PHP删除var上的第一个零

I want to remove all 0s placed at the beginning of some variable. I'm sending

var = 93 

by ajax when i echo it's 093

I tried

  $exam_sn = ltrim($exam_sn, "0")   ;

  $exam_sn = (float)$exam_sn    ;

  $exam_sn =  preg_replace('~^[0]*([1-9][0-9]*)$~','$1',$exam_sn) ;

doesn't work. I also tried

$exam_sn = ltrim($exam_sn, "09")    ;

the value = 03