Truncating log from first line

Question

I am making a simple IRC bot in bash and I want prevent its log from growing to infinity. For example it could be shortened always when reaching set number of lines. How can I do that easily? For example by cutting the file with removing first line(s)?

If possible, I would like to avoid sed/awk this time :)

Answer 1

As jordanm said, logrotate is best. But if you do want to roll your own,

tail -n 50 logfile.txt > logfile.new
mv logfile.new logfile.txt

would save only the last 50 lines.