No it won't, it matches 0 or more non-white-spaces, followed by one or more white-spaces, followed by 0 or more non-white-spaces. If the first column is empty, that counts as 0 non-white-spaces and $1 will contain the empty string. If the second column is empty that counts as 0 non-white-spaces and $2 will contain the empty string. The only lines that will get skipped are lines that don't contain at least one white-space character.