diff --git a/install b/install
index 6c02cc7..798a892 100755
--- a/install
+++ b/install
@@ -5,7 +5,7 @@
 # Downloads and installs rpi-clone and rpi-clone-setup into /usr/local/sbin
 #
 # Command to use to install rpi-clone:
-#	   curl https://raw.githubusercontent.com/geerlingguy/rpi-clone/master/install | sudo bash
+#    curl https://raw.githubusercontent.com/geerlingguy/rpi-clone/master/install | sudo bash
 #
 # rpi-clone is Copyright (c) 2018-2019 Bill Wilson
 #
@@ -17,54 +17,62 @@
 # This updated code is located in a fork of Bill Willsons git repository
 # at https://github.com/geerlingguy/rpi-clone
 
+# shellcheck enable=require-variable-braces
+
 set -uo pipefail
 
 readonly PACKAGE="rpi-clone"
-readonly DOWNLOAD_REPOSITORY="https://raw.githubusercontent.com/geerlingguy/rpi-clone/master"
-readonly FILES_2_DOWNLOAD"=rpi-clone rpi-clone-setup"
-readonly TMP_DIR=$(mktemp -d)
+readonly GITHUB_USER="geerlingguy"
+readonly DOWNLOAD_REPOSITORY="https://raw.githubusercontent.com/${GITHUB_USER}/${PACKAGE}/master"
+readonly FILES_TO_DOWNLOAD=("rpi-clone" "rpi-clone-setup")
 readonly DEFAULT_INSTALLATION_DIR="/usr/local/sbin"
 
-pwd=$PWD
-trap "{ cd $pwd; rmdir $TMP_DIR &>/dev/null; }" SIGINT SIGTERM EXIT
-cd $TMP_DIR
+TMP_DIR=$(mktemp -d)
+OLD_PWD=${PWD}
+
+trap 'cd "${OLD_PWD}"; rmdir "${TMP_DIR}" &>/dev/null' SIGINT SIGTERM EXIT
+
+cd "${TMP_DIR}" || exit 1
 
-installDir="${1:-$DEFAULT_INSTALLATION_DIR}"
+installDir="${1:-${DEFAULT_INSTALLATION_DIR}}"
 
-if [[ ! -d $installDir ]]; then
-    echo "Installation directory $installDir not found"
+if [[ ! -d "${installDir}" ]]; then
+    echo "Installation directory ${installDir} not found"
     echo "Pass a valid installation directory as a parameter to $0"
     exit 1
 fi
 
-echo "Installing $PACKAGE into $installDir ..."
+echo "Installing ${PACKAGE} into ${installDir}..."
 
-for file in $FILES_2_DOWNLOAD; do
-    echo -n "Downloading $file from $DOWNLOAD_REPOSITORY/$file ... "
-    http_code=$(curl -w "%{http_code}" -L -s $DOWNLOAD_REPOSITORY/$file -o $file)
-    (($?)) && {
+for file in "${FILES_TO_DOWNLOAD[@]}"; do
+    echo -n "Downloading ${file} from ${DOWNLOAD_REPOSITORY}/${file}..."
+
+    if ! http_code=$(curl -w "%{http_code}" -L -s "${DOWNLOAD_REPOSITORY}/${file}" -o "${file}"); then
         echo "Curl failed"
         exit 1
-    }
-    [[ $http_code != 200 ]] && {
-        echo "http request failed with $http_code"
+    fi
+
+    if [[ "${http_code}" != 200 ]]; then
+        echo "http request failed with ${http_code}"
         exit 1
-    }
+    fi
+
     echo "done"
-    echo -n "Installing $file into $installDir ... "
-    sudo chmod +x $file
-    (($?)) && {
+
+    echo -n "Installing ${file} into ${installDir}..."
+
+    if ! sudo chmod +x "${file}"; then
         echo "chmod failed"
         exit 1
-    }
-    sudo mv $file $installDir
-    (($?)) && {
+    fi
+
+    if ! sudo mv "${file}" "${installDir}"; then
         echo "mv failed"
         exit 1
-    }
-    echo "done"
+    fi
 
