PHP Tutorial Tutorials - PHP Strings

A string is series of characters.
A string literal can be specified in four different ways:

<?php
    echo 'this is a simple string'; // Single quoted
    echo "This is a string in double quotes"; // Double quoted

    $foo = <<<LABEL
bar
LABEL;
    echo $foo; // heredoc

    echo <<<'NOWDOC'
    Nowdoc string example:Backslashes are always treated literally,
e.g. \\ and \'.
NOWDOC;
    //Nowdoc 
?>

PHP Single quoted

Single quoted strings are treated almost literally.

<?php

// Outputs: Hello world!
echo 'Hello world!';
echo "<br>";

// Outputs: Hello Lautturi!
echo 'Hello
 Lautturi!';
echo "<br>";
 
// Outputs: I\'ll be back.
echo 'I\'ll be back.';
echo "<br>";

// Outputs: single backslash with newline character \n
echo 'single backslash with newline character \\n';

// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';

// Outputs: Variables do not $expand
echo 'Variables do not $expand';

?>

PHP Double quoted

1. When a string is specified in double quotes, variables are parsed within it. (Variable names will be expanded)
2. Escape sequences will be replaced with special characters
   \n is replaced by the newline character
   \r is replaced by the carriage-return character
   \t is replaced by the tab character
   $ is replaced by the dollar sign itself ($)
   " is replaced by a double-quote (")
   \ is replaced by a single backslash ()
   [0-7]{1,3} the sequence of characters matching the regular expression is a character in octal notation, which silently overflows to fit in a byte (e.g. "\400" === "\000")
   \x[0-9A-Fa-f]{1,2} the sequence of characters in hexadecimal notation
   \u{[0-9A-Fa-f]+} Unicode codepoint

<?php
$str = "PHP Double quoted String";

echo "str:$str."."<br>";

echo "strs:$strs."."<br>"; // Invalid. $strs is undefined

echo "strs:${str}s."."<br>"; // Valid. the $ must immediately follows the {. 
?>

Output:

str:PHP Double quoted String.
strs:.
strs:PHP Double quoted Strings.

The Complex (curly) syntax `${} is used to get the value of a var named by a return value.

<?php
$var = "str";
$str = "PHP Variable parsing syntax";

// Output:PHP Variable parsing syntax
echo ${$var}; // ${str} => $str
echo "<br>";

$fruit = "apple";
$price_apple = 30;

// Output:Price:30
echo "Price:". ${'price_'.$fruit} ."<br>";
?>

PHP Variable parsing

When a string is specified in double quotes or with heredoc, variables are parsed within it. (replaced with their values), but Single quoted strings are treated almost literally.

Single quoted vs Double quoted

<?php
$variable = "PHP strings";

echo 'The $variable value will not print.'."<br>";
// The $variable value will not print.

echo "The value $variable will print."."<br>";
// The value PHP strings will print.

?>

PHP Heredoc

heredoc syntax is: <<< .After this operator, an identifier(LABEL) is provided, then a newline.
Then multiple lines string follows.Finally the same identifier(LABEL) again to close the quotation.

<?php
    $foo = <<<LABEL
string
multiple lines
LABEL;
    var_dump($foo); // heredoc
?>

Output:

string(23) "string
multiple lines"

Notes
$foo = <<<LABEL(newline) Valid
LABEL;(whitespace) Invalid
LABEL; Valid
(whitespace)LABEL; Invalid, Identifier must not be indented

<?php
$str = <<<EOT
Example of string
spanning multiple lines
using heredoc syntax.
EOT;
//   EOT; // Invalid, Identifier must not be indented
//EOT;;  // Invalid, the semicolon(;) could not follows any character
echo $str

PHP Nowdoc

Nowdocs are to single-quoted strings what heredocs are to double-quoted strings.

PHP Nowdoc vs Heredoc

The differences are:

1. When a string is specified in double quotes or with heredoc, variables are parsed within it.
   No parsing is done inside a nowdoc.
2. Heredoc: the identifier is enclosed in double quotes or No quotes. <<<"EOT",<<<EOD.
   Nowdoc: the identifier is enclosed in single quotes. <<<'EOT'.

<?php
echo <<<'EOD'
Example of string spanning multiple lines
using nowdoc syntax. Backslashes(\) are always treated literally,
e.g. \\ and \'.
EOD;