The default HISTSIZE and HISTFILESIZE have been set for as long as I can remember (and the repo only seems to back to bash 3.2).
For those concerned about privacy or security, 500 lines is probably too much.
For those concerned about disk space, it's hard to come up with a sensible default. My roughly 500,000-command long ~/.bash_history is getting on for 10 years old or so, but only about 12Mb.
I suggest therefore that the default be set to unlimited history (both HISTSIZE and HISTFILESIZE), so that more users benefit out of the box from the amazing powers unleashed by being able to get any command you ever typed.
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