Set session variable in laravel

I think your question ultimately can be boiled down to this:

Where can I set a long-lived value that is accessible globally in my application?

The obvious answer is that it depends. What it depends on are a couple of factors:

• Will the value ever be different, or is it going to be the same for everybody?
• How long exactly is long-lived? (Forever? A Day? One browsing 'session'?)

Config

If the value is the same for everyone and will seldom change, the best place to probably put it is in a configuration file somewhere underneath app/config, e.g. app/config/companyname.php:

<?php
return [
    'somevalue' => 10,
];

You could access this value from anywhere in your application via Config::get('companyname.somevalue')

Session

If the value you are intending to store is going to be different for each user, the most logical place to put it is in Session. This is what you allude to in your question, but you are using incorrect syntax. The correct syntax to store a variable in Session is:

Session::put('somekey', 'somevalue');

The correct syntax to retrieve it back out later is:

Session::get('somekey');

As far as when to perform these operations, that's a little up to you. I would probably choose a route filter if on Laravel 4.x or Middleware if using Laravel 5. Below is an example of using a route filter that leverages another class to actually come up with the value:

// File: ValueMaker.php (saved in some folder that can be autoloaded)
class ValueMaker
{
    public function makeValue()
    {
        return 42;
    }
}

// File: app/filters.php is probably the best place
Route::filter('set_value', function() {
    $valueMaker = app()->make('ValueMaker');
    Session::put('somevalue', $valueMaker->makeValue());
});

// File: app/routes.php
Route::group(['before' => 'set_value'], function() {
   // Value has already been 'made' by this point. 
   return View::make('view')
       ->with('value', Session::get('somevalue'))
   ;
});

The correct syntax for this is:

Session::set('variableName', $value);

For Laravel 5.4 and later, the correct method to use is put:

Session::put('variableName', $value);

To get the variable, you would use:

Session::get('variableName');

If you need to set it once, I'd figure out when exactly you want it set and use Events to do it.

For example, if you want to set it when someone logs in, you'd use:

Event::listen('auth.login', function() {
    Session::set('variableName', $value);
});