Bash script to detect whether two paths/files are in the same file system

same_fs.sh

#!/bin/bash

MOUNTS=`cat /proc/mounts | cut -d ' ' -f 2 | sort | uniq | tr '/' '\\/'`
IFS=$'\n'

what_fs() {
    for MOUNT in ${MOUNTS}; do
        readlink -f $1 | grep -o "^${MOUNT}"
        # echo -e "$1"
        # echo -e "${MOUNT}"
    done
}

if [ $# -ne 2 ]; then
        echo "Please provide exactly 2 arguments"
        exit 2
fi
if [ ! -e "$1" ]; then
        echo "File not found: $1"
        exit 2
fi
if [ ! -e "$2" ]; then
        echo "File not found: $2"
        exit 2
fi

FS1=$(what_fs $1 | tail -n 1)
FS2=$(what_fs $2 | tail -n 1)

# echo -e "FS for '${1}': ${FS1}"
# echo -e "FS for '${2}': ${FS2}"

if [ "${FS1}" = "${FS2}" ]; then
    echo "Same file system"
    exit 0
else
    echo -e "Different file system on ${FS2}"
    exit 1
fi