If you want an exit code that clearly shows whether or not the script successfully created the two files it is trying to create, a simpler solution would be:

Code:

#!/bin/sh
# Usage: cleanup2 [Directory_Full_Path]
# POSIX compliant (sort of... POSIX does not require that /bin/sh be the
#                             pathname of a conforming shell).
# When using the default '/var/log/' this HAS to be run as root.
# No need to detect root as the error generated by redirection is enough
# and this script can be used by other users when a different directory is
# given as an operand.

# Use given directory path if present, otherwise default to /var/log.
LOG_DIR=${1:-/var/log}

# Clear the required files.
# The exit code will be zero if and only if both files are successfully cleared.
> "${LOG_DIR}/message" > "${LOG_DIR}/wtmp"

Note that the last line could be replaced by:

Code:

> "${LOG_DIR}/message" && > "${LOG_DIR}/wtmp"

or:

Code:

: > "${LOG_DIR}/message" > "${LOG_DIR}/wtmp"

or:

Code:

: > "${LOG_DIR}/message"
: > "${LOG_DIR}/wtmp"

and get exactly the same results. You don't need a null command or a placeholder for a command when the command(s) that is(are) being executed is a(are) redirection(s). Why give the shell extra work to do parsing an extra command that isn't needed to get the job done?

Note also, however, that the two commands:

Code:

: > "${LOG_DIR}/message"
: > "${LOG_DIR}/wtmp"

(and any of the other suggestions above) do not necessarily produce the same results as:

Code:

> "${LOG_DIR}/message"
> "${LOG_DIR}/wtmp"

Since : is a shell special built-in utility, the shell will exit with a non-zero exit code if the first : command fails due to a redirection failure, but the last form will not. So, if the script fails to clear message but successfully clears wtmp the last form above will produce a zero exit status while all of the other suggestions in this post will correctly produce a non-zero exit status indicating that at least one of the files was not cleared.