#!/usr/bin/env bash

master="master.txt"
out=""

while IFS= read -r line; do
    if [[ "$line" =~ ^===\ FILE:\ (.*)\ ===$ ]]; then
        out="${BASH_REMATCH[1]}"
        dir=$(dirname "$out")
        mkdir -p "$dir"
        : > "$out"
        continue
    fi

    if [[ -n "$out" ]]; then
        echo "$line" >> "$out"
    fi
done < "$master"