Add your real code here.įor line in lines : print ( line ) if not readable : # This OutStream is finished.įds. read_lines () # Example: Just print every line. select ( fds, , ) break except InterruptedError : continue # Handle all file descriptors that are ready.įor f in rlist : lines, readable = f. Answer by Molly Wang Using subprocess.Popen, subprocess.call, or subprocess.checkoutput will all invoke a process using Python, but if you want live output coming from stdout you need use subprocess.Popen in tandem with the Popen.poll method.,If you start a process using process.call() or process.checkoutput(), then you cannot get the output until the process is compete. While True : try : rlist, _, _ = select.
close ( err_w ) fds = while fds : # Call select(), anticipating interruption by signals. close ( out_w ) # if we do not write to process, close these. Popen (, stdout = out_w, stderr = err_w ) os. That it has a method fileno() that returns the file descriptor as an It can also do the sameįor descriptors that should be written to, details can be found inĪll that is required from an object passed to Python’s select() is List of those that are ready to be read from.
You pass a list of file descriptors and it returns a Treat stdout and stderr differently? Here, the select() system callĬomes into play. More than one process? Or, to make the example simple, you want to This is all very nice, but what if you want to capture the output of You could improve the read_lines() method to add theĬorrect newline characters where needed if that is important. When readable is false, though, the last line did not have a The final newlines are stripped, so re-add them if if not readable : breakĮvery time read_lines() returns, we may get zero, one, or many lines So the main loop looks like this now:į = OutStream ( out_r ) while True : lines, readable = f. The second return value indicates if we should keep reading (true), or Note that we call decode() on all finished lines in order to get Somehow carriage returns (\r) appear in the output when using pseudo Lines = finished_lines = lines readable = False finished_lines = return finished_lines, readable _buffer = b"" if len ( lines ) = 1 and not lines : # We did not have buffer left, so no output at all. _buffer = lines finished_lines = lines readable = True else : self. _fileno, 1000 ) except OSError as e : if e. _buffer = b"" def read_lines ( self ): try : output = os. Let’s make a class for that, which will come in handyĬlass OutStream : def _init_ ( self, fileno ): self. For this, you need to buffer unfinished lines and thus You probably prefer having it in theįorm of lines. The output is still in the form of random bytes from somewhere in the Therefore, you want to break out of the loop when you get Capture the output of n() but also print it in real time python, subprocess / By Boris I would like to run a command using n() and then get its stdout/stderr as a string, but I want the subprocess to also print its output to the console normally while running. Simulating os.read()’s behaviour in case of reaching the end of theįile ( EOF). In this case, output is set to the empty string, Needed because an EIO error is raised when you can no longer read from def runcommand (command): process subprocess.Popen (shlex.split (command), stdoutsubprocess.PIPE) while True : output () if output '' and process.poll () is not None : break if output: print output.strip () rc process.poll () return rc. If the application did not do any custom buffering, you should getĮach line as soon as it is finished.
Note that os.read() returns bytes, but we cannot decode EIO : raise output = b"" if not output : break. read ( out_r, 1000 ) except OSError as e : if e. close ( out_w ) # if we do not write to process, close this. If output = '' and process.poll() is not None : #process = Popen(split(cmd), stdout = PIPE, stderr = PIPE, encoding='utf8') #This works but when use pipe '|' in commands it doesn't e.g. Process = Popen(cmd, stdout = PIPE, stderr = PIPE, shell = True, encoding='utf8') Adding, shell = True and removing the split function gets me the output here.īut, can someone tell me why using split doesn't work and if there is a way that we can achieve the same using 'shlex.split'? Thanks.
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