Create a shortcode in WordPress

function1.php

<?php
function shortcode_function( $params ) {
    return "Shortcode content";
}
add_shortcode( 'shortcode_name', 'shortcode_function' );
?>

function2.php

<?php
function shortcode_function( $params ) {
    //Extract parameters and supply default values
    extract( shortcode_atts( array(
        'param1' => 'this',
        'param2' => 'that',
    ), $params ) );
    
    //The parameters are now stored as variables
    return "First parameter = " . $param1 . " | Second parameter = " . $param2;
}
add_shortcode( 'shortcode_name', 'shortcode_function' );
?>

function3.php

<?php
function shortcode_function( $params, $content = null ) {
    return "<div id='shortcode_content'>" . $content . "</div>";
}
add_shortcode( 'shortcode_name', 'shortcode_function' );
?>