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

How about

function runfrom {
    local input="$1"
    shift
    case "$input" in
        -) "$@" ;;
        *) "$@" < "$input" ;;
    esac
}

I've used the minus sign to denote standard input because that's traditional for many Unix programs.

Now you write

[ ... condition ... ] && input="$fileName" || input="-"
runfrom "$input" my-complicated-command with many arguments

I find these functions/commands which take commands as arguments (like xargs(1)) can be very useful, and they compose well.