diff --git a/language/variables.sgml b/language/variables.sgml index 277e219342..3cdef52348 100644 --- a/language/variables.sgml +++ b/language/variables.sgml @@ -5,47 +5,44 @@ Basics - Variables in PHP are represented by a dollar sign followed by the - name of the variable. The variable name is case-sensitive. - - + Variables in PHP are represented by a dollar sign followed by the + name of the variable. The variable name is case-sensitive. + + $var = "Bob"; $Var = "Joe"; echo "$var, $Var"; // outputs "Bob, Joe" - - + + - - In PHP3, variables are always assigned by value. That is to say, - when you assign an expression to a variable, the entire value of - the original expression is copied into the destination - variable. This means, for instance, that after assigning one - variable's value to another, changing one of those variables will - have no effect on the other. For more information on this kind of - assignment, see Expressions. + In PHP3, variables are always assigned by value. That is to say, + when you assign an expression to a variable, the entire value of + the original expression is copied into the destination + variable. This means, for instance, that after assigning one + variable's value to another, changing one of those variables will + have no effect on the other. For more information on this kind of + assignment, see Expressions. - - PHP4 offers another way to assign values to variables: - assign by reference. This means that the new - variable simply references (in other words, "becomes an alias for" - or "points to") the original variable. Changes to the new variable - affect the original, and vice versa. This also means that no - copying is performed; thus, the assignment happens more - quickly. However, any speedup will likely be noticed only in tight - loops or when assigning large arrays or objects. + PHP4 offers another way to assign values to variables: + assign by reference. This means that the new + variable simply references (in other words, "becomes an alias for" + or "points to") the original variable. Changes to the new variable + affect the original, and vice versa. This also means that no + copying is performed; thus, the assignment happens more + quickly. However, any speedup will likely be noticed only in tight + loops or when assigning large arrays or objects. - - To assign by reference, simply prepend an ampersand (&) to the - beginning of the variable which is being assigned (the source - variable). For instance, the following code snippet outputs 'My - name is Bob' twice: + To assign by reference, simply prepend an ampersand (&) to the + beginning of the variable which is being assigned (the source + variable). For instance, the following code snippet outputs 'My + name is Bob' twice: - - + + <?php $foo = 'Bob'; // Assign the value 'Bob' to $foo $bar = &$foo; // Reference $foo via $bar. @@ -53,16 +50,15 @@ $bar = "My name is $bar"; // Alter $bar... echo $foo; // $foo is altered too. echo $bar; ?> - - - + + - One important thing to note is that only named variables may be - assigned by reference. - - + One important thing to note is that only named variables may be + assigned by reference. + + <?php $foo = 25; $bar = &$foo; // This is a valid assignment. @@ -74,8 +70,8 @@ function test() { $bar = &test(); // Invalid. ?> - - + + @@ -84,449 +80,445 @@ $bar = &test(); // Invalid. Predefined variables - PHP provides a large number of predefined variables to any script - which it runs. Many of these variables, however, cannot be fully - documented as they are dependent upon which server is running, the - version and setup of the server, and other factors. Some of these - variables will not be available when PHP is run on the - command-line. + PHP provides a large number of predefined variables to any script + which it runs. Many of these variables, however, cannot be fully + documented as they are dependent upon which server is running, the + version and setup of the server, and other factors. Some of these + variables will not be available when PHP is run on the + command-line. - - Despite these factors, here is a list of predefined variables - available under a stock installation of PHP 3 running as a module - under a stock installation of Apache 1.3.6. + Despite these factors, here is a list of predefined variables + available under a stock installation of PHP 3 running as a module + under a stock installation of Apache 1.3.6. - - For a list of all predefined variables (and lots of other useful - information), please see (and use) phpinfo. + For a list of all predefined variables (and lots of other useful + information), please see (and use) phpinfo. - - This list is neither exhaustive nor intended to be. It is simply - a guideline as to what sorts of predefined variables you can - expect to have access to in your script. - + + This list is neither exhaustive nor intended to be. It is simply + a guideline