Embedded Files
What is PHP?
What is PHP?
PHP (recursive acronym for PHP: Hypertext Preprocessor) is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML.
Nice, but what does that mean? An example:
Example #1 An introductory example
<!DOCTYPE html>
<html>
<head>
<title>Example</title>
</head>
<body>
<?php
echo "Hi, I'm a PHP script!";
?>
</body>
</html>
Instead of lots of commands to output HTML (as seen in C or Perl), PHP pages contain HTML with embedded code that does "something" (in this case, output "Hi, I'm a PHP script!"). The PHP code is enclosed in special start and end processing instructions <?php and ?> that allow you to jump into and out of "PHP mode."
What distinguishes PHP from something like client-side JavaScript is that the code is executed on the server, generating HTML which is then sent to the client. The client would receive the results of running that script, but would not know what the underlying code was. You can even configure your web server to process all your HTML files with PHP, and then there's really no way that users can tell what you have up your sleeve.
The best part about using PHP is that it is extremely simple for a newcomer, but offers many advanced features for a professional programmer. Don't be afraid to read the long list of PHP's features. You can jump in, in a short time, and start writing simple scripts in a few hours.
Although PHP's development is focused on server-side scripting, you can do much more with it. Read on, and see more in the What can PHP do? section, or go right to the introductory tutorial if you are only interested in web programming.
What can PHP do?
What can PHP do?
Anything. PHP is mainly focused on server-side scripting, so you can do anything any other CGI program can do, such as collect form data, generate dynamic page content, or send and receive cookies. But PHP can do much more.
There are three main areas where PHP scripts are used.
Server-side scripting. This is the most traditional and main target field for PHP. You need three things to make this work: the PHP parser (CGI or server module), a web server and a web browser. You need to run the web server, with a connected PHP installation. You can access the PHP program output with a web browser, viewing the PHP page through the server. All these can run on your home machine if you are just experimenting with PHP programming. See the installation instructions section for more information.
Command line scripting. You can make a PHP script to run it without any server or browser. You only need the PHP parser to use it this way. This type of usage is ideal for scripts regularly executed using cron (on *nix or Linux) or Task Scheduler (on Windows). These scripts can also be used for simple text processing tasks. See the section about Command line usage of PHP for more information.
Writing desktop applications. PHP is probably not the very best language to create a desktop application with a graphical user interface, but if you know PHP very well, and would like to use some advanced PHP features in your client-side applications you can also use PHP-GTK to write such programs. You also have the ability to write cross-platform applications this way. PHP-GTK is an extension to PHP, not available in the main distribution. If you are interested in PHP-GTK, visit » its own website.
PHP can be used on all major operating systems, including Linux, many Unix variants (including HP-UX, Solaris and OpenBSD), Microsoft Windows, macOS, RISC OS, and probably others. PHP also has support for most of the web servers today. This includes Apache, IIS, and many others. And this includes any web server that can utilize the FastCGI PHP binary, like lighttpd and nginx. PHP works as either a module, or as a CGI processor.
So with PHP, you have the freedom of choosing an operating system and a web server. Furthermore, you also have the choice of using procedural programming or object-oriented programming (OOP), or a mixture of them both.
With PHP you are not limited to output HTML. PHP's abilities include outputting rich file types, such as images or PDF files, encrypting data, and sending emails. You can also output easily any text, such as JSON or XML. PHP can autogenerate these files, and save them in the file system, instead of printing it out, forming a server-side cache for your dynamic content.
One of the strongest and most significant features in PHP is its support for a wide range of databases. Writing a database-enabled web page is incredibly simple using one of the database specific extensions (e.g., for mysql), or using an abstraction layer like PDO, or connect to any database supporting the Open Database Connection standard via the ODBC extension. Other databases may utilize cURL or sockets, like CouchDB.
PHP also has support for talking to other services using protocols such as LDAP, IMAP, SNMP, NNTP, POP3, HTTP, COM (on Windows) and countless others. You can also open raw network sockets and interact using any other protocol. PHP has support for the WDDX complex data exchange between virtually all Web programming languages. Talking about interconnection, PHP has support for instantiation of Java objects and using them transparently as PHP objects.
PHP has useful text processing features, which includes the Perl compatible regular expressions (PCRE), and many extensions and tools to parse and access XML documents. PHP standardizes all of the XML extensions on the solid base of libxml2, and extends the feature set adding SimpleXML, XMLReader and XMLWriter support.
