fbsdembdev/box.sh

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

function printtop () {
	blank = ""
	for (i = 0; i < maxlength + 4; i++)
		blank = 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"