Appending rather than overwriting files when moving

Question

I have the following directory structure:

+-archive
  +-a
    +-data.txt
  +-b
    +-data.txt 
+-incoming
  +-a
    +-data.txt
  +-c
    +-data.txt

How do I do the equivalent of mv incoming/* archive/ but have the contents of the files in incoming appended to those in archive rather than overwrite them?

Answer 1

# move to incoming/ so that we don't
# need to strip a path prefix
cd incoming

# create directories that are missing in archive
for d in `find . -type d`; do
  if [ ! -d "../archive/$d" ]; then
    mkdir -p "../archive/$d"
  fi
done

# concatenate all files to already existing
# ones (or automatically create them)
for f in `find . -type f`; do
  cat "$f" >> "../archive/$f"
done

This should find any file in incoming and concatenate it to an existing file in archive.

The important part is to be inside incoming, because else we'd had to strip the path prefix (which is possible, but in the above case unnecessary). In the above case, a value of $f typically looks like ./a/data.txt, and hence the redirection goes to ../archive/./a/data.txt.