If opening a file to write to it destroys an existing file by that name
you might be wondering how log files work. After all they just grow as new
events occur and are added to the log of events that have already occurred.
The answer is that there is one more mode, a for append
which allows you to open a file to append things to it, i.e. the existing
file data is not destroyed, and the insertion point is placed at the end of
the file so further writes add to the existing file content.