PHP strpos to match querystring text pattern

Question

I need to execute a bit of script only if the $_GET['page'] parameter has the text "mytext-"

Querystring is: admin.php?page=mytext-option

This is returning 0:

$myPage = $_GET['page'];
$match = strpos($myPage, 'mytext-');
echo $match;

Answer 1

strpos returns the position of the string. Since it's 0, that means it was found at position 0, meaning, at the start of the string.

To make an easy way to understand if it's there, add the boolean === to an if statement like this:

<?php

$myPage = $_GET['page'];
$match = strpos($myPage, 'mytext-');

if ( $match === false ) {
    echo 'Not found';
} else {
    echo 'Found';
}

?>

This will let you know, if the string is present or not.

Or, if you just need to know, if it's there:

$myPage = $_GET['page'];
$match = strpos($myPage, 'mytext-');

if ( $match !== false ) {
    echo 'Found';
}

?>

Answer 2

Use substr() once you get the location of 'mytext-', like so:

$match = substr($myPage, strpos( $myPage, 'mytext-') + strlen( 'mytext-'));

Otherwise, strpos() will just return the numerical index of where 'mytext-' starts in the string.

You can also use str_replace() to accomplish this if your string only has 'mytext-' once:

$match = str_replace( 'mytext-', '', $myPage);

Answer 3

The function strpos() returns the position where the searched string starts which is 0. If the string is not found, the function will return false. See the strpos documentation which tells you as well:

WARNING This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE. Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.

A solution to your question would be to use substr(), preg_match() or check if strpos() !== false.

The easiest solution should be this:

if (preg_match('/^mytext-/i', $_GET['page'])) {
    // do something
}

You may also consider using more than just one GET parameter like

http://www.example.com/foo.php?page=mysite&option1=123&option2=456

You then use your parameters lik $_GET['page'], $_GET['option1'], $_GET['option2'], etc.

However, you should also be careful what you do with raw $_GETor $_POST data since users can directly input them and may inject harmful code to your website.

Answer 4

That is expected since the substring starts at index 0. Read the warning on php.net/strpos:

Warning

This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE. Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.

If you only need to check if $myPage contains 'mytext-', use stristr:

if(stristr($myPage, 'mytext-') !== false) {
   // contains..
}

Answer 5

What's wrong about preg_match?

$myPage = $_GET['page'];
if (preg_match("/\bmytext-\b/i", $myPage)) {
    //Do Something
}

Or do you need the "option" out of "mytext-option"?

If yes you can use this:

$myPage = $_GET['page'];
$querystrings = explode("-", $myPage);
if ($querystrings[0] == 'mytext')) {
    //Do Something
    echo $querystrings[1]; //outputs option
}

With this you can even use more "options" in your querystring like "mytext-option-whatever". That's the same as when you use
$_GET['page'], $_GET['option'], $_GET['whatever']
when you use
?page=mysite&option=x&whatever=y