Re: sh(1) read: add LINE_MAX safeguard and "-n" option

As I understand, the performance problem of the read built-in utility 
originates from its need to read one byte at a time in order not to 
swallow input it doesn't process.

Would it make sense to add an "exclusive" option (call it "-x" for now) 
to read, where "read -x" essentially means "I promise to do all processing 
on this open file with read -x or not to complain if input gets lost"? 

This may be infeasable due to not being able to guarantee that any 
"read -x" really uses the built-in version.

The point, of course, is to allow the shell to buffer the input.