add outline to PDF using ghostscript and PDFMark

pdfoutline.sh

#!/usr/bin/env bash
# add outline to PDF using ghostscript and PDFMark
# reference: https://www.meadowmead.com/wp-content/uploads/2011/04/PDFMarkRecipes.pdf

if [ $# -lt 2 ]; then
	echo "usage: $0 INPDF OUTPDF < OUTLINE"
	echo '
Outline example: 

1	Title
	2	Subtitle 1
		3	Heading 1
		5	Heading 2
		6	Heading 3
	7	Subtitle 2

Hierarchy is represented as indent level.
Noticed there is a tab between page number and outline name.
'
	exit 1
fi

INFILE="$1"
OUTFILE="$2"

awk '
BEGIN {
	FS="\t"
}
{
	level=NF-2
	pages[NR] = $(NF-1)
	titles[NR] = $(NF)
	if (level > prev_level) { # start of a child, prev is parent
		parent[level] = NR-1
	}
	childcount[parent[level]]++
	prev_level = level
}
END {
	for (i = 1; i <= NR; i++) {
		if (!childcount[i]) {
			print("[ /Page "pages[i]" /Title ("titles[i]") /OUT pdfmark")
		} else {
			print("[ /Page "pages[i]" /Title ("titles[i]") /Count "childcount[i]" /OUT pdfmark")
		}
	}
}
' \
| gs -o "$OUTFILE" -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress "$INFILE" -