<?php
$test = 'Variable';
echo 'Double quotes: ';
echo "$test";
echo '
';
echo 'Single quotes: ';
echo '$test';
echo '
';

echo 'Variable in variable definition: ';
$anotherVar = '$test'."$test";
echo $anotherVar;
?>

Double quotes: Variable
Single quotes: $test
Variable in variable definition: $testVariable