MKTEMP(1) | General Commands Manual | MKTEMP(1) |
mktemp | [-dqu] [-p tmpdir] {-t prefix | template ...} |
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.
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 ‘/
’).
.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.
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 schem 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 should 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.
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
November 4, 2012 | NetBSD 6.99 |