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How can I use rsync (but neither rsnapshot nor rdiff-backup nor any other application) to create a differential backup of a directory located on my local drive to another directory located on that same local drive?

F. Hauri posted the following in an anwser to How to create a local backup?:

#!/bin/bash

backRepo=/media/mydisk

backSrce=/home/user

backDest=home

backCopy=copy

backCount=9



[ -d "$backRepo/$backDest" ] || mkdir "$backRepo/$backDest"



cd $backSrce || exit 1

rsync -ax --delete --exclude '*~' --exclude '.DStore' . "$backRepo/$backDest/."



cd $backRepo

[ -d "$backCopy.$backCount" ] && rm -fR "$backCopy.$backCount"

for ((i=$backCount;i--;));do

    [ -d "$backCopy.$i" ] && mv "$backCopy.$i" "$backCopy.$((i+1))"

  done

((i++))



cp -al $backDest $backCopy.$i

It seems like the above script is fairly close to what I want, but frankly despite spending about an hour studying Easy Automated Snapshot-Style Backups with Linux and Rsync I still only have a vague idea of how to make rsync do what I want.

Here's my use case:

I am editing a video locally on my machine. The sum of all of the hundreds of files associated with that video will be less than 5 gb (five gigabytes).

Currently, I use Grsync to back up my internal drive to an external USB drive. Although I actually figured out how to accomplish the identical task using rsync I prefer using Grsync because I merely need to launch it and then click on one button to backup my internal directory containing my video files to my external USB drive. The entire process is silky smooth.

Every few hours, I want a fairly smooth way to back up my the above-mentioned data associated with my video, to my Google Drive account. I don’t mind manually choosing to upload a folder to Google Drive. I actually sort of prefer having to do so because it would help me to ensure the backup was actually being accomplished.

Every few nights before I go to bed, I have been copying the entire folder containing the video files, which contains many gigs of data, up to my Google Drive account.

I prefer differential backups to incremental ones because in case I were to need to restore my data from Google Drive I would likely be able to do so manually without becoming confused.

Please keep in mind that I am certainly not a unix sys admin at a large corporation supporting hundreds of users. I am a merely one guy who wants an easy method, but not necessarily a completely automated method, to back up his data offsite every few hours in case of a catastrophic loss of data, which would be most likely due to the theft of my computer. I am almost certain rsync can do what I want. Therefore, I am reluctant to install another application.

Here ya go!

#!/bin/bash



# written by strobelight, you know who you are.

# license, MIT, go for it.



me=`basename $0`



EXCLUDES="

    --exclude '*~'

    --exclude '.DS_Store'

"



CANDIDATES=/tmp/candidates



usage() {

    cat <<EOF



$me last_diff_dir new_diff_dir [ dir_to_copy ]



where:

    last_diff_dir  is the directory containing the last differential

    new_diff_dir   is the directory you want files saved to

    dir_to_copy    is optional and is the directory to copy from (default .)



cd directory_to_backup

Full backup: $me full_back full_back

Diff backup: $me full_back diff_1

Diff backup: $me full_back diff_2



EOF

    exit 1

}



get_dir() {

    HERE=`pwd`

    cd $1

    x=`pwd`

    cd $HERE

    echo $x

}



if [ $# -lt 2 ]; then

    usage

fi



LAST_DIR="$1"

NEW_DIR="$2"

DIR_TO_COPY="${3:-.}"



mkdir -p "$LAST_DIR" || exit 1

mkdir -p "$NEW_DIR" || exit 1



[ -d "$LAST_DIR" ] || usage

[ -d "$NEW_DIR" ] || usage

[ -d "$DIR_TO_COPY" ] || usage



LAST_DIR=`get_dir "$LAST_DIR"`

NEW_DIR=`get_dir "$NEW_DIR"`

DIR_TO_COPY=`get_dir "$DIR_TO_COPY"`



# get list of what's different

eval rsync -v --dry-run -axH --delete --update $EXCLUDES "$DIR_TO_COPY/" "$LAST_DIR" | awk '

    /building file list/ { next }

    /^$/ {next}

    /bytes.*received/ { nextfile }

    {

        for(i=5;i<NF;i++) {

            printf("%s ",$i)

        }

        printf("%sn",$NF)

    }

    ' | sed 's:/$::' > $CANDIDATES

#cat $CANDIDATES



# use list to backup 

eval rsync --files-from=$CANDIDATES -lptgoDxH --delete $EXCLUDES ${DIR_TO_COPY}/ $NEW_DIR

For example, my current directory has 3 8k files:

$ ls -1sk

total 24

 8 seg1

 8 seg2

 8 seg3

My full backup doesn't yet exist, let's call that directory full_bak

ls ../full_bak

ls: ../full_bak: No such file or directory

First we need a full backup from which to do differentials. I've copied the script to my $HOME/bin directory as test123.sh. When both args are the same, that's essentially performing a full backup.

$HOME/bin/test123.sh ../full_bak ../full_bak

script outputs

.

seg1

seg2

seg3

Now look at ../full_bak

$ ls -1sk ../full_bak

total 24

 8 seg1

 8 seg2

 8 seg3

Make some changes

dd if=/dev/zero of=seg2 bs=512 count=11

Confirm there are differences:

$ diff -q . ../full_bak

Files ./seg2 and ../full_bak/seg2 differ

Now create a differential

$ $HOME/bin/test123.sh ../full_bak ../differential1

seg2

Look at differential having just the file thats different from the last full backup

$ ls -1sk ../differential1/

total 8

 8 seg2

Make another change

dd if=/dev/zero of=seg4 bs=512 count=10

Check what's different

diff -q . ../full_bak

Files ./seg2 and ../full_bak/seg2 differ

Only in .: seg4

and see we have a new file that's not in our full backup, and a changed file from before.

Do another differential to another directory

$ $HOME/bin/test123.sh ../full_bak ../differential2

.

seg2

seg4

and see the new differential has the 1st differential as well as the new file

$ ls -1sk ../differential2

total 16

 8 seg2

 8 seg4

Differential Backups

Here's a fullbackup wrapper using test123.sh:

#!/bin/bash



FULLDIR=/media/mydisk/home

SRCDIR=/home/user



$HOME/bin/test123.sh $FULLDIR $FULLDIR $SRCDIR

Here's a differential script creating sub directories based on the hour:

#!/bin/bash



FULLDIR=/media/mydisk/fullbackup/home

DIFFDIR=/media/mydisk/differentials/home

SRCDIR=/home/user

DIFFSUB=`date '+BAK_%H'`



$HOME/bin/test123.sh $FULLDIR $DIFFDIR/$DIFFSUB $SRCDIR