Allow Backspace in input. It's really frustrating otherwise if a typo
cannot be corrected, and worse, the backspace key actually produces a
character that becomes part of the input.
Complete input with Enter. It is surprising when the script just
moves on right away once a fourth/second digit is entered, and worse,
users expecting to press Enter could reasonably press it before
realizing the script did not require it, which then skips the _next_
prompt inadvertently. Users with imperfect typing might double a
digit unintentionally, do not force them to proceed with an incorrect
value.
Removing '-n $digits' from read does both of those. Add '-r' so
backslashes do not have unexpected behavior.
Don't require leading zeroes, zero-pad automatically.
Signed-off-by: Jonathon Hall <jonathon.hall@puri.sm>
770815cba8