MKTEMP(1) User Commands MKTEMP(1)


NAME


mktemp - make temporary filename

SYNOPSIS


mktemp [-dtqu] [-p directory] [template]


DESCRIPTION


The mktemp utility makes a temporary filename. To do this, mktemp takes
the specified filename template and overwrites a portion of it to create
a unique filename. See OPERANDS.


The template is passed to mkdtemp(3C) for directories or mkstemp(3C) for
ordinary files.


If mktemp can successfully generate a unique filename, the file (or
directory) is created with file permissions such that it is only readable
and writable by its owner (unless the -u flag is given) and the filename
is printed to standard output.


mktemp allows shell scripts to safely use temporary files. Traditionally,
many shell scripts take the name of the program with the PID as a suffix
and used that as a temporary filename. 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 guarantees that a
temporary file is not subverted, it still allows a simple denial of
service attack. Use mktemp instead.

OPTIONS


The following options are supported:

-d
Make a directory instead of a file.


-p directory
Use the specified directory as a prefix when generating
the temporary filename. The directory is overridden by
the user's TMPDIR environment variable if it is set. This
option implies the -t flag.


-q
Fail silently if an error occurs. This is useful if a
script does not want error output to go to standard
error.


-t
Generate a path rooted in a temporary directory. This
directory is chosen as follows: If the user's TMPDIR
environment variable is set, the directory contained
therein is used. Otherwise, if the -p flag was given the
specified directory is used. If none of the above apply,
/tmp is used. In this mode, the template (if specified)
should be a directory component (as opposed to a full
path) and thus should not contain any forward slashes.


-u
Operate in unsafe mode. The temp file is unlinked before
mktemp exits. This is slightly better than mktemp(3C),
but still introduces a race condition. Use of this option
is discouraged.


OPERANDS


The following operands are supported:

template
template can be any filename with one or more Xs appended to
it, for example /tmp/tfile.XXXXXX.

If template is not specified, a default of tmp.XXXXXX is used
and the -t flag is implied.


EXAMPLES


Example 1: Using mktemp




The following example illustrates a simple use of mktemp in a sh(1)
script. In this example, the script quits if it cannot get a safe
temporary file.


TMPFILE=`mktemp /tmp/example.XXXXXX`
if [ -z "$TMPFILE" ]; then exit 1; fi
echo "program output" >> $TMPFILE


Example 2: Using mktemp to Support TMPDIR




The following example uses mktemp to support for a user's TMPDIR
environment variable:


TMPFILE=`mktemp -t example.XXXXXX`
if [ -z "$TMPFILE" ]; then exit 1; fi
echo "program output" >> $TMPFILE


Example 3: Using mktemp Without Specifying the Name of the Temporary File




The following example uses mktemp without specifying the name of the
temporary file. In this case the -t flag is implied.


TMPFILE=`mktemp`
if [ -z "$TMPFILE" ]; then exit 1; fi
echo "program output" >> $TMPFILE


Example 4: Using mktemp with a Default Temporary Directory Other than /tmp




The following example creates the temporary file in /extra/tmp unless the
user's TMPDIR environment variable specifies otherwise:


TMPFILE=`mktemp -p /extra/tmp example.XXXXX`
if [ -z "$TMPFILE" ]; then exit 1; fi
echo "program output" >> $TMPFILE


Example 5: Using mktemp to Remove a File




The following example attempts to create two temporary files. If creation
of the second temporary file fails, mktemp removes the first file before
exiting:


TMP1=`mktemp -t example.1.XXXXXX`
if [ -z "$TMP1" ]; then exit 1; fi
TMP2=`mktemp -t example.2.XXXXXX`
if [ -z "$TMP2" ]; then
rm -f $TMP1
exit 1
fi


Example 6: Using mktemp




The following example does not exit if mktemp is unable to create the
file. That part of the script has been protected.


TMPFILE=`mktemp -q -t example.XXXXXX`
if [ ! -z "$TMPFILE" ]
then
# Safe to use $TMPFILE in this block
echo data > $TMPFILE
...
rm -f $TMPFILE
fi


ENVIRONMENT VARIABLES


See environ(7) for descriptions of the following environment variables
that affect the execution of mktemp with the -t option: TMPDIR.

EXIT STATUS


The following exit values are returned:

0
Successful completion.


1
An error occurred.


ATTRIBUTES


See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Committed |
+--------------------+-----------------+

SEE ALSO


sh(1), mkdtemp(3C), mkstemp(3C), attributes(7), environ(7)

NOTES


The mktemp utility appeared in OpenBSD 2.1. The Solaris implementation
uses only as many `Xs' as are significant for mktemp(3C) and mkstemp(3C).


January 10, 2008 MKTEMP(1)