mktemp
MKTEMP(1) 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
selecting 1 of 56800235584 (62 ** 6) possible file names. On case-
insensitive file systems, the effective number of unique names is
significantly less; given six ‘Xs’, mktemp will instead select 1 of
2176782336 (36 ** 6) possible unique file names.
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 _CS_DARWIN_USER_TEMP_DIR configuration variable
if available. Fallback locations if _CS_DARWIN_USER_TEMP_DIR is not
available are TMPDIR and /tmp. Care should be taken to ensure that it is
appropriate to use an environment variable potentially supplied by the
user.
If no arguments are passed or if only the -d flag is passed mktemp behaves
as if -t tmp was supplied.
Any number of temporary files may be created in a single invocation,
including one based on the internal template resulting from the -t flag.
The mktemp 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 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.
-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.
EXIT STATUS
The mktemp utility exits 0 on success, and >0 if an error occurs.
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.
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), confstr(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.
macOS 12.1 December 30, 2005 macOS 12.1