And many other interesting extensions exist, which are categorized both alphabetically and by category. And there are additional PECL extensions that may or may not be documented within the PHP manual itself, like » XDebug.
As you can see this page is not enough to list all the features and benefits PHP can offer. Read on in the sections about installing PHP, and see the function reference part for explanation of the extensions mentioned here.
When PHP parses a file, it looks for opening and closing tags, which are <?php and ?> which tell PHP to start and stop interpreting the code between them. Parsing in this manner allows PHP to be embedded in all sorts of different documents, as everything outside of a pair of opening and closing tags is ignored by the PHP parser.
PHP includes a short echo tag <?= which is a short-hand to the more verbose <?php echo.
Example #1 PHP Opening and Closing Tags
1. <?php echo 'if you want to serve PHP code in XHTML or XML documents,
use these tags'; ?>
2. You can use the short echo tag to <?= 'print this string' ?>.
It's equivalent to <?php echo 'print this string' ?>.
3. <? echo 'this code is within short tags, but will only work '.
'if short_open_tag is enabled'; ?>
Short tags (example three) are available by default but can be disabled either via the short_open_tag php.ini configuration file directive, or are disabled by default if PHP is built with the --disable-short-tags configuration.
Note:
As short tags can be disabled it is recommended to only use the normal tags (<?php ?> and <?= ?>) to maximise compatibility.
If a file contains only PHP code, it is preferable to omit the PHP closing tag at the end of the file. This prevents accidental whitespace or new lines being added after the PHP closing tag, which may cause unwanted effects because PHP will start output buffering when there is no intention from the programmer to send any output at that point in the script.
<?php
echo "Hello world";
// ... more code
echo "Last statement";
// the script ends here with no PHP closing tag
Everything outside of a pair of opening and closing tags is ignored by the PHP parser which allows PHP files to have mixed content. This allows PHP to be embedded in HTML documents, for example to create templates.
<p>This is going to be ignored by PHP and displayed by the browser.</p>
<?php echo 'While this is going to be parsed.'; ?>
<p>This will also be ignored by PHP and displayed by the browser.</p>
This works as expected, because when the PHP interpreter hits the ?> closing tags, it simply starts outputting whatever it finds (except for the immediately following newline - see instruction separation) until it hits another opening tag unless in the middle of a conditional statement in which case the interpreter will determine the outcome of the conditional before making a decision of what to skip over. See the next example.
Using structures with conditions
Example #1 Advanced escaping using conditions
<?php if ($expression == true): ?>
This will show if the expression is true.
<?php else: ?>
Otherwise this will show.
<?php endif; ?>
In this example PHP will skip the blocks where the condition is not met, even though they are outside of the PHP open/close tags; PHP skips them according to the condition since the PHP interpreter will jump over blocks contained within a condition that is not met.
For outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo or print.
Note:
If PHP is embeded within XML or XHTML the normal PHP <?php ?> must be used to remain compliant with the standards.
As in C or Perl, PHP requires instructions to be terminated with a semicolon at the end of each statement. The closing tag of a block of PHP code automatically implies a semicolon; you do not need to have a semicolon terminating the last line of a PHP block. The closing tag for the block will include the immediately trailing newline if one is present.
Example #1 Example showing the closing tag encompassing the trailing newline
<?php echo "Some text"; ?>
No newline
<?= "But newline now" ?>
The above example will output:
Some textNo newline
But newline now
Examples of entering and exiting the PHP parser:
<?php
echo 'This is a test';
?>
<?php echo 'This is a test' ?>
<?php echo 'We omitted the last closing tag';
Note:
The closing tag of a PHP block at the end of a file is optional, and in some cases omitting it is helpful when using include or require, so unwanted whitespace will not occur at the end of files, and you will still be able to add headers to the response later. It is also handy if you use output buffering, and would not like to see added unwanted whitespace at the end of the parts generated by the included files.
PHP supports 'C', 'C++' and Unix shell-style (Perl style) comments. For example:
<?php
echo 'This is a test'; // This is a one-line c++ style comment
/* This is a multi line comment
yet another line of comment */
echo 'This is yet another test';
echo 'One Final Test'; # This is a one-line shell-style comment
?>
The "one-line" comment styles only comment to the end of the line or the current block of PHP code, whichever comes first. This means that HTML code after // ... ?> or # ... ?> WILL be printed: ?> breaks out of PHP mode and returns to HTML mode, and // or # cannot influence that.
