Get subprocess error output from shell command
I'm running a shell command like: plutil -convert xml1 ~/Library/Preferences/iCab/iCab 4 Bookmarks Getting error: ~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied How would I capture this error using a method of subprocess? I read the doc at http://docs.python.org/release/3.0.1/library/subprocess.html but confess I don't understand it. -- Gnarlie http://Gnarlodious.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
On Sat, Apr 2, 2011 at 11:07 PM, Gnarlodious gnarlodi...@gmail.com wrote: I'm running a shell command like: plutil -convert xml1 ~/Library/Preferences/iCab/iCab 4 Bookmarks Getting error: ~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied How would I capture this error using a method of subprocess? I read the doc at http://docs.python.org/release/3.0.1/library/subprocess.html but confess I don't understand it. -- Gnarlie http://Gnarlodious.com/ -- Yeah, the subprocess docs are a bit confusing. Here's what you need to do. from subprocess import Popen, PIPE #create a Popen object #note that I'm putting the command in a list #the stdout=PIPE thing says I want to capture it process = Popen( ['plutil', '-convert', 'xml1', '~/Library/Preferences/iCab/iCab 4 Bookmarks'], stdout = PIPE, stderr = PIPE) #then, you communicate with the process outdata, errdata = process.communicate() -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
On Sat, Apr 2, 2011 at 8:07 PM, Gnarlodious gnarlodi...@gmail.com wrote: I'm running a shell command like: plutil -convert xml1 ~/Library/Preferences/iCab/iCab 4 Bookmarks Getting error: ~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied How would I capture this error using a method of subprocess? I read the doc at http://docs.python.org/release/3.0.1/library/subprocess.html but confess I don't understand it. from subprocess import Popen, PIPE target = '~/Library/Preferences/iCab/iCab 4 Bookmarks' args = ['plutil', '-convert', 'xml1', target] proc = Popen(args, stdout=PIPE, stderr=PIPE) output, error_output = proc.communicate() if proc.returncode: # non-zero exit status, indicating error print(Encountered error:) print(error_output) # output the error message Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
OK I get it, and that seems like it should work. But when I simulate a permissions error by setting the file to unwritable I get an error: outdata, errdata = process.communicate() Traceback (most recent call last): File stdin, line 1, in module File /Library/Frameworks/Python.framework/Versions/3.1/lib/ python3.1/subprocess.py, line 715, in communicate return self._communicate(input) File /Library/Frameworks/Python.framework/Versions/3.1/lib/ python3.1/subprocess.py, line 1191, in _communicate stdout, stderr = self._communicate_with_poll(input) File /Library/Frameworks/Python.framework/Versions/3.1/lib/ python3.1/subprocess.py, line 1236, in _communicate_with_poll register_and_append(self.stdout, select_POLLIN_POLLPRI) File /Library/Frameworks/Python.framework/Versions/3.1/lib/ python3.1/subprocess.py, line 1223, in register_and_append poller.register(file_obj.fileno(), eventmask) ValueError: I/O operation on closed file Is there a way to trap the last line and handle it instead of crashing my webapp? -- Gnarlie -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
I get it, you instantiate an object, call a method and get a tuple in response. However, here is what I see: process.communicate() (b'~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied\n', b'') So all I get is the string and no error message, which is the same thing I get with the simpler subprocess.call(). I can parse out the error out and handle it if I need to. Is this a failing in the OSX plutil tool? -- Gnarlie -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
On Sat, Apr 2, 2011 at 11:50 PM, Gnarlodious gnarlodi...@gmail.com wrote: I get it, you instantiate an object, call a method and get a tuple in response. However, here is what I see: process.communicate() (b'~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied\n', b'') So all I get is the string and no error message, which is the same thing I get with the simpler subprocess.call(). I can parse out the error out and handle it if I need to. Is this a failing in the OSX plutil tool? -- Gnarlie -- Were you expecting a Python error? That's not how POSIX shells work. A process that fails just gives you a non-zero return code, not an exception. You can call process.poll() to get the return code. http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
On Apr 2, 9:29 pm, Chris Rebert wrote: if proc.returncode: # non-zero exit status, indicating error print(Encountered error:) print(error_output) # output the error message Like in my previous post, this only outputs an empty string. Apparently plutil doesn't communicate well. -- Gnarlie -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
On Sat, Apr 2, 2011 at 9:03 PM, Benjamin Kaplan benjamin.kap...@case.edu wrote: On Sat, Apr 2, 2011 at 11:50 PM, Gnarlodious gnarlodi...@gmail.com wrote: I get it, you instantiate an object, call a method and get a tuple in response. However, here is what I see: process.communicate() (b'~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied\n', b'') So all I get is the string and no error message, which is the same thing I get with the simpler subprocess.call(). I can parse out the error out and handle it if I need to. Is this a failing in the OSX plutil tool? Were you expecting a Python error? That's not how POSIX shells work. A process that fails just gives you a non-zero return code, not an exception. You can call process.poll() to get the return code. However, using subprocess.check_call() or subprocess.check_output() will cause a non-zero exit code to raise a Python exception, CalledProcessError. http://docs.python.org/library/subprocess.html#subprocess.check_call http://docs.python.org/library/subprocess.html#subprocess.check_output Cheers, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: Get subprocess error output from shell command
quote what=earlier relevant post reason=context On Sat, Apr 2, 2011 at 8:50 PM, Gnarlodious gnarlodi...@gmail.com wrote: I get it, you instantiate an object, call a method and get a tuple in response. However, here is what I see: process.communicate() (b'~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied\n', b'') So all I get is the string and no error message, /quote On Sat, Apr 2, 2011 at 9:00 PM, Gnarlodious gnarlodi...@gmail.com wrote: On Apr 2, 9:29 pm, Chris Rebert wrote: if proc.returncode: # non-zero exit status, indicating error print(Encountered error:) print(error_output) # output the error message Like in my previous post, this only outputs an empty string. Apparently plutil doesn't communicate well. Yes, it seems to output its error message to stdout, rather than stderr in line with *nix conventions as one would expect. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
