MKTEMP(1) BSD General Commands Manual MKTEMP(1)NAMEmktemp — make temporary file name (unique)
SYNOPSISmktemp [-dqu] [-p tmpdir] {-t prefix | template ...}
DESCRIPTION
The mktemp utility takes each of the given file name templates and over‐
writes 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 ‘Xs’ appended to it, for example /tmp/temp.XXXX.
The trailing ‘Xs’ are replaced with the current process number and/or a
unique letter combination. The number of unique file names mktemp can
return depends on the number of ‘Xs’ provided; six ‘Xs’ will result in
mktemp testing roughly 26 ** 6 combinations.
If mktemp can successfully generate a unique file name, the file is cre‐
ated with mode 0600 (unless the -u flag is given) and the filename is
printed to standard output.
If the -t prefix option is given, mktemp will generate a template string
based on the prefix and the TMPDIR environment variable, if set. The
default location if TMPDIR is not set is /tmp. The default location of
the temporary directory can be overridden with the -p tmpdir option. The
template string created will consist of the prefix followed by a ‘.’ and
an eight character unique letter combination. ‘Xs’ in the prefix string
will be treated as literal. If an additional 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 sup‐
plied by the user.
Any number of temporary files may be created in a single invocation using
multiple template arguments, also a single one based on the internal tem‐
plate with the -t option value as filename prefix.
At least one template argument or the -t option must be present.
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 nam‐
ing 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 mktemp be used instead.
OPTIONS
The available options are as follows:
-d Make a directory instead of a file.
-q Fail silently if an error occurs. This is useful if a script
does not want error output to go to standard error.
-t prefix
Generate a template (using the supplied prefix and TMPDIR if set)
to create a filename template. If -t prefix and template are
both given, prefix will not apply to template.
-u Operate in “unsafe” mode. The temp file will be unlinked before
mktemp exits. This is slightly better than mktemp(3) but still
introduces a race condition. Use of this option is not encour‐
aged.
EXIT STATUS
The mktemp utility exits with a value of 0 on success, and 1 on any fail‐
ure.
EXAMPLES
The following sh(1) fragment illustrates a simple use of mktemp where the
script should quit if it cannot get a safe temporary file.
TMPFILE=`mktemp /tmp/${0##*/}.XXXXXX` || exit 1
echo "program output" >> $TMPFILE
To allow the use of $TMPDIR:
TMPFILE=`mktemp -t ${0##*/}` || exit 1
echo "program output" >> $TMPFILE
In this case, we want the script to catch the error itself.
TMPFILE=`mktemp -q /tmp/${0##*/}.XXXXXX`
if [ $? -ne 0 ]; then
echo "$0: Can't create temp file, exiting..."
exit 1
fi
SEE ALSOmkdtemp(3), mkstemp(3), mktemp(3), environ(7)HISTORY
The mktemp utility appeared in NetBSD 1.5. It has been imported from
FreeBSD, the idea and the manual page were taken from OpenBSD.
BSD August 15, 2009 BSD
