usr.bin/mktemp/mktemp.1

.\" $NetBSD: mktemp.1,v 1.19 2009/08/15 20:44:56 wiz Exp $
.\" From: $FreeBSD: src/usr.bin/mktemp/mktemp.1,v 1.5 1999/08/28 01:04:13 peter Exp $
.\" From: $OpenBSD: mktemp.1,v 1.8 1998/03/19 06:13:37 millert Exp $
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.\" $FreeBSD: src/usr.bin/mktemp/mktemp.1,v 1.5 1999/08/28 01:04:13 peter Exp $
.\"
.Dd August 15, 2009
.Dt MKTEMP 1
.Os
.Sh NAME
.Nm mktemp
.Nd make temporary file name (unique)
.Sh SYNOPSIS
.Nm mktemp
.Op Fl dqu
.Op Fl p Ar tmpdir
.Bro
.Fl t Ar prefix
.No |
.Ar template ...
.Brc
.Sh DESCRIPTION
The
.Nm
utility takes each of the given file name templates 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.XXXX .
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
If the
.Fl t Ar prefix
option is given,
.Nm
will generate a template string based on the
.Ar prefix
and the
.Ev TMPDIR
environment variable, if set.
The default location if
.Ev TMPDIR
is not set is
.Pa /tmp .
The default location of the temporary directory can be overridden with the
.Fl p Ar tmpdir
option.
The template string created will consist of the
.Ar prefix
followed by a
.So . Sc
and an eight character unique letter combination.
.Ql X Ns s
in the
.Ar prefix
string will be treated as literal.
If an additional
.Ar template
argument is passed, a second file will be created.
Care should be taken to ensure that it is appropriate to use an
environment variable potentially supplied by the user.
.Pp
Any number of temporary files may be created in a single invocation
using multiple
.Ar template
arguments, also a single one based on the internal template with the
.Fl t
option value as filename prefix.
.Pp
At least one
.Ar template
argument or the
.Fl t
option must be present.
.Pp
.Nm
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
The available options are as follows:
.Bl -tag -width indent
.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 t Ar prefix
Generate a template (using the supplied
.Ar prefix
and
.Ev TMPDIR
if set) to create a filename template.
If
.Fl t Ar prefix
and
.Ar template
are both given,
.Ar prefix
will not apply to
.Ar template .
.It Fl u
Operate in
.Dq unsafe
mode.
The temp file will be unlinked before
.Nm
exits.
This is slightly better than
.Xr mktemp 3
but still introduces a race condition.
Use of this option is not encouraged.
.El
.Sh EXIT STATUS
The
.Nm
utility exits with a value of 0 on success, and 1 on any 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" \*[Gt]\*[Gt] $TMPFILE
.Ed
.Pp
To allow the use of $TMPDIR:
.Bd -literal -offset indent
TMPFILE=`mktemp -t ${0##*/}` || exit 1
echo "program output" \*[Gt]\*[Gt] $TMPFILE
.Ed
.Pp
In this case, we want the script to catch the error itself.
.Bd -literal -offset indent
TMPFILE=`mktemp -q /tmp/${0##*/}.XXXXXX`
if [ $? -ne 0 ]; then
	echo "$0: Can't create temp file, exiting..."
	exit 1
fi
.Ed
.Sh SEE ALSO
.Xr mkdtemp 3 ,
.Xr mkstemp 3 ,
.Xr mktemp 3 ,
.Xr environ 7
.Sh HISTORY
The
.Nm
utility appeared in
.Nx 1.5 .
It has been imported from
.Fx ,
the idea and the manual page were taken from
.Ox .