bash - Using a variable in brace expansion range fed to a for loop

Question

Here is myscript.sh

#!/bin/bash
for i in {1..$1};
do
    echo $1 $i;
done

If I run myscript.sh 3 the output is

3 {1..3}

instead of

3 1
3 2
3 3

Clearly $3 contains the right value, so why doesn't for i in {1..$1} behave the same as if I had written for i in {1..3} directly?

Answer 1

You should use a C-style for loop to accomplish this:

for ((i=1; i<=$1; i++)); do
   echo $i
done

This avoids external commands and nasty eval statements.