How to make a pipe loop in bash

Question

Assume that I have programs P0, P1, ...P(n-1) for some n > 0. How can I easily redirect the output of program Pi

Answer 1

A command stack can be composed as string from an array of arbitrary commands and evaluated with eval. The following example gives the result 65536.

function square ()
{
  read n
  echo $((n*n))
}    # ----------  end of function square  ----------

declare -a  commands=( 'echo 4' 'square' 'square' 'square' )

#-------------------------------------------------------------------------------
#   build the command stack using pipes
#-------------------------------------------------------------------------------
declare     stack=${commands[0]}

for (( COUNTER=1; COUNTER<${#commands[@]}; COUNTER++ )); do
  stack="${stack} | ${commands[${COUNTER}]}"
done

#-------------------------------------------------------------------------------
#   run the command stack
#-------------------------------------------------------------------------------
eval "$stack"