Script to incrementally copy the end of a local file to a destination over SSH

copy-tail

usage() {
    cat <<EOF
Usage:
    copy-tail SOURCE_PATH REMOTE_HOST REMOTE_PATH
EOF
}

if [ "$#" -ne "3" ]; then
    echo "Wrong number of arguments!"
    usage
    exit 1
fi

local_file="$1"
remote_host="$2"
remote_file="$3"

cat <<EOF
local_file  = $local_file
remote_host = $remote_host
remote_file = $remote_file
EOF

ssh "$remote_host" touch "$remote_file"

curr_local_len=$(ls -lA "$local_file" | awk '{print $5}')
remote_len=$(ssh "$remote_host" ls -lA "$remote_file" | awk '{print $5}')

local_intro_hash=$(head -c$remote_len "$local_file" | md5sum | awk "{print \$1}")
remote_intro_hash=$(ssh "$remote_host" "head -c$remote_len \"$remote_file\" | md5sum" | awk "{print \$1}")

cat <<EOF
curr_local_len = $curr_local_len
local_intro_hash = $local_intro_hash

remote_len = $remote_len
remote_intro_hash = $remote_intro_hash
EOF

if [ "$remote_intro_hash" != "$local_intro_hash" ]; then
    echo "Intro hashes don't match. Data is corrupted."
    exit 1
fi

echo
echo Copying...
tail -c+$((remote_len + 1)) "$local_file" | pv -s $((curr_local_len - remote_len)) | ssh "$remote_host" "cat >> \"$remote_file\""

echo
new_remote_len=$(ssh "$remote_host" ls -lA "$remote_file" | awk '{print $5}')

cat <<EOF
new_remote_len = $new_remote_len
EOF