How to display some selected user meta data on a specific page with a shortcode?

Question

I need to display on some specific pages some selected user meta data (not all), for some users.

On the Wordpress Codex page for the get_user_meta() function we have this example (user_id = 9):

<?php
  $all_meta_for_user = get_user_meta( 9 );
  print_r( $all_meta_for_user );
?>

The results of this example:

Array ( [first_name] => Array ( [0] => Tom ) [last_name] => Array ( [0] => Auger) [nickname] => Array ( [0] => tomauger ) [description] => etc.... )

And a Note (shortened):

... you may want to run a simple array_map() on the results of get_user_meta() in order to take only the first index of each result (this emulating what the $single argument does when $key is provided:

if( $all_meta_for_user = get_user_meta( $user_id ) ) 
    $all_meta_for_user = array_map( function( $a ){ return $a[0]; }, get_user_meta( $user_id ) );

  print_r( $all_meta_for_user );

The result:

Array ( [first_name] => Tom [last_name] => Auger [nickname] => tomauger [description] => etc.... )

My question is:

How to put this in a function that will display, for example, the user last and first names with a shortcode (but really I need more user meta data)?

What I mean? On a specific page we put a shortcode with the user ID and the related function must return the meta data for each selected key of this user. Is this possible? Can anyone help me?

Answer 1

Here is the simplest shortcode that will do the job for you

add_shortcode('USER_META', 'user_meta_shortcode_handler');
/**
 * User Meta Shortcode handler
 * usage: [USER_META user_id=1 meta="first_name"]
 * @param  array $atts   
 * @param  string $content
 * @return stirng
 */
function user_meta_shortcode_handler($atts,$content=null){
    return esc_html(get_user_meta($atts['user_id'], $atts['meta'], true));
}

USAGE:

[USER_META user_id=1 meta="first_name"]
[USER_META user_id=1 meta="last_name"]

Answer 2

Bellow you can see the adapted code of @Bainternet (thank you!) that I use currently. Now I can display with only one row/shortcode a big list of only custom user metadata that I need, in a custom order and formatted specifically for each type of input (text field input or textarea). Maybe the code can look better if I could get and display (HTML formatted) all the user meta data at once, excluding maybe a few, but this is too hard for me. Here is only an excerpt of the list of custom user metadata that I need to display, in reality it is longer.

add_shortcode( 'user_meta', 'user_meta_shortcode_handler' );
/**
 * User Meta Shortcode handler
 * usage: [user_meta user_id=1]
 * @param  array $atts   
 * @param  string $content
 * @return string
 */
function user_meta_shortcode_handler( $atts, $content=null ) {
    $output = "";
    echo '<div class="academic">';
    echo '<h3>Teaching position</h3>';
    echo esc_html( get_user_meta( $atts['user_id'], 'teaching_position', true ) );
    echo '<h3>Scientific title</h3>';
    echo esc_html( get_user_meta( $atts['user_id'], 'scientific_title', true ) );
    echo '<h3>Publications</h3>';
    echo wpautop( get_user_meta( $atts['user_id'], 'publications', true ) );
    echo '</div><!-- .academic -->';
}