Bash parameter reference

I want to refer to a parameter in bash by using a number generated by a sum. How do I do this?

More specifically:

    #!/bin/bash

    $sum=${$1}
    echo $sum

When I execute the script ./script.bash A B C D, if $sum = 3, then I want to开发者_Python百科 return C. How do I do this, does anyone know?

You can use the indirect expansion syntax:

${!parameter}

as described here.

(Also note that variable assignments should not have a $ on the left-hand side!)

Example:

$ cat script.bash 
#!/bin/bash

sum=3
arg=${!sum}
echo $arg
$ ./script.bash A B C D
C
$