join PDFs on macOS from the command line with zero dependencies

join_pdf.bash

#!/bin/bash
if [ "$#" -lt 2 ]; then
    echo "usage: $0 output_pdf_path input_path1..."
    echo
    echo "This script joins the PDFs at input_path1, input_path2, etc."
    echo "into one pdf at output_pdf_path"
    echo
    echo "Known good: macOS 11.1, and below for many versions"
    echo
    exit 1
fi
script_path="/System/Library/Automator/Combine PDF Pages.action/Contents/Resources/join.py"
command -v "$script_path" >/dev/null 2>&1 || { echo >&2 "I require $script_path but it's not there. macOS has probably changed too much for me to be useful. Aborting."; exit 1; }
exec "$script_path" -o "$@"