How to create a directory tree with only the changed files of two source directory trees

Question

I have two directory trees (actually macOS volumes) with similar files and want to create a third directory tree containing only the files which are changed between the two source trees.

How can I do this with rsync? Or should I use another tool for this?

Answer 1

• Using rsync (based on this answer):

  SOURCE_TREE_1="/some/where/tree_1"
  SOURCE_TREE_2="/some/where/tree_2"
  DIFF_DIR="/some/where/diff"
  rsync --dry-run 
  
        --recursive 
  
        --checksum 
  
        --itemize-changes 
  
        "$SOURCE_TREE_1/" "$SOURCE_TREE_2" | # trailing '/' in source directory is necessary!
    grep -E '^>fc' | # grep files with different checksums
    cut -d ' ' -f 2- |
  while read file; do
    subdir="${file%/*}";
    [ "$file" != "$subdir" ] && mkdir -p "$DIFF_DIR/$subdir";
  Change "$SOURCE_TREE_1/$file" to "$SOURCE_TREE_1/$file" in the next
  line if you want copy from source tree #2.
  cp -a "$SOURCE_TREE_1/$file" "$DIFF_DIR/$file";
  done
  

• Using git:

  cd "$SOURCE_TREE_1"
  git init .
  git add .
  git commit -m 'Init' # Note: Here git may ask you to set name and email
  replace all files with files from source tree #2
  rm -rf $(git ls-tree --name-only HEAD)
  rsync --archive "$SOURCE_TREE_2/" .
  show changes briefly:
  git status -uno
  show changes for some file:
  git diff "path/to/file"
  restore source tree #1 state
  git restore .