docker_generate_ignore.sh

#!/usr/bin/env bash
set -euf -o pipefail # https://sipb.mit.edu/doc/safe-shell/

# https://medium.com/@LihauTan/2f87c770ea9c
find . -name .gitignore \
  -exec awk '
    FNR==1  { print "\n## " FILENAME } \
    FNR==1  { cmd = "dirname " FILENAME; cmd | getline DIRNAME; close(cmd) } \
    /^ *#/  { print $0; next } \
    /^[^!]/ { print DIRNAME "/" $0 } \
    /^!/    { print "!" DIRNAME "/" substr($0,2) } \
  ' '{}' '+' \
  > .dockerignore