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.\" $OpenBSD: mktemp.1,v 1.18 2000/11/09 17:52:25 aaron Exp $
.\"
.\" Copyright (c) 1996, 2000 Todd C. Miller <Todd.Miller@courtesan.com>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
.\" AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
.\" THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd November 20, 1996
.Dt MKTEMP 1
.Os
.Sh NAME
.Nm mktemp
.Nd make temporary file name (unique)
.Sh SYNOPSIS
.Nm mktemp
.Op Fl d
.Op Fl q
.Op Fl u
.Ar template
.Sh DESCRIPTION
The
.Nm mktemp
utility takes the given file name template and overwrites a
portion of it to create a unique file name.
The template may be any file name with some number of
.Ql X Ns s
appended
to it, for example
.Pa /tmp/temp.XXXXXXXXXX .
.Pp
The trailing
.Ql X Ns s
are replaced with a combination of the current process number and
random letters.
The name chosen depends both on the number of
.Ql X Ns s
in the template and the number of collisions with pre-existing files.
The number of unique file names
.Nm
can return depends on the number of
.Ql X Ns s
provided; ten
.Ql X Ns s
will
result in
.Nm
testing roughly 26 ** 10 combinations.
.Pp
If
.Nm
can successfully generate a unique file name, the file (or directory)
is created with file permissions such that it is only readable and writable
by its owner (unless the
.Fl u
flag is given) and the filename is printed to standard output.
.Pp
.Nm mktemp
is provided to allow shell scripts to safely use temporary files.
Traditionally, many shell scripts take the name of the program with
the PID as a suffix and use that as a temporary file name.
This kind of naming scheme is predictable and the race condition it creates
is easy for an attacker to win.
A safer, though still inferior approach
is to make a temporary directory using the same naming scheme.
While this does allow one to guarantee that a temporary file will not be
subverted, it still allows a simple denial of service attack.
For these reasons it is suggested that
.Nm
be used instead.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl d
Make a directory instead of a file.
.It Fl q
Fail silently if an error occurs.
This is useful if
a script does not want error output to go to standard error.
.It Fl u
Operate in
.Dq unsafe
mode.
The temp file will be unlinked before
.Nm
exits.
This is slightly better than
.Fn mktemp 3
but still introduces a race condition.
Use of this option is not encouraged.
.El
.Pp
The
.Nm
utility
exits with a value of 0 on success or 1 on failure.
.Sh EXAMPLES
The following
.Xr sh 1
fragment illustrates a simple use of
.Nm
where the script should quit if it cannot get a safe
temporary file.
.Bd -literal -offset indent
CMD=`basename $0`
TMPFILE=`mktemp /tmp/$CMD.XXXXXXXXXX` || exit 1
echo "program output" >> $TMPFILE
.Ed
.Pp
In this case, we want the script to catch the error ourselves.
.Bd -literal -offset indent
CMD=`basename $0`
TMPFILE=`mktemp -q /tmp/$CMD.XXXXXXXXXX`
if [ $? -ne 0 ]; then
echo "$CMD: Can't create temp file, exiting..."
exit 1
fi
.Ed
.Pp
Or perhaps you don't want to exit if
.Nm
is unable to create the file.
In this case you can protect the part of the script thusly.
.Bd -literal -offset indent
CMD=`basename $0`
TMPFILE=`mktemp /tmp/$CMD.XXXXXXXXXX` && {
# Safe to use $TMPFILE in this block
echo data > $TMPFILE
...
rm -f $TMPFILE
}
.Ed
.Sh SEE ALSO
.Xr mkdtemp 3 ,
.Xr mkstemp 3 ,
.Xr mktemp 3
.Sh HISTORY
The
.Nm
utility appeared in
.Ox 2.1 .
|
