Something

#!/bin/sh
#
if [ $# -ne 1 ]; then
cat 2>&1 << EOF
##############################################
 fanctrl
 -------
 purpose: adjusts Kurobox fan speed based on supplied argument

 author: Mathias Weiersmueller ( matti_at_weiersmuellerdotcom )
 version: 1.0
 date:    20060917
 license: LGPL, no warranty, use at your own risk

 arguments:
 auto     = sets fan to low/high speed depending on current temp
            (based in variable HD_TEMP)
 low      = sets fan to low speed
 high     = sets fan to high speed
 (number) = sets fan to high speed if HD temp is
            equal or higher than (number), or to low speed
            if HD temp is lower
###############################################
EOF
exit 127
fi

MAX_TEMP=37     # this is Celsius, not Fahrenheit
HD_TEMP=`/usr/sbin/hddtemp -nq /dev/hda`

# AVR
#
TTY="/dev/ttyS1"
STR_L="\\\\"
STR_H="]]]]"

###############################
# functions

fanlow() {
  echo -n "${STR_L}" > $TTY
  echo LOW
}

fanhigh() {
echo -n "${STR_H}" > $TTY
   echo HIGH
}

################################
# main

case $1 in

  auto)
    if [ $HD_TEMP -ge $MAX_TEMP ]
      then fanhigh
    else fanlow
    fi
  ;;

  low)
    fanlow
  ;;

  high)
    fanhigh
  ;;

  -h|--help|-help|-\?)
    exec fanctrl # calls fanctrl without arguments, thus displaying help...
   ;;

  *)
    if expr "$1" : "[0-9][0-9]" >/dev/null     # check for 2-digit number
      then
        if [ $HD_TEMP -ge $1 ]
          then fanhigh
        else fanlow
        fi
    else echo "error: wrong arguments";exit 127;
    fi
  ;;
esac