1. Variable names are case sensitive
1 <?php
2 $abc = 'abcd';
3 echo $abc; // output 'abcd'
4 echo $aBc; //no output
5 echo $ABC; //no output
2. The constant name is case-sensitive by default, and is usually written in uppercase
(but I did not find a configuration item that can change this default, solve it)
1 <?php
2 define("ABC","Hello World");
3 echo ABC; //output Hello World
4 echo abc; //output abc
3. The php.ini configuration item directive is case-sensitive,
such as file_uploads = 1 and cannot be written as File_uploads = 1
3. Function names, method names, and class names are not case-sensitive,
but it is recommended to use the same name as the definition
1 <?php
2 function show(){
3 echo "Hello World";
4 }
5 show(); //Output Hello World recommended writing
6 SHOW(); //Output Hello World
1 <?php
2 class cls{
3 static function func(){
4 echo "hello world";
5 }
6 }
7
8 Cls::FunC(); //Output hello world
4. Magic constants are not case-sensitive. Recommended uppercase
includes: __LINE__, __FILE__, __DIR__, __FUNCTION__, __CLASS__, __METHOD__, __NAMESPACE__.
1 <?php
2 echo __line__; //output 2
3 echo __LINE__; //output 3
5. NULL, TRUE, FALSE are not case sensitive
01 <?php
02 $a = null;
03 $b = NULL;
04
05 $c = true;
06 $d = TRUE;
07
08 $ e = false;
09 $f = FALSE;
10
11 var_dump($a == $b); //output boolean true
12 var_dump($c == $d); //output boolean true
13 var_dump($e == $f); //output boolean true