/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 created 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 template string created will consist of the
prefix
followed by a
`.blm Pp.'
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 supplied 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 template 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 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 mktemp be used instead.
TMPDIR
if set) to create a filename template.
If
-t prefix
and
template
are both given,
prefix
will not apply to
template.
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