usr.bin/mktemp/mktemp.1

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.\" From: $OpenBSD: mktemp.1,v 1.8 1998/03/19 06:13:37 millert Exp $
.\" $FreeBSD$
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.Dd December 30, 2005
.Dt MKTEMP 1
.Os
.Sh NAME
.Nm mktemp
.Nd make temporary file name (unique)
.Sh SYNOPSIS
.Nm
.Op Fl d
.Op Fl q
.Op Fl t Ar prefix
.Op Fl u
.Ar template ...
.Nm
.Op Fl d
.Op Fl q
.Op Fl u
.Fl t Ar prefix
.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
selecting 1 of 56800235584 (62 ** 6) possible file names.
.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 .
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,
including one based on the internal template resulting from the
.Fl t
flag.
.Pp
The
.Nm
utility 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.
.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 0 on success, and 1 if an error occurs.
.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
tempfoo=`basename $0`
TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1
echo "program output" >> $TMPFILE
.Ed
.Pp
To allow the use of $TMPDIR:
.Bd -literal -offset indent
tempfoo=`basename $0`
TMPFILE=`mktemp -t ${tempfoo}` || exit 1
echo "program output" >> $TMPFILE
.Ed
.Pp
In this case, we want the script to catch the error itself.
.Bd -literal -offset indent
tempfoo=`basename $0`
TMPFILE=`mktemp -q /tmp/${tempfoo}.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
A
.Nm
utility appeared in
.Ox 2.1 .
This implementation was written independently based on the
.Ox
man page, and
first appeared in
.Fx 2.2.7 .
This man page is taken from
.Ox .