<h1>This is an <?php # echo 'simple';?> example</h1>
<p>The header above will say 'This is an example'.</p>
'C' style comments end at the first */ encountered. Make sure you don't nest 'C' style comments. It is easy to make this mistake if you are trying to comment out a large block of code.
<?php
/*
echo 'This is a test'; /* This comment will cause a problem */
*/
?>
Every single expression in PHP has one of the following built-in types depending on its value:
null
bool
int
float (floating-point number)
string
array
object
resource
PHP is a dynamically typed language, which means that by default there is no need to specify the type of a variable, as this will be determined at runtime. However, it is possible to statically type some aspect of the language via the use of type declarations.
Types restrict the kind of operations that can be performed on them. However, if an expression/variable is used in an operation which its type does not support, PHP will attempt to type juggle the value into a type that supports the operation. This process depends on the context in which the value is used. For more information, see the section on Type Juggling.
Tip
The type comparison tables may also be useful, as various examples of comparison between values of different types are present.
Note: It is possible to force an expression to be evaluated to a certain type by using a type cast. A variable can also be type cast in-place by using the settype() function on it.
To check the value and type of an expression, use the var_dump() function. To retrieve the type of an expression, use the get_debug_type() function. However, to check if an expression is of a certain type use the is_type functions instead.
<?php
$a_bool = true; // a bool
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an int
echo get_debug_type($a_bool), "\n";
echo get_debug_type($a_str), "\n";
// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}
var_dump($an_int);
// If $a_bool is a string, print it out
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>
Output of the above example in PHP 8:
bool
string
int(16)
PHP uses a nominal type system with a strong behavioral subtyping relation. The subtyping relation is checked at compile time whereas the verification of types is dynamically checked at run time.
PHP's type system supports various atomic types that can be composed together to create more complex types. Some of these types can be written as type declarations.
Some atomic types are built-in types which are tightly integrated with the language and cannot be reproduced with user defined types.
The list of base types is:
Built-in types
null type
Scalar types:
bool type
int type
float type
string type
array type
object type
resource type
never type
void type
Relative class types: self, parent, and static
false
true
User-defined types (generally referred to as class-types)
callable type
It is possible to combine multiple atomic types into composite types. PHP allows types to be combined in the following ways:
Intersection of class-types (interfaces and class names).
Union of types.
An intersection type accepts values which satisfies multiple class-type declarations, rather than a single one. Individual types which form the intersection type are joined by the & symbol. Therefore, an intersection type comprised of the types T, U, and V will be written as T&U&V.
A union type accepts values of multiple different types, rather than a single one. Individual types which form the union type are joined by the | symbol. Therefore, a union type comprised of the types T, U, and V will be written as T|U|V. If one of the types is an intersection type, it needs to be bracketed with parenthesis for it to written in DNF: T|(X&Y).
PHP supports two type aliases: mixed and iterable which corresponds to the union type of object|resource|array|string|float|int|bool|null and Traversable|array respectively.
Note: PHP does not support user-defined type aliases.
The null type is PHP's unit type, i.e. it has only one value: null.
Undefined, and unset() variables will resolve to the value null.
There is only one value of type null, and that is the case-insensitive constant null.
<?php
$var = NULL;
?>
Warning
This feature has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. Relying on this feature is highly discouraged.
Casting a variable to null using (unset) $var will not remove the variable or unset its value. It will only return a null value.
Booleans
Booleans
The bool type only has two values, and is used to express a truth value. It can be either true or false.
To specify a bool literal, use the constants true or false. Both are case-insensitive.
<?php
$foo = True; // assign the value TRUE to $foo
?>
Typically, the result of an operator which returns a bool value is passed on to a control structure.
<?php
// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
echo "The version is 1.23";
}
// this is not necessary...
if ($show_separators == TRUE) {
echo "<hr>\n";
}
// ...because this can be used with exactly the same meaning:
if ($show_separators) {
echo "<hr>\n";
}
?>
To explicitly convert a value to bool, use the (bool) cast. Generally this is not necessary because when a value is used in a logical context it will be automatically interpreted as a value of type bool. For more information see the Type Juggling page.
