PHP

Strings in PHP

A string is a series of characters. In PHP a character is the same as a byte, so there are exactly 256 different characters possible. Text in UTF-8 (for example Hindi: नमस्ते) uses several bytes per character; for such text use the multibyte functions mb_strlen(), mb_substr() and so on. (Older books suggest utf8_encode()/utf8_decode(); these are deprecated since PHP 8.2 – use mb_convert_encoding() instead.)

A string literal can be specified in four different ways:

• single quoted
• double quoted
• heredoc syntax
• nowdoc syntax

Single-Quoted Strings

The simplest way to specify a string is to enclose it in single quotes (').

• To specify a literal single quote, escape it with a backslash: \'.
• To specify a literal backslash, double it: \\.
• All other backslashes are treated literally: escape sequences such as \r or \n are output as written, without any special meaning.
• Variables are not expanded inside single-quoted strings.

<?php
echo 'this is a simple string';
echo '<br>';
echo 'You can also have embedded newlines in
strings this way as it is okay to do';
echo '<br>';
// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I\'ll be back"';
echo '<br>';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\\*.*?';
echo '<br>';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\*.*?';
echo '<br>';
// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';
echo '<br>';
// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
?>

this is a simple string
You can also have embedded newlines in strings this way as it is okay to do
Arnold once said: "I'll be back"
You deleted C:\*.*?
You deleted C:\*.*?
This will not expand: \n a newline
Variables do not $expand $either

(The newline inside the second string is displayed as a space, because the browser treats line breaks in HTML as white space.)

Double-Quoted Strings

If the string is enclosed in double quotes ("), PHP interprets more escape sequences:

As in single-quoted strings, escaping any other character prints the backslash too. The most important feature of double-quoted strings is that variable names are expanded (variable parsing / interpolation).

<?php
$name = "Asha";
$fruits = ["apple", "mango"];
$user = ["city" => "Bhopal"];
echo "<pre>";
echo "Hello $name!\n";
echo "Tab\tseparated\tvalues\n";
echo "A quote: \" and a dollar: \$name\n";
echo "Octal \101, hex \x41, rupee \u{20B9}\n";
echo "First fruit: $fruits[0]\n";
echo "City: {$user['city']}\n";        // curly syntax for complex expressions
echo "Name in capitals: " . strtoupper($name) . "\n";
echo "</pre>";
?>

Hello Asha!
Tab	separated	values
A quote: " and a dollar: $name
Octal A, hex A, rupee ₹
First fruit: apple
City: Bhopal
Name in capitals: ASHA

Heredoc

A third way to delimit strings is the heredoc syntax: <<<. After this operator an identifier is given, then a new line. The string follows, and then the same identifier again to close the quotation.

• The identifier must follow the same naming rules as other labels in PHP: only letters, digits and underscores, not starting with a digit.
• Heredoc text behaves just like a double-quoted string without the double quotes: quotes need not be escaped, escape codes work and variables are expanded.
• Since PHP 7.3 the closing identifier may be indented, and the same amount of indentation is removed from every line of the text. In older versions it had to start in the first column, with nothing but an optional ; after it.
• Heredoc can be used to initialise static variables, class properties and constants (with static values).

<?php
class Foo
{
    public $foo;
    public $bar;
    function __construct()
    {
        $this->foo = 'Foo';
        $this->bar = array('Bar1', 'Bar2', 'Bar3');
    }
}
$foo = new Foo();
$name = 'MyName';
echo <<<EOT
<pre>
My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should print a capital 'A': \x41
</pre>
EOT;
?>

My name is "MyName". I am printing some Foo.
Now, I am printing some Bar2.
This should print a capital 'A': A

Heredoc is also convenient for passing long text as a function argument, or for building HTML:

<?php
$product = "Laptop";
$price = 45999;
$html = <<<HTML
    <div style="border:1px solid #999;padding:6px;width:220px">
        <b>$product</b><br>
        Price: Rs. {$price}/-
    </div>
    HTML;
echo $html;
echo "<pre>";
var_dump(array(<<<EOD
foobar!
EOD));
echo "</pre>";
?>

Laptop
Price: Rs. 45999/-
array(1) {
  [0]=>
  string(7) "foobar!"
}

Nowdoc

Nowdocs are to single-quoted strings what heredocs are to double-quoted strings. A nowdoc is written like a heredoc, but the identifier is enclosed in single quotes, e.g. <<<'EOT', and no parsing is done inside it: variables are not expanded and escape sequences are not interpreted. It is ideal for embedding PHP code or other large blocks of text without escaping.

<?php
$name = 'MyName';
echo <<<'EOT'
<pre>
My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should not print a capital 'A': \x41
</pre>
EOT;
?>

My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should not print a capital 'A': \x41

Nowdoc (available since PHP 5.3) can be used in any static data context, for example to initialise class properties or constants:

<?php
class Notice
{
    const TITLE = <<<'EOT'
Office closed on Monday
EOT;
    public $body = <<<'EOT'
Fees can be paid online at $site.
EOT;
}
$n = new Notice();
echo Notice::TITLE . "<br>" . $n->body;
?>

Office closed on Monday
Fees can be paid online at $site.

Frequently Used String Functions

Part II gives the complete list of string functions. The following are used in almost every program:

<?php
$s = "  Welcome to PHP Programming  ";
$t = trim($s);
echo "trim: '$t'<br>";
echo "strlen: " . strlen($t) . "<br>";
echo "str_word_count: " . str_word_count($t) . "<br>";
echo "strtoupper: " . strtoupper($t) . "<br>";
echo "strtolower: " . strtolower($t) . "<br>";
echo "ucwords: " . ucwords("php and mysqli") . "<br>";
echo "strrev: " . strrev("PHP") . "<br>";
echo "strpos of 'PHP': " . strpos($t, "PHP") . "<br>";
echo "substr(11, 3): " . substr($t, 11, 3) . "<br>";
echo "str_replace: " . str_replace("PHP", "MySQLi", $t) . "<br>";
echo "str_contains (PHP 8): " . (str_contains($t, "come") ? "yes" : "no") . "<br>";
echo "str_pad: " . str_pad("7", 3, "0", STR_PAD_LEFT) . "<br>";
echo "number_format: " . number_format(1234567.891, 2);
?>

trim: 'Welcome to PHP Programming'
strlen: 26
str_word_count: 4
strtoupper: WELCOME TO PHP PROGRAMMING
strtolower: welcome to php programming
ucwords: Php And Mysqli
strrev: PHP
strpos of 'PHP': 11
substr(11, 3): PHP
str_replace: Welcome to MySQLi Programming
str_contains (PHP 8): yes
str_pad: 007
number_format: 1,234,567.89