Redirect terminal output to tkinter

You can create class with function write() which insert text to tkinter.Text and assign its instance to sys.stdout - and then print() will send to tkinter.Text

class Redirect():
    
    def __init__(self, widget):
        self.widget = widget

    def write(self, text):
        self.widget.insert('end', text)
        #self.widget.see('end') # autoscroll

    # some widget may need it
    #def flush(self):
    #    pass

and

text = tk.Text(root)
text.pack()

# keep original stdout
old_stdout = sys.stdout    

# assing Redirect with widget Text 
sys.stdout = Redirect(text)

root.mainloop()

# assign back original stdout (if you need it)
sys.stdout = old_stdout

But os.system you will have to replace with ie. subprocess.run() to catch output and print() it.

def test():
    print("Hello World")
    p = subprocess.run("ping -c 4 stackoverflow.com", shell=True, stdout=subprocess.PIPE)
    print(p.stdout.decode())

Minimal working code

import tkinter as tk
import os
import sys
import subprocess

# --- functions ---

def test():
    print("Hello World")
    p = subprocess.run("ping -c 4 stackoverflow.com", shell=True, stdout=subprocess.PIPE)
    print(p.stdout.decode())
    
# --- classes ---

class Redirect():
    
    def __init__(self, widget):
        self.widget = widget

    def write(self, text):
        self.widget.insert('end', text)
        #self.widget.see('end') # autoscroll

    #def flush(self):
    #    pass
    
# --- main ---    
   
root = tk.Tk()

text = tk.Text(root)
text.pack()

button = tk.Button(root, text='TEST', command=test)
button.pack()

old_stdout = sys.stdout    
sys.stdout = Redirect(text)

root.mainloop()

sys.stdout = old_stdout

Two problems:

It sends text from subprocess to widget Text after getting all text from ping. It may need more work to display line by line.

test() needs some time to finish work and it blocks tkinter so it can't update widgets and it freezes. It may need to run test() in separated thread but I don't know if this will not gives other problems because in many GUI frameworks you can't use widgets in separated threat.

EDIT:

Version with threading. It resolvs previous problems.

But it may have new problems :)

• you can click button two times and it will run two pings at the same time and mix strings from both pings

• code doesn't have method to stop thread (ie. when you run ping without -c 4)

Code:

import tkinter as tk
import sys
import subprocess
import threading 

# --- functions ---

def run():
    threading.Thread(target=test).start()

def test():
    print("Hello World")

    p = subprocess.Popen("ping -c 4 stackoverflow.com".split(), stdout=subprocess.PIPE, bufsize=1, text=True)
    while p.poll() is None:
        msg = p.stdout.readline().strip() # read a line from the process output
        if msg:
            print(msg)

    print("Finished")
             
# --- classes ---

class Redirect():

    def __init__(self, widget):
        self.widget = widget

    def write(self, text):
        self.widget.insert('end', text)
        #self.widget.see('end') # autoscroll

    #def flush(self):
    #    pass

# --- main ---    

root = tk.Tk()

text = tk.Text(root)
text.pack()

button = tk.Button(root, text='TEST', command=run)
button.pack()

old_stdout = sys.stdout    
sys.stdout = Redirect(text)

root.mainloop()

sys.stdout = old_stdout

EDIT: 2021.08.19

Version with Scrollbar and autoscroll

import tkinter as tk
import sys
import subprocess
import threading 

# --- classes ---

class Redirect():

    def __init__(self, widget, autoscroll=True):
        self.widget = widget
        self.autoscroll = autoscroll

    def write(self, text):
        self.widget.insert('end', text)
        if self.autoscroll:
            self.widget.see("end")  # autoscroll
        
    #def flush(self):
    #    pass

# --- functions ---

def run():
    threading.Thread(target=test).start()

def test():
    print("Thread: start")

    p = subprocess.Popen("ping -c 4 stackoverflow.com".split(), stdout=subprocess.PIPE, bufsize=1, text=True)
    while p.poll() is None:
        msg = p.stdout.readline().strip() # read a line from the process output
        if msg:
            print(msg)

    print("Thread: end")

# --- main ---    

root = tk.Tk()

# - Frame with Text and Scrollbar -

frame = tk.Frame(root)
frame.pack(expand=True, fill='both')

text = tk.Text(frame)
text.pack(side='left', fill='both', expand=True)

scrollbar = tk.Scrollbar(frame)
scrollbar.pack(side='right', fill='y')

text['yscrollcommand'] = scrollbar.set
scrollbar['command'] = text.yview

old_stdout = sys.stdout    
sys.stdout = Redirect(text)

# - rest -

button = tk.Button(root, text='TEST', command=run)
button.pack()

root.mainloop()

# - after close window -

sys.stdout = old_stdout