sieve.sh

aecho -n "Enter the last number to check for prime-iness: "
read MAX
while [ -n "$(echo ${MAX} | sed -E "s/[0-9]*//g")" -o ${MAX} -ge 274 ]
   if [ ${MAX} -ge 274 ]
      aecho "Sorry, the line buffers are too short to hold that many numbers."
      aecho -n "Please enter a number: "
   else
      aecho -n "'${MAX}' is not a number. Please enter a number: "
   end
   read MAX
end
envset IX 2
while [ ${IX} -le ${MAX} ]
   envset NUMS "${NUMS} ${IX}"
   envset IX $(expr ${IX} + 1)
end
aecho -n "Would you like to display composite numbers as well? (y/n) "
read SHOW_COMP
while [ ${SHOW_COMP} != "y" -a ${SHOW_COMP} != "n" ]
   aecho -n "Please enter a 'y' or 'n' "
   read SHOW_COMP
end
#While NUMS is not empty
while echo ${NUMS} | grep "[0-9]" > /dev/null
   #Copy NUMS to TNUMS, delete NUMS
   envset TNUMS "${NUMS}"
   envunset NUMS
   #set PRIME to the first element of TNUMS
   if [ -n "$(echo ${TNUMS} | sed -E "s/[0-9]*\s+(.*)?/\1/g")" ]
      envset PRIME "$(echo ${TNUMS} | sed -E "s/([0-9]*)\s+.*/\1/g")"
   else
      envunset TNUMS
   end
   #remove the first element of TNUMS
   if [ -n "$(echo ${TNUMS} | sed -E "s/[0-9]*\s*(.*)?/\1/g")" ]
      envset TNUMS "$(echo ${TNUMS} | sed -E "s/[0-9]*\s+(.*)?/\1/g")"
   else
      envunset TNUMS
   end
   echo ${PRIME} is a prime!
   #while TNUMS is not empty
   while echo ${TNUMS} | grep "[0-9]" > /dev/null
      #set CAND to the first element of TNUMS
      envset CAND "$(echo ${TNUMS} | sed -E "s/([0-9]*)(\s+.*)?/\1/g")"
      #remove the first element of TNUMS
      if [ -n "$(echo ${TNUMS} | sed -E "s/[0-9]*\s+(.*)?/\1/g")" ]
         envset TNUMS "$(echo ${TNUMS} | sed -E "s/([0-9]*)(\s+.*)?/\2/g")"
      else
         envunset TNUMS
      end
      #if PRIME is a factor of CAND
      if [ $(expr ${CAND} % ${PRIME}) -eq 0 ]
         if [ ${SHOW_COMP} = y ]
            echo "   ${CAND} is composite: ${PRIME} is a factor"
         end
      else
         envset NUMS "${NUMS} ${CAND}"
      end
   end
end