Shell script "for" loop syntax

Question

I have gotten the following to work:

for i in {2..10}
do
    echo "output: $i"
done

It produces a bunch of lines of output: 2, output: 3, so on.

However, trying to run the following:

max=10
for i in {2..$max}
do
    echo "$i"
done

produces the following:

output: {2..10}

How can I get the compiler to realize it should treat $max as the other end of the array, and not part of a string?

user_6714430 · Answer

We can iterate loop like as C programming.

#!/bin/bash
for ((i=1; i<=20; i=i+1))
do 
      echo $i
done

user_2458916 · Answer

Here it worked on Mac OS X.

It includes the example of a BSD date, how to increment and decrement the date also:

for ((i=28; i>=6 ; i--));
do
    dat=`date -v-${i}d -j "+%Y%m%d"` 
    echo $dat
done