<"cat isn't \n dog";
$result = nl2br($str);
echo $result;
/**结果
cat isn't
dog
*/

<"Hello world ";
echo strlen($str)."<br>";
$result = rtrim($str);
echo strlen($result);
/**结果
14
11
*/

<"<font color = 'red'>Hello world</font>";
$result = strip_tags($str);
echo $result;
/**结果
Hello world
*/

<"Hello World!";
$result = strtolower($str);
echo $result."<br>";
$result = strtoupper($str);
echo $result;
/**结果
hello world!
HELLO WORLD!
*/

<" Hello World! ";
$result = trim($str);
echo $str."<br>";
echo $result."<br>";
echo strlen($str)."<br>";
echo strlen($result);
/**结果
Hello World!
Hello World!
16
12
*/

<"zhang san";
$result = str_ireplace("zhang","li",$str);
echo $str."<br>";
echo $result;
/**结果
zhang san
li san
*/

<"Hello jiqing!";
$result = str_repeat($str,4);
echo $str."<br>";
echo $result;
/**结果
Hello jiqing!
Hello jiqing!Hello jiqing!Hello jiqing!Hello jiqing!
*/

<"hello jiqing!";
$result1 = str_ireplace("Hello","Hi",$str); //不区分大小写
$result2 = str_replace("Hello","Hi",$str); //区分大小写
echo $str."<br>";
echo $result1."<br>";
echo $result2."<br>";
/**结果
hello jiqing!
Hi jiqing!
hello jiqing!
*/

<"hello jiqing a!";
$result1 = str_word_count($str); //返回个数
$result2 = str_word_count($str,1); //返回数组
echo $str."<br>";
echo $result1."<br>";
print_r($result2);
/**结果
hello jiqing a!
3
Array ( [0] => hello [1] => jiqing [2] => a )
*/

<"hello jiqing a!";
$result = strlen($str);
echo $result;
/**结果
15
*/

<"hello jiqing ,hello jim!";
$result = substr_count($str,"hello");
echo $result;
/**结果
2
*/

<"hello jiqing ,hello jim!";
$result = substr_replace($str,"zhangsan",6);
echo $result."<br>";
$result = substr_replace($str,"zhangsan",6,6);//从某个位置替换，替换几个字符串
echo $result;
/**结果
hello zhangsan
hello zhangsan ,hello jim!
*/

<"abcdef";
$result = substr($str,0,1); //从第0个开始，获取1个
echo $result."<br>";
$result = substr($str,0,-1);//从第0个开始，获取到除了最后一个的字符串
echo $result."<br>";
$result = substr($str,2,-1);//从第2个开始，获取到除了最后一个的字符串
echo $result."<br>";
$result = substr($str,-3,-1);//从第-3个开始，获取到除了最后一个的字符串
echo $result."<br>";
$result = substr($str,-3,1);//从第-3个开始，获取到除了最后一个的字符串
echo $result."<br>";
/**结果
a
abcde
cde
de
d
*/

<"2013","6","3");
$date = implode("/",$array);
echo $date;
/**结果
2013/6/3
*/

<"Hello world";
$result = md5($str);
echo $result;
/**结果
3e25960a79dbc69b674cd4ec67a72c62
*/