How to capture the output of a top command in a file in linux?

Here is the 1-liner I like to use on my mac:

top -o -pid -l 1 | grep "some regexp"

Cheers.

How about using while loop and -n 1:

while sleep 3; do 
  top -b -n1 | grep init > top-output.txt
done

for me top -b > test.txt will store all output from top ok even if i break it with ctrl-c. I suggest you dump first, and then grep the resulting file.

It looks like the output is not writing to the file until all iterations are finished. You could solve this by wrapping with an external loop like this:

touch top-output.txt
while true; do
    top -b | grep init >> top-output.txt
done