Shell Programming and Scripting

num_null_key=0			#for counting the number of null keys
num_non_null_key=0		#for counting the number of non null keys
while (key <= last_key)
{
        if ($key == "")
        {
                full_key = full_key " NULL"		#full_key will be concatenated
                if ($num_non_null_key == 0)	#this condition will be matched once
                	num_null_key++		#only when num_non_null_key=0
                printf("%d",num_null_key)
        }
        else
        {
                full_key = full_key " " key		#full_key will be concatenated
                num_non_null_key++		#so in the next loop the inner 'if' of the previous block will be tested
                non_null_key = non_null_key " " key #non_nulll_key will concatenated
                printf("%d",num_non_null_key)
        }
        key++
}