diff --git a/writeimage.sh b/writeimage.sh
index 665df07481..6531da7d40 100755
--- a/writeimage.sh
+++ b/writeimage.sh
@@ -2,14 +2,16 @@
 
 
 function usage() {
-    echo "Usage: $0 [options...]"
-    echo ""
-    echo "Available options:"
-    echo "    <-i image_file> - indicates the path to the image file (e.g. -i /home/user/Download/file.img.gz)"
-    echo "    <-d sdcard_dev> - indicates the path to the sdcard block device (e.g. -d /dev/mmcblk0)"
-    echo "    [-m modem:apn:user:pwd:pin] - configures the mobile network modem (e.g. -m ttyUSB0:internet)"
-    echo "    [-n ssid:psk] - sets the wireless network name and key (e.g. -n mynet:mykey1234)"
-    echo "    [-s ip/cidr:gw:dns] - sets a static IP configuration instead of DHCP (e.g. -s 192.168.1.101/24:192.168.1.1:8.8.8.8)"
+    cat <<END_USAGE
+Usage: $0 [options...]
+
+Available options:
+    <-i image_file> - indicates the path to the image file (e.g. -i /home/user/Download/file.img.gz)
+    <-d sdcard_dev> - indicates the path to the sdcard block device (e.g. -d /dev/mmcblk0)
+    [-m modem:apn:user:pwd:pin] - configures the mobile network modem (e.g. -m ttyUSB0:internet)
+    [-n ssid:psk] - sets the wireless network name and key (e.g. -n mynet:mykey1234)
+    [-s ip/cidr:gw:dns] - sets a static IP configuration instead of DHCP (e.g. -s 192.168.1.101/24:192.168.1.1:8.8.8.8)
+END_USAGE
     exit 1
 }
 
@@ -64,14 +66,14 @@ function cleanup {
     set +e
 
     # unmount sdcard
-    umount ${SDCARD_DEV}* >/dev/null 2>&1
+    umount "${SDCARD_DEV}"* >/dev/null 2>&1
 }
 
 trap cleanup EXIT
 
-BOOT=$(dirname $0)/.boot
+BOOT=$(dirname "$0")/.boot
 
-if ! [ -f $DISK_IMG ]; then
+if ! [ -f "$DISK_IMG" ]; then
     echo "could not find image file $DISK_IMG"
     exit 1
 fi
@@ -85,7 +87,7 @@ if [[ $DISK_IMG == *.gz ]]; then
         exit 1
     fi
     msg "decompressing the .gz compressed image"
-    $gunzip -c $DISK_IMG > ${DISK_IMG%???}
+    $gunzip -c "$DISK_IMG" > "${DISK_IMG%???}"
     DISK_IMG=${DISK_IMG%???}
 elif [[ $DISK_IMG == *.xz ]]; then
     if [ -z "$unxz" ]; then
@@ -93,84 +95,90 @@ elif [[ $DISK_IMG == *.xz ]]; then
         exit 1
     fi
     msg "decompressing the .xz compressed image"
-    $unxz -T 0 -c $DISK_IMG > ${DISK_IMG%???}
+    $unxz -T 0 -c "$DISK_IMG" > "${DISK_IMG%???}"
     DISK_IMG=${DISK_IMG%???}
 fi
 
-umount ${SDCARD_DEV}* 2>/dev/null || true
+umount "${SDCARD_DEV}"* 2>/dev/null || true
 msg "writing disk image to sdcard"
-dd if=$DISK_IMG of=$SDCARD_DEV bs=1048576
+dd if="$DISK_IMG" of="$SDCARD_DEV" bs=1048576
 sync
 
 if which partprobe > /dev/null 2>&1; then
     msg "re-reading sdcard partition table"
-    partprobe ${SDCARD_DEV}
+    partprobe "${SDCARD_DEV}"
     sleep 1
 fi
 
 msg "mounting sdcard"
-mkdir -p $BOOT
+mkdir -p "$BOOT"
 
