I'm trying to use a Python script to change directory, but I am getting an error.
The python code:
import subprocess
p = subprocess.Popen(['cd', '~'], stdout=subprocess.PIPE)
output = p.communicate()
print output
I get this error:
File "test_sub.py", line 2, in <module>
p = subprocess.Popen(['cd', '~'], stdout=subprocess.PIPE)
File "/usr/lib/python2.7/subprocess.py", line 710, in __init__
errread, errwrite)
File "/usr/lib/python2.7/subprocess.py", line 1327, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory
What does the error mean, what am I doing wrong, and how do I change directory in a python subprocess?
>>> Popen('cd ~', shell=True, stdout=PIPE).communicate()
(b'', None)
Without shell=True (which, emulates a shell)
>>> Popen(['cd', '~'], stdout=PIPE).communicate()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.4/subprocess.py", line 858, in __init__
restore_signals, start_new_session)
File "/usr/lib/python3.4/subprocess.py", line 1456, in _execute_child
raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'cd'
>>>
You can't change directory unless you do it via:
import os
os.chdir(os.path.abspath(os.path.expanduser('~')))
So the problem isn't that the path ~ doesn't exist, but rather cd doesn't exist as an option in the emulated terminal of Python. Passing directly to an actual shell makes cd work. But note that shell=True is a risk, never use it unless you need to..
So use os.chdir instead.
A working scenario:
import os, subprocess
os.chdir(os.path.abspath('/tmp/'))
print(subprocess.Popen(['ls', '-lah'], stdout=subprocess.PIPE).communicate()[0].decode('utf-8'))
Resulting in:
[torxed@archie ~]$ python
Python 3.4.1 (default, May 19 2014, 17:23:49)
>>> import os, subprocess
>>> os.chdir(os.path.abspath('/tmp/'))
>>> print(subprocess.Popen(['ls', '-lah'], stdout=subprocess.PIPE).communicate()[0].decode('utf-8'))
total 12K
drwxrwxrwt 9 root root 220 Jun 11 12:08 .
drwxr-xr-x 19 root root 4.0K May 28 08:03 ..
drwxrwxrwt 2 root root 40 Jun 11 09:30 .font-unix
drwx------ 2 torxed users 60 Jun 11 09:33 gpg-LBLcdd
drwxrwxrwt 2 root root 40 Jun 11 09:30 .ICE-unix
drwx------ 2 torxed users 80 Jun 11 09:34 .org.chromium.Chromium.LEqfXB
-rw------- 1 torxed users 153 Jun 11 09:34 serverauth.EHWB0LqCv6
drwxrwxrwt 2 root root 40 Jun 11 09:30 .Test-unix
-r--r--r-- 1 root users 11 Jun 11 09:34 .X0-lock
drwxrwxrwt 2 root root 60 Jun 11 09:34 .X11-unix
drwxrwxrwt 2 root root 40 Jun 11 09:30 .XIM-unix
>>>
Note that i started the shell in ~ and via os.chdir changed it to tmp and actually got my tmp directory content.
Explanation of shells and commands:
A shell-command is something that's built into the shell while a regular old command is something you'll find under /bin, for instance:
[torxed@archie ~]$ ls /bin
2to3 2to3-2.7
7z 7za
...
Where 7z is a command i can actually execute:
>>> from subprocess import *
>>> Popen(['7z'], stdout=PIPE).communicate()
(b'\n7-Zip [64] 9.20 Copyright (c) 1999-2010 Igor Pavlov 2010-11-18\np7zip Version 9.20 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,8 CPUs)\n
While for instance cd is a built in shell command, something that you will not find under /bin but works anyway in most "terminals" (using a shell) because it's (as mentioned), built into the shell you normally see.
But because Python will emulate a shell there are only a certain set of commands that are built-in and works, cd being one of those that doesn't but to compensate you can use os.chdir(...) to execute the exact same function and affects the entire program.
cd is a builtin command of the shell which change the environment of the shell to set the current directory of next commands will be run into. It is not a regular program. So it can't be called as a subprocess with Popen.
The right way to change the current directory inside python is:
import os
os.chdir(os.path.abspath(os.path.expanduser('~')))
#now the current directory is home of user
You need to include all path with
path = os.path.dirname('$0')
currentpath = os.path.abspath(path)
os.chdir(path)
