How to limit log file size using >>

If your program doesn't need to write any OTHER files that would be larger than this limit, you can inform the kernel of this limit using ulimit. Before you run your command, run this to setup a 200MB file size limit for all process run in your current shell session:

ulimit -f $((200*1024))

This will protect your system but it might be jaring for the program writing the file. As eyazici suggests, consider setting up logrotate to prune log files once they reach a certain size or age. You can discard old data or archive it for a period of time in a series of compressed files.

If your application (ie. run_program) does not support limiting the size of the log file, then you can check the file size periodically in a loop with an external application or script.

You can also use logrotate(8) to rotate your logs, it has size parameter which you can use for your purpose:

With this, the log file is rotated when the specified size is reached. Size may be specified in bytes (default), kilobytes (sizek), or megabytes (sizem).

You can truncate the output with head:

size=$((200*1024*1024-$(stat -c %s myprogram.log)))
run_program | head -c ${size} >> myprogram.log