<?php

function wp_scotch(){

    global $wpdb;

    $post_id = 1000;//place any value here
    $meta = array("thumb"=>"delete_target.php");
    $file = "../../tralalal.txt";

    //simulate the file value is taken via get_attached_file
    if ( $file && 0 !== strpos( $file, '/' ) && ! preg_match( '|^.:\\\|', $file ) && ( ( $uploads = wp_get_upload_dir() ) && false === $uploads['error'] ) ) {
        $file = $uploads['basedir'] . "/$file";
    }

    $uploadpath = wp_get_upload_dir();
    $deleted    = true;

    if ( ! empty( $meta['thumb'] ) ) {
        // Don't delete the thumb if another attachment uses it.
        if ( ! $wpdb->get_row( $wpdb->prepare( "SELECT meta_id FROM $wpdb->postmeta WHERE meta_key = '_wp_attachment_metadata' AND meta_value LIKE %s AND post_id <> %d", '%' . $wpdb->esc_like( $meta['thumb'] ) . '%', $post_id ) ) ) {
            $thumbfile = str_replace( basename( $file ), $meta['thumb'], $file );
            if ( ! empty( $thumbfile ) ) {
                $thumbfile = path_join( $uploadpath['basedir'], $thumbfile );
                $thumbdir  = path_join( $uploadpath['basedir'], dirname( $file ) );

                if ( ! wp_delete_file_from_directory( $thumbfile, $thumbdir ) ) {
                    $deleted = false;
                }
            }
        }
    }
}

add_action("init", "wp_scotch");