Diff two very similar directories

dir_diff.lib.sh

#!/bin/bash

IFF_ARGS='-dbB'

dir_diff() {
  local a=$1
  local b=$2
  exit=0
  rm -rf a b diff &> /dev/null || true
  local thisn=a
  local opposite=$b
  local oppositen=b
  for x in $a $b; do
    (cd $x; find . -type f) | while read f; do
      mkdn "$oppositen/$f"
      mkdn "$thisn/$f"
      [[ -e "$thisn/$f" ]] || ln -s "$(pwd)/$x/$f" "$thisn/$f"
      [[ -e "$oppositen/$f" ]] || {
        [[ -e $opposite/$f ]] \
          && ln -s "$(pwd)/$opposite/$f" "$oppositen/$f" \
          || mkf "$oppositen/$f" \
        ;
      }
    done
    opposite=$a
    oppositen=a
    thisn=b
  done
  local diff=''
  (cd a; find .) | while read f; do
    [[ -d "a/$f" ]] || {
      diff=$(diff $DIFF_ARGS "a/$f" "b/$f") || {
        exit=$?
        mkdn "diff/$f"
        echo "$diff" > "diff/$f"
      }
    }
  done
  [[ -d diff ]] || mkdir diff ;
  diff -r $DIFF_ARGS "$a" "$b" > diff/DIFF_REPORT.txt
  return $exit
}
mkdn() {
  local f=$1
  local dn=$(dirname $f)
  [[ -d "$dn" ]] || mkdir -p "$dn"
}
mkf() {
  local f=$1
  mkdn "$f"
  touch "$f"
}

#