Bash, If file is empty leave script if not continue

Question

the first command in my bash script is a grep from an existing file for errors. EX:

cat /usr/local/avamar/var/ddrmaintlogs/ddrmaint.log | grep "hfscheck-finish Backup directory missing for backup" > PartialBackups
cat PartialBackups | sed -n -e 's#^.*cur/ ##p' >P2                                          
cat P2 | sed 's#/# / /#g' > P3                                                              
cat P3 | awk {'print $1'} >> S1                                                              
cat P3 | awk {'print $3'} >> S2

if newfile is empty (PartialBackups File) i want to exit the script, if not i want the script to continue

how can i do that?

Answer 1

Put the grep in an if statement.

if ! grep -err /file >> newfile; then
    exit
fi

newfile may or may not be empty--you are appending to a possibly non-empty file to begin with--but grep will have a non-zero exit status if it doesn't add anything to the file.

Answer 2

You can use

if ! [ -s "/file" ];then
    exit
fi

or shorter with less obvious syntax

test -s "/file" && exit

test -s tests if a file exists and has non-zero size. The second syntax is exploiting, that binary operators only evaluate as much as needed, so a positive return value from test prevents exit from running, as the expression would be false anyway.