File exists and is empty

UNIX for Beginners Q & A UNIX for Dummies Questions & Answers
1

I've got a script with this snippet:

if [ -s $DATA_DIR/file.dat ]
then

I know that the -s indicates that the file exists and is not empty. How can I specify that the file exists, but is empty? I thought I could do:

if [[ -a $DATA_DIR/file.dat && ! -s $DATA_DIR/file.dat ]]
then

But this generates a "else unmatched" error on the else that follows.

2

if [ ! -s $DATA_DIR/file.dat ]
then

3

But wouldn't that test to true if either:
File does not exist OR
File exists but is empty

If so, I don't think that would work for me because I want something different to happen for each of those two scenarios.

If file does not exist, do this
If files exists, but is empty, do this

4 
if [ ! -f file1 ]
then
echo "no such file"
fi

if [ ! -s file1 ]
then
echo "file exists but empty"
fi
5

Aha...when I looked at man ksh for -f, it said:
-f file
TRUE, if file exists and is an ordinary file.

What does "ordinary file" mean?

6

Ordinary = A regular disk file - data, text, executable, etc.