How to use Rainbow Tables

Hi.

I have this script in Linux which finds a password by using brute force:

#!/bin/bash

space="a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z"

if [  $# -le 1 ]
then 
	echo "Usage: " $0 SALT PASSWORD_CODED
	exit
fi

for i in $space
do
for j in $space
do
for k in $space
do

	variable=$(openssl passwd -crypt -salt "$1" "$i$j$k")
	if [ "$variable" = $2 ]
	    then
		echo password found: $i$j$k
		exit
	fi
done
done
done

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If I execute it as:

 ./script ok okZdSfLRp/FqA

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then I get the password "abc".

However, if I execute it as:

./script vt vt/4.cscQFn1M

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then the program last a lot.

Is there a way to modify this script so it works quickly? Maybe using the Rainbow Tables technique? How can this be done?

Thank you