Merge 2 directory trees in Linux without copying?

I have two directory trees with similar layouts, i.e.

.
 |-- dir1
 |   |-- a
 |   |   |-- file1.txt
 |   |   `-- file2.txt
 |   |-- b
 |   |   `-- file3.txt
 |   `-- c
 |       `-- file4.txt
 `-- dir2
     |-- a
     |   |-- file5.txt
     |   `-- file6.txt
     |-- b
     |   |-- file7.txt
     |   `-- file8.txt
     `-- c
         |-- file10.txt
         `-- file9.txt

I would like to merge the the dir1 and dir2 directory trees to create:

 merged/
 |-- a
 |   |-- file1.txt
 |   |-- file2.txt
 |   |-- file5.txt
 |   `-- file6.txt
 |-- b
 |   |-- file3.txt
 |   |-- file7.txt
 |   `-- file8.txt
 `-- c
     |-- file10.txt
     |-- file4.txt
     `-- file9.txt

I know that I can do this using the "cp" command, but I want to move the files instead of copying, because the actual directories I want to merge are really large and contain lots of files (millions). If I use "mv" I get the "File exists" error because of conflicting directory names.

UPDATE: You can assume that there are no duplicate files between the two directory trees.

Solution 1:

rsync -ax --link-dest=dir1/ dir1/ merged/
rsync -ax --link-dest=dir2/ dir2/ merged/

This would create hardlinks rather than moving them, you can verify that they were moved correctly, then, remove dir1/ and dir2/.

Solution 2:

It's strange nobody noted that cp has option -l:

-l, --link
       hard link files instead of copying

You can do something like

% mkdir merge
% cp -rl dir1/* dir2/* merge
% rm -r dir*
% tree merge 
merge
├── a
│   ├── file1.txt
│   ├── file2.txt
│   ├── file5.txt
│   └── file6.txt
├── b
│   ├── file3.txt
│   ├── file7.txt
│   └── file8.txt
└── c
    ├── file10.txt
    ├── file4.txt
    └── file9.txt

13 directories, 0 files

Solution 3:

You can use rename (aka prename, from the perl package) for that. Beware that the name doesn't necessarily refer to the command I describe outside of debian/ubuntu (though it's a single portable perl file if you need it).

mv -T dir1 merged
rename 's:^dir2/:merged/:' dir2/* dir2/*/*
find dir2 -maxdepth 1 -type d -empty -delete

You also have the option of using vidir (from moreutils), and editing the file paths from your preferred text editor.

Solution 4:

I like the rsync and prename solutions, but if you really want to make mv do the work and

your find knows -print0 and -depth,
your xargs knows -0,
you have printf,

then it is possible to handle a large number of files that might have random whitespace in their names, all with a Bourne-style shell script:

#!/bin/sh

die() {
    printf '%s: %s\n' "${0##*/}" "$*"
    exit 127
}
maybe=''
maybe() {
    if test -z "$maybe"; then
        "$@"
    else
        printf '%s\n' "$*"
    fi
}

case "$1" in
    -h|--help)
        printf "usage: %s [-n] merge-dir src-dir [src-dir [...]]\n" "${0##*/}"
        printf "\n    Merge the <src-dir> trees into <merge-dir>.\n"
        exit 127
    ;;
    -n|--dry-run)
        maybe=NotRightNow,Thanks.; shift
    ;;
esac

test "$#" -lt 2 && die 'not enough arguments'

mergeDir="$1"; shift

if ! test -e "$mergeDir"; then
    maybe mv "$1" "$mergeDir"
    shift
else
    if ! test -d "$mergeDir"; then
        die "not a directory: $mergeDir"
    fi
fi

xtrace=''
case "$-" in *x*) xtrace=yes; esac
for srcDir; do
    (cd "$srcDir" && find . -print0) |
    xargs -0 sh -c '

        maybe() {
            if test -z "$maybe"; then
                "$@"
            else
                printf "%s\n" "$*"
            fi
        }
        xtrace="$1"; shift
        maybe="$1"; shift
        mergeDir="$1"; shift
        srcDir="$1"; shift
        test -n "$xtrace" && set -x

        for entry; do
            if test -d "$srcDir/$entry"; then
                maybe false >/dev/null && continue
                test -d "$mergeDir/$entry" || mkdir -p "$mergeDir/$entry"
                continue
            else
                maybe mv "$srcDir/$entry" "$mergeDir/$entry"
            fi
        done

    ' - "$xtrace" "$maybe" "$mergeDir" "$srcDir"
    maybe false >/dev/null ||
    find "$srcDir" -depth -type d -print0 | xargs -0 rmdir
done

Solution 5:

Brute force bash

#! /bin/bash

for f in $(find dir2 -type f)
do
  old=$(dirname $f)
  new=dir1${old##dir2}
  [ -e $new ] || mkdir $new
  mv $f $new
done

test does this

# setup 
for d in dir1/{a,b,c} dir2/{a,b,c,d} ; do mkdir -p $d ;done
touch dir1/a/file{1,2} dir1/b/file{3,4} dir2/a/file{5,6} dir2/b/file{7,8} dir2/c/file{9,10} dir2/d/file11

# do it and look
$ find dir{1,2} -type f
dir1/a/file1
dir1/a/file2
dir1/a/file5
dir1/a/file6
dir1/b/file3
dir1/b/file7
dir1/b/file8
dir1/c/file4
dir1/c/file9
dir1/c/file10
dir1/d/file11