Surely you have a wardrobe or dresser at home. The principle of their use is simple: we remove things that we do not need right now, but may need after a while.

Variables are arranged in the same way. They can put some value and store there until it takes.

Creating variables

Put the value to the variable as follows:

In the code above, we created a variable $ name and put it in it the value of Ivan, then created a variable $ Age and assigned a value of 20.

The name "variable" means that its value may vary during the execution of the script:

In some languages, the variable must first "declare", and then use it. There are no ads in PHP - the variable is created at the moment when you put it in it.
However, PHP programmers often say "declare a variable" instead of "create a variable".

Also, instead of "put in variable value", it is often said to "assign a value".
The reason is simple - symbol \u003d, thanks to which we save the value to a variable, called the "assignment operator". Hence the term "assign".

Rules naming variables

1. The name of the variable begins with the $ symbol.

2. The second symbol may be the letter or the shutting symbol _

Names of variables are case-durable. $ Name and $ Name are different variables.

Output variable value on screen

You can withdraw the variable using the Echo team already known to us:

The ECHO command allows you to display several values \u200b\u200bat once:

Note, we were transferred to Echo 2 values, separating them with a comma. So we can transmit any sets of values. The following two examples will lead to the same result:

Also in PHP there is an abbreviated syntax of the output of variables. Instead

Prior to the version of PHP 5.4, the abbreviated syntax worked only when the short_open_tag directive is turned on in the PHP settings, which also allows the abbreviated opening tag

Check the value of the variable

The ECHO command is not always convenient to check the current value of the variable. For example, when you try to output an empty string "" absolutely nothing will be displayed on the screen. And it is not clear what cause is in an empty variable or non-working code.

Therefore, to check the variable value, the var_DUMP () function is used:

The result of the script:

String (5) "Vasya" String (0) ""

As you can see, PHP output not only the contents of the variable, but also the number of characters, and even the type of variable (String - line). Types of data we consider in detail in the following lessons.

Delete variables

You can delete an existing variable using the Unset () function:

And now it's time to practice a little.

Remember, almost any task on PHP can have several solutions. Therefore, if your solutions are different from writing on this site - this does not mean at all that you did something wrong.

Write a script that:
1. Creates variables with title and Content names and some values.
2. Displays the value of the Title variable inside the H1 tag, and the value of the CONTENT variable within the DIV tag.

Show a decision

", $ title,""; Echo"

"; ?>

I want to once again draw your attention that this decision is not the only true. For example, the following code will lead to the same result:

Environment Variables (Environments) in Windows contain various information about the system settings and user environment. There are variables of the environment, systems and processes.

The easiest way to view the contents of environment variables in Windows - open the properties of the system ( sysdm.cpl) -\u003e Advanced -\u003e Wednesday variables. As you can see, there are two sections in the current sections: in the top there are variables of the user's environment, in the lower - systemic.

In addition, environment variables are stored in the system registry. Custom variables are stored in the section. System - B. HKLM \\ SYSTEM \\ CURRENTCONTROLSET \\ CONTROL \\ SESSION MANAGER \\ ENVIRONMENT.

You can withdraw the values \u200b\u200bof all environment variables at the Windows command prompt. The team is simple:

The command will display the list of environment variables and their values.

In PowerShell, to display all environment variables, you can use the command:

If you want to display only one variable, you need to use the echo command, and the name of the variable must be concluded in interest signs. For example,

Echo% Systemroot%

sET\u003e C: \\ TMP \\ ENV_VAR.TXT

Variables of the environment of a specific process can be obtained using free process Explorer utilities (from sysinternals). Just open the properties of the process and go to the tab Environment.

Variables in PHP. - This is a kind of information container that can contain various types of data (text, numbers, arrays, and so on). In general, variables allow you to create, store, change, and in the future to quickly refer to the information specified in them.

How to create a variable in php

First, variables contain a sign $ (dollar) - designation of the use of variable, then letters latin alphabet (from a to z and small and large), at the end I can contain numbers. Also in the title is allowed to use lower stress (not at the end).

How can I call variables:

$ var.
$ variable
$ year1945
$ _Variable.
How can not be called variables:

$ 1 - consists only of numbers
$ 1Var - You can not start the name of the variable with the numbers
$ / var - from additional characters only the lower undercuting _
$ variable - Cyrillic is allowed by PHP documentation, but not recommended
$ Var IABLE - You can not use gaps

Each variable is assigned a value. To assign a value to the value = (equally). During the processing of the script, the value of the variable can repeatedly vary depending on different conditions.

