Summary of PHP case-sensitive issues (practical)

$abc = 'abcd';
echo $abc; //Output 'abcd'
echo $aBc; //No output
echo $ABC; //No output
?>

2. Constant names are case-sensitive by default and are usually written in uppercase (But I couldn’t find a configuration item that can change this default, please solve it) example:

define("ABC","Hello World");
echo ABC; //Output Hello World
echo abc; //Output abc
?>

3. php.ini configuration item instructions are case sensitive For example, file_uploads = 1 cannot be written as File_uploads = 1

2. Case insensitive 1. Function names, method names, and class names are not case-sensitive, but it is recommended to use the same names as when they were defined. example:

function show(){
 echo "Hello World";
}
show(); //Output Hello World Recommended writing method
SHOW(); //Output Hello World
?> ;

Example:

class cls{
 static function func(){
 echo "hello world";
 }
}
Cls:: FunC(); //Output hello world
?>

2. Magic constants are not case-sensitive, uppercase is recommended Includes: __LINE__, __FILE__, __DIR__, __FUNCTION__, __CLASS__, __METHOD__, __NAMESPACE__. example:

echo __line__; //Output 2
echo __LINE__; //Output 3
?>

3. NULL, TRUE, FALSE are not case sensitive example:

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

4. Type coercion, case-insensitive include

$a=1;
var_dump($a); //Output int 1
$b=(STRING)$a;
var_dump($b); //Output string ' 1' (length=1)
$c=(string)$a;
var_dump($c); //Output string '1' (length=1)
?>