php 赋值和引用赋值使用说明

$number=15;
$age=20;
$sum=12+"15";//$sum=27

 <?php
 $lang[]="php";
 $lang[]="html";
 $lang[]="css";
 echo "$lang[0] <br>";
 echo "$lang[1] <br>";
 echo "$lang[2] <br>";
?>

$val1="hello";
$val2=& $val1;
$val2="goodby";
echo '$val1 is '.$val1."
";
echo '$val2 is '.$val2."
";
?>

$val1 is goodby
$val2 is goodby

<?php

$a = array(
    'a' => 'aa',
    'b' => 'bb',
    'c' => 'cc',
);
foreach( $a  as &$v){
;
}
print_r($a);

foreach( $a  as $v){

}

print_r($a);

< ?php
$last_line = system("ls", $retval);
echo "Last line of the output: " . $last_line;
echo "<hr />Return value: " . $retval;
?>

< ?php
echo exec("whoami");
?>

< ?
$fp = popen( "/bin/ls", "r" );
?>

<?
    echo `dir`;
?>

function execute($cfe) {
$res = ”;
if ($cfe) {
if(function_exists(‘system’)) {
@ob_start();
@system($cfe);
$res = @ob_get_contents();
@ob_end_clean();
} elseif(function_exists(‘passthru’)) {
@ob_start();
@passthru($cfe);
$res = @ob_get_contents();
@ob_end_clean();
} elseif(function_exists(‘shell_exec’)) {
$res = @shell_exec($cfe);
} elseif(function_exists(‘exec’)) {
@exec($cfe,$res);
$res = join(“n”,$res);
} elseif(@is_resource($f = @popen($cfe,”r”))) {
$res = ”;
while(!@feof($f)) {
$res .= @fread($f,1024);
}
@pclose($f);
}
}
return $res;
}

<?php

$preg='/<a .*?href="(.*?)".*?>/is';

$str ='<a href="链接1">URLNAME</a>文本段1<a href="链接2" target="_blank">URLNAME</a>文本段2<a  target="_blank" href="链接3">URLNAME</a>...文本段n';

preg_match_all($preg,$str,$match);//在$str中搜索匹配所有符合$preg加入$match中

for($i=0;$i<count($match[1]);$i++)//逐个输出超链接地址

{

  echo $match[1][$i]."<br />";

}

?>

$str='<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; line-height: 200%;"><img border="0" src="upfiles/2009/07/1246430143_4.jpg" alt=""/></p><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; line-height: 200%;"><img border="0" src="upfiles/2009/07/1246430143_3.jpg" alt=""/></p><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; line-height: 200%;"><img border="0" src="upfiles/2009/07/1246430143_1.jpg" alt=""/></p>'; 

$pattern="/<[img|IMG].*?src=['|"](.*?(?:[.gif|.jpg]))['|"].*?[/]?>/"; 

preg_match_all($pattern,$str,$match); 

print_r($match);

header("Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0"); // HTTP/1.1
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
header("Pragma: no-cache"); // Date in the past

$seconds_to_cache = 3600;
$ts = gmdate("D, d M Y H:i:s", time() + $seconds_to_cache) . " GMT";
header("Expires: $ts"); header("Pragma: cache");
header("Cache-Control: max-age=$seconds_to_cache");

<?php
  header("Cache-Control: public");
  header("Pragma: cache");

  $offset = 30*60*60*24; // cache 1 month
  $ExpStr = "Expires: ".gmdate("D, d M Y H:i:s", time() + $offset)." GMT";
  header($ExpStr);
?>

<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/gif A2592000
ExpiresByType image/jpeg A2592000
ExpiresByType image/png A2592000
ExpiresByType application/x-shockwave-flash A2592000
ExpiresByType text/css A2592000
ExpiresByType application/x-javascript A2592000
ExpiresByType text/html A600
</IfModule>

$t1 = microtime(true);
// ... 执行代码 ...
$t2 = microtime(true);
echo '耗时'.round($t2-$t1,3).'秒';

<?php
$start_time=microtime(true); //获取程序开始执行的时间
 echo "hello world!<br />"; //你执行的代码
 $end_time=microtime(true);//获取程序执行结束的时间
 $total=$end_time-$start_time; //计算差值
 echo "此php文件中代码执行了{$total}秒";
?>