How to Verify If $_Get Exists

How to verify if $_GET exists?

You can use isset function:

if(isset($_GET['id'])) {
    // id index exists
}

You can create a handy function to return default value if index doesn't exist:

function Get($index, $defaultValue) {
    return isset($_GET[$index]) ? $_GET[$index] : $defaultValue;
}

// prints "invalid id" if $_GET['id'] is not set
echo Get('id', 'invalid id');

You can also try to validate it at the same time:

function GetInt($index, $defaultValue) {
    return isset($_GET[$index]) && ctype_digit($_GET[$index])
            ? (int)$_GET[$index] 
            : $defaultValue;
}

// prints 0 if $_GET['id'] is not set or is not numeric
echo GetInt('id', 0);

check whether ANY variable of type $_GET exists

Since $_GET is an associative array, you could check if it's empty or not, with the empty function.

empty($_GET);

You can test it here

P.S. the empty function works on multiple data types, not just associative arrays.

How to check if $_GET is empty?

You said it yourself, check that it's empty:

if (empty($_GET)) {
    // no data passed by get
}

See, PHP is so straightforward. You may simply write, what you think ;)

This method is quite secure. !$_GET could give you an undefined variable E_NOTICE if $_GET was unset (not probable, but possible).

How do I check if a $_GET parameter exists but has no value?

Empty is correct. You want to use both is set and empty together

if(isset($_GET['app']) && !empty($_GET['app'])){
    echo "App = ".$_GET['app'];
} else {
    echo "App is empty";
}

PHP check if url parameter exists

Use isset()

$matchFound = (isset($_GET["id"]) && trim($_GET["id"]) == 'link1');
$slide = $matchFound ? trim($_GET["id"]) : '';

EDIT:
This is added for the completeness sake. $_GET in php is a reserved variable that is an associative array. Hence, you could also make use of 'array_key_exists(mixed $key, array $array)'. It will return a boolean that the key is found or not. So, the following also will be okay.

$matchFound = (array_key_exists("id", $_GET)) && trim($_GET["id"]) == 'link1');
$slide = $matchFound ? trim($_GET["id"]) : '';

How to check if $_GET is empty?

You said it yourself, check that it's empty:

if (empty($_GET)) {
    // no data passed by get
}

See, PHP is so straightforward. You may simply write, what you think ;)

This method is quite secure. !$_GET could give you an undefined variable E_NOTICE if $_GET was unset (not probable, but possible).

Check if $_POST exists

if( isset($_POST['fromPerson']) )
{
     $fromPerson = '+from%3A'.$_POST['fromPerson'];
     echo $fromPerson;
}

isset() vs check if exists for a variable in PHP

$_GET[''] is usually retrieved from the browser, so if you had something like the following:
www.hello.com/index.php?var=hello

You could use:

if(isset($_GET['var'])) {
echo $_GET['var']; // would print out hello
}

Using isset() will stop the undefined index error, so if you just had www.hello.com/index.php for example then you would not see the error even though the var is not set.

Posts are usually when one page posts information to another, the method is the same but using $_POST[''] instead of $_GET['']. Example you have a form posting information:

<form method="post" action="anotherpage.php">
    <label></label>
    <input type="text" name="text">
</form>

In anotherpage.php to get the information would be something like:

$text = isset($_POST['text']);
echo $text; // would echo what ever you input into the text field on the other page

In a nut shell, just putting $_GET['name'] if name is not set you will get an error.
Using isset($_GET['name']) will check is the var name has any value before continuing.

Not sure if this is what you were after, but from the question this is my best guess at an answer

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