Python redirect stdout to null I have tried all sorts of ways to redirect both stdout and stderr to /dev/null without any success. stdout inside the with-statement. The wrapper function is an inner function within the decorator, which does the actual work of redirecting and restoring stdout and stderr. Popen( [exe_name], stdin=subprocess. From the docs contain [s] the original values of stdin, stderr and stdout at the start of the program. 4, and redirect_stderr in 3. Null Device: A null device is a special file or device that discards any data written to it. This can be done by specifying the file object as the value for the stdout parameter of the subprocess. stdout / sys. Possible Duplicate: redirect output of a running program to /dev/null Is it possible to change stdout after starting something as a background application in the command line? Say I run test. your I want to run a command in pythong, using the subprocess module, and store the output in a variable. micro neat picks: you could use os. Refer to the official sys package documentation for full information. sh 0 </dev/null 1> /dev/null 2> /dev/null & When we write to the null device, nothing happens. let’s take a look at a simple example: Mar 4, 2016 · 2>&1 will redirect stderr to wherever stdout currently points to. I'm new to python but well versed on other languages such as C and Perl I'm have problems redirecting stdout and stderr to /dev/null in a program that does a fork and exec. This option is equivalent to the options stdout=PIPE, stderr=PIPE in older versions of Python. stdout = saved_stdout # restore stdout This way you'll temporarily suppress the text normally written to sys. stdout. All of these examples can be modified slightly to support redirecting stderr or both stdout and stderr. This is just a small note to remember how to do the same in Windows. 5; if you're still on 2. Snippet of the program def May 11, 2009 · pass print "1 - this will print to STDOUT" original_stdout = sys. By providing the stdout parameter as the file object, the output is written to the file instead of being displayed on the console. devnull if subprocess. May 24, 2025 · What it does: Redirects both stdout and stderr to /dev/null, silencing all output. In Python, we can achieve similar functionality, which is what we'll explore in this blog. In the intended case, & is in reference to file handles, while in this backwards case, it's indicating that the job should be backgrounded. devnull function covering null device usage, output suppression, and practical examples. redirect_stdout () method takes a target and temporarily redirects sys. std* object has been redirected. print "Redirecting stdout" 3. flush() # <--- important Python 将stdout重定向到“无” 在本文中，我们将介绍如何在Python中将标准输出 (stdout)重定向到”nothing”，即不将输出显示在屏幕上。 阅读更多： Python 教程 为什么需要重定向stdout？ 在Python中，stdout是一个重要的流对象，它负责向屏幕输出程序的结果。然而，在某些情况下，我们可能希望将输出结果 Mar 6, 2025 · In Python, working with file operations often requires handling scenarios where we don't want the output to be printed or stored in a regular file. What you can do, is read the output from the child process in your python script and then write it back to whatever file you want to. check_output, but how can I redirect the stdout to /dev/null (or ignore it in any other way), >& /dev/null isn't what you're going for, it's &> /dev/null, which is basically a bash idiom for >/dev/null 2>/dev/null. Oct 2, 2024 · The second one will redirect the stdout of the entire sh script to /dev/null. We only need to combine these two built-in context managers in a custom context manager of ours, which can be easily done using the nice pattern in Martijn's answer here. Nov 21, 2011 · You use: yourcommand > /dev/null 2>&1 If it should run in the Background add an & yourcommand > /dev/null 2>&1 & >/dev/null 2>&1 means redirect stdout to /dev/null AND stderr to the place where stdout points at that time If you want stderr to occur on console and only stdout going to /dev/null you can use: yourcommand 2>&1 > /dev/null In this case stderr is redirected to stdout (e. Nov 6, 2024 · Introduction In large Python projects, excessive output to standard output (stdout) can significantly slow down your program’s execution. You'll have to be careful about any exceptions thrown in create_kms_key, as they could skip over the restoration line of code, preventing sys. Example: 1 day ago · If capture_output is true, stdout and stderr will be captured. ps -aux shows that server. That's where your (undesired) subprocess comes in. The output of the print() and help() functions is set to sys. Everything is on stderr. You can attach any file stream object to each run of ffmpeg to capture every line of the log. Aug 8, 2024 · By default, stdout is associated with the console or terminal window. Mar 7, 2018 · I am working on a French chatbot using python. It can be used to suppress any output. Let's look at how to use these objects. T found this method googling around and it is quite elegant compared to to the Perl version. StringIO() object. set_log_stream(f) Is there an e Python sends print output to stdout Redirecting the scripts stdout only captures the print message, leaving the log messages in the terminal. >& will try to write stdout to nothing (not sure the exact logic