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MKTEMP(1) FreeBSD General Commands Manual MKTEMP(1)
NAME
mktemp - make temporary file name (unique)
SYNOPSIS
mktemp [-d] [-p tmpdir] [-q] [-t prefix] [-u] template ...
mktemp [-d] [-p tmpdir] [-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.
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. If the
-p option is set, then the given tmpdir will be used if the TMPDIR
environment variable is not set. Finally, /tmp will be used if neither
TMPDIR or -p are set and used. 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, --directory
Make a directory instead of a file.
-p tmpdir, --tmpdir[=tmpdir]
Use tmpdir for the -t flag if the TMPDIR environment variable is
not set. Additionally, any provided template arguments will be
interpreted relative to the path specified as tmpdir. If tmpdir
is either empty or omitted, then the TMPDIR environment variable
Generate a template (using the supplied prefix and TMPDIR if set)
to create a filename template.
-u, --dry-run
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), 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.
FreeBSD 14.0-RELEASE-p11 August 4, 2022 FreeBSD 14.0-RELEASE-p11