NetBSD/usr.bin/mktemp/mktemp.1

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.\" $NetBSD: mktemp.1,v 1.15 2006/09/19 14:22:51 hubertf Exp $
.\" From: $FreeBSD: src/usr.bin/mktemp/mktemp.1,v 1.5 1999/08/28 01:04:13 peter Exp $
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.\" 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 January 12, 2006
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.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
.Bro
.Fl t Ar Prefix
.No |
.Ar template ...
.Brc
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.Sh DESCRIPTION
The
.Nm
utility takes each of the given file name templates and overwrites a
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portion of it to create a file name.
This file name is unique
and suitable for use by the application.
The template may be
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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
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will generate a template string based on the
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.Ar prefix
and the
.Ev TMPDIR
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environment variable if set.
The default location if
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.Ev TMPDIR
is not set is
.Pa /tmp .
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.
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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
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.Fl t
option must be present.
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.Pp
.Nm
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is provided to allow shell scripts to safely use temporary files.
Traditionally, many shell scripts take the name of the program with
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the pid as a suffix and use that as a temporary file name.
This
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kind of naming scheme is predictable and the race condition it creates
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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
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this does allow one to guarantee that a temporary file will not be
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subverted, it still allows a simple denial of service attack.
For these
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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
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Fail silently if an error occurs.
This is useful if
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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.
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.It Fl u
Operate in
.Dq unsafe
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mode.
The temp file will be unlinked before
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.Nm
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exits.
This is slightly better than
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.Xr mktemp 3
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but still introduces a race condition.
Use of this
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option is not encouraged.
.El
.Sh EXIT STATUS
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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
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.Ed
.Pp
To allow the use of $TMPDIR:
.Bd -literal -offset indent
TMPFILE=`mktemp -t ${0##*/}` || exit 1
echo "program output" \*[Gt]\*[Gt] $TMPFILE
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.Ed
.Pp
In this case, we want the script to catch the error itself.
.Bd -literal -offset indent
TMPFILE=`mktemp -q /tmp/${0##*/}.XXXXXX`
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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
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.Nm
utility appeared in
.Nx 1.5 .
It has been imported from
.Fx ,
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the idea and the manual page were taken from
.Ox .