Bash- How to check if file is empty in a loop

Question

I need to check in Bash file is empty,

if it's empty keep tracking him until something is written to it.

In case something was written to it echo it to the screen and stop checking the file content.

for [ -s diff.txt ]; do
echo "file is empty - keep checking it "
done
echo "file is not empty "
cat  diff.txt

Tom Fenech · Accepted Answer · 2017-10-25 09:10:29Z

10

Why not just use a while?

while ! [ -s diff.txt ]; do
    echo "file is empty - keep checking it "
    sleep 1 # throttle the check
done
echo "file is not empty "
cat  diff.txt

The loop will run as long as ! [ -s diff.txt ] is true. If you prefer, you can use until instead of while and remove the negation (!).

answered Oct 25, 2017 at 9:10

Tom Fenech

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1 Comment

Adrian B. Over a year ago

Note : '-s' is for testing if a file is not zero size.

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