-if [ `uname` == "Darwin" ]; then
+if [ "$(uname)" == "Darwin" ]; then
     BOOT_DEV=${SDCARD_DEV}s1 # e.g. /dev/disk4s1
-    diskutil unmountDisk ${SDCARD_DEV}
-    mount -ft msdos $BOOT_DEV $BOOT
+    diskutil unmountDisk "${SDCARD_DEV}"
+    mount -ft msdos "$BOOT_DEV" "$BOOT"
 else # assuming Linux
     BOOT_DEV=${SDCARD_DEV}p1 # e.g. /dev/mmcblk0p1
-    if ! [ -e ${SDCARD_DEV}p1 ]; then
+    if ! [ -e "${SDCARD_DEV}p1" ]; then
         BOOT_DEV=${SDCARD_DEV}1 # e.g. /dev/sdc1
     fi
-    mount $BOOT_DEV $BOOT
+    mount "$BOOT_DEV" "$BOOT"
 fi
 
 # wifi
 if [ -n "$SSID" ]; then
     msg "creating wireless configuration"
     conf=$BOOT/wpa_supplicant.conf
-    echo "update_config=1" > $conf
-    echo "ctrl_interface=/var/run/wpa_supplicant" >> $conf
-    echo "network={" >> $conf
-    echo "    scan_ssid=1" >> $conf
-    echo "    ssid=\"$SSID\"" >> $conf
+    {
+    echo "update_config=1"
+    echo "ctrl_interface=/var/run/wpa_supplicant"
+    echo "network={"
+    echo "    scan_ssid=1"
+    echo "    ssid=\"$SSID\""
     if [ -n "$PSK" ]; then
-        echo "    psk=\"$PSK\"" >> $conf
+        echo "    psk=\"$PSK\""
     fi
-    echo "}" >> $conf
-    echo "" >> $conf
+    echo "}"
+    echo ""
+    } > "$conf"
 fi
 
 # modem
 if [ -n "$MODEM" ]; then
     msg "creating mobile network configuration"
     conf=$BOOT/ppp
-    mkdir -p $conf
-    echo $MODEM > $conf/modem
-    echo "AT+CGDCONT=1,\"IP\",\"$APN\"" > $conf/apn
-    echo > $conf/extra
-    echo > $conf/auth
-    echo > $conf/pin
+    mkdir -p "$conf"
+    echo "$MODEM" > "$conf/modem"
+    echo "AT+CGDCONT=1,\"IP\",\"$APN\"" > "$conf/apn"
+    echo > "$conf/extra"
     if [ -n "$MUSER" ]; then
-        echo "user \"$MUSER\"" > $conf/auth
-        echo "password \"$MPWD\"" >> $conf/auth
-    fi
+        echo "user \"$MUSER\""
+        echo "password \"$MPWD\""
+    else
+        echo
+    fi > "$conf/auth"
     if [ -n "$PIN" ]; then
-        echo "AT+CPIN=$PIN" > $conf/pin
-    fi
+        echo "AT+CPIN=$PIN"
+    else
+        echo
+    fi > "$conf/pin"
 fi
 
 # static ip
 if [ -n "$IP" ] && [ -n "$GW" ] && [ -n "$DNS" ]; then
     msg "setting static IP configuration"
     conf=$BOOT/static_ip.conf
-    echo "STATIC_IP=\"$IP\"" > $conf
-    echo "STATIC_GW=\"$GW\"" >> $conf
-    echo "STATIC_DNS=\"$DNS\"" >> $conf
+    {
+    echo "STATIC_IP=\"$IP\""
+    echo "STATIC_GW=\"$GW\""
+    echo "STATIC_DNS=\"$DNS\""
+    } > "$conf"
 fi
 
 msg "unmounting sdcard"
 sync
-umount $BOOT
-rmdir $BOOT
+umount "$BOOT"
+rmdir "$BOOT"
 
 msg "you can now remove the sdcard"