as to what sorts of predefined variables you can + expect to have access to in your script. + - Apache variables + Apache variables + + These variables are created by the Apache webserver. If you are running + another webserver, there is no guarantee that it will provide the + same variables; it may omit some, or provide others not listed + here. That said, a large number of these variables are accounted + for in the CGI 1.1 + specification, so you should be able to expect those. + + + Note that few, if any, of these will be available (or indeed have + any meaning) if running PHP on the command line. + + + + + + GATEWAY_INTERFACE + - These variables are created by the Apache webserver. If you are running - another webserver, there is no guarantee that it will provide the - same variables; it may omit some, or provide others not listed - here. That said, a large number of these variables are accounted - for in the CGI 1.1 - specification, so you should be able to expect those. + What revision of the CGI specification the server is using; + i.e. 'CGI/1.1'. + + + + SERVER_NAME + - Note that few, if any, of these will be available (or indeed have - any meaning) if running PHP on the command line. + The name of the server host under which the current script is + executing. If the script is running on a virtual host, this + will be the value defined for that virtual host. + + - - - - GATEWAY_INTERFACE - - - What revision of the CGI specification the server is using; - i.e. 'CGI/1.1'. - - - + + SERVER_SOFTWARE + + + Server identification string, given in the headers when + responding to requests. + + + - - SERVER_NAME - - - The name of the server host under which the current script is - executing. If the script is running on a virtual host, this - will be the value defined for that virtual host. - - - - - - SERVER_SOFTWARE - - - Server identification string, given in the headers when - responding to requests. - - - - - - SERVER_PROTOCOL - - - Name and revision of the information protocol via which the - page was requested; i.e. 'HTTP/1.0'; - - - - - - REQUEST_METHOD - - - Which request method was used to access the page; i.e. 'GET', - 'HEAD', 'POST', 'PUT'. - - - + + SERVER_PROTOCOL + + + Name and revision of the information protocol via which the + page was requested; i.e. 'HTTP/1.0'; + + + + + + REQUEST_METHOD + + + Which request method was used to access the page; i.e. 'GET', + 'HEAD', 'POST', 'PUT'. + + + - - QUERY_STRING - - - The query string, if any, via which the page was accessed. - - - + + QUERY_STRING + + + The query string, if any, via which the page was accessed. + + + - - DOCUMENT_ROOT - - - The document root directory under which the current script is - executing, as defined in the server's configuration file. - - - + + DOCUMENT_ROOT + + + The document root directory under which the current script is + executing, as defined in the server's configuration file. + + + - - HTTP_ACCEPT - - - Contents of the Accept: header - from the current request, if there is one. - - - + + HTTP_ACCEPT + + + Contents of the Accept: header from the + current request, if there is one. + + + - - HTTP_ACCEPT_CHARSET - - - Contents of the Accept-Charset: header - from the current request, if there is one. Example: - 'iso-8859-1,*,utf-8'. - - - + + HTTP_ACCEPT_CHARSET + + + Contents of the Accept-Charset: header + from the current request, if there is one. Example: + 'iso-8859-1,*,utf-8'. + + + - - HTTP_ENCODING - - - Contents of the Accept-Encoding: header - from the current request, if there is one. Example: 'gzip'. - - - + + HTTP_ENCODING + + + Contents of the Accept-Encoding: header + from the current request, if there is one. Example: 'gzip'. + + + + + + HTTP_ACCEPT_LANGUAGE + + + Contents of the Accept-Language: header + from the current request, if there is one. Example: 'en'. + + + + + + HTTP_CONNECTION + + + Contents of the Connection: header from + the current request, if there is one. Example: 'Keep-Alive'. + + + - - HTTP_ACCEPT_LANGUAGE - - - Contents of the Accept-Language: header - from the current request, if there is one. Example: 'en'. - - - + + HTTP_HOST + + + Contents of the Host: header from the + current request, if there is one. + + + - - HTTP_CONNECTION - - - Contents of the Connection: header - from the current request, if there is one. Example: - 'Keep-Alive'. - - - + + HTTP_REFERER + + + The address of the page (if any) which referred the browser + to the current page. This is set by the user's browser; not + all browsers will set this. + + + - - HTTP_HOST - - - Contents of the Host: header - from the current request, if there is one. - - - + + HTTP_USER_AGENT + + + Contents of the User_Agent: header from + the current request, if there is one. This is a string + denoting the browser software being used to view the current + page; i.e. Mozilla/4.5 [en] (X11; U; Linux + 2.2.9 i586). Among other things, you can use + this value with