bash script not doing as a cron, but manually

Question

The script itself is working well, when executed manually. It fails a cron job

function ban_this {
while IFS= read -r line
do
printf $line >> /tmp/test.file
done < <(printf '%s\n' "$a") 
}

a=$(journalctl | grep "client @")
ban_this

Answer 1

function ban_this {
printf %s "$a" |
while IFS= read -r line; do
echo "$line"
done
}