How to use path- and filename from GUI in matlab script?

I have created a GUI that will ask the user to browse for a file, display it and then open the file when prompted. I wish to use the same pathname and filename in the script used to analyze the file which is run by pressing a button in the GUI. So far I have to find the file and pathname twice, both in the GUI to be displayed and again in the script to further analyze the file. Is there a way where I can call for the file- and pathname already found in the GUI in the script, possibly by using global variables? I have posted my code below with the GUI first followed by some of the script. Thanks in advance.

function varargout = GUI(varargin)
% GUI MATLAB code for GUI.fig
%      GUI, by itself, creates a new GUI or raises the existing
%      singleton*.
%
%      H = GUI returns the handle to a new GUI or the handle to
%      the existing singleton*.
%
%      GUI('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in GUI.M with the given input arguments.
%
%      GUI('Property','Value',...) creates a new GUI or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before GUI_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to GUI_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES
% Edit the above text to modify the response to help GUI
% Last Modified by GUIDE v2.5 20-May-2016 11:37:49
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                 'gui_Singleton',  gui_Singleton, ...
                 'gui_OpeningFcn', @GUI_OpeningFcn, ...
                 'gui_OutputFcn',  @GUI_OutputFcn, ...
                 'gui_LayoutFcn',  [] , ...
                 'gui_Callback',   []);
if nargin && ischar(varargin{1})
  gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
  [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
  gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
% --- Executes just before GUI is made visible.
function GUI_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to GUI (see VARARGIN)
% Choose default command line output for GUI
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes GUI wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = GUI_OutputFcn(hObject, eventdata, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
handles=guidata(hObject);
[filename, pathname] = uigetfile('*.DAT');
assignin('base','filename', filename);
[fullpathname] = strcat(pathname, filename);
text = fileread(filename);
set(handles.text3, 'String', filename);
guidata(hObject, handles);
% --- Executes on button press in Start_button.
function Start_button_Callback(hObject, eventdata, handles)
% hObject    handle to Start_button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
handles=guidata(hObject);
run FixedLineString.m;
guidata(hObject, handles);
% --- Executes on button press in Exit_button.
function Exit_button_Callback(hObject, eventdata, handles)
% hObject    handle to Exit_button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
close(handles.figure1);

SCRIPT

[filename,pathname] = uigetfile('*.DAT','Select the .DAT file');
fid = fopen(fullfile(pathname, filename),'r');
RawData = textscan(fid, '%s', 'delimiter', '/n');
fclose(fid);
%Read .DAT file
GPSdata = strfind(RawData{1}, '$PSTMDRGPS');
GPSrows = find(~cellfun('isempty',GPSdata));
GPSdata = RawData{1}(GPSrows);
GPSlength = length(GPSdata);
%Get GPSdata

Answer 1

[Geoff Hayes]

Thore - rather than using global variables, try changing your script into a function which accepts the path to and name of some file. For example,

 function FixedLineString(filename, pathname)

 if isempty(filename) || isempty(pathname) 
     [filename,pathname] = uigetfile('*.DAT','Select the .DAT file');
 end

 % etc.

The above code allows for the filename and pathname to be optional so that if at least one is not provided, then the user is prompted to choose a file.

Now in your GUI, you would save the path to and the name of the file to your handles structure as

 function pushbutton1_Callback(hObject, eventdata, handles)
 [filename, pathname] = uigetfile('*.DAT');
 set(handles.text3, 'String', filename);
 handles.filename = filename;
 handles.pathname = pathname;
 guidata(hObject,handles);

Then, when you want to pass the path and name of the file to your (new) function, you would do

 function Start_button_Callback(hObject, eventdata, handles)
 pathname = [];
 filename = [];
 if isfield(handles,'pathname') && isfield(handles,'filename')
    pathname = handles.pathname;
    filename = handles.filename;
 end
 FixedLineString(pathname,filename);

In the above, we check to make sure that handles has fields for both pathname and filename before trying to access either. If both exist, then we pass both to your function. Else we pass empty input parameters which will cause your function to request the the user choose a file.

Try the above and see what happens!

As an aside, I noticed that in your callbacks you typically did

 handles = guidata(hObject);

This is unnecessary as the third input to all callbacks is already the handles structure and so calling the above just duplicates what already has been done. Also, you only need to call

 uidata(hObject, handles);

if you have updated the handles structure as we did in pushbutton1_Callback. Otherwise, there is no need to call it.

[Thore]

Thank you for the in depth answer! Also, thanks for elaborating what the syntax for callbacks is.