Tracy Rotton

By default, the “Search” widget in WordPress will include the searchform.php template file in your theme (if it exists), or the search code in wp-includes/general-template.php (if it doesn’t). However, if you want a distinctive search form (or forms!) to use as a widget, this allows you to enter it in using the “searchform-identifier.php” format that you can use to distinguish other templates elsewhere in your theme. You just have to have that file set up in your theme with the HTML you want to use.
Example: If you want to have a distinct searchform file specifically for your widgets, create the template file and call it something like “searchform-widget.php” (what goes between the dash and the dot is up to you, so long as it meets filename requirements). In the “Template” field of the widget settings, enter only “widget”, and that searchform file will be called in your widget automagically.
Note: Actually coding the search form is up to you. That requires some theming skillz, but I have confidence in you!
To Do: Make a short-code version of this, for use in pages and posts.

TC Specify Search Form

Replaces the default WordPress "Search" widget with one that will use a customized searchform template in your theme.

VarDump s.r.l.

Get the PRO version: <a href="https://www.advancedcustomsearch.com/" rel="nofollow ugc">https://www.advancedcustomsearch.com/</a>
Advanced Post Search is a WordPress plugin for anyone who needs an advanced search for posts (or custom posts) in WordPress admin. 
Easily find posts by performing complex queries directly from the posts list and using specific filters for each field. It works with any post type and custom post type.
Advanced Post Search lets you search posts by any post attribute; search by:
<ul>
<li>Post Title</li>
<li>Post Content</li>
<li>Post Publish (date or date interval)</li>
<li>Post Last Modified (date or date interval)</li>
<li>Post Status</li>
<li>Post Password</li>
<li>Post Author</li>
<li>Post Excerpt</li>
<li>Post Slug</li>
</ul>
Specify which comparison operator you want to use; each field has its own comparison operators, according to the field type: for example, in <code>text</code> fields you can perform a <code>strict</code> or a <code>like</code> search.
You can manage search preferences from <code>Advanced Post Search » Views</code> in order to show/hide any search field for each post type.
<h4>Advanced Post Search PRO</h4>
Unlock extra features by upgrading Advanced Post Search to PRO version: 
<a href="https://www.advancedcustomsearch.com/" rel="nofollow ugc">https://www.advancedcustomsearch.com/</a>
<ul>
<li>Advanced Custom Fields support</li>
<li>Search posts by any of ACF custom fields (text, images, etc.)</li>
</ul>
<h4>Tested on</h4>
<ul>
<li>Microsoft Windows – Google Chrome</li>
<li>Microsoft Windows – IE9+ / Edge</li>
<li>Mac OS X – Firefox</li>
<li>Mac OS X – Google Chrome</li>
</ul>

Advanced Post Search

Add a search form based on Wordpress fields in posts list

TC Specify Search Form vs Advanced Post Search