When converting to bool, the following values are considered false:
the boolean false itself
the integer 0 (zero)
the floats 0.0 and -0.0 (zero)
an array with zero elements
the unit type NULL (including unset variables)
Internal objects that overload their casting behaviour to bool. For example: SimpleXML objects created from empty elements without attributes.
An int is a number of the set ℤ = {..., -2, -1, 0, 1, 2, ...}.
See Also
See Also
Ints can be specified in decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation. The negation operator can be used to denote a negative int.
To use octal notation, precede the number with a 0 (zero). As of PHP 8.1.0, octal notation can also be preceded with 0o or 0O. To use hexadecimal notation precede the number with 0x. To use binary notation precede the number with 0b.
As of PHP 7.4.0, integer literals may contain underscores (_) between digits, for better readability of literals. These underscores are removed by PHP's scanner.
Example #1 Integer literals
<?php
$a = 1234; // decimal number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0o123; // octal number (as of PHP 8.1.0)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
$a = 0b11111111; // binary number (equivalent to 255 decimal)
$a = 1_234_567; // decimal number (as of PHP 7.4.0)
?>
Formally, the structure for int literals is as of PHP 8.1.0 (previously, the 0o or 0O octal prefixes were not allowed, and prior to PHP 7.4.0 the underscores were not allowed):
decimal : [1-9][0-9]*(_[0-9]+)*
| 0
hexadecimal : 0[xX][0-9a-fA-F]+(_[0-9a-fA-F]+)*
octal : 0[oO]?[0-7]+(_[0-7]+)*
binary : 0[bB][01]+(_[01]+)*
integer : decimal
| hexadecimal
| octal
| binary
The size of an int is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). 64-bit platforms usually have a maximum value of about 9E18. PHP does not support unsigned ints. int size can be determined using the constant PHP_INT_SIZE, maximum value using the constant PHP_INT_MAX, and minimum value using the constant PHP_INT_MIN.
If PHP encounters a number beyond the bounds of the int type, it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the int type will return a float instead.
Example #2 Integer overflow on a 32-bit system
<?php
$large_number = 2147483647;
var_dump($large_number); // int(2147483647)
$large_number = 2147483648;
var_dump($large_number); // float(2147483648)
$million = 1000000;
$large_number = 50000 * $million;
var_dump($large_number); // float(50000000000)
?>
Example #3 Integer overflow on a 64-bit system
<?php
$large_number = 9223372036854775807;
var_dump($large_number); // int(9223372036854775807)
$large_number = 9223372036854775808;
var_dump($large_number); // float(9.2233720368548E+18)
$million = 1000000;
$large_number = 50000000000000 * $million;
var_dump($large_number); // float(5.0E+19)
?>
There is no int division operator in PHP, to achieve this use the intdiv() function. 1/2 yields the float 0.5. The value can be cast to an int to round it towards zero, or the round() function provides finer control over rounding.
<?php
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
?>
To explicitly convert a value to int, use either the (int) or (integer) casts. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an int argument. A value can also be converted to int with the intval() function.
If a resource is converted to an int, then the result will be the unique resource number assigned to the resource by PHP at runtime.
See also Type Juggling.
false will yield 0 (zero), and true will yield 1 (one).
From floating point numbers ¶
When converting from float to int, the number will be rounded towards zero. As of PHP 8.1.0, a deprecation notice is emitted when implicitly converting a non-integral float to int which loses precision.
<?php
function foo($value): int {
return $value;
}
var_dump(foo(8.1)); // "Deprecated: Implicit conversion from float 8.1 to int loses precision" as of PHP 8.1.0
var_dump(foo(8.1)); // 8 prior to PHP 8.1.0
var_dump(foo(8.0)); // 8 in both cases
var_dump((int)8.1); // 8 in both cases
var_dump(intval(8.1)); // 8 in both cases
?>
If the float is beyond the boundaries of int (usually +/- 2.15e+9 = 2^31 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms), the result is undefined, since the float doesn't have enough precision to give an exact int result. No warning, not even a notice will be issued when this happens!
Note:
NaN and Infinity will always be zero when cast to int.
Warning
Never cast an unknown fraction to int, as this can sometimes lead to unexpected results.
<?php
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>
See also the warning about float precision.
From strings ¶
If the string is numeric or leading numeric then it will resolve to the corresponding integer value, otherwise it is converted to zero (0).
From NULL ¶
null is always converted to zero (0).
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