use variables to define counters in nested for loop

Question

I'm new to bash scripting. I'm trying to use variables for counters in a nested for loop, like this:

dir_count=$(find dump_${d}/* -maxdepth 0 -type d | wc -l)
count_by=11

for ((i=0;i<=$dir_count;i+=$count_by))
do
    ((start=$i+1))
    ((end=$count_by+$i))
    echo  $start $end
    for dir in {$start..$end}
        echo $dir
    done
done

Output is this (I'm getting errors):

1 11
./loopy.sh: line 23: [: {1..11}: integer expression expected
12 22
./loopy.sh: line 23: [: {12..22}: integer expression expected
23 33
./loopy.sh: line 23: [: {23..33}: integer expression expected

1, 11, 12, 22, 23, 33 all look like integers to me! Is it possible to type variables? I thought it wasn't.

Thanks!

Inian · Accepted Answer · 2017-03-31 18:14:17Z

1

In bash, brace-expansion will happen much before variable-expansion, so your code

for dir in {$start..$end}

will never do what it is supposed to do; use a proper loop in bash with a C-style for-loop as

for ((dir=start; dir<=end; dir++)); do
    echo "$dir"
done

Quoting from the man bash page,

[..] Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result. It is strictly textual [..]

edited Mar 31, 2017 at 18:14

answered Mar 31, 2017 at 17:51

Inian

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