MKTEMP(1) | General Commands Manual | MKTEMP(1) |
mktemp
—
mktemp |
[-dqu ] [-p
tmpdir] {-t
prefix | template ...} |
mktemp
utility is provided to allow shell scripts to
safely use temporary files. It creates temporary files or directories using
unique names, and prints the names.
The name of each temporary file or directory is derived from a
template that includes several trailing
‘X
’ characters, such as
/tmp/prefix.XXXX. The trailing
‘X
’ characters in the template are
replaced by unique values derived from the current process number and
additional letters or numbers. Any ‘X
’
characters other than at the end of the template are taken literally. The
number of unique file names mktemp
can return
depends on the number of trailing ‘Xs
’
in the template; six ‘Xs
’ will result
in mktemp
testing roughly 26 ** 6 combinations.
The templates used to create the unique names are derived from the
-t
prefix option, or the
template arguments, possibly modified by other
options. Any number of temporary files or directories may be created in a
single invocation using multiple template arguments.
It is possible to specify both a -t
prefix option and one or more
template arguments, but this is not usually done.
If neither a -t
prefix option, nor any template
arguments are specified, then the default is equivalent to
-t
mktemp
.
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.
-d
-p
tmpdir-t
prefix option, and those created as a result of a
template argument.
If the -p
tmpdir
option is not specified, then temporary files created as a result of a
-t
prefix option will use
a default temporary directory (as described under the
-t
option), but temporary files created as a
result of a template argument will not use a
default temporary directory (so they will be created relative to the
current working directory, if the template does
not begin with ‘/
’).
-t
prefix.XXXXXXXX
’. Any
‘X
’ characters in the supplied
prefix are taken literally, but the trailing
‘X
’ characters in the appended
‘.XXXXXXXX
’ are replaced by unique
values.
The directory name used for the template generated by the
-t
prefix option is taken
from the -p
tmpdir option,
or from the TMPDIR
environment variable, or
/tmp as a default.
If one or more template arguments are
used in addition to the -t
prefix option, then the
prefix does not apply to the
template arguments.
-q
-u
mktemp
exits. This is slightly better than
mktemp(3) but still
introduces a race condition. Use of this option is not encouraged.mktemp
takes care to create the files or directories in
a way that is safe from race conditions (provided the
-u
option is not used).
Traditionally, without mktemp
, many shell
scripts created temporary files using the name of the program with the pid
as a suffix. This kind of naming scheme is predictable and creates a race
condition that allows an attacker to subvert the program by creating a
different file, directory, or symbolic link under the same name. 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 recommended that
mktemp
be used instead of simpler schemes.
Care should be taken to ensure that it is appropriate to use an environment variable potentially supplied by the user.
mktemp
utility exits with a value of 0 on success,
and 1 on any failure.
mktemp
where the script
should quit if it cannot get a safe temporary file.
TMPFILE=`mktemp /tmp/${0##*/}.XXXXXX` || exit 1 echo "program output" >> $TMPFILE
To allow the use of $TMPDIR:
TMPFILE=`mktemp -t ${0##*/}` || exit 1 echo "program output" >> $TMPFILE
In this case, we want the script to catch the error itself.
TMPFILE=`mktemp -q /tmp/${0##*/}.XXXXXX` if [ $? -ne 0 ]; then echo "$0: Can't create temp file, exiting..." exit 1 fi
mktemp
utility appeared in NetBSD
1.5. It was imported from FreeBSD, and the idea
and the manual page were taken from OpenBSD.
November 4, 2012 | NetBSD 9.4 |