fbsdembdev/box.sh

#!/bin/sh
fname=$(mktemp foobar.XXXXX)
cat > "$fname"
awk '
maxline == 1 {
	if (maxlength < length)
		maxlength = length
}

function printtop () {
	blank = sprintf("%*s", maxlength + 4, "")
	gsub(" ", "*", blank)
	printf("%s\n", blank)
}

output == 1 && FNR == 1 {
	printtop()
	printf("* %*s *\n", maxlength, "")
}

output == 1 {
	printf("* %s%*s *\n", $0, maxlength - length, "")
}

END {
	printf("* %*s *\n", maxlength, "")
	printtop()
}
' maxline=1 "$fname" maxline=0 output=1 "$fname"

rm "$fname"