usr.bin/mktemp/mktemp.1

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.\" From: $OpenBSD: mktemp.1,v 1.8 1998/03/19 06:13:37 millert Exp $
.\"
.Dd August 4, 2022
.Dt MKTEMP 1
.Os
.Sh NAME
.Nm mktemp
.Nd make temporary file name (unique)
.Sh SYNOPSIS
.Nm
.Op Fl d
.Op Fl p Ar tmpdir
.Op Fl q
.Op Fl t Ar prefix
.Op Fl u
.Ar template ...
.Nm
.Op Fl d
.Op Fl p Ar tmpdir
.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.
If the
.Fl p
option is set, then the given
.Ar tmpdir
will be used if the
.Ev TMPDIR
environment variable is not set.
Finally,
.Pa /tmp
will be used if neither
.Ev TMPDIR
or
.Fl p
are set and used.
Care should
be taken to ensure that it is appropriate to use an environment variable
potentially supplied by the user.
.Pp
If no arguments are passed or if only the
.Fl d
flag is passed
.Nm
behaves as if
.Fl t Li tmp
was supplied.
.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 , Fl -directory
Make a directory instead of a file.
.It Fl p Ar tmpdir , Fl -tmpdir Ns Oo = Ns Ar tmpdir Oc
Use
.Ar tmpdir
for the
.Fl t
flag if the
.Ev TMPDIR
environment variable is not set.
Additionally, any provided
.Ar template
arguments will be interpreted relative to the path specified as
.Ar tmpdir .
If
.Ar tmpdir
is either empty or omitted, then the
.Ev TMPDIR
environment variable will be used.
.It Fl q , Fl -quiet
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 , Fl -dry-run
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
.Ex -std
.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 .