Example
A string in PHP is a series of single-byte characters (i.e. there is no native Unicode support) that can be specified in four ways:
Single Quoted
Displays things almost completely "as is". Variables and most escape sequences will not be interpreted. The exception is that to display a literal single quote, one can escape it with a back slash ', and to display a back slash, one can escape it with another backslash \
$my_string = 'Nothing is parsed, except an escap\'d apostrophe or backslash. $foo\n';
var_dump($my_string);
/*
string(68) "Nothing is parsed, except an escap'd apostrophe or backslash. $foo\n"
*/
Double Quoted
Unlike a single-quoted string, simple variable names and escape sequences in the strings will be evaluated. Curly braces (as in the last example) can be used to isolate complex variable names.
$variable1 = "Testing!";
$variable2 = [ "Testing?", [ "Failure", "Success" ] ];
$my_string = "Variables and escape characters are parsed:\n\n";
$my_string .= "$variable1\n\n$variable2[0]\n\n";
$my_string .= "There are limits: $variable2[1][0]";
$my_string .= "But we can get around them by wrapping the whole variable in braces: {$variable2[1][1]}";
var_dump($my_string);
/*
string(98) "Variables and escape characters are parsed:
Testing!
Testing?
There are limits: Array[0]"
But we can get around them by wrapping the whole variable in braces: Success
*/
Heredoc
In a heredoc string, variable names and escape sequences are parsed in a similar manner to double-quoted strings, though braces are not available for complex variable names. The start of the string is delimited by <<<identifier, and the end by identifier, where identifier is any valid PHP name. The ending identifier must appear on a line by itself. No whitespace is allowed before or after the identifier, although like any line in PHP, it must also be terminated by a semicolon.
$variable1 = "Including text blocks is easier";
$my_string = <<< EOF
Everything is parsed in the same fashion as a double-quoted string,
but there are advantages. $variable1; database queries and HTML output
can benefit from this formatting.
Once we hit a line containing nothing but the identifier, the string ends.
EOF;
var_dump($my_string);
/*
string(268) "Everything is parsed in the same fashion as a double-quoted string,
but there are advantages. Including text blocks is easier; database queries and HTML output
can benefit from this formatting.
Once we hit a line containing nothing but the identifier, the string ends."
*/
Nowdoc
A nowdoc string is like the single-quoted version of heredoc, although not even the most basic escape sequences are evaluated. The identifier at the beginning of the string is wrapped in single quotes.
PHP 5.x5.3
$my_string = <<< 'EOF'
A similar syntax to heredoc but, similar to single quoted strings,
nothing is parsed (not even escaped apostrophes \' and backslashes \\.)
EOF;
var_dump($my_string);
/*
string(116) "A similar syntax to heredoc but, similar to single quoted strings,
nothing is parsed (not even escaped apostrophes \' and backslashes \\.)"
*/
