//First add the filters functions

function wpe_excerptlength_teaser($length) {
    return 45;
}
function wpe_excerptlength_index($length) {
    return 30;
}
function wpe_excerptmore($more) {
    return '...';
}

// Then the function

function wpe_excerpt($length_callback='', $more_callback='') {
    global $post;
    if(function_exists($length_callback)){
        add_filter('excerpt_length', $length_callback);
    }
    if(function_exists($more_callback)){
        add_filter('excerpt_more', $more_callback);
    }
    $output = get_the_excerpt();
    $output = apply_filters('wptexturize', $output);
    $output = apply_filters('convert_chars', $output);
    $output = '<p>'.$output.'</p>';
    echo $output;
}

//The code for the template

<?php wpe_excerpt('wpe_excerptlength_index', 'wpe_excerptmore'); ?>
// the other one
<?php wpe_excerpt('wpe_excerptlength_teaser', 'wpe_excerptmore'); ?>

Change the excerpt value in functions.php

Custom wordpress excerpt lengths

wordpress

PHP