -offset indent
1.17 pjanzen 144: CMD=`basename $0`
145: TMPFILE=`mktemp /tmp/$CMD.XXXXXXXXXX` && {
1.12 millert 146: # Safe to use $TMPFILE in this block
147: echo data > $TMPFILE
148: ...
149: rm -f $TMPFILE
150: }
1.1 millert 151: .Ed
152: .Sh SEE ALSO
1.8 millert 153: .Xr mkdtemp 3 ,
1.10 aaron 154: .Xr mkstemp 3 ,
155: .Xr mktemp 3
1.1 millert 156: .Sh HISTORY
157: The
158: .Nm
159: utility appeared in
1.7 millert 160: .Ox 2.1 .
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