"I want to use the input of the textbox of my gui which i have created with guide, in a seperate Matlab script"
There are several ways to share data stored in a GUI with an external file. This method below involves saving the data from the callback function to the GUI figure and then extracting that data from the external function [background info].
function execute_Callback(hObject, eventdata, handles)
minVelocity = str2double(get(handles.minVelocity, 'string'));
maxVelocity = str2double(get(handles.maxVelocity, 'string'));
data.minVelocity = minVelocity;
data.amxVelocity = maxVelocity;
hObject.Parent.UserData = data;
Before you can extract this data form the external function, you must give your GUI a meaningful tag so it can be found by the external function. You can set the "Tag" property of the GUI figure from within GUIDE or from within your startup function. The code below assumes you've assigned the tag MyUniqueGuiTag but you should repace that with a more meaningful name.
From the external function....
guiHandle = findobj('Type','Figure','Tag','MyUniqueGuiTag');
data = guiHandle.UserData
This hasn't been tested (I don't have Matlab opened right now). If you have any questions or problems that you can't resolve please leave a comment below.