NAME
mktemp —
make temporary file name
(unique)
SYNOPSIS
mktemp |
[-d] [-q]
[-t prefix]
[-u] template ... |
mktemp |
[-d] [-q]
[-u] -t
prefix |
DESCRIPTION
Themktemp 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. 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.
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.
-tprefix- Generate a template (using the supplied prefix and
TMPDIRif set) to create a filename template. -u- Operate in “unsafe” mode. The temp file will be unlinked
before
mktempexits. 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
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.