Customize the excerpt length, strip tags, append, and change the "Read More" text

functions.php

<?php
// DO NOT INCLUDE OPENING PHP TAG

/**
 * Customize the excerpt length and strip tags
 */
function custom_excerpt ( $text ) {

	global $post;

	// Set defaults
	$excerpt_length    = 30;     // excerpt length in words
	$allowed_html_tags = '';     // allowed html tags, e.g., <a><p><strong>  etc...
	$append_with       = '...';  // append the excerpt with something special, e.g., ... or [...]

	// If there is an excerpt
	if ( '' === $text ) {
		$text  = get_the_content( '' );
		$text  = str_replace( '\]\]\>', ']]&gt;', $text );
		$text  = strip_shortcodes( $text );
		$text  = apply_filters( 'the_content', $text );
		$text  = strip_tags( $text, $allowed_html_tags );
		$words = explode( ' ', $text, $excerpt_length + 1 );

		// Shorten the excerpt
		if ( count( $words ) > $excerpt_length ) {
			array_pop( $words );
			array_push( $words, $append_with );
			$text = implode( ' ', $words );
		}
	}

	return $text;
}
remove_filter( 'get_the_excerpt', 'wp_trim_excerpt' );
add_filter( 'get_the_excerpt', 'custom_excerpt' );

functions2.php

<?php
// DO NOT INCLUDE OPENING PHP TAG

/**
 * Customize the Read More text
 */
function custom_excerpt_read_more( $output ) {
	return $output . '<a class="read-more" href="'. get_permalink( get_the_ID() ) . '"> ' . __( 'Read More', 'textdomain' ) . '</a>';
}
add_filter( 'the_excerpt', 'custom_excerpt_read_more' );