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

In Vim, I would use the following command:

:%s/$/\=repeat(' ',64-virtcol('$'))

(The use of the virtcol() function, as opposed to the col() one, is guided by the necessity to properly handle tab characters as well as multibyte non-ASCII characters that might occur in the text.)

Answer 2

$ awk '{printf "%-63s\n", $0}' testfile > newfile