PHP Single vs double quotation string

Description

Single and double quotation marks work in different ways.

If you enclose a string in single quotation marks, PHP uses the string exactly as typed.

However, double quotation marks has extra features:

• variable names within the string are parsed and replaced with the variable's value
• special characters need escaping in the string

Example

Here are some examples to make these differences clear:

<?PHP/*from ww w. j a v  a 2 s  .  c  om*/
$myString = 'world'; 
echo "Hello, $myString! \n"; // Displays "Hello, world!" 
echo 'Hello, $myString! \n'; // Displays "Hello, $myString!" 
echo " Hi\tthere! "; // Displays "Hi      there!" 
echo ' Hi\tthere! '; // Displays "Hi\tthere!"   
?>

The code above generates the following result.

Using double quotes causes the $myString variable name to be substituted with the actual value of $myString.

However, when using single quotes, the text $myString is retained in the string as-is.

With the "Hi there!" example, an escaped tab character (\t) is included within the string literal.

When double quotes are used, the \t is replaced with an actual tab character; hence the big gap between Hi and there! in the output. The same string enclosed in single quotes results in the \t characters being passed through intact.

Within single-quoted strings, we can use a couple of escape sequences. Use \' to include a literal single quote within a string.

To include the literal characters \' within a single-quoted string, use \\\'.