How to append output to the end of a text file

Question

How do I append the output of a command to the end of a text file?

Answer 1

Use the >> operator to append text to a file.

Answer 2

for the whole question:

cmd >> o.txt && [[ $(wc -l <o.txt) -eq 720 ]] && mv o.txt $(date +%F).o.txt

this will append 720 lines (30*24) into o.txt and after will rename the file based on the current date.

Run the above with the cron every hour, or

while :
do
    cmd >> o.txt && [[ $(wc -l <o.txt) -eq 720 ]] && mv o.txt $(date +%F).o.txt
    sleep 3600
done