rtrim函数

string rtrim ( string $str [, string $charlist ] )
      Strip whitespace (or other characters) from the end of a string

" " (ASCII 32 (0x20)), an ordinary space.
"\t" (ASCII 9 (0x09)), a tab.
"\n" (ASCII 10 (0x0A)), a new line (line feed).
"\r" (ASCII 13 (0x0D)), a carriage return.
"\0" (ASCII 0 (0x00)), the NUL-byte.
"\x0B" (ASCII 11 (0x0B)), a vertical tab.

<?php
    echo rtrim('dir/','/');
?>

  dir