get_browser to tailor + your page's functionality to the capabilities of the user's + browser. + + + - - HTTP_REFERER - - - The address of the page (if any) which referred the browser - to the current page. This is set by the user's browser; not - all browsers will set this. - - - + + REMOTE_ADDR + + + The IP address from which the user is viewing the current + page. + + + - - HTTP_USER_AGENT - - - Contents of the User_Agent: header from - the current request, if there is one. This is a string - denoting the browser software being used to view the current - page; i.e. Mozilla/4.5 [en] (X11; U; Linux - 2.2.9 i586). Among other things, you can use - this value with get_browser to tailor - your page's functionality to the capabilities of the user's - browser. - - - + + REMOTE_PORT + + + The port being used on the user's machine to communicate with + the web server. + + + - - REMOTE_ADDR - - - The IP address from which the user is viewing the current - page. - - - + + SCRIPT_FILENAME + + + The absolute pathname of the currently executing script. + + + - - REMOTE_PORT - - - The port being used on the user's machine to communicate with - the web server. - - - + + SERVER_ADMIN + + + The value given to the SERVER_ADMIN (for Apache) directive in + the web server configuration file. If the script is running + on a virtual host, this will be the value defined for that + virtual host. + + + + + + SERVER_PORT + + + The port on the server machine being used by the web server + for communication. For default setups, this will be '80'; + using SSL, for instance, will change this to whatever your + defined secure HTTP port is. + + + - - SCRIPT_FILENAME - - - The absolute pathname of the currently executing script. - - - + + SERVER_SIGNATURE + + + String containing the server version and virtual host name + which are added to server-generated pages, if enabled. + + + - - SERVER_ADMIN - - - The value given to the SERVER_ADMIN (for Apache) directive in - the web server configuration file. If the script is running - on a virtual host, this will be the value defined for that - virtual host. - - - + + PATH_TRANSLATED + + + Filesystem- (not document root-) based path to the current + script, after the server has done any virtual-to-real + mapping. + + + - - SERVER_PORT - - - The port on the server machine being used by the web server - for communication. For default setups, this will be '80'; - using SSL, for instance, will change this to whatever your - defined secure HTTP port is. - - - + + SCRIPT_NAME + + + Contains the current script's path. This is useful for pages + which need to point to themselves. + + + - - SERVER_SIGNATURE - - - String containing the server version and virtual host name - which are added to server-generated pages, if enabled. - - - + + REQUEST_URI + + + The URI which was given in order to access this page; for + instance, '/index.html'. + + + + + - - PATH_TRANSLATED - - - Filesystem- (not document root-) based path to the current - script, after the server has done any virtual-to-real - mapping. - - - - - - SCRIPT_NAME - - - Contains the current script's path. This is useful for pages - which need to point to themselves. - - - - - - REQUEST_URI - - - The URI which was given in order to access this page; for - instance, '/index.html'. - - - - - - - Environment variables + Environment variables - - These variables are imported into PHP's global namespace from the - environment under which the PHP parser is running. Many are - provided by the shell under which PHP is running and different - systems are likely running different kinds of shells, a - definitive list is impossible. Please see your shell's - documentation for a list of defined environment variables. - - - - Other environment variables include the CGI variables, placed - there regardless of whether PHP is running as a server module or - CGI processor. - + + These variables are imported into PHP's global namespace from the + environment under which the PHP parser is running. Many are + provided by the shell under which PHP is running and different + systems are likely running different kinds of shells, a + definitive list is impossible. Please see your shell's + documentation for a list of defined environment variables. + + + Other environment variables include the CGI variables, placed + there regardless of whether PHP is running as a server module or + CGI processor. + - PHP variables + PHP variables + + These variables are created by PHP itself. + + + + + + argv + - These variables are created by PHP itself. + Array of arguments passed to the script. When the script is + run on the command line, this gives C-style access to the + command line parameters. When called via the GET method, this + will contain the query string. + + - - - - argv - - - Array of arguments passed to the script. When the script is - run on the command line, this gives C-style access to the - command line