寫PHP必知的單引號和雙引號區別

單引號內的變號，是不會被PHP解譯的。
因為PHP會當成字串處理！
所單引號和雙引號的使用，有必要釐清，建立好的使用習慣。


節錄自
10 Tips That Every PHP Developer Should Know, Part 2

Single and double quotes confused me for some time and it really should not have. I see this quite often in the forum as well. It's very easy to understand that double quotes allow php to parse and single quotes do not. Here are some examples:

$var = $value; // ok
$var = "$value"; // ok, but double quotes are not necessary
$var = '$value'; // will not work (single quotes will not allow parsing)

('.' the period adds/connects variables, functions, etc. together.
Oftentimes programmers will leave spaces around the ' . ' to make
things easier to read.)

$var = 'This is the ' . $value . ' of things.'; // ok - preferred
technique
$var = "This is the $value of things."; // ok, but harder to read/debug
$var = 'This is the $value of things.'; // will not parse $value
$var = This is the $value of things.; // error

$var = $array['name']; // ok, generally the preferred technique
$var = $array["name"]; // ok, but why use double quotes if they are not
necessary?
$var = "$array[name]"; // ok, but harder to read/debug - poor coding
style

$var = 'Name: ' . $array['name']; // ok - preferred technique
$var = "Name: $array[name]"; // ok, but harder to read/debug - poor
coding style
$var = "Name: $array["name"]"; // error
$var = "Name: $array['name']"; // error

exampleFunction($value); // ok
exampleFunction("$value"); // ok, but double quotes are not necessary
exampleFunction('$value'); // will not parse $value