[Shell] 求素数的脚本

#!/bin/bash

#
# primes.sh - find all prime numbers up to a certain number
#
#

factorial ()  {
 local factorial_count=$1
 if [ "$factorial_count" -eq 0 ]
 then
  factorial_count=1
 fi
 for (( factor=$((factorial_count -1)); $factor >= 1; --factor ))
 do
  factorial_count=$(($factorial_count * $factor))
 done
 echo $factorial_count
}

prime_number ()  {
 local prime=$1
 p_minus_1=$(($prime - 1))
 fact_p_minus_1=`factorial "$p_minus_1"`
 fact_plus_1=$(($fact_p_minus_1 + 1))
 echo $fact_plus_1
}

highest_number=$1

if [ -z $highest_number ]
then
 echo
 echo "Usage: $0 highestNumber"
 echo
 exit 1
fi

if [ $highest_number -eq 0 ]
then
 echo
 echo "Sorry.  0 is not a prime number"
 echo
 exit 0
elif [ $highest_number -eq 1 ]
then
 echo
 echo "Sorry.  0 and 1 are not prime numbers"
 echo
 exit 0
fi

echo "Generating Prime Numbers Up To $highest_number"
if [ $highest_number -eq 2 ]
then
 echo
 echo -n "2" 
else
 echo
 echo -n "2 3 " 
fi

count=4
while [ $count -le $highest_number ]
do
 prime_return=`prime_number "$count"`
 prime_test=$(($prime_return % count))
 if [ $prime_test -eq 0 ]
 then
  echo -n "$count "
 fi
 count=$(($count + 1))
done

echo
echo
echo "All Set!"
echo

exit 0