mktemp(1) - NetBSD Manual Pages

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MKTEMP(1)                   NetBSD Reference Manual                  MKTEMP(1)

mktemp - make temporary file name (unique)
mktemp [-d] [-q] [-t prefix] [-u] [template ...]
The mktemp utility takes each of the given file name templates and over- writes 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 testing roughly 26 ** 6 combinations. If mktemp can successfully generate a unique file name, the file is cre- ated 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 an template string based on the prefix and the TMPDIR environment variable if set. The de- fault location if TMPDIR is not set is /tmp. Care should be taken to en- sure that it is appropriate to use an environment variable potentially supplied by the user. Any number of temporary files may be created in a single invocation, in- cluding one based on the internal template resulting from the -t flag. Mktemp 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 nam- ing 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 al- low 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 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. -t prefix Generate a template (using the supplied prefix and TMPDIR if set) to create a filename template. -u Operate in ``unsafe'' mode. The temp file will be unlinked be- fore mktemp exits. This is slightly better than mktemp(3) but still introduces a race condition. Use of this option is not en- couraged.
The mktemp utility exits with a value of 0 on success, and 1 on any fail- ure.
The following sh(1) fragment illustrates a simple use of 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
mkdtemp(3), mkstemp(3), mktemp(3), environ(7)
The mktemp utility appeared in NetBSD 1.5. It has been imported from FreeBSD, the idea and the manual page were taken from OpenBSD. NetBSD 1.4 November, 20, 1996 2
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