+    echo "done"
 done
 
-echo "$PACKAGE installed"
-cd $pwd
+echo "${PACKAGE} installed"
+cd "${OLD_PWD}" || exit 1
diff --git a/rpi-clone b/rpi-clone
index cbb8d6b..5382bf3 100755
--- a/rpi-clone
+++ b/rpi-clone
@@ -157,41 +157,39 @@ usage: $PGM sdN {-v|--verbose} {-f|--force-initialize} {-f2}
     exit 1
 }
 
-readable_MiB() {
+readable_size() {
     val=$1
-    if [ "$val" == "" ]; then
-        result="   ??"
-    else
-        blk_size=$2
-        val=$((val / 1024 * blk_size))
+    blk_size=$2
+    format=${4:-MiB} # Default to MiB if not specified
 
-        if ((val < 1024 * 1024)); then
-            result=$(echo $val | awk '{ byte = $1 / 1024; printf "%.1f%s", byte, "M" }')
-        elif ((val < 1024 * 1024 * 1024)); then
-            result=$(echo $val | awk '{ byte = $1 / 1024 / 1024; printf "%.1f%s", byte, "G" }')
-        else
-            result=$(echo $val | awk '{ byte = $1 / 1024 / 1024 / 1024; printf "%.1f%s", byte, "T" }')
-        fi
-    fi
-    printf -v "${3}" "%s" "$result"
-}
-
-readable_MB() {
-    val=$1
     if [ "$val" == "" ]; then
         result="   ??"
     else
-        blk_size=$2
-        val=$((val / 1000 * blk_size))
-
-        if ((val < 1000 * 1000)); then
-            result=$(echo $val | awk '{ byte = $1 / 1000; printf "%.1f%s", byte, "MB" }')
-        elif ((val < 1000 * 1000 * 1000)); then
-            result=$(echo $val | awk '{ byte = $1 / 1000 / 1000; printf "%.1f%s", byte, "GB" }')
+        if [ "$format" == "MB" ]; then
+            # Decimal (MB, GB, TB)
+            val=$((val / 1000 * blk_size))
+
+            if ((val < 1000 * 1000)); then
+                result=$(echo $val | awk '{ byte = $1 / 1000; printf "%.1f%s", byte, "MB" }')
+            elif ((val < 1000 * 1000 * 1000)); then
+                result=$(echo $val | awk '{ byte = $1 / 1000 / 1000; printf "%.1f%s", byte, "GB" }')
+            else
+                result=$(echo $val | awk '{ byte = $1 / 1000 / 1000 / 1000; printf "%.1f%s", byte, "TB" }')
+            fi
         else
-            result=$(echo $val | awk '{ byte = $1 / 1000 / 1000 / 1000; printf "%.1f%s", byte, "TB" }')
+            # Binary (MiB, GiB, TiB)
+            val=$((val / 1024 * blk_size))
+
+            if ((val < 1024 * 1024)); then
+                result=$(echo $val | awk '{ byte = $1 / 1024; printf "%.1f%s", byte, "M" }')
+            elif ((val < 1024 * 1024 * 1024)); then
+                result=$(echo $val | awk '{ byte = $1 / 1024 / 1024; printf "%.1f%s", byte, "G" }')
+            else
+                result=$(echo $val | awk '{ byte = $1 / 1024 / 1024 / 1024; printf "%.1f%s", byte, "T" }')
+            fi
         fi
     fi
+
     printf -v "${3}" "%s" "$result"
 }
 
@@ -299,8 +297,8 @@ print_partitions() {
 
     n_parts=$(((n_src_parts >= n_dst_parts) ? n_src_parts : n_dst_parts))
 