$ city \u003d "Moscow"; // variable $ city Assigned a string (in quotes) Moscow value
$ year \u003d 1147; // A variable $ year Assigned numeric value 1147
?>

$ Name \u003d "Alexander";
$ Name \u003d "Alexey";
Echo "$ Name, $ Name"; // withdrawn "Alexander, Alexey"
?>

Display of variables PHP.

Separately, you should disassemble how to display variables with output operatorswhose work we disassembled in the past lesson creating a PHP wonder. Output operators. . Below I will give a number of visual examples with comments.

// so specify the values \u200b\u200bof the variable
$ Name1 \u003d "Alexey";
$ Name2 \u003d "Alexander";

// Display variables
Echo $ Name2; // Will out: Alexander
Echo "Name1 is $ Name1"; // Name1 is Alexey

// When using single quotes output
// variable name, not meaning
Echo "Name1 is $ Name1"; // Release: Name1 is $ Name1

// You can display just values \u200b\u200bof variables
Echo $ Name1; // Alexei
Echo $ Name1, $ Name2; // Aleksealeksandr
Echo $ Name1. "" $ Name2; // Alexey Alexander
Echo "$ Name1, $ Name2"; // Alexey, Alexander

Echo.<< Here uses the syntax "HERE Document" for output
Multiple lines with a variable substitution $ variable.
End;

Operations with PHP variables

Arithmetic operations in PHP
In the case of numeric values, arithmetic operations can be carried out: addition, subtraction, multiplication, and so on.

- $ A. (denial) Changing the mark $ a.
$ a + $ b (addition) Amount $ a and $ b.
$ A - $ B (subtraction) The difference is $ a and $ b.
$ A * $ b (Multiplication) Product $ A and $ B.
$ A / $ B (division) private from dividing $ A to $ b.
$ A% $ b (division in the module) An integer balance from dividing $ A by $ b.
Consider examples

$ a \u003d 2; // Notice, in the case of digits, the quotes are not set
$ b \u003d 3; // Notice, in the case of digits, the quotes are not set

$ result \u003d $ A + $ B; // fold variables
Echo $ Result; // Will out 5.

$ result \u003d $ b - $ A; // fold variables
Echo $ Result; // Will out 1.

Operations of increment and decrement in PHP
These operations will be used mainly when building cycles, which we will talk about a little later.
Prefix - Operators prescribed before the variable ( - $ A.; ++ $ A.). Return the value of the variable to the changes.
Postfix - operators prescribed after a variable ( $ A--; $ A--). Return the value of a variable with change.
Increment - increase value.
Decrement - Reduction of value.

++ $ A. Prefix increment. Increases $ A per unit and returns the value $ a.
$ a ++. Postfix increment. Returns the value of $ a, and then increases $ A per unit.
- $ A. Prefix decrement. Reduces $ A per unit and returns the value $ a.
$ A-- Postfix decrement. Returns the value of $ A, and then reduces $ A per unit.
Echo "

Postfix Increment

";
$ a \u003d 5;
Echo "should be 5:". $ A ++. "\\ n";

Echo "

Prefix Increment

";
$ a \u003d 5;
Echo "should be 6:". ++ $ a. "\\ n";
Echo "should be 6:". $ a. "\\ n";

Echo "

Postfix decrement

";
$ a \u003d 5;
Echo "should be 5:". $ a-- "\\ n";

Echo "

Prefix decrement

";
$ a \u003d 5;
Echo "should be 4:". - $ a. "\\ n";
Echo "should be 4:". $ a. "\\ n";
?>

PHP assignment operations
Basic operator looks like = . At first glance it may seem that this operator is equal. In fact, it is not. In fact, the assignment operator means that the left operand receives the value of the right expression, (i.e. is set by the resulting value). Combined operators - These are operators that allow the use of previous values \u200b\u200bof variables for subsequent operations (add to the string variable (with text) or add numerical values).

$ a \u003d ($ b \u003d 2) + 4; // Result: $ A is set by value 6, the $ B variable is assigned 2.

$ a \u003d 2;
$ a + \u003d 3; // Sets $ a with a value 5, similarly to the recording: $ a \u003d $ A + 3;
$ b \u003d "hello";
$ b. \u003d "Peace!"; // Sets $ B string "Hello the world!", like $ b \u003d $ b. "There!";

There are also operations of comparison and brain teaserBut we will talk about them in the following lessons. I will try to immediately not scare you with a large amount of information!)

