You may be looking for fmt:
fmt file
This pretty aggressively reformats your text, so it may do more than what you want.
Alternatively, the cut command can cut text to a specific column width, discarding text beyond the right margin:
cat file | cut -c1-80
Another handy option is the less -S command, which displays a file in a full screen window with left/right scrolling for long lines:
less -S file