Redirect standard input dynamically in a bash script

Question

I was trying to do this to decide whether to redirect stdin to a file or not:

[ ...some condition here... ] && input=$fileName || input=\"&0\"
./         


        

Answer 1

(
    if [ ...some condition here... ]; then
        exec <$fileName
    fi
    exec ./myscript
)

In a subshell, conditionally redirect stdin and exec the script.