#!/bin/sh
# Usage: cleanup2 [/optional/full/path/to]
# POSIX compliant.
# Due to '/var/log/' this HAS to be run from root.
# No need to detect root as the error generated is enough.

# Attempt to obtain the user path argument.
LOG_DIR="$1"

# Fall back to the default if user path is NOT supplied.
if [ "${LOG_DIR}" = "" ]
then
    LOG_DIR="/var/log"
fi

# *****************************
# Not required but commented out so you can try both meathods.
# cd "${LOG_DIR}"
# Clear require files. ":" is a NULL, NOP or true command.
# : > messages
# : > wtmp
# These eight lines can be deleted.
# *****************************

# Create empty files in the required path.
: > "${LOG_DIR}"/messages
: > "${LOG_DIR}"/wtmp

# Print success and exit script.
echo "Success! Logs cleaned up."
exit

AMIGA:amiga~/Desktop/Code/Shell> chmod 700 cleanup2
AMIGA:amiga~/Desktop/Code/Shell> ls -l /tmp/
total 0
drwx------  4 root   wheel  128 16 Nov 12:34 PKInstallSandbox.MMTz8b
drwx------  3 amiga  wheel   96 30 Jan 18:07 com.apple.launchd.CPHRzeQ4Vr
drwx------  3 amiga  wheel   96 30 Jan 18:07 com.apple.launchd.qgu8OpjEvP
drwxr-xr-x  2 root   wheel   64 30 Jan 18:00 powerlog
AMIGA:amiga~/Desktop/Code/Shell> ./cleanup2 /tmp
Success! Logs cleaned up.
AMIGA:amiga~/Desktop/Code/Shell> echo $?
0
AMIGA:amiga~/Desktop/Code/Shell> ls -l /tmp/
total 0
drwx------  4 root   wheel  128 16 Nov 12:34 PKInstallSandbox.MMTz8b
drwx------  3 amiga  wheel   96 30 Jan 18:07 com.apple.launchd.CPHRzeQ4Vr
drwx------  3 amiga  wheel   96 30 Jan 18:07 com.apple.launchd.qgu8OpjEvP
-rw-r--r--  1 amiga  wheel    0 30 Jan 19:44 messages
drwxr-xr-x  2 root   wheel   64 30 Jan 18:00 powerlog
-rw-r--r--  1 amiga  wheel    0 30 Jan 19:44 wtmp
AMIGA:amiga~/Desktop/Code/Shell> ./cleanup2
./cleanup2: line 25: /var/log/messages: Permission denied
AMIGA:amiga~/Desktop/Code/Shell> echo $?
1
AMIGA:amiga~/Desktop/Code/Shell> _