为什么 php 动态值不显示（回显）？

Question

the "echo $FacebookURL" does not display but if I move it to the inner most "foreach" it works. I need to display after all foreach are completed. note: [the conditional below is valid]

$acf_metas = ['FacebookURL','SpotifyURL'];

foreach ($acf_metas as $acf_meta) {
    foreach ( get_field($acf_meta, 95013) as $k => $v) {
        ///set dynamic value
       ${$acf_meta}  = ( $k ==='main_url' ? $v .' -- ': false );
       // displays here ok 
       // echo $FacebookURL;
    }

}
//display dynamic value here does not display [the conditional above is valid]
echo $FacebookURL;

Answer 1

You seem to be overwriting the value of $FacebookURL in the foreach at every iteration. This way, it becomes false at a certain point of time and does not echo any output. To see values at each iteration, do

 var_dump($FacebookURL);