Is php case sensitive?

In the process of developing PHP, because naming case issues can easily lead to code errors, we have compiled some information on PHP case sensitivity from the Internet. Friends who need it can refer to it.

PHP’s handling of case-sensitive issues is messy, and problems may occasionally occur when writing code, so I’ll summarize it here. But I'm not encouraging everyone to use these rules. It is recommended that everyone always adhere to "case sensitivity" and follow unified coding standards.

1. Variable names are case-sensitive

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

2. Constant names are case-sensitive by default and are usually written in uppercase

Constants defined using define 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. Function names, method names, and class names are not case-sensitive

But it is recommended to use the same name as when defined

<?php
 function show(){
 echo "Hello World";
 }

show (); //Output Hello World. Recommended writing method

SHOW(); //Output Hello World

<?php
 class cls{
 static function func(){
 echo "hello world";
 }
 }
 Cls::FunC(); //输出hello world

4. Magic constants are not case-sensitive. Capital letters are recommended

Includes: __LINE__, __FILE__, __DIR__, __FUNCTION__, __CLASS__, __METHOD__, __NAMESPACE__.

<?php
 echo __line__; //输出 2
 echo __LINE__; //输出 3

5. NULL, TRUE and FALSE are not case-sensitive

<?php
 $a = null;
 $b = NULL;
 $c = true;
 $d = TRUE;
 $e = false;
 $f = FALSE;
 var_dump($a == $b); //输出 boolean true
 var_dump($c == $d); //输出 boolean true
 var_dump($e == $f); //输出 boolean true

5. 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
?>

Summary:

In PHP, function names, method names, class names, and keywords are not case-sensitive; but variables Names and constant names are case-sensitive.

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