PHP: String Syntax ＆ Heredoc

Xah Lee, 2007-11-30, 2012-09-26

String can be quoted by a single quote.

<?php
echo 'sweet home';
?>

String can also be quoted using a double quote. When using double quote, any variables in the form $‹variableName› or ${‹variableName›} will be evaluated and its value used.

<?php
$x = 3;
echo "I bet you\n ${x} dollars";

/* output:
I bet you
 3 dollars
 */
?>

Escape character sequence such as {\n, \r, \t} will also be interpreted when using double quote.

Heredoc ＆ Nowdoc: Quoting Long Text

If you have a large block of text, you can use a form called “heredoc”.

You start the quote delimiter by <<<randomLetterSequence and end it by the same letter sequence, followed by a semicolon, on a line by itself. Example:

<?php
$herName = 'Alice';

$longText = <<<HHHHH
'and what is the use of a book,' thought $herName
'without pictures or conversation?'.
HHHHH;

echo $longText;
?>

The output of above is this:

'and what is the use of a book,' thought Alice
'without pictures or conversation?'.

Note that in the above, we used this random string: HHHHH for the delimiter. The ending delimiter must be exactly that followed by a semicolon, on a line by itself. No other chars can be there.

Heredoc is especially useful for large block of text (such as a template) that may itself contain many single quotes or double quotes.

Variables inside heredoc will still be interpreted (replaced by their values). Same for escape sequences (⁖ {\n, \t, …}).

Nowdoc: Literal Quoting

To not have variables interpreted, use a form called “nowdoc”. The syntax is the same as heredoc, except you start it like this <<<'anyLetterSequence'. Example:

<?php
$herName = 'Alice';

$longText = <<<'HHHHH'
'and what is the use of a book,' thought $herName
'without pictures or conversation?'.
HHHHH;

echo $longText;
?>

The output of above is this:

'and what is the use of a book,' thought $herName
'without pictures or conversation?'.

string