MKTEMP(1) BSD General Commands Manual MKTEMP(1)
NAME
mktemp -- make temporary file name (unique)
SYNOPSIS
mktemp [-d] [-q] [-t prefix] [-u] template ...
mktemp [-d] [-q] [-u] -t prefix
DESCRIPTION
The mktemp 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 `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 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 an template string based on the prefix and the
TMPDIR environment variable if set. The default location if TMPDIR is not set is /tmp. 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, including one based on the inter-nal internal
nal template resulting from the -t flag.
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.
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 tem-plate. template.
plate.
-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.
DIAGNOSTICS
The mktemp utility exits 0 on success, and 1 if an error occurs.
EXAMPLES
The following sh(1) fragment illustrates a simple use of mktemp where the script should quit if it can-not cannot
not get a safe temporary file.
tempfoo=`basename $0`
TMPFILE=`mktemp /tmp/${tempfoo}.XXXXXX` || exit 1
echo "program output" >> $TMPFILE
To allow the use of $TMPDIR:
tempfoo=`basename $0`
TMPFILE=`mktemp -t ${tempfoo}` || exit 1
echo "program output" >> $TMPFILE
In this case, we want the script to catch the error itself.
tempfoo=`basename $0`
TMPFILE=`mktemp -q /tmp/${tempfoo}.XXXXXX`
if [ $? -ne 0 ]; then
echo "$0: Can't create temp file, exiting..."
exit 1
fi
SEE ALSO
mkdtemp(3), mkstemp(3), mktemp(3), environ(7)
HISTORY
A mktemp utility appeared in OpenBSD 2.1. This implementation was written independently based on the
OpenBSD man page, and first appeared in FreeBSD 2.2.7. This man page is taken from OpenBSD
BSD November 20, 1996 BSD
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