#!/bin/sh

set -e

if [ "$#" -ne 2 ]; then
    echo "Usage: $0 <init> <expr>"
    echo ""
    echo "Run the given command for each newline-separated line in stdin."
    echo 'The expression computes the next value of "$ACC" (think reduce in many programming languages).'
    echo 'The initial value of "$ACC" is the first argument to the script.'
    echo 'The iterator variable is called "$ELEM", and the index variable is called "$IDX".'
    echo 'The final value of "$ACC" is printed after all lines have been processed.'
    exit 1
fi

i=0
ACC="$1"
while IFS=$'\n' read -r line; do
    j=0
    for item in $line; do
        eval "X${j}='$item'"
        j=$((j+1))
    done

    IDX=$i ELEM="$line" eval "ACC=\"$2\""
    i=$((i+1))
done

echo "$ACC"