shell pipe process repeat

Question

I want to do something like this:

~ cat dump.sh
command 1 | command 2 | command 1 | command 2 | ...(ten times) | command 1 | command2

~ ./dump.sh < demo.log

So how to modify dump.sh while I can specify exactly n times of command 1 and command 2 in pair to process demo.log?

Answer 1

You can write a simple recursive helper function, something like this:

loop () {
    case $1 in
      0) cat;;
      *) command 1 | command 2 | loop $(($1 - 1)) ;;
    esac
}

Invoke it like

loop 3 <demo.log