rtrim関数

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.
""(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