php 一个表单有多个按钮判断是哪个按钮提交的

if(!empty($_POST['submit1'])) {
$fileValue = "file1";
} else if(!empty($_POST['submit2'])) {
$fileValue = "file2";
}else if(!empty($_POST['submit3'])) {
$fileValue = "file3";
}else if(!empty($_POST['submit4'])) {
$fileValue = "file4";
}else if(!empty($_POST['submit5'])) {
$fileValue = "file5";
}