WordPress at a glance
function is not described

_wp_relative_upload_path() WP 2.9.0

Return relative path to an uploaded file.

The path is relative to the current upload dir.

Hooks in function
Return

String. Relative path on success, unchanged path on failure.

Usage

_wp_relative_upload_path( $path );
$path(string) (required)
Full path to the file.

Code of wp relative upload path: wp-includes/post.php WP 5.2.2

<?php
function _wp_relative_upload_path( $path ) {
	$new_path = $path;

	$uploads = wp_get_upload_dir();
	if ( 0 === strpos( $new_path, $uploads['basedir'] ) ) {
			$new_path = str_replace( $uploads['basedir'], '', $new_path );
			$new_path = ltrim( $new_path, '/' );
	}

	/**
	 * Filters the relative path to an uploaded file.
	 *
	 * @since 2.9.0
	 *
	 * @param string $new_path Relative path to the file.
	 * @param string $path     Full path to the file.
	 */
	return apply_filters( '_wp_relative_upload_path', $new_path, $path );
}