Pad all lines with spaces to a fixed width in Vim or using sed, awk, etc

Question

How can I pad each line of a file to a certain width (say, 63 characters wide), padding with spaces if need be?

For now, let’s assume all lines are guaranteed to be less

Answer 1

Just for fun, a Perl version:

$ perl -lpe '$_ .= " " x (63 - length $_)'