parameters. When called via the GET method, this - will contain the query string. - - - + + argc + + + Contains the number of command line parameters passed to the + script (if run on the command line). + + + - - argc - - - Contains the number of command line parameters passed to the - script (if run on the command line). - - - - - - PHP_SELF - - - The filename of the currently executing script, relative to - the document root. If PHP is running as a command-line - processor, this variable is not available. - - - + + PHP_SELF + + + The filename of the currently executing script, relative to + the document root. If PHP is running as a command-line + processor, this variable is not available. + + + - - HTTP_COOKIE_VARS - - - An associative array of variables passed to the current - script via HTTP cookies. Only available if variable - tracking has been turned on via either the track_vars configuration - directive or the - <?php_track_vars?> - directive. - - - + + HTTP_COOKIE_VARS + + + An associative array of variables passed to the current + script via HTTP cookies. Only available if variable tracking + has been turned on via either the track_vars configuration + directive or the + <?php_track_vars?> + directive. + + + + + + HTTP_GET_VARS + + + An associative array of variables passed to the current + script via the HTTP GET method. Only available if variable + tracking has been turned on via either the track_vars configuration + directive or the + <?php_track_vars?> + directive. + + + - - HTTP_GET_VARS - - - An associative array of variables passed to the current - script via the HTTP GET method. Only available if variable - tracking has been turned on via either the track_vars configuration - directive or the - <?php_track_vars?> - directive. - - - - - - HTTP_POST_VARS - - - An associative array of variables passed to the current - script via the HTTP POST method. Only available if variable - tracking has been turned on via either the track_vars configuration - directive or the - <?php_track_vars?> - directive. - - - - - - + + HTTP_POST_VARS + + + An associative array of variables passed to the current + script via the HTTP POST method. Only available if variable + tracking has been turned on via either the track_vars configuration + directive or the + <?php_track_vars?> + directive. + + + + + - - Variable scope + + Variable scope - - The scope of a variable is the context within which it is defined. - For the most part all PHP variables only have a single scope. This - single scope spans included and required files as well. For example: - - - + + The scope of a variable is the context within which it is defined. + For the most part all PHP variables only have a single scope. + This single scope spans included and required files as well. For + example: + + + $a = 1; include "b.inc"; - - - - Here the $a variable will be available within the included b.inc - script. - However, within user-defined functions a local function scope is - introduced. Any variable used inside a function is by default - limited to the local function scope. For example: + + + + Here the $a variable will be available within the included b.inc + script. However, within user-defined functions a local function + scope is introduced. Any variable used inside a function is by + default limited to the local function scope. For + example: + - - + + $a = 1; /* global scope */ Function Test () { @@ -534,22 +526,22 @@ Function Test () { } Test (); - - + + - - This script will not produce any output because the echo statement - refers to a local version of the $a variable, and it has not been - assigned a value within this scope. You may notice that this is a - little bit different from the C language in that global variables - in C are automatically available to functions unless specifically - overridden by a local definition. This can cause some problems in - that people may inadvertently change a global variable. In PHP - global variables must be declared global inside a function if they - are going to be used in that function. An example: + + This script will not produce any output because the echo statement + refers to a local version of the $a variable, and it has not been + assigned a value within this scope. You may notice that this is a + little bit different from the C language in that global variables + in C are automatically available to functions unless specifically + overridden by a local definition. This can cause some problems in + that people may inadvertently change a global variable. In PHP + global variables must be declared global inside a function if they + are going to be used in that function. An example: - - + + $a = 1; $b = 2; @@ -561,22 +553,25 @@ Function Sum () { Sum (); echo $b; - - + + - - The above script will output "3". By declaring $a and - $b global within the function, all references to either variable - will refer to the global version. There