PHP Case Sensitivity

PHP is partly case-sensitive. That surprises many beginners, so learn the rule once.

Variables are case-sensitive

$name, $Name and $NAME are three different variables.

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<?php
$name = "Sam";
$Name = "Tina";

echo $name . " and " . $Name;

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Sam and Tina

A typo in a variable’s capital letter is a real bug, because PHP treats it as a brand-new variable.

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<?php
$total = 100;
echo $Total;

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Warning: Undefined variable $Total in /path/to/index.php on line 3

Function and keyword names are not

PHP does not care about case for built-in function names, class names or keywords such as echo and if.

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<?php
ECHO strtoupper("hello");
echo STRTOLOWER("WORLD");

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HELLOworld

This works, but nobody writes code this way. Always use the standard lowercase style so the code stays readable.

Constants are case-sensitive

Constants such as PHP_VERSION or your own MAX_SIZE are case-sensitive. By habit, we write them in capitals.

Quick summary