embulk の liquid template でハマったトコ ref: http://qiita.com/ukisoft/items/f628de4feb9335f99a68

file0.txt

{% include 'child', args = env.ARGS %}

file1.txt

{% assign args = env.ARGS %}
{% include 'child', args = args %}

file2.txt

# parent.yml.liquid
{% include 'child', args = 'ar' %}

file3.txt

# _child.yml.liquid
{% assing args = args | append: 'gs' %}
{% include 'grandchild1', args: args %}  # 'ar' が渡される
{% include 'grandchild2', args = args %}  # 'args' が渡される