I have a shell script that gets whois info for domains, and outputs taken or available to the shell depending on the domain.
I'd like to execute the script, and be able to read this value inside my Python script.
I've been playing around with subprocess.call but can't figure out how to get the output.
e.g.,
subprocess.call('myscript www.google.com', shell=True)
will output taken to the shell.
subprocess.call() does not give you the output, only the return code. For the output you should use subprocess.check_output() instead. These are friendly wrappers around the popen family of functions, which you could also use directly.
For more details, see: http://docs.python.org/library/subprocess.html
Manually using stdin and stdout with Popen was such a common pattern that it has been abstracted into a very useful method in the subprocess module: communicate
Example:
p = subprocess.Popen(['myscript', 'www.google.com'], stdin=subprocess.PIPE, stdout=subprocess.PIPE)
(stdoutdata, stderrdata) = p.communicate(input="myinputstring")
# all done!
import subprocess as sp
p = sp.Popen(["/usr/bin/svn", "update"], stdin=sp.PIPE, stdout=sp.PIPE, close_fds=True)
(stdout, stdin) = (p.stdout, p.stdin)
data = stdout.readline()
while data:
# Do stuff with data, linewise.
data = stdout.readline()
stdout.close()
stdin.close()
Is the idiom I use, obviously in this case I was updating an svn repository.
try subprocess.check_output.
Related
My python script (python 3.4.3) calls a bash script via subprocess.
OutPST = subprocess.check_output(cmd,shell=True)
It works, but the problem is, that I only get half of the data. The subprocess I call, calls a different subprocess and I have the guess, that if the "sub subprocess" sends the EOF, my programm thinks, that that´s it and ends the check_output.
Has someone an idea how to get all the data?
You should use subprocess.run() unless you really need that fine grained of control over talking to the processing via its stdin (or doing something else while the process is running instead of blocking for it to finish). It makes capturing output super easy:
from subprocess import run, PIPE
result = run(cmd, stdout=PIPE, stderr=PIPE)
print(result.stdout)
print(result.stderr)
If you want to merge stdout and stderr (like how you'd see it in your terminal if you didn't do any redirection), you can use the special destination STDOUT for stderr:
from subprocess import STDOUT
result = run(cmd, stdout=PIPE, stderr=STDOUT)
print(result.stdout)
We are having some problems with the dreaded "too many open files" on our Ubuntu Linux machine rrunning a python Twisted application. In many places in our program, we are using subprocess Popen, something like this:
Popen('ifconfig ' + iface, shell=True, stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
output = process.stdout.read()
while in other places we use subprocess communicate:
process = subprocess.Popen(['/usr/bin/env', 'python', self._get_script_path(script_name)],
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
close_fds=True)
out, err = process.communicate(data)
What exactly do I need to do in both cases in order to close any open file descriptors? Python documentation is not clear on this. From what I gather (which could be wrong) both communicate() and wait() will indeed clean up any open fds on their own. But what about Popen? Do I need to close stdin, stdout, and stderr explicitly after calling Popen if I don't call communicate or wait?
According to this source for the subprocess module (link) if you call communicate you should not need to close the stdout and stderr pipes.
Otherwise I would try:
process.stdout.close()
process.stderr.close()
after you are done using the process object.
For instance, when you call .read() directly:
output = process.stdout.read()
process.stdout.close()
Look in the above module source for how communicate() is defined and you'll see that it closes each pipe after it reads from it, so that is what you should also do.
If you're using Twisted, don't use subprocess. If you were using spawnProcess instead, you wouldn't need to deal with annoying resource-management problems like this.
So this is the scenario. I'm trying to program to run like namefile.py (argument) using this code:
process=subprocess.Popen([sys.executable,filename],stdout=subprocess.PIPE)
res=process.communicate(argument)
z=res[0].strip("\n").strip("\r")
Much of my supriseness, the program passes the (argument) not by the command line argument, but by standard output. What is the correct way?
Note: I want to send it, not receive it.
Simply consult the documentation.
The command-line arguments are passed to the Popen call, and have nothing to do with stdin/stdout.
import subprocess
args = ['/path/to/executable', 'first_arg', 'second_arg']
p = subprocess.Popen(args, stdout=subprocess.PIPE)
all_of_stdout = p.stdout.read()
exit_code = p.wait()
I have a script which runs a subprocess as follows:
child_process = subprocess.Popen(["python", testset['dir'] + testname, \
output_spec_file, plugin_directory],\
stderr=subprocess.PIPE, stdout=subprocess.PIPE)
In that process, I am trying to insert print statements but they are not appearing to stdout. I tried using sys.stdout.write() in that subprocess and then sys.stduout.read() right after child_process but it is not capturing the output.
I am new to Python and I haven't gotten to that level of complexity in Python. I am actually working low level in C and there are some Python test scripts and I'm not sure how to print out from the subprocess.
Any suggestions?
sys.stdout.read (and write) are for standard input/output of the current process (not the subprocess). If you want to write to stdin of the child process, you need to use:
child_process.stdin.write("this goes to child") #Popen(..., stdin=subprocess.PIPE)
and similar for reading from the child's stdout stream:
child_process = subprocess.Popen( ... , stdout=subprocess.PIPE)
child_process.stdout.read("This is the data that comes back")
Of course, it is generally more idiomatic to use:
stdoutdata, stderrdata = child_process.communicate(stdindata)
(taking care to pass subprocess.PIPE to the Popen constructor where appropriate) provided that your input data can be passed all at once.
I am using the subprocess module to call an external program (plink.exe) to log-in to a server; but when I call communicate to read the output, it is blocking. The code is below:
import subprocess
process = subprocess.Popen('plink.exe hello#10.120.139.170 -pw 123456'.split(), shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
print process.communicate() #block here
I know the block is because plink.exe it still running; but I need to read the output before the subprocess terminates. Is there anyway to do that?
The whole purpose of the communicate method is to wait for the process to finish and return all the output. If you don't want to wait, don't call communicate. Instead, read from the stdout or stderr attribute to read the output.
If the process outputs to both stdout and stderr (and you want to read it separately), you will have to be careful to actually read from both without blocking, or you can deadlock. This is fairly hard on Windows, and you may wish to use the pexpect module instead.
Maybe because "plink.exe" needs to take in input arguments, if you don't pass them, it will block until data are given, you could try adding arguments in method communicate(input)
I faced a similar situation where I had to execute a single command lmstat -a and then get the output of the terminal.
If you just need to run a single command and then read the output, you can use the following code:
import subprocess
Username = 'your_username'
Password = 'your_password'
IP = 'IP_of_system'
Connection_type = '-ssh' #can have values -ssh -telnet -rlogin -raw -serial
p = subprocess.Popen(['plink', Connection_type, '-l', Username, '-pw', Password, IP], \
shell = False, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
out, err = p.communicate('lmstat -a\nexit\n'.encode())
print(out.decode())