Is it possible for a user to enter a value into a form and then, on submit, have the page redirect to a new one with the value entered into the form stored in a PHP variable?
This if my form code;
<form id="loc-search" method="post">
<input type="text" id="search-by-location" name="custom-location" value="" placeholder="Sheffield, UK"/>
<input type="submit" id="submit" value=""/>
</form>
Once the user has entered a value in #search-by-location the page needs to redirect to weather.php with the value stored in a PHP variable called $location
AJAX / JS aren't my strong suits so if someone could point me in the right direction that would be great
Add the argument action="weather.php" to your form tag. Then, when clicked on the submit button, you will get redirected to that page. Depending on your method, in your case POST, the input values will be available in the superglobal $_POST array in PHP.
In your example, $location = $_POST["custom-location"]; will suffice. Note that the name, not the ID, determines the array key in the target PHP document.
Javascript or AJAX are not needed to achieve this.
This is just a normal form so why not just use $_POST after the redirect on the weather.php page:
$location = $_POST["custom-location"];
As @Tacticus pointed out you also need to have the form redirect (if you did not already do this in JS). By adding action="weather.php" in the form:
<form id="loc-search" method="post" action="weather.php" >
...
</form>
As stated in other answers you should modify your form to look like this:
<form id="loc-search" method="post" action="weather.php">
<input type="text" id="search-by-location" name="custom-location" value="" placeholder="Sheffield, UK"/>
<input type="submit" id="submit" value=""/>
</form>
In your weather.php file, you can get the value from the $_POST global variable, just like this:
<?php
$location = $_POST["custom-location"];
//Interpret data
?>
Note that you can access the value of an input tag from your form witch was passed, with the input's name. In html you specify the following:
<input name="yourname" />
And when you want to access that value, you simply refer to his name.
$_POST['yourname']
If you use GET method for the form to pass the values, then you do the same, only the value will be stored in the $_GET global variable, so in your case with a GET method the variable initialization would look like this:
<?php
$location = $_GET["custom-location"];
//Interpret data
?>