#!/bin/bash

#####################
## Prepare overlay ##
#####################

echo "Create Upper, Lower, and Overlay Directory"
mkdir lower upper overlay work

echo "Create test files; onlyUpper, both, onlyLower"
echo "Lower" > lower/onlyLower
echo "Lower" > lower/both
echo "Upper" > upper/both
echo "Upper" > upper/onlyUpper

echo "Mount as a OverlayFS"
mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work overlay overlay

echo "Check mount status"
mount -l | grep overlay
ls -lF overlay/
#=> total 12
#=> -rw-r--r-- 1 root root 6 Mar 14 07:24 both
#=> -rw-r--r-- 1 root root 6 Mar 14 07:24 onlyLower
#=> -rw-r--r-- 1 root root 6 Mar 14 07:24 onlyUpper

#####################
##  Read / Write   ##
#####################

echo "Read File"
cat overlay/onlyUpper
#=> Upper
cat overlay/both
#=> Upper
cat overlay/onlyLower
#=> Lower

echo "Write into File"
echo "Add" >> overlay/onlyUpper
echo "Add" >> overlay/both
echo "Add" >> overlay/onlyLower

echo "Read File again"
cat overlay/onlyUpper
#=> Upper
#=> Add
cat overlay/both
#=> Upper
#=> Add
cat overlay/onlyLower
#=> Lower
#=> Add

echo "Check new file is created on Upper"
ls -lF upper/
#=> total 12
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 both
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 onlyLower
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 onlyUpper


#####################
##     Delete      ##
#####################

echo "Remove File only exist Upper"
rm overlay/onlyUpper

echo "Check File is deleted"
ls -lF overlay/
#=> total 8
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 both
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 onlyLower
ls -lF upper/
#=> total 8
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 both
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 onlyLower

echo "Remove File exist both Lower and Upper"
rm overlay/both

echo "Check File is deleted"
ls -lF overlay/
#=> total 4
#=> -rw-r--r-- 1 root root 10 Mar 14 07:25 onlyLower

echo "Check whitefile is created"
ls -lF upper/
#=> total 4
#=> c--------- 1 root root 0, 0 Mar 14 07:30 both
#=> -rw-r--r-- 1 root root   10 Mar 14 07:25 onlyLower

echo "Check Lower file exist"
ls -lF lower/
#=> total 8
#=> -rw-r--r-- 1 root root 6 Mar 14 07:24 both
#=> -rw-r--r-- 1 root root 6 Mar 14 07:24 onlyLower

cat lower/both
#=> Lower