Getting value of variable from functions.php and debugging it

Question

I am trying to inspect a variable obtained in functions.php for debugging purposes. I am defining a variable $current_user by executing the shortcode to obtain the current logged-in user. Then I am using an if statement to validate that there is a currently logged-in user, in which case the CSS styling defined earlier in the function should be applied. It's not currently working, so I'm trying to investigate the $current_user variable, but none of the variations I have tried are working, including error_log.

functions.php (fragment):

add_shortcode('show_css_code_conditionally', 'show_css_code_conditionally_fn');
function show_css_code_conditionally_fn($atts) {

ob_start(); ?>
//   CSS code to show the button conditionally
<style type="text/css">

.special-button {
    display: block !important;
}

</style> <?php

    $CSS_output = ob_get_clean();

    $current_user = do_shortcode('[wpv-current-user]');
    error_log($current_user);
    echo($current_user);
    echo do_shortocde('[wpv-current-user]');
    print 'zzzy';
    ?><pre><?php var_dump( $current_user ); echo do_shortocde('[wpv-current-user]'); print 'zzzy'; ?></pre><?php

    if ($current_user) {
        // this is confirmed that the user is logged in
        return $CSS_output;
    }    
}

Answer 1

If nothing has been placed into your shortcode "wpv-current-user", you won't see anything in any of your output.

You should use the built-in function wp_get_current_user() for this.

Just beware that the Codex page warning. This may need to be called within an action that fires with or after the 'init' hook.

I have modified your code so you should get results from both error_log() and from placing your shortcode [show_css_code_conditionally] in a post/page.

add_shortcode('show_css_code_conditionally', 'show_css_code_conditionally_fn');
function show_css_code_conditionally_fn($atts) {

    ob_start(); ?>
    <!---   CSS code to show the button conditionally   -->
    <style type="text/css">

    .special-button {
        display: block !important;
    }

    </style> 
<?php
    $CSS_output = ob_get_clean();

    $current_user = wp_get_current_user();
    error_log($current_user->ID!==0 ? $current_user->user_email : 'User not logged in',0);        

<?php
    if ($current_user->ID!==0) {
        // this is confirmed that the user is logged in
        return $CSS_output;
    }  else {
        return "\n<!--  No valid user currently logged in  -->\n\n";
    }
}

Since I don't know what the shortcode [wpv-current-user] refers to, I just left it out. Usually, you would just do_shortcodes() to execute all applicable shortcodes, especially when you are already in a shortcode function.