is no limit to the number - of global variables that can be manipulated by a function. + + The above script will output "3". By declaring $a and + $b global within the function, all references to either variable + will refer to the global version. There is no limit to the number + of global variables that can be manipulated by a + function. + - - A second way to access variables from the global scope is to use - the special PHP-defined $GLOBALS array. The previous example can - be rewritten as: + + A second way to access variables from the global scope is to use + the special PHP-defined $GLOBALS array. The previous example can + be rewritten as: + - - + + $a = 1; $b = 2; @@ -586,65 +581,68 @@ Function Sum () { Sum (); echo $b; - - + + - - The $GLOBALS array is an associative array with the name of the - global variable being the key and the contents of that variable - being the value of the array element. + + The $GLOBALS array is an associative array with the name of the + global variable being the key and the contents of that variable + being the value of the array element. + - - Another important feature of variable scoping is the - static variable. A static variable exists - only in a local function scope, but it does not lose its value - when program execution leaves this scope. Consider the following - example: + + Another important feature of variable scoping is the + static variable. A static variable exists + only in a local function scope, but it does not lose its value + when program execution leaves this scope. Consider the following + example: + - - + + Function Test () { $a = 0; echo $a; $a++; } - - + + - - This function is quite useless since every time it is called it - sets $a to 0 and prints "0". The $a++ which increments - the variable serves no purpose since as soon as the function exits - the $a variable disappears. To make a useful counting function - which will not lose track of the current count, the $a variable is - declared static: + + This function is quite useless since every time it is called it + sets $a to 0 and prints "0". The $a++ which increments + the variable serves no purpose since as soon as the function exits + the $a variable disappears. To make a useful counting function + which will not lose track of the current count, the $a variable is + declared static: - - + + Function Test () { static $a = 0; echo $a; $a++; } - - - - - Now, every time the Test() function is called it will print the - value of $a and increment it. + + - Static variables also provide one way to deal with recursive - functions. A recursive function is one which calls itself. Care - must be taken when writing a recursive function because it is - possible to make it recurse indefinitely. You must make sure you - have an adequate way of terminating the recursion. The following - simple function recursively counts to 10, using the static - variable $count to know when to stop: + Now, every time the Test() function is called it will print the + value of $a and increment it. - - + + Static variables also provide one way to deal with recursive + functions. A recursive function is one which calls itself. Care + must be taken when writing a recursive function because it is + possible to make it recurse indefinitely. You must make sure you + have an adequate way of terminating the recursion. The following + simple function recursively counts to 10, using the static + variable $count to know when to stop: + + + + Function Test () { static $count = 0; @@ -655,108 +653,118 @@ Function Test () { } $count--; } - - + + - - Variable variables + - - Sometimes it is convenient to be able to have variable variable - names. That is, a variable name which can be set and used - dynamically. A normal variable is set with a statement such as: + + Variable variables + + + Sometimes it is convenient to be able to have variable variable + names. That is, a variable name which can be set and used + dynamically. A normal variable is set with a statement such as: - - + + $a = "hello"; - - + + - - A variable variable takes the value of a variable and treats that as the - name of a variable. In the above example, hello, can - be used as the name of a variable by using two dollar signs. i.e. + + A variable variable takes the value of a variable and treats that + as the name of a variable. In the above example, + hello, can be used as the name of a variable + by using two dollar signs. i.e. - - + + $$a = "world"; - - + + - - At this point two variables have been defined and stored in the - PHP symbol tree: $a with contents "hello" and $hello with contents - "world". Therefore, this statement: + + At this point two variables have been defined and stored in the + PHP symbol tree: $a with contents "hello" and $hello with contents + "world". Therefore, this statement: - - + + echo "$a ${$a}"; - - + + - - produces the exact same output as: + + produces the exact