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DESCRIPTION

The trailing ‘Xs’ are replaced with a unique digit and letter combination. The name chosen depends both on the number of ‘Xs’ in the template and the number of collisions with pre-existing files. The number of unique filenames mktemp can return depends on the number of ‘Xs’ provided; ten ‘Xs’ will result in mktemp testing roughly 26 ** 10 combinations.

If mktemp can successfully generate a unique filename, the file (or directory) is created with file permissions such that it is only readable and writable by its owner (unless the -u flag is given) and the filename is printed to standard output.

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 filename. 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.

The options are as follows:

-d

Make a directory instead of a file.

-p directory

Use the specified directory as a prefix when generating the temporary filename. The directory will be overridden by the user's TMPDIR environment variable if it is set. This option implies the -t flag (see below).

-q

Fail silently if an error occurs. This is useful if a script does not want error output to go to standard error.

-t

Generate a path rooted in a temporary directory. This directory is chosen as follows:

• If the user's TMPDIR environment variable is set, the directory contained therein is used.
• Otherwise, if the -p flag was given the specified directory is used.
• If none of the above apply, /tmp is used.

In this mode, the template (if specified) should be a directory component (as opposed to a full path) and thus should not contain any forward slashes.

-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 encouraged.

TMPFILE=`mktemp /tmp/example.XXXXXXXXXX` || exit 1
echo "program output" >> $TMPFILE

TMPFILE=`mktemp -t example.XXXXXXXXXX` || exit 1
echo "program output" >> $TMPFILE

TMPFILE=`mktemp` || exit 1
echo "program output" >> $TMPFILE

TMPFILE=`mktemp -p /extra/tmp example.XXXXXXXXXX` || exit 1
echo "program output" >> $TMPFILE

TMP1=`mktemp -t example.1.XXXXXXXXXX` || exit 1
TMP2=`mktemp -t example.2.XXXXXXXXXX`
if [ $? -ne 0 ]; then
	rm -f $TMP1
	exit 1
fi

TMPFILE=`mktemp -q -t example.XXXXXXXXXX` && {
	# Safe to use $TMPFILE in this block
	echo data > $TMPFILE
	...
	rm -f $TMPFILE
}