Are php variable names case sensitive?

1. Variable names are case-sensitive

All variables are case-sensitive, including ordinary variables and $_GET,$_POST,$_REQUEST ,$_COOKIE,$_SESSION,$GLOBALS,$_SERVER,$_FILES,$_ENV, etc.;

<?php
$abc = &#39;abc&#39;;
echo $abc;    //输出&#39;abc&#39;
echo $aBc;    //无输出
echo $ABC;    //无输出
?>

2. Constant names are case-sensitive

Use define to define Constants are case-sensitive.

<?php
define(&#39;BLOGGER&#39;,&#39;Veitor&#39;);
echo BLOGGER;    //输出&#39;Veitor&#39;
echo BLOgger;    //报NOTICE提示，并输出&#39;BLOgger&#39;
echo blogger;    //报NOTICE提示，并输出&#39;blogger&#39;
?>

3. Array index (key name) is case-sensitive

<?php
$arr = array(&#39;one&#39;=>&#39;first&#39;);
echo $arr[&#39;one&#39;];    //输出&#39;first&#39;
echo $arr[&#39;One&#39;];    //无输出并报错
echo $Arr[&#39;one&#39;];    //上面讲过，变量名区分大小写，所以无输出并报错
?>

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