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)
}

function printline(a)
{
	printf("* %s%*s *\n", a, maxlength - length(a), "")
}

# return the string a, with the character at pos, replaced with chr
function replace(a, pos, chr)
{
	return substr(a, 1, pos - 1) chr substr(a, pos + 1)
}

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

	prevline = $0
	next
}

output == 1 {
	# fix up horizontal issues
	gsub("\\|-", "+-", prevline)
	gsub("\\| -", "+--", prevline)
	gsub("-\\|", "-+", prevline)
	gsub("- \\|", "--+", prevline)

	# Fix up vertical issues

	# first fix edges from below
	r = split($0, a, "|")
	pos = 0
	for (i = 2; i <= r; i++) {
		pos += length(a[i - 1]) + 1
		if (substr(prevline, pos, 1) == "-")
			prevline = replace(prevline, pos, "+")
	}

	# fix edges from above
	r = split(prevline, a, "|")
	pos = 0
	for (i = 2; i <= r; i++) {
		pos += length(a[i - 1]) + 1
		if (substr($0, pos, 1) == "-")
			$0 = replace($0, pos, "+")
	}

	printline(prevline)

	prevline = $0
}

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

rm "$fname"