Printing first line of content in wordpress

Question

I'm trying to print just the first line of content on wordpress post:

$lines=the_content();
$lines=explode("\n", $string);
echo $lines['0'];

But it doesn't work. I must say I have looked everywhere, even trying with this and this. But nothing works... what can I do? Thanks in advance.

EDIT: I add this for you to understand better what I want to do. I want to print different content depending of the publishing date of the post. So, I have more than 300 posts that have a link of youtube/vimeo in the first line that converts into an iframe when it is printed. So i need that the first line of the content gets printed, because the rest is given by the different snippets: titulo, duracion, sinopsis, etc...

        $pdate  = strtotime(get_the_date("d/m/y")); 
$mydate =   strtotime('09/10/2019');
if ($pdate < $mydate)
{
           echo ONLY FIRST LINE OF CONTENT;

            echo '<br/>';
            echo '<strong>Título:</strong> ';
            echo ''.the_title().'.<br/>';


    echo '<strong>Duración:</strong> '.get_post_meta(get_the_ID(), 'time_duration', TRUE).'';
    echo '<br/>';

    echo '<strong>Sinopsis:</strong> ';
    echo get_the_excerpt();
    echo '<br/>';

    echo '<strong>Director/@s:</strong> ';
    echo get_the_term_list( $post->ID, 'director', '', ', ', '');
    echo '.<br/>';

    echo '<strong>Género:</strong> ';
    echo get_the_term_list( $post->ID, 'genero', '', ', ', '');
    echo '.<br/>';

    echo '<strong>Año de producción:</strong> ';
    echo get_the_term_list( $post->ID, 'any');
    echo '.<br/>';

    echo '<strong>Recomendación por edades:</strong> ';
    $category = get_the_category();
    $first_category = $category[0];
    echo sprintf( '<a href="%s">%s</a>', get_category_link( $first_category ), $first_category->name );
    echo '.<br/>';

    echo '<strong>País/es:</strong> ';
    echo get_the_term_list( $post->ID, 'pais');
    echo '.<br/>';

    echo '<strong>Idioma:</strong> ';
    echo get_the_term_list( $post->ID, 'idioma');
    echo '.<br/>';

    echo '<strong>Información adicional:</strong> '.get_post_meta(get_the_ID(), 'informacionadicional', TRUE).'';
    echo '<br/>';
    echo '<br/>';

}
else {
        echo '<br/>';
        echo $td_mod_single->get_content();
        echo '<strong>Título:</strong> ';
        echo ''.the_title().'.<br/>';


    echo '<strong>Duración:</strong> '.get_post_meta(get_the_ID(), 'time_duration', TRUE).'';
    echo '<br/>';

    echo '<strong>Sinopsis:</strong> ';
    echo get_the_excerpt();
    echo '<br/>';

    echo '<strong>Director/@s:</strong> ';
    echo get_the_term_list( $post->ID, 'director', '', ', ', '');
    echo '.<br/>';

    echo '<strong>Género:</strong> ';
    echo get_the_term_list( $post->ID, 'genero', '', ', ', '');
    echo '.<br/>';

    echo '<strong>Año de producción:</strong> ';
    echo get_the_term_list( $post->ID, 'any');
    echo '.<br/>';

    echo '<strong>Recomendación por edades:</strong> ';
    $category = get_the_category();
    $first_category = $category[0];
    echo sprintf( '<a href="%s">%s</a>', get_category_link( $first_category ), $first_category->name );
    echo '.<br/>';

    echo '<strong>País/es:</strong> ';
    echo get_the_term_list( $post->ID, 'pais');
    echo '.<br/>';

    echo '<strong>Idioma:</strong> ';
    echo get_the_term_list( $post->ID, 'idioma');
    echo '.<br/>';

    echo '<strong>Información adicional:</strong> '.get_post_meta(get_the_ID(), 'informacionadicional', TRUE).'';
    echo '<br/>';
    echo '<br/>';

}

Answer 1

What you can do is work with this the_excerpt() change this instead of the_content();

And give the amount of words that you want, add this in functions.php after you add the_excerpt();

function custom_excerpt_length( $length ) {
    return 20;
}
add_filter( 'excerpt_length', 'custom_excerpt_length', 999 );

Read more in here: https://developer.wordpress.org/reference/functions/the_excerpt/