path), and then it forks the process. I have tried addind stdout=None to the Popen function: subprocess. /simple. However, when working with multiple processes, handling the standard output (`stdout`) can become challenging. stdout to nothing. Understanding To redirect output of a subprocess, use stdout parameter as shown in Ryan Thompson's answer. Jun 8, 2010 · I've tried redirecting both stdout and stderr to /dev/null and running the program in the background by suffixing an ampersand, but simply can't get it to play ball. And I doubt any of this was changed in later versions. At the beginning of my python program I have the following line: sys. g. I call it with subprocess : from subprocess import run, DEVNULL def speak (text): STDERR redirects to THE ADDRESS of STDOUT (File descriptor 1 in that moment, or /proc/self/fd/1), and then STDOUT redirects to /dev/null , but STDERR keeps redirecting to fd1!! Jun 22, 2016 · redirect stdout to a wxpython text control redirecting stdout the easiest way to redirect stdout in python is to just assign it an open file object. stdout for standard output, with examples on writing and redirecting output for efficient Python scripting. Feb 23, 2015 · A common task in Python (especially while testing or debugging) is to redirect sys. How could it? If the compiler can't finish compiling the code, it won't run the code, so your redirection hasn't even taken effect yet. redirect_stdout. Feb 15, 2020 · Basic usage In Python, the sys. I work in Windows and often use Command Prompt (cmd. I do not want console output. dup and os. Here's how you can use it: import os # Open /dev/null or equivalent on Unix-like systems null_device = open (os. Oct 26, 2019 · In Python 3. I'm using ctypes with python3 to invoke the functions. txt # This overwrites output. , in background jobs or cron scripts. Sep 3, 2022 · That's incorrect. The output from the first set of cells Jan 6, 2013 · How do I insert the output of the exec process to /dev/null and keep the print output of my python process as usual? As in, don't redirect everything to stdout? Jun 21, 2012 · 从 python 3. 5 we can do this with minimal work using built-ins in contextlib, namely redirect_stdout and redirect_stderr. Example (For visualizing difference): $ ls file1 file2 $ ls file1 > /dev/null Jul 10, 2021 · I would like to redirect the STDOUT and STDERR of the whole pipe to /dev/null. Mar 18, 2024 · 5. 5 开始，我们可以使用内置的. e. Is there a way to re-redirect the ou server = subprocess. 我们只需要将这两个内置的上下文管理器组合在我们的自定义上下文管理器中，这可以使用 Martijn 的答案中的 nice 模式 轻松完成。 Sep 12, 2012 · I've run a command and redirected it's output via > /dev/null Now that it's been running significantly longer than I expected I want to see what it's doing. In order to call the flush() method directly in . stdout and sys. But if you also want to discard (make silent) the stderr, then after redirecting stdout to /dev/null, specify 2>&1 to redirect stderr to the same place. In this case, they are equivalent, but if your sh script contained other lines they wouldn't be silenced (just script-python. silence_stdout redirects both sys. Jul 14, 2016 · On a unix system, you can redirect stderr and stdout to /dev/null as part of the command itself. os. Considering this is my command: sudo lsof -i:22000 -t | xargs kill -9 I know this is the wrong way of doing it: sudo Apr 11, 2025 · Complete guide to Python's os. And at the moment, I can't think of any way to write a new context manager that would change all direct references to sys. run() function is used to execute the ls -l command and redirect its output to the specified file. This works fine if I manually launch server. PIPE, None) for l in proc. However, simply "redirecting stdout" is If you wanted to use the output of those print statements somehow in Python, you could redirect the default target of print (stdout), to some other place, like an io. I have almost my entire life run bash which I've never had this issue with, but for once in BSD I'm stuck with /bin/sh. To explain the specific behavior Aug 29, 2025 · noisy_code() here is a testbench that replicates various ways to write to stdout. That said, you could write a context manager that . I know I can use subprocess. Here’s an example: Jul 22, 2025 · Explore effective methods for redirecting Python's standard output (stdout) to files, capturing process output, and managing streams for robust scripting. In Python, you can achieve this by temporarily replacing sys. I found the output of the print statement in a python script is not showing on the screen until a "sys. However, I do not want the command's output to be printed to the terminal. DEVNULL is not available (<3. PIPE, subprocess. run () function in Python, you can redirect the output to the special file /dev/null on Unix-like systems or NUL on Windows. subprocess. This can significantly speed up tasks that can be divided into independent parts. p Jul 4, 2017 · I'm trying to redirect the output of printf functions to a file on Windows. This guide explains how to effectively suppress stdout in Python, using the recommended contextlib. Use a launcher process to capture your python program’s stdout by redirecting before your python interpreter starts, if you want to safely funnel its stdout somewhere. When