same output as: - - + + echo "$a $hello"; - - + + - + i.e. they both produce: hello world. + + In order to use variable variables with arrays, you have to + resolve an ambiguity problem. That is, if you write $$a[1] then + the parser needs to know if you meant to use $a[1] as a variable, + or if you wanted $$a as the variable and then the [1] index from + that variable. The syntax for resolving this ambiguity is: + ${$a[1]} for the first case and ${$a}[1] for the + second. + + + + + + Variables from outside PHP + + + HTML Forms (GET and POST) + - In order to use variable variables with arrays, you have to - resolve an ambiguity problem. That is, if you write $$a[1] then - the parser needs to know if you meant to use $a[1] as a variable, - or if you wanted $$a as the variable and then the [1] index from - that variable. The syntax for resolving this ambiguity is: - ${$a[1]} for the first case and ${$a}[1] for the second. + When a form is submitted to a PHP script, any variables from that + form will be automatically made available to the script by + PHP. For instance, consider the following form: + - - Variables from outside PHP - - - HTML Forms (GET and POST) - - - When a form is submitted to a PHP script, any variables from that - form will be automatically made available to the script by - PHP. For instance, consider the following form: - - - - Simple form variable - + + + Simple form variable + <form action="foo.php3" method="post"> Name: <input type="text" name="name"><br> <input type="submit"> </form> - - + + + - - When submitted, PHP will create the variable - $name, which will will contain - whatever what entered into the Name: field - on the form. + + When submitted, PHP will create the variable + $name, which will will contain + whatever what entered into the Name: field + on the form. + - - PHP also understands arrays in the context of form variables, but - only in one dimension. You may, for example, group related - variables together, or use this feature to retrieve values from a - multiple select input: + + PHP also understands arrays in the context of form variables, but + only in one dimension. You may, for example, group related + variables together, or use this feature to retrieve values from a + multiple select input: - + More complex form variables - + <form action="array.php" method="post"> Name: <input type="text" name="personal[name]"><br> Email: <input type="text" name="personal[email]"><br> @@ -764,144 +772,163 @@ echo "$a $hello"; <select multiple name="beer[]"> <option value="warthog">Warthog <option value="guinness">Guinness + <option value="stuttgarter">Stuttgarter Schwabenbräu </select> <input type="submit"> </form> - - + + + - - If PHP's track_vars feature is turned on, either by the track_vars configuration setting - or the <?php_track_vars?> - directive, then variables submitted via the POST or GET methods - will also be found in the global associative arrays - $HTTP_POST_VARS and $HTTP_GET_VARS as appropriate. + + If PHP's track_vars feature is turned on, either by the track_vars configuration setting + or the <?php_track_vars?> + directive, then variables submitted via the POST or GET methods + will also be found in the global associative arrays + $HTTP_POST_VARS and $HTTP_GET_VARS as appropriate. + - - IMAGE SUBMIT variable names - - - When submitting a form, it is possible to use an image instead - of the standard submit button with a tag like: - - - -<input type=image src="image.gif" name="sub"> - - - - - When the user clicks somewhere on the image, the accompanying - form will be transmitted to the server with two additional - variables, sub_x and sub_y. These contain the coordinates of - the user click within the image. The experienced may note that - the actual variable names sent by the browser contains a period - rather than an underscore, but PHP converts the period to an - underscore automatically. - - - HTTP Cookies + + IMAGE SUBMIT variable names - PHP transparently supports HTTP cookies as defined by Netscape's Spec. Cookies are a - mechanism for storing data in the remote browser and thus - tracking or identifying return users. You can set cookies using - the SetCookie function. Cookies are part - of the HTTP header, so the SetCookie function must be called - before any output is sent to the browser. This is the same - restriction as for the Header function. - Any cookies sent to you from the client will automatically be - turned into a PHP variable just like GET and POST method data. - - - If you wish to assign multiple values to a single cookie, just - add [] to the cookie name. For example: + When submitting a form, it is possible to use an image instead + of the standard submit button with a tag like: - -SetCookie ("MyCookie[]", "Testing", time()+3600); + +<input type=image src="image.gif" name="sub"> - Note that a cookie will replace a previous cookie by the same - name in your browser unless