-    readable_MB $src_disk_size "512" src_size_readable
-    readable_MB $dst_disk_size "512" dst_size_readable
+    readable_size $src_disk_size "512" src_size_readable "MB"
+    readable_size $dst_disk_size "512" dst_size_readable "MB"
 
     printf "\n%-43s%s" "Booted disk: $src_disk $src_size_readable" \
         "Destination disk: $dst_disk $dst_size_readable"
@@ -309,7 +307,7 @@ print_partitions() {
     out=$'Part, Size,FS,Label         ,Part, Size,FS,Label\n'
     for ((p = 1; p <= n_parts; p++)); do
         if ((p <= n_src_parts && src_exists[p])); then
-            readable_MiB ${src_size_sectors[p]} "512" tmp
+            readable_size ${src_size_sectors[p]} "512" tmp
             printf -v sectors_readable "%7s" $tmp
             pname="$p ${src_name[p]}"
             out=${out}$"$pname,$sectors_readable,${src_fs_type[p]},${src_label[p]},"
@@ -318,7 +316,7 @@ print_partitions() {
         fi
 
         if ((p <= n_dst_parts && dst_exists[p])); then
-            readable_MiB ${dst_size_sectors[p]} "512" tmp
+            readable_size ${dst_size_sectors[p]} "512" tmp
             printf -v sectors_readable "%7s" $tmp
             out=${out}$"$p,$sectors_readable,${dst_fs_type[p]},${dst_label[p]},"
         else
@@ -361,8 +359,8 @@ print_sync_actions() {
                 src_label="/dev/${src_partition[p]}"
                 action_label="MOUNT SYNC"
             fi
-            readable_MiB ${src_used_sectors[p]} "512" used
-            readable_MiB ${dst_size_sectors[p]} "512" size
+            readable_size ${src_used_sectors[p]} "512" used
+            readable_size ${dst_size_sectors[p]} "512" size
             printf "%-22s%-14s : %s %s\n" \
                 "$src_label" "(${used} used)" "$action_label" \
                 "$flow (${size} size)"
@@ -410,10 +408,10 @@ print_image_actions() {
         fi
 
         if ((p == n_image_parts)); then
-            readable_MiB ${src_used_sectors[n_image_parts]} "512" used
+            readable_size ${src_used_sectors[n_image_parts]} "512" used
             printf "%-22s%-14s : RESIZE  %s\n" "$pname" "(${used} used)" "$action"
         elif ((src_used_sectors[$p] > 0 && p < n_image_parts)); then
-            readable_MiB ${src_used_sectors[p]} "512" used
+            readable_size ${src_used_sectors[p]} "512" used
             printf "%-22s%-14s : $action\n" "$pname" "(${used} used)"
         elif [ "$action" != "" ]; then
             printf "%-36s : $action\n" "$pname"
@@ -561,6 +559,45 @@ get_src_disk() {
     printf -v "${3}" "%s" "$num"
 }
 
+change_disk_id() {
+    local disk=$1
+    local msg=${2:-}
+
+    if [ -n "$msg" ]; then
+        qecho "$msg"
+    fi
+
+    new_id=$(od -A n -t x -N 4 /dev/urandom | tr -d " ")
+    qprintf "x\ni\n0x$new_id\nr\nw\nq\n" | fdisk /dev/"$disk" > /dev/null
+
+    sync
+    sleep 2
+}
+
+find_extended_partition() {
+    local -r fdisk_table=$1
+    local -r dev=$(grep "Extended" <<< "${fdisk_table}" | awk '{print $1}')
+
+    if [ -n "${dev}" ]; then
+        echo "${dev: -1}"
+    else
+        echo "0"
+    fi
+}
+
+edit_disk_reference() {
+    local file=$1
+    local description=$2
+
+    if grep -q "$src_disk_ID" "$file"; then
+        qecho "Editing $description PARTUUID to use $dst_disk_ID"
+        sed -i "s/${src_disk_ID}/${dst_disk_ID}/g" "$file"
+    elif [ "$edit_fstab_name" != "" ] && grep -q "${src_part_base}" "$file"; then
+        qecho "Editing $description references from $src_part_base to $edit_fstab_name"
+        sed -i "s/${src_part_base}/${edit_fstab_name}/" "$file"
+    fi
+}
+
 # ==== source (booted) disk info and default mount list
 #
 src_boot_dev=$(findmnt /boot -o source -n | grep "/dev/")
@@ -634,13 +671,7 @@ Don't know how to partition the destination disk!
     exit 1
 fi
 