used, the internal Popen object is automatically created with stdout and stderr both set to PIPE. 7 or the like, your only option is reassigning sys. Apr 3, 2019 · kms_key_id = create_kms_key(user_name, kms_client) sys. The constant STDOUT should do that, shouldn't it? However, $ python >/dev/null -c 'import subprocess;\ Dec 3, 2014 · The problem is that this message is produced by something other than stdout, probably stderr and I can easily redirect it to /dev/null using ping -c 1 192. stdout = open ('stdout_file', 'w') Halfway through my program I would like to set stdout back to the normal stdout. For the output redirection, instead of storing the file descriptor (s), you can just conditionally redirect the stream (s) before the body of your script or (possibly more cleanly), just close the stream (s) using exec n>&- where n is the numeric file descriptor of the stream (1 = stdout, 2 = stderr). Instead I was going to redirect output through a fifo. Popen() for this work but it seems to catch some error when redirecting stdout stream. exe Start command: Sep 26, 2013 · &> file redirects stdout and stderr to file > file 2>&1 redirects stdout and stderr to file /dev/null is the null device it takes any input you want and throws it away. stdout by default so printing any messages in the with block has no effect. In this guide, we’ll demystify how to implement robust logging in Python daemons, ensuring you never fly blind when debugging. Is it possible to temporarily redirect stdout/stderr in Python (i. Apr 9, 2024 · The contextlib. For a first text-to-speech attempt, I am using espeak with mbrola. `/dev/null` is a special device file that discards all data written to it. Aug 27, 2023 · Using contextlib. Thanks for the "-s" flag. File handle 0 is stdin. There’s no output printed to the terminal, and no other files are Aug 30, 2024 · Your report is well titled. My code is: import os, sys from ctypes import * if __name__ == ' May 7, 2019 · Using Python 3. For this code: def s the script being developed will basically be like a shell script, running many command with some logic between many of them. Suppressing nohup. It temporarily redirects stdout and stderr to /dev/null (a special file that discards everything written to it on Linux/Unix systems). Example 1: Suppressing Output If you want to suppress the output of the subprocess. Use Case: Running commands silently, e. stdout to a stream or a file while executing some piece of code. py I want to redirect the stderr output of a subprocess to stdout. NET application using pythonnet. redirect_stdout, you can safely and temporarily suppress output without altering source code. How to redirect output with reduce and show it but not show “None”? Thanks in advance. 10. The stdout and stderr arguments may not be supplied at the same time as capture_output. Jun 21, 2012 · As of python 3. In the context of redirecting stdout to “nothing” in Python, we can redirect stdout to a null device to effectively suppress any output. For example, the output of help() normally is sent to sys. run() doesn't capture stdout or stderr by default, to do so requires passing PIPE s for the stdout and/or stderr arguments (it's right in the linked documentation). __stdout__ to null. 2 LTS I am trying to invoke a shell script through python script, and expect the stdout to be null i. The suppress_output decorator function is defined. sys. at the start of the script i want to redirect STDOUT and/or STDERR to output to a specified file, to record all the output f I want to redirect all output (stdout and stderr) of console to the text file. stdout with a file-like object that discards all data written to it. 2. This tool adds flexibility to existing functions or classes whose output is hardwired to stdout. Feb 9, 2017 · Python is embedded in my . You can redirect stdout just using command > /dev/null If you need to redirect stderr as well. PIPE) as the program may not flush. redirect_stdout(new_target) ¶ Context manager for temporarily redirecting sys. e discard/silent the output by command. stdin, sys. system(cmd + "> /dev/null 2>&1") Dec 25, 2023 · Speaking of which, Python 3 also has a function for redirecting stderr. py was launched correctly. You can write Python code that redirects the stdout, then invokes the Python interpreter to compile some other piece of code. out which I need to run against 10 files and redirect their output to 10 files. py but obviously not if I Popen() cause redirect doesnt work. stdout from being properly restored. I don't known how to redirect sys. 0. Nov 13, 2025 · The solution? **Structured logging** and **capturing stdout/stderr** to persistent storage. Even writing output to file is faster than directly writing to the terminal. 168. txt with the command output This operator stores the command output in txt file Appending Output to an Existing File If you need to append new output to an Jan 6, 2024 · Example 1: Redirecting Output to a File One common use case for redirecting output with subprocess in Python is redirecting the output of a command to a file. Popen(['java', Jul 23, 2025 · Redirecting Standard Output (stdout) to a File To redirect standard output (stdout) to a file, the > operator is used. dup2 calls (dup2 stays as dup2) and flush stdout before doing any group of os. redirect_stdout Another useful feature of the contextlib module is the ability to redirect stdout to a different stream using contextlib. stdout = NullDevice() # redirect the real STDOUT print "2 - this won't print" sys. contextlib 即 redirect_stdout 和 redirect_stderr. This allows you to discard or redirect output and is compatible with both Unix-like systems (e. PIPE to the stdout value: subprocess. 