How to write shell script for finding number of pages in PDF?

Question

Without any extra package:

strings < file.pdf | sed -n 's|.*/Count -\{0,1\}\([0-9]\{1,\}\).*|\1|p' \
    | sort -rn | head -n 1

Using pdfinfo:

pdfinfo file.pdf | awk '/^Pages:/ {print $2}'

Using pdftk:

pdftk file.pdf dump_data | grep NumberOfPages | awk '{print $2}'

You can also recursively sum the total number of pages in all PDFs via pdfinfo as follows:

find . -xdev -type f -name "*.pdf" -exec pdfinfo "{}" ";" | \
    awk '/^Pages:/ {n += $2} END {print n}'