Mine

#!/bin/sh

# default values
PREFIX="/usr/local"
ARCH="C"

case $(uname -m) in
        i*86) ARCH="x86" ;;
        x86_64) ARCH="amd64" ;;
esac

for opt do
        case "$opt" in
                --prefix=*) PREFIX="${opt#*=}"
        esac
done

rm -f config.make
echo "PREFIX   = ${PREFIX}" >> config.make
echo "ARCH     = ${ARCH}" >> config.make

echo "prefix:   ${PREFIX}"
echo "arch:     ${ARCH}"