$fileContent = file_get_contents($_FILES['upload_file']['tmp_name']);

有关概述，请参见手册: $_FILES 本教程: Tizag PHP-文件上传进行演练.

Refer to the manual: $_FILES for an overview and this tutorial: Tizag PHP - File Upload for a walkthrough.

此PHP手册部分也是必读内容:处理文件上传-从hakre的评论中移出.

This PHP Manual section is a must-read as well: Handling File Uploads - moved from hakre's comment.