Return to mktemp.1 CVS log

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Nuke paragraph about checking for zero length file.  Doing things that
way would allow a race.  Niall Smart <rotel@indigo.ie>

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.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 file name.  This file name is unique
and suitable for use by the application.  The template may be
any file name with some number of
.Ql X Ns s
appended
to it, for example
.Pa /tmp/temp.XXXXXX .
The trailing
.Ql X Ns s
are replaced with the current process number and/or a
unique letter combination.
The number of unique file names
.Nm
can return depends on the number of
.Ql X Ns s
provided; six
.Ql X Ns s
will
result in
.Nm
testing roughly 26 ** 6 combinations.
.Pp
If
.Nm
can successfully generate a unique file name, the file
is created with mode 0600 (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.
.Sh OPTIONS
.Bl -tag -width indent
The available options are as follows:
.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
.Sh RETURN VALUES
The
.Nm
utility
exits with a value of 0 on success, and 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
TMPFILE=`mktemp /tmp/$0.XXXXXX` || exit 1
echo "program output" >> $TMPFILE
.Ed
.Pp
In this case, we want the script to catch the error itself.
.Bd -literal -offset indent
TMPFILE=`mktemp -q /tmp/$0.XXXXXX`
if [ $? -ne 0 ]; then
	echo "$0: Can't create temp file, exiting..."
	exit 1
fi
.Ed
.Sh SEE ALSO
.Xr mktemp 3 ,
.Xr mkdtemp 3 ,
.Xr mkstemp 3
.Sh HISTORY
The
.Nm
utility appeared in
.Ox 2.1 .