Create bare Ruby docker image

ruby_image.sh

#!/bin/bash
TARGET=$1

mkdir -p $TARGET

files=$(
  dpkg -L ruby | grep '/usr/bin/'
  dpkg -L ruby1.9.1 | grep '/usr/bin/'
  echo '/usr/lib/ruby'
)

tar cpf - $files | tar xpf - -C $TARGET

find_executable() {
  find ${TARGET} -type f -a -perm +0100 -print0 \
    | xargs -0 -n1 ldd 2>/dev/null \
    | awk '{ print $(NF-1) }' | sort -u | egrep "^/"
}

find_so() {
  find ${TARGET} -name \*.so -a  -print0 \
    | xargs -0 -n1 ldd 2>/dev/null \
    | awk '{ print $(NF-1) }' | sort -u | egrep "^/"
}

nss() {
  for nssdir in {/usr,}/lib {/usr,}/lib/x86_64-linux-gnu/{,libnss}; do
    if [[ -d $nssdir ]]; then
     find $nssdir -maxdepth 1 \( -type f -o -type l \) -name 'libnss*'
    fi
  done
  if [[ -d /usr/lib/nss ]]; then
    find /usr/lib/nss -maxdepth 1 \( -type f -o -type l \)
  fi
}

{ # automatically find and copy needed libraries
  find_executable
  find_so
  nss
} | sort | uniq | cpio -L -p -d -u ${v} ${TARGET}