do_subst.sh

#!/bin/bash

function get_new_names() {
    local input_names=$1
    sed 's/[ \t]\+/:/g' $input_names
}

function gen_subst_func() {
    local from=$1
    local to=$2
    local func_name=$3

    eval "
        function $func_name () {
            sed \"s/$from/$to/g\"
        }"
}

main() {
    local input_names=$1

    if [ -z "$input_names" ]; then
        echo "Usage: $0 <config file>" 1>&2
        exit 1
    elif [ ! -e "$input_names" ]; then
        echo "File \"$input_names\" not found" 1>&2
        exit 1
    fi

    local new_names=$(get_new_names $input_names)
    local i=1
    local chain_str=''
    local func_name=''

    for nn in $new_names; do
        gen_subst_func "${nn%%:*}" "${nn##*:}" "subst_func_$i"
        chain_str="$chain_str | subst_func_$i"
        i=$(expr $i + 1)
    done

    eval "cat $chain_str"
}

main $@