MKTEMP(1) | General Commands Manual | MKTEMP(1) |
mktemp
— make
temporary file name (unique)
mktemp |
[-d ] [-p
tmpdir] [-q ]
[-t prefix]
[-u ] template ... |
mktemp |
[-d ] [-p
tmpdir] [-q ]
[-u ] -t
prefix |
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
, the -p
option's
tmpdir
if set, 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.
The available options are as follows:
-d
,
--directory
-p
tmpdir,
--tmpdir
[=tmpdir]-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 will be used.-q
,
--quiet
-t
prefixTMPDIR
if set) to create a filename template.-u
,
--dry-run
mktemp
exits. This is slightly better than
mktemp(3) but still introduces a race
condition. Use of this option is not encouraged.The mktemp
utility exits 0 on
success, and >0 if an error occurs.
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
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.
August 4, 2022 | macOS 14.6 |