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I have a case to want to execute the following shell command in Python and get the output,
echo This_is_a_testing | grep -c test I could use this python code to execute the above shell command in python,
>>> import subprocess >>> subprocess.check_output("echo This_is_a_testing | grep -c test", shell=True) '1\n' However, as I do not want to use the "shell=True" option, I tried the following python code,
>>> import subprocess >>> p1 = subprocess.Popen(["echo", "This_is_a_testing"], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(["grep", "-c", "test"], stdin=p1.stdout) >>> p1.stdout.close() >>> p2.communicate() (None, None) I wonder why the output is "None" as I have referred to the descriptions in the webpage : http://docs.python.org/library/subprocess.html#subprocess.PIPE
Had I missed some points in my code ? Any suggestion / idea ? Thanks in advance.
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Python allows you to execute shell commands, which you can use to start other programs or better manage shell scripts that you use for automation. Depending on our use case, we can use os. system() , subprocess. run() or subprocess.
pipe() method in Python is used to create a pipe. A pipe is a method to pass information from one process to another process.
pipe module can be used to run shell commands in a program Code Example.
The subprocess. check_output() is used to get the output of the calling program in python. It has 5 arguments; args, stdin, stderr, shell, universal_newlines. The args argument holds the commands that are to be passed as a string.
Please look here:
>>> import subprocess >>> p1 = subprocess.Popen(["echo", "This_is_a_testing"], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(["grep", "-c", "test"], stdin=p1.stdout) >>> 1 p1.stdout.close() >>> p2.communicate() (None, None) >>> here you get 1 as output after you write p2 = subprocess.Popen(["grep", "-c", "test"], stdin=p1.stdout), Do not ignore this output in the context of your question.
If this is what you want, then pass stdout=subprocess.PIPE as argument to the second Popen:
>>> p1 = subprocess.Popen(["echo", "This_is_a_testing"], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(["grep", "test"], stdin=p1.stdout, stdout=subprocess.PIPE) >>> p2.communicate() ('This_is_a_testing\n', None) >>> If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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