Unexpected loop behaviour in bash for loop

Question

Why does this code not execute the for loop in bash but print what it should loop over? How would execute the for loop like this?

read N R 
for i in {0..$[(N-1)*R]..$R};do
echo $i;done

Yes the code looks horrible but it was for a least amount of characters code challenge.

For code challenge purposes, you might want to consider `eval 'read N R; for i in {0..$[(N-1)*R]..$R}; do echo $i; done'`. — chepner, Nov 18 '20 at 21:53

markp-fuso · Accepted Answer · 2020-11-18T22:08:11.863

One idea for dynamically generating the desired range:

read N R

for i in $(seq 0 ${R} $(( (N-1)*R )) )
do
    echo $i
done

And reducing to the least number of characters:

read N R;for i in $(seq 0 $R $((N*R-R)));do echo $i;done

Though, generally speaking, I'd probably opt for something like:

$ cat ezrah
read N R

for (( i=0 ; i<= (N-1)*R ; i=i+R ))
do
    echo $i
done

A couple sample runs:

$ ezrah
3 4
0
4
8

$ ezrah
6 3
0
3
6
9
12
15

1 Answers1