all_products object
Looks up a product by its slug: all_products['slug']. The result is a product object, or nil.
A page can look up at most 20 different products this way. Further lookups return nil. To list products, use a collection instead, for example collections['all'].products.
liquid
{% assign product = all_products['linen-shirt'] %}
{% if product %}
<a href="{{ product.url }}">{{ product.name }}</a>
{% endif %}