13 Years Ago.

A Little Gotcha to Watch Out for:

If You Turn Off Registerglobals and Related, Then Use Get_Defined_Vars (), You May See Something Like The Following:

Array.
[Globals] \u003d\u003e Array
[Globals] \u003d\u003e Array
* Recursion *
[_Post] \u003d\u003e Array ()
[_GET] \u003d\u003e Array ()
[_Cookie] \u003d\u003e Array ()
[_Files] \u003d\u003e Array ()
)

[_Post] \u003d\u003e Array ()
[_GET] \u003d\u003e Array ()
[_Cookie] \u003d\u003e Array ()
[_Files] \u003d\u003e Array ()

)
?>

Notice That $ _Server ISN "T There. IT Sems That PHP Only Loads The Superglobal $ _Server If IT IS Used Somewhere. You Could do this:

print "

". HTMLSPECIALCHARS (print_r (get_defined_vars (), True))."

" ;
print "

". HTMLSPECIALCHARS (Print_R ($ _Server, True))."

" ;
?>

And then $ _Server Will Appear in Both Lists. I Guess IT "S Not Really A Gotcha, Because Nothing Bad Will Happen Either Way, But It" S An Interesting Curiosity Nonetheless.

6 YEARS AGO.

SINCE Get_Defined_Vars () Only Gets The Variables At The Point You Call The Function, There Is a Simple Way to Get The Variables Defined Within The Current Scope.

// The Very Top Of Your PHP Script
$ vars \u003d get_defined_vars ();

// NOW DO YOUR STUFF
$ foo \u003d "foo";
$ Bar \u003d "Bar";

// Get All The Variables Defined in Current Scope
$ vars \u003d array_diff (get_defined_vars (), $ vars);

echo "

"
;
print_R ($ vars); 
echo "

" ;
?>

15 YEARS AGO.

HERE IS A FUNCTION WHICH GENERATES A DEBUG REPORT FOR DISPLAY OR EMAIL
using get_defined_vars. Great for Getting A Detailed Snapshot Worthout
relying On User Input.

function GenerateDebugreport ($ Method, $ Defined_Vars, $ email \u003d "undefined") (
// Function to Create A Debug Report to Display or Email.
// Usage: GenerateDebugreport (Method, Get_Defined_Vars (), Email);
// WHERE METHOD IS "BROWSER" OR "Email".

// CREATE AN IGNORE LIST FOR KEYS RETURNED by "get_defined_vars".
// for example, http_post_vars, http_get_vars and other
// Redundant (SAME AS _POST, _GET)
// Also Include Vars You Want Ignored for Security ReaSons - I.E. Phpsessid.
$ ignorelist \u003d array ("http_post_vars", "http_get_vars",
"Http_cookie_vars", "http_server_vars",
"Http_env_vars", "http_session_vars",
"_Env", "phpsessid", "sess_dbuser",
"Sess_dbpass", "http_cookie");

$ timestamp \u003d date ("m / d / y h: m: s");
$ message \u003d "Debug Report Created $ TimeStamp \\ N";

// Get The Last SQL Error for Good Measure, Where $ Link Is The Resource Identifier
// for mysql_connect. Comment Out or Modify for Your Database or Abstraction Setup.
global $ Link;
$ SQL_ERROR \u003d MYSQL_ERROR ($ LINK);
if ($ sql_error) (
$ message. \u003d "\\ Nmysql Messages: \\ n". mysql_error ($ LINK);
}
// End MySQL.

// COULD USE A RECURSIVE FUNCTION HERE. You get the idea ;-)
foreach ($ defined_vars as $ Key \u003d\u003e $ Val) (
If (IS_ARRAY ($ VAL) &&! IN_ARRAY ($ Key, $ ignorelist) && Count ($ Val)\u003e 0) (
$ Message. \u003d "\\ N $ Key Array (Key \u003d Value): \\ n";
Foreach ($ Val AS $ subkey \u003d\u003e $ subval) (
If (! in_array ($ subkey, $ ignorelist) &&! is_array ($ subval)) (
$ Message. \u003d $ subkey. "\u003d". $ subval. "\\ n";
}
Elseif (! In_array ($ subkey, $ ignorelist) && is_array ($ subval)) (
Foreach ($ Subval AS $ subsubkey \u003d\u003e $ subsubval) (
if (! in_array ($ subsubkey, $ ignorelist)) (
$ message. \u003d $ subsubkey. "\u003d". $ subsubval. "\\ n" ;
}
}
}
}
}
ELSEIF (!iS_Array ($ Val) &&! IN_ARRAY ($ Key, $ ignorelist) && $ Val) (
$ Message. \u003d "\\ Nvariable". $ Key. "\u003d". $ Val. "\\ n";
}
}

