.sh script: check if file exist
#The most readable option when checking whether a file exist or not is to use the
#test command or the old '[' or the new '[[' in combination with the if statement.
#Any of the snippets below will check whether the /etc/resolv.conf file exists:
FILE=/etc/resolv.conf
if test -f "$FILE"; then
echo "$FILE exist"
fi
# or
FILE=/etc/resolv.conf
if [ -f "$FILE" ]; then
echo "$FILE exist"
fi
# or
FILE=/etc/resolv.conf
if [[ -f "$FILE" ]]; then
echo "$FILE exist"
fi