7+, the output (stdout and stderr) of commands can be captured by specifying the option capture_output=True. I am using subprocess. Aug 20, 2024 · In the above example, the subprocess. calls. out If we want to suppress all visible output from a process launched with nohup, we can also redirect stdout and stderr to the null device: $ nohup . 04. Nov 19, 2015 · 7 Because subprocess doesn't allow use > to redirect neither output nor error message, from the document: stdin, stdout and stderr specify the executed program’s standard input, standard output and standard error file handles, respectively. stdout to the specified target. 7 on Ubuntu 18. stdout, and sys. stdout # keep a reference to STDOUT sys. run() function. Though you don't need a subprocess (cat) in your case, you could concatenate files using pure Python. flush()" called. devnull, 'w') # Redirect stdout to /dev/null or Nov 23, 2021 · And there is no buffering level more immediate than buffering=1 to avoid that. 6. Jan 10, 2012 · From a python module I am calling a Hello World executable that simply prints Hello World to the stdout. How do I do Dec 5, 2024 · Learn various techniques for redirecting stdout to a file in Python to streamline output management. Mar 21, 2025 · In Python, the `multiprocessing` module allows you to spawn multiple processes, enabling parallel execution of code. Sep 21, 2018 · I've been trying out how not to print shell outputs from Python's subprocess. __stdout__. exe) as the command shell. This is particularly useful in scenarios where you want to suppress output, log it elsewhere, or modify it for testing purposes. We used a None object as the target to redirect the output of sys. system() should be discouraged, &> doesn't work for sh on Ubuntu an explicit >/dev/null 2>&1 could be used. Apr 19, 2024 · Techniques for Silencing stdout 1. I make the following steps: Open cmd. write(l) Obivously, you'll Nov 23, 2024 · Overall, redirecting subprocess stderr to stdout in Python 3 can help simplify the handling of error messages and make it easier to analyze and process the output of subprocesses in your Python scripts. Nov 1, 2024 · Learn to use Python's sys. stderr are file-like objects that can perform expected operations like read() and write(). dup2 function covering file descriptor duplication, I/O redirection, and practical examples. Apr 11, 2025 · Complete guide to Python's os. The critical part of this answer is this code segment: 1. host >& /dev/null However, when I use that in python, I get the following error: sh: 1: Syntax error: Bad fd number Is it possible to solve this? Jan 13, 2011 · How do I redirect stdout to an arbitrary file in Python? When a long-running Python script (e. I am interested in redirecting that output to a python StringIO and ran into this answer which almost brings me all the way to the solution. To stop this, you need to temporarily redirect stdout somewhere else, so the messages don't appear on your screen. Start a process and redirect its stdout and stderr to /dev/null. PIPE, stdout=subprocess. Feb 11, 2009 · Explains how to redirect output (stdout) and errors (stderr) to /dev/null under UNIX / Linux / BSD shell scripting or cron jobs. I believe the cause is the program spawns other processes, and the output redirection of the parent process doesn't affect them. For instance, if your project has numerous print statements scattered across various modules, the cumulative effect could lead to performance bottlenecks. May 29, 2010 · I'm using the following code to hide stderr on Linux/OSX for a Python library I do not control that writes to stderr by default: f = open("/dev/null","w") zookeeper. It is part of the sys module and requires import sys before use. Feb 23, 2021 · 0 I have a program script. Jun 20, 2022 · I assume that the “None” is caused by print function. The challenge lies in finding a way to conditionally mute these print statements at runtime without Oct 30, 2025 · Conclusion Redirecting stdout to os. smontanaro (Skip Montanaro) June 20, 2022, 10:40am 2 Feb 11, 2021 · How to output a single print statement out of many and redirect the rest to null in python Asked 3 years, 11 months ago Modified 3 years, 11 months ago Viewed 244 times Jul 15, 2025 · sys. , Linux and macOS) and Windows. In Python, you can achieve a cross-platform equivalent of /dev/null by using the os. g, web application) is started from within the ssh session and backgounded, and the ssh session is clo Nov 23, 2024 · Is it Possible to Redirect stdout and stderr in Python Temporarily? When working with Python, there are times when you might need to temporarily redirect the output generated by stdout and stderr. NET. At least not in python 3. command > output. It returns the number of characters written instead of None. The argument >/dev/null will redirect stdout to /dev/null i. use command > /dev/null 2>&1 Dec 20, 2020 · You probable meant to redirect stdout to /dev/null, so it should be > /dev/null, but as davidxxx mentioned, it should be the other way around (not especially intuitive, imo). That was the intended behavior, so this isn't a bug and is more just a fact of life. stderr manually, or using os. out instead of /dev/null, even though I'm explicitly redirecting stdout and stderr to /dev/null in the command I'm running. stdout to another file or file-like object. Mar 20, 2024 · Understanding these techniques allows you to have more control over the behavior of subprocesses in your Python programs. It’s easy to use, but robust usage with proper error checking requires few more Jan 24, 2022 · A lot of Linux code redirects output to /dev/null as a way of not sending any output to the console. Feb 21, 2020 · Wow, that shows a huge difference for printing to stdout and redirecting stdout to /dev/null. write () is a built-in Python method that writes output directly to the console without automatically adding a newline (\n). I always forgot how to redirect stderr to /dev/null, grep -s is much easier to remember! Jul 14, 2018 · You can revert to the original stream by reassigning to sys. call (command, stdout=open (os. unknown. This command will execute and overwrite the specified file with the output. dup2 to replace the underlying file descriptors, but I'd recommend using modern Python first. devnull constant. stdout in . This approach silences much of the output from my noisy module import. Popen(path, 0, None, subprocess. - start_process. Unlike print (), it does not insert spaces between multiple arguments, allowing precise control over text formatting. def redirect_stdout(): 2. Thus, to redirect both the stderr and stdout output of any command to \dev\null (which deletes the output), we simply type $ command &> /dev/null or in case of my example: Dec 28, 2010 · Like unwind said, you cannot change the file descriptor that the child process is writing its output to. Jul 18, 2011 · This question is a combination of How to capture stdout output from a Python function call? - Stack Overflow and Cross platform /dev/null in Python - Stack Overflow, but there exists a more efficient solution in this special case, see below. So to isolate things I made a much shorter test program and it still is not This almost does what I want, except that it still redirects output to nohup. E. stderr to turn off STDERR. They are used during finalization, and could be useful to print to the actual standard stream no matter if the sys. readlines(): output_file. devnull is a powerful way to suppress unwanted prints in Python, especially in large projects with third-party or legacy code. stdout = original_stdout # turn STDOUT back on print "3 - this will print to SDTDOUT" You can also do the same thing with sys. devnull, 'w') and subprocess. NET, I tried Python’s subprocess module provides several methods of running external programs. Related Evidence The effectiveness of implementing cross-platform /dev/null functionality in Python 3 has been widely recognized 2 days ago · contextlib. : proc = subprocess. Note that > file 2>&1 is an older syntax which still works, &> file is neater, but would not have worked on older systems. call () by assigning open (os. In fact, the redirection does only apply to new references to sys. 3), use check_call() instead of call() if you don't check its returned code, open files in binary mode for stdin/stdout/stderr, usage of os. Jul 11, 2019 · Note: redirect_stdout was introduced in 3. redirect_stdout context manager and, for completeness, discusses alternative (but less preferred) approaches. Redirecting stdout to a null device: One approach to silencing stdout is to redirect it to a null device. Stdout redirection in the context of multiprocessing helps in better management of the So I was trying to redirect stdout for a some of the cells in my Jupyter Notebook to a file with this and then cancel it with this for the rest of the cells. for the duration of a method)? Edit: The problem with the current solutions (which I at first remembered but then forgot) is tha Oct 6, 2022 · Learn how to redirect output or error or both to /dev/null in Linux so that it doesn't show up on the screen. call in Python 3 can be achieved by redirecting the standard output and error streams to a null device or by using the appropriate parameters in the subprocess functions. The redirect_stdout context manager may be used instead of manually Sep 12, 2016 · I want to run an external process in python, and process its stderr only. The concept similar to `/dev/null` in Unix-like systems is crucial. Feb 7, 2013 · I am calling a java program from my Python script, and it is outputting a lot of useless information I don't want. (that is, assuming ffmpeg-python is not redirecting stderr to stdout) Nov 3, 2024 · In conclusion, the quiet version of subprocess. Nov 17, 2017 · If you want to do this for stdout, use 1 instead of 2 in the os. py). By using context managers like contextlib. Sep 11, 2025 · The core problem is that the module is writing directly to the standard output stream, or stdout. dnkrq zjydzk cgl usfogo qjvyw kabyif ukxq qyvs ikw lyym cai azvvlcr nwz mmik eeai