public function edit($id)
    {
        $category = Categories::getall();
        $categories = Categories::find($id);
        return view('back.categories.edit', ['categories' => $categories, 'category' => $category]);
    }

Route::group(['middleware'=>'admin'],function(){

    Route::get('/dashboard','BackendController@index')->name('backend');
    Route::group(['prefix' => 'categories'], function () {
        Route::any('/show/{id}', ['as' => 'backend.categories.show', 'uses' => 'backendCategoriesController@show']);
        Route::get('/index', ['as' => 'back.categories.index', 'uses' => 'backendCategoriesController@index']);
        Route::any('/store', ['as' => 'back.categories.store', 'uses' => 'backendCategoriesController@store']);
        Route::any('/create', ['as' => 'back.categories.create', 'uses' => 'backendCategoriesController@create']);
        Route::any('/edit/{id}', ['as' => 'back.categories.edit', 'uses' => 'backendCategoriesController@edit']);
        Route::any('/update', ['as' => 'back.categories.update', 'uses' => 'backendCategoriesController@update']);
        Route::any('/destroy/{id}', ['as' => 'back.categories.destroy', 'uses' => 'backendCategoriesController@destroy']);
    });

});

<a href="{{ url('back/categories/edit/'.$category->cat_id) }}" class="btn btn-success btn-sm">
<span class="fa fa-edit"></span> edit</a>