-line=$(echo "$src_fdisk_table" | grep "Extended")
-if [ "$line" != "" ]; then
-    dev=$(echo "$line" | cut -d " " -f 1)
-    ext_part_num="${dev: -1}"
-else
-    ext_part_num=0
-fi
+ext_part_num=$(find_extended_partition "$src_fdisk_table")
 
 for ((p = 1; p <= n_src_parts; p++)); do
     line=$(echo "$src_partition_table" | grep -e "^${p}:")
@@ -1028,13 +1059,7 @@ dst_root_dev=/dev/${dst_part_base}${root_part_num}
 dst_mount_table=$(findmnt -o source,target -n -l | grep "^/dev/$dst_disk" | tr -s " ")
 
 dst_fdisk_table=$(fdisk -l /dev/$dst_disk | grep "^/dev/")
-line=$(echo "$dst_fdisk_table" | grep "Extended")
-if [ "$line" != "" ]; then
-    dev=$(echo "$line" | cut -d " " -f 1)
-    ext_num="${dev: -1}"
-else
-    ext_num=0
-fi
+ext_num=$(find_extended_partition "$dst_fdisk_table")
 
 for ((p = 1; p <= n_dst_parts; p++)); do
     line=$(echo "$dst_partition_table" | grep -e "^${p}:")
@@ -1203,7 +1228,7 @@ Use -U for unattended even if initializing.
         printf "%-22s : %s\n" "** FATAL **" "Initialize needed - $reason"
         printf "%-22s : %s %s %s\n" "" \
             "But destination is too small to clone" "$n_image_parts" "partitions."
-        readable_MiB $((start_sector + 7812)) "512" min_size
+        readable_size $((start_sector + 7812)) "512" min_size
         printf "%-22s : %s\n" "" "Minimum destination size required is $min_size."
         if ((n_image_parts > 2)); then
             printf "%-22s : %s\n" " " "Possible options:"
@@ -1222,7 +1247,7 @@ Use -U for unattended even if initializing.
         exit 1
     fi
 
-    readable_MiB $((last_part_sectors + 7812)) "512" image_space_readable
+    readable_size $((last_part_sectors + 7812)) "512" image_space_readable
 
     echo "== Initialize: IMAGE partition table - $reason =="
     print_image_actions
@@ -1239,7 +1264,7 @@ Use -U for unattended even if initializing.
 
     abort=0
     if ((!last_part_space)); then
-        readable_MiB $last_part_used "512" used_readable
+        readable_size $last_part_used "512" used_readable
         printf "%-22s : %s\n" "** WARNING **" \
             "Destination last partition resize to $image_space_readable"
         printf "%-22s : %s\n" "" "  is too small to hold source used $used_readable."
@@ -1320,20 +1345,13 @@ Use -U for unattended even if initializing.
             printf "    Try running $PGM again.\n\n"
 
