如何修复bash脚本中的数组错误？

Question

This is a bash script I can run it normally

#!/bin/bash
array=$(awk '{print $4}' /var/log/httpd/access_log | uniq -c | cut -d[ -f1)
sum=0 
sum1=0
arr=(${array[*]}) 
echo "After unquoted expansion: ${#arr[*]}"

for (( i=1; i<${#arr[@]}; i++ )); 
do 
sum=$( expr $sum - ${arr[$i]} ) 
sum1=$( expr $sum1 + $sum ) 
done 
echo 
echo "Sum of \$arr = ${sum1}" 
exit $sum

but When I change

sum=$( expr $sum - ${arr[$i]} )

by

sum=$( expr ${arr[$i+1]} - ${arr[$i]} )

or

j=$( expr $i + 1) sum=$( expr ${arr[$j]} - ${arr[$i]} )

it has error: expr: syntax error

Answer 1

Change the shebang to #!/bin/bash -x to see how the commands are executed and to see the arguments of the expr when it fails. When you see it, you might know the answer yourself. Otherwise, add it to your post.