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

This might work for you:

$ sed -i ':a;/.\{63\}/!{s/$/ /;ba}' file

or perhaps more efficient but less elegant:

$ sed -i '1{x;:a;/.\{63\}/!{s/^/ /;ba};x};/\(.\{63\}\).*/b;G;s//\1/;y/\n/ /' file