             # Don't let dst disk keep source disk ID.  Can lead to remounts.
-            new_id=$(od -A n -t x -N 4 /dev/urandom | tr -d " ")
-            qprintf "x\ni\n0x$new_id\nr\nw\nq\n" | fdisk /dev/$dst_disk > /dev/null
+            change_disk_id "$dst_disk"
             exit 1
         fi
     done
     printf "\n    Resize success.\n"
     printf "  Changing destination Disk ID ..."
-    sync
-    sleep 2
-
-    new_id=$(od -A n -t x -N 4 /dev/urandom | tr -d " ")
-    qprintf "x\ni\n0x$new_id\nr\nw\nq\n" | fdisk /dev/$dst_disk > /dev/null
-    sync
-    sleep 2
+    change_disk_id "$dst_disk"
     partprobe "/dev/$dst_disk"
     sleep 2
     echo ""
@@ -1457,11 +1475,7 @@ fi
 line=$(fdisk -l /dev/$dst_disk | grep "Disk identifier:")
 dst_disk_ID=${line#*x}
 if [ "$dst_disk_ID" == "$src_disk_ID" ]; then
-    qecho "Destination disk has same Disk ID as source, changing it."
-    new_id=$(od -A n -t x -N 4 /dev/urandom | tr -d " ")
-    qprintf "x\ni\n0x$new_id\nr\nw\nq\n" | fdisk /dev/$dst_disk | grep changed
-    sync
-    sleep 2
+    change_disk_id "$dst_disk" "Destination disk has same Disk ID as source, changing it."
     partprobe "/dev/$dst_disk"
     sleep 2
 
@@ -1538,13 +1552,7 @@ if [ -f $cmdline_txt ]; then
         cp $cmdline_txt ${clone}/${cmdlinedir}/cmdline.boot
         cmdline_txt=${clone}/${cmdlinedir}/cmdline.boot
     fi
-    if grep -q $src_disk_ID $cmdline_txt; then
-        qecho "Editing $cmdline_txt PARTUUID to use $dst_disk_ID"
-        sed -i "s/${src_disk_ID}/${dst_disk_ID}/" "$cmdline_txt"
-    elif [ "$edit_fstab_name" != "" ] && grep -q ${src_part_base} $cmdline_txt; then
-        qecho "Editing $cmdline_txt references from $src_part_base to $edit_fstab_name"
-        sed -i "s/${src_part_base}/$edit_fstab_name/" "$cmdline_txt"
-    fi
+    edit_disk_reference "$cmdline_txt" "$cmdline_txt"
     if ((leave_sd_usb_boot && SD_slot_boot)); then
         qecho "Copying USB cmdline.txt to SD card to set up USB boot."
         cp /${cmdlinedir}/cmdline.txt /${cmdlinedir}/cmdline.boot
@@ -1552,13 +1560,7 @@ if [ -f $cmdline_txt ]; then
     fi
 fi
 
-if grep -q $src_disk_ID $fstab; then
-    qecho "Editing $fstab PARTUUID to use $dst_disk_ID"
-    sed -i "s/${src_disk_ID}/${dst_disk_ID}/g" "$fstab"
-elif [ "$edit_fstab_name" != "" ] && grep -q ${src_part_base} $fstab; then
-    qecho "Editing $fstab references from $src_part_base to $edit_fstab_name"
-    sed -i "s/${src_part_base}/${edit_fstab_name}/" "$fstab"
-fi
+edit_disk_reference "$fstab" "$fstab"
 
 rm -f $clone/etc/udev/rules.d/70-persistent-net.rules
 
diff --git a/rpi-clone-setup b/rpi-clone-setup
index 5a3ff2e..00e5737 100755
--- a/rpi-clone-setup
+++ b/rpi-clone-setup
@@ -25,40 +25,43 @@
 #    Test new scripting by running:  rpi-clone-setup -t newhostname
 #
 
-file_list="etc/hostname etc/hosts"
+# shellcheck enable=require-variable-braces
 
+file_list=("etc/hostname" "etc/hosts")
 clone=/mnt/clone
 clone_test=/tmp/clone-test
 
-PGM=$(basename $0)
+PGM=$(basename "$0")
 
-if [ $(id -u) != 0 ]; then
-    echo "You must be root to run $PGM"
-    exit 0
+if [ "$(id -u)" != 0 ]; then
+    echo "You must be root to run ${PGM}"
+    exit 1
 fi
 
