Syntax

get_option( string $option, mixed $default = false )

Usage

It is used to check whether you need to install an option. get_option() is commonly used during the installation of plugin options and to test whether upgrading is required or not.
Add this below code in wp-includes/plugin.php

function get_option( $option, $default = false ) {
    global $wpdb;
    $option = trim( $option );
    if ( empty( $option ) ) {
        return false;
    }
    $pre = apply_filters( "pre_option_{$option}", false, $option, $default );
    if ( false !== $pre ) {
        return $pre;
    }
    if ( defined( 'WP_SETUP_CONFIG' ) ) {
        return false;
    }
    $passed_default = func_num_args() > 1;
    if ( ! wp_installing() ) {
        // prevent non-existent options from triggering multiple queries
        $notoptions = wp_cache_get( 'notoptions', 'options' );
        if ( isset( $notoptions[ $option ] ) ) {
            return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
        }
    $alloptions = wp_load_alloptions();
        if ( isset( $alloptions[ $option ] ) ) {
            $value = $alloptions[ $option ];
        } else {
            $value = wp_cache_get( $option, 'options' );
            if ( false === $value ) {
                $row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
                // Has to be get_row instead of get_var because of funkiness with 0, false, null values
                if ( is_object( $row ) ) {
                    $value = $row->option_value;
                    wp_cache_add( $option, $value, 'options' );
                } else { // option does not exist, so we must cache its non-existence
                    if ( ! is_array( $notoptions ) ) {
                        $notoptions = array();
                    }
                    $notoptions[ $option ] = true;
                    wp_cache_set( 'notoptions', $notoptions, 'options' );
                    /** This filter is documented in wp-includes/option.php */
                    return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
                }
            }
        }
    } else {
        $suppress = $wpdb->suppress_errors();
        $row   = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
        $wpdb->suppress_errors( $suppress );
        if ( is_object( $row ) ) {
            $value = $row->option_value;
        } else {
            /** This filter is documented in wp-includes/option.php */
            return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
        }
    }
    if ( 'home' == $option && '' == $value ) {
        return get_option( 'siteurl' );
    }
    if ( in_array( $option, array( 'siteurl', 'home', 'category_base', 'tag_base' ) ) ) {
        $value = untrailingslashit( $value );
    }
    return apply_filters( "option_{$option}", maybe_unserialize( $value ), $option );
}