If ($ Method \u003d\u003d "Browser") (
Echo NL2BR ($ Message);
}
Elseif ($ Method \u003d\u003d "Email") (
if ($ email \u003d\u003d "undefined") (
$ email \u003d $ _Server ["Server_admin"];
}

$ MResult \u003d Mail ($ email, "Debug Report for". $ _env ["HostName"]. "", $ message);
if ($ MResult \u003d\u003d 1) (
Echo. "Debug Report Sent SuccessFully. \\ N";
}
ELSE (
Echo. "FAILED TO SEND DEBUG REORT. \\ N";
}
}
}
?>

17 YEARS AGO.

Simple Routine to Convert A Get_Defined_Vars Object to XML.

fUNCTION OBJ2XML ($ V, $ Indent \u003d "") (
While (List ($ Key, $ Val) \u003d Each ($ V)) (
if ($ Key \u003d\u003d "__attr") Continue;
// Check for __attr
if (IS_Object ($ Val -\u003e __attr)) (
While (List ($ Key2, $ val2) \u003d Each ($ val -\u003e __attr)) (
$ ATTR \u003d "$ Key2 \u003d \\" $ val2 \\ "";
}
}
ELSE $ ATTR \u003d "";
if (IS_ARRAY ($ VAL) || IS_Object ($ Val)) (
Print ("$ Indent< $key$attr >\\ n ");
oBJ2XML ($ Val, $ Indent. "");
Print ("$ Indent\\ n ");
}
ELSE PRINT ("$ Indent< $key$attr > $ val.\\ n ");
}
}

// Example Object.
$ x -\u003e Name -\u003e first \u003d "john";
$ x -\u003e Name -\u003e Last \u003d "smith";
$ x -\u003e arr ["fruit"] \u003d "bannana";
$ x -\u003e arr ["veg"] \u003d "carrot";
$ Y -\u003e Customer \u003d $ x;
$ Y -\u003e Customer -\u003e __attr -\u003e id \u003d "176c4";

$ z \u003d get_defined_vars ();
oBJ2XML ($ z ["y"]);
?>
will Output:


John.
Smith


Bannana.
Carrot.

11 Years Ago.

AS A NOTE, Get_Defined_Vars () Does Not Return A Set Of Variable References (As I Hoped). For example:

// Define A Variable
$ MY_VAR \u003d "FOO";

// Get Our List of Defined Variables
$ defined_vars \u003d get_defined_vars ();

NOW TRY TO CHANGE THE VALUE THROUGH THE RETURNED ARRAY
$ defined_vars ["MY_VAR"] \u003d "BAR";

echo $ MY_VAR, "\\ N";

?>

will Output "Foo" (The Original Value). IT "D BE Nice If Get_Defined_Vars () Had An Optional Argument to Make Them References, But i Imagine Its a Rather Specialized Request. You Can Do It Yourself (LESS Convenly) with Something Like:

$ defined_vars \u003d array ();
$ var_names \u003d array_keys (get_defined_vars ());

foreach ($ var_names as $ var_name)
{
$ defined_vars [$ var_name] \u003d & $ var_name;
}

?>

1 Year Ago.

I Posted Here Before About "This" being in get_defined_vars.

IT TURNS OUT IT "S NOT ALWAYS THERE BUT IN CERTIAIN CASES IT WILL INEXPLICABLY APPEAR.

Php -r "
Class Test (
public function a () (var_dump (array_keys (get_defined_vars ()); $ a \u003d 123;)
Public Function B () (var_dump (array_keys (get_defined_vars ()); $ this;)
}
$ t \u003d new test ();
$ T-\u003e A ();
$ T-\u003e B ();
"

Array ()
Array ("this")

This Does Not Happen in PHP 7.2 But Will Happen in PHP 5.6.

1 Year Ago.

Some Comments Here Point Out That This Function Wont Return References. IT Does However Return Names and Names Are "References".

I Would Not Recommend The Suggestions Here That Convert IT to References.

Public Function X ($ A, $ B, $ C) (
Foreach (Array_Keys (Get_Defined_Vars ()) AS $ Key)
if ($ Key! \u003d\u003d "this")
$ this-\u003e y ($ ($ Key));
}

Public Function Y (& $ Input) (
$ input ++;
}

Instead of $ () You can Also use $$.

I Have Done Some Whacky Things in My Time to Make Extremely Generic Code But i "Ve Never Had to Do Anything Like The Above. IT Might Not Even Work (But Should Since IT" S NO Different to $ A [$ Key]).

You Could Also Do $$ KEY ++ But i "Ve Never Seen Code Like That Which Wasn" T Horrifically Dynamic ISN "T Beneficial).

IF You "Re Doing Something Like That Then Give It Additional Scrutiny.