-function usage {
-    echo "Usage: $PGM hostname  {-t|--test}"
-    echo "   Eg:  $PGM rpi1"
+usage() {
+    echo "Usage: ${PGM} hostname  {-t|--test}"
+    echo "   Eg:  ${PGM} rpi1"
     echo "   Modify files appropriate to set up for a new host."
     echo "   Files handled are:"
-    for file in $file_list; do
-        echo "        $file"
+    for file in "${file_list[@]}"; do
+        echo "        ${file}"
     done
     echo ""
-    echo "If testing (-t flag) files are copied and processed to $clone_test"
+    echo "If testing (-t flag) files are copied and processed to ${clone_test}"
     echo ""
-    exit 0
+    exit 1
 }
 
 testing=0
-while [ "$1" ]; do
+newhost=""
+
+while [ "$#" -gt 0 ]; do
     case "$1" in
         -t | --test)
             testing=1
             ;;
         *)
-            if [ "$newhost" != "" ]; then
+            if [ -n "${newhost}" ]; then
                 echo "Bad args"
                 usage
             fi
@@ -68,31 +71,31 @@ while [ "$1" ]; do
     shift
 done
 
-if [ "$newhost" = "" ]; then
+if [ -z "${newhost}" ]; then
     echo -e "You must specify a target hostname\n"
     usage
 fi
 
-echo -e "\t$newhost\t- target hostname"
+echo -e "\t${newhost}\t- target hostname"
 
 if ((!testing)) && [ ! -d /mnt/clone/etc ]; then
     echo "A destination clone file system is not mounted on /mnt/clone"
     echo "Aborting!"
-    exit 0
+    exit 1
 fi
 
 if ((testing)); then
-    cd /tmp
-    rm -rf $clone_test
-    clone=$clone_test
+    cd /tmp || exit 1
+    rm -rf "${clone_test}"
+    clone=${clone_test}
 
-    mkdir -p $clone/etc
+    mkdir -p "${clone}/etc"
 
     echo "**********************************************"
-    echo "Testing setup: copying files to $clone"
-    for file in $file_list; do
-        echo "    cp /$file $clone/$file"
-        cp /$file $clone/$file
+    echo "Testing setup: copying files to ${clone}"
+    for file in "${file_list[@]}"; do
+        echo "    cp /${file} ${clone}/${file}"
+        cp "/${file}" "${clone}/${file}"
     done
     echo "This test run will modify those files."
     echo "**********************************************"
@@ -102,26 +105,26 @@ fi
 ##
 # Set /etc/hostname
 #
-cd $clone/etc
-echo $newhost > hostname
+echo "${newhost}" > "${clone}/etc/hostname"
+
 #
 # Read it back to verify.
 #
-echo "$clone/etc/hostname - set new hostname: "
-LINE=$(cat hostname)
-echo -e "$LINE\n"
+echo "${clone}/etc/hostname - set new hostname: "
+LINE=$(cat "${clone}/etc/hostname")
+echo -e "${LINE}\n"
 
 ##
 # Edit /etc/hosts - edit the sed command if editing fails for your /etc/hosts.
 #
-cd $clone/etc
-sed -i s/"$HOSTNAME"/"$newhost"/g hosts
+sed -i "s/${HOSTNAME}/${newhost}/g" "${clone}/etc/hosts"
+
 #
 # Read it back to verify.
 #
-echo "$clone/etc/hosts - set new hostname \"$newhost\" in lines: "
-LINE=$(grep $newhost hosts)
-echo -e "$LINE\n"
+echo "${clone}/etc/hosts - set new hostname \"${newhost}\" in lines: "
+LINE=$(grep "${newhost}" "${clone}/etc/hosts")
+echo -e "${LINE}\n"
 
 ##
 # Add more customizations if needed.