the path or domain is different. So, - for a shopping cart application you may want to keep a counter - and pass this along. i.e. + When the user clicks somewhere on the image, the accompanying + form will be transmitted to the server with two additional + variables, sub_x and sub_y. These contain the coordinates of the + user click within the image. The experienced may note that the + actual variable names sent by the browser contains a period + rather than an underscore, but PHP converts the period to an + underscore automatically. + + - - SetCookie Example - + + + + HTTP Cookies + + + PHP transparently supports HTTP cookies as defined by Netscape's Spec. Cookies are a + mechanism for storing data in the remote browser and thus + tracking or identifying return users. You can set cookies using + the SetCookie function. Cookies are part of + the HTTP header, so the SetCookie function must be called before + any output is sent to the browser. This is the same restriction + as for the Header function. Any cookies + sent to you from the client will automatically be turned into a + PHP variable just like GET and POST method data. + + + If you wish to assign multiple values to a single cookie, just + add [] to the cookie name. For + example: + + + + +SetCookie ("MyCookie[]", "Testing", time()+3600); + + + + + Note that a cookie will replace a previous cookie by the same + name in your browser unless the path or domain is different. So, + for a shopping cart application you may want to keep a counter + and pass this along. i.e. + + + + SetCookie Example + $Count++; SetCookie ("Count", $Count, time()+3600); SetCookie ("Cart[$Count]", $item, time()+3600); - - + + - - Environment variables + - - PHP automatically makes environment variables available as normal - PHP variables. + + Environment variables + + + PHP automatically makes environment variables available as normal + PHP variables. - + echo $HOME; /* Shows the HOME environment variable, if set. */ - + + - - Since information coming in via GET, POST and Cookie mechanisms - also automatically create PHP variables, it is sometimes best to - explicitly read a variable from the environment in order to make - sure that you are getting the right version. The - getenv function can be used for this. You - can also set an environment variable with the - putenv function. - - - Dots in incoming variable names - - - Typically, PHP does not alter the names of variables when they are - passed into a script. However, it should be noted that the dot - (period, full stop) is not a valid character in a PHP - variable name. For the reason, look at it: - -$varname.ext; /* invalid variable name */ - - Now, what the parser sees is a variable named $varname, followed - by the string concatenation operator, followed by the barestring - (i.e. unquoted string which doesn't match any known key or - reserved words) 'ext'. Obviously, this doesn't have the intended - result. - - - - For this reason, it is important to note that PHP will - automatically replace any dots in incoming variable names with - underscores. - - - - - Determining variable types - - - Because PHP determines the types of variables and converts them - (generally) as needed, it is not always obvious what type a given - variable is at any one time. PHP includes several functions - which find out what type a variable is. They are - gettype, is_long, - is_double, is_string, - is_array, and - is_object. - + + Since information coming in via GET, POST and Cookie mechanisms + also automatically create PHP variables, it is sometimes best to + explicitly read a variable from the environment in order to make + sure that you are getting the right version. The + getenv function can be used for this. You + can also set an environment variable with the + putenv function. + + + + Dots in incoming variable names + + + Typically, PHP does not alter the names of variables when they + are passed into a script. However, it should be noted that the + dot (period, full stop) is not a valid character in a PHP + variable name. For the reason, look at it: + +$varname.ext; /* invalid variable name */ + + Now, what the parser sees is a variable named $varname, followed + by the string concatenation operator, followed by the barestring + (i.e. unquoted string which doesn't match any known key or + reserved words) 'ext'. Obviously, this doesn't have the intended + result. + + + + For this reason, it is important to note that PHP will + automatically replace any dots in incoming variable names with + underscores. + + + + + + Determining variable types + + + Because PHP determines the types of variables and converts them + (generally) as needed, it is not always obvious what type a given + variable is at any one time. PHP includes several functions + which find out what type a variable is. They are + gettype, is_long, + is_double, is_string, + is_array, and + is_object. + + + - +