use Text::Wrap qw( wrap );

local $Text::Wrap::columns = 80;
print wrap('', '', <IN>);
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Text::Wrap

Update: I misunderstood the question and missed the magnitude of the file!

use Text::Wrap qw( wrap );

local $Text::Wrap::columns = 80;
local $Text::Wrap::break   = qr/(?<=,)/;
local $/ = ',';
print wrap('', '', $_) while <IN>;
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Downside: Will break on every comma, even those in the middle of a field.

You can get rid of the Text::Wrap entirely if none of the fields are overly large.