automatic jekyll breadcrumb

header_breadcrumb.html

<ol class="breadcrumb">
<li><a href="{{ site.baseurl }}/">Home</a></li>
{% capture page_url_without_index_html %}{{ page.url | remove: "/index.html" }}{% endcapture %}
{% assign splitted_url_parts = page_url_without_index_html | split: '/' %}
{% capture forLoopMaxInt %}{{ splitted_url_parts.size | minus:1 }}{% endcapture %}
{% for i in (1..forLoopMaxInt) %}
    {% capture current_breadcrumb_url %}{{next_prepender}}/{{ splitted_url_parts[i] }}/index.html{% endcapture %}
    {% capture current_breadcrumb_md_url %}{{next_prepender}}/{{ splitted_url_parts[i] }}/{% endcapture %}
    {% capture next_prepender %}{{next_prepender}}/{{ splitted_url_parts[i] }}{% endcapture %}
    {% for breadcrumb_page in site.pages %}
        {% if current_breadcrumb_url == breadcrumb_page.url or current_breadcrumb_md_url == breadcrumb_page.url  %}
        {% assign j = forLoopMaxInt | plus: 0 %}
            <li {% if i == j %}class="active"{% endif %}>
                {% capture breadcrumb_page_page_url_without_index_html %}{{ breadcrumb_page.url | remove: "index.html" }}{% endcapture %}
                <a href="{{ site.baseurl }}{{breadcrumb_page_page_url_without_index_html}}">{{breadcrumb_page.breadcrumb}}</a>
            </li>
        {% endif %}
    {% endfor %}
{% endfor %}
</ol>

Thanks for this gist.
For Bootstrap 4.1.1 breadcrumbs, the markup has changed a bit, and the active item doesn't need link. I've made these changes in my fork of this gist.