What is the difference between ' and " in PHP? [duplicate]

Answer 1

There are 3 syntax used to declare strings, in PHP <= 5.2 :

• single quoted
• double quoted
• heredoc

With single quotes :

variables and escape sequences for special characters will not be expanded

For instance :

echo 'Variables do not $expand $either';

Will output :

Variables do not $expand $either

With double-quotes :

The most important feature of double-quoted strings is the fact that variable names will be expanded.

For instance :

$a = 10;
echo "a is $a";

Will output :

a is 10

And, with heredoc :

Heredoc text behaves just like a double-quoted string, without the double quotes. This means that quotes in a heredoc do not need to be escaped,

For instance :

$a = 10;
$b = 'hello';

$str = <<<END_STR
a is $a
and "b" is $b.
END_STR;

echo $str;

Will get you :

a is 10
and "b" is hello.

Answer 2

" interprets escape characters and variables. ' doesn't do either.

Answer 3

Basically, single-quoted strings are plain text with virtually no special case whereas double-quoted strings have variable interpolation (e.g. echo "Hello $username";) as well as escaped sequences such as "\n" (newline.)

You can learn more about strings in PHP's manual.

Answer 4

Any variables inside a " quoted string will be parsed. Any variables in a ' quoted string will not be parsed, and will be shown literally as the variable name. For this reason, ' quoted strings are very slightly faster for PHP to process.

$test = 'hello';
echo "this is a $test"; // returns this is a hello
echo 'this is a $test'; // returns this is a $test

I'd say use ' quotes unless you want variables inside your strings.

Answer 5

The difference is, strings between double quotes (") are parsed for variable and escape sequence substitution. Strings in single quotes (') aren't.

So, using double quotes (") you can do:

$count = 3;
echo "The count is:\t$count";

which will produce

The count is:<tab>3

The same in single quotes returns the literal string.

Also, the characters that need to be escaped. If you have a string like:

'John said, "Hello"'

you would probably use single quotes, to avoid having to escape the quotes in the string and vice-versa.

Answer 6

In one word: when you would like to all your special chars (like \n) and varables (like $number) be noticed and process.