重定向sed输出

#!/bin/bash

# add commas to numbers in factorial answer

factorial=1
counter=1
number=$1

while [ $counter -le $number ]
do
    factorial=$[ $factorial * $counter ]
    counter=$[ $counter + 1 ]
done

result=`echo $factorial | sed '{
:start
s/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/
t start
}'`

echo "The result is $result"