Template file shortcode

short-code-template.php

<?php
/**
 * Register shortcode [my-template]
 * 
 * File based short code.
 * 
 * @param array  $atts    Shoutcode attribures.
 * @param string $string  Content wrapped in shortcode.
 * @return string Rendered result.
 */
add_shortcode( 'my-template', function( $atts = [], $string = '' ) {
	// Get attributes default values.
	$atts = shortcode_atts( [
		'template' => '',
	], $atts, 'my-template' );
	// Buffer rendered result.
	// For more details, see {http://php.net/manual/en/function.ob-start.php}
	ob_start();
	// In this example, simply load template file.
	get_template_part( 'template-parts/page', $atts['template'] );
	// Grab buffered strint output.
	$content = ob_get_contents();
	// Clear output because this is shortcode!
	ob_end_clean();
	// Remove all tabs and line breaks step by step.
	// Explode rendered string with line break.
	$lines = explode( "\n", $content );
	// Trim each line.
	$lines = array_map( function( $line ){
		return trim( $line );
	}, $lines );
	// Filter empty line.
	// Because, empty line causes unexpected 'p' in WordPress.
	$lines = array_filter( $lines );
	// Now return them combineded with line break.
	return implode( "\n", $lines );
} );