How to fix a error with array in bash script?

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

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. — janos
– janos, Commented Nov 17, 2013 at 15:44
when I use #!/bin/bash -x , I saw where the problem is. Thanks @janos a lot. — TrungTrung
– TrungTrung, Commented Nov 17, 2013 at 16:20
Instead of using expr you can do sum=$(( ${arr[$i+1]} - ${arr[$i]} )) for arithmetic expansion. You could possibly also use let ... — bryn
– bryn, Commented Nov 17, 2013 at 17:10

janos · Accepted Answer · 2013-11-17 16:22:26Z

2

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.

answered Nov 17, 2013 at 16:22

janos

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