How to move a directory, file by file? (instead of "copy then remove")

Question

My computer has one 500GB drive.

I want to move 400GB of data from /unencrypted to /encrypted.

Both directories are on the same partition, but /encrypted is handled by ecryptfs, so mv /uncrypted/* /encrypted would:

1. Copy all files to destination
2. Then remove them from source

...which I can't afford, because it requires 800GB.
If files were moved one-by-one, there would be no problem (the ecryptfs zone is dynamic).

Is there an mv option or another tool, that moves a directory file-by-file?
There is a huge number of files, so ARG_MAX might be a problem for script-based solutions.

Answer 1

If you have rsync (remove --dry-run to do it for real):

rsync --dry-run --remove-source-files -avHAX /unencrypted/ /encrypted

Otherwise, using bash4+ and GNU stat:

#!/bin/bash

set -e

shopt -s nullglob globstar

for from in /unencrypted/**/*; do
    to="${from/\/un//}"
    if [[ -d "$from" ]]; then
        echo mkdir -p "$to"
        echo chmod "$(stat -c %a "$from")" "$to"
        echo chown "$(stat -c %u:%g "$from")" "$to"
    else
        echo cp -a "$from" "$to" && echo rm "$from"
    fi
done

echo rm -r /unencrypted

To run it for real, remove echo from each command.