I am trying to get output of subprocess.Popen in variable.
It is working fine for pwd command, but not working for pwdx $(pgrep -U $USER -f SimpleHTTPServer) command.
This works:
(Pdb++) p = subprocess.Popen("pwd", stdout=subprocess.PIPE)
(Pdb++) result = p.communicate()[0]
(Pdb++) result
'xyz'
This is not working:
(Pdb++) subprocess.Popen("pwdx $(pgrep -U $USER -f SimpleHTTPServer)", stdout=subprocess.PIPE)
*** OSError: [Errno 2] No such file or directory
Can someone please let me know how can I save the output of it to a variable?
If you want to pass a command with arguments to Popen(), you have to pass it as a list, like so:
subprocess.Popen(['/bin/ls', '-lat'])
If you just pass a single string as in your example, it assumes the entire thing is the command name, and obviously there is no command literally named pwdx $(pgrep -U $USER -f SimpleHTTPServer).
As the docs and previous answers already state the command you want to execute via subprocess.Popen() needs to be passed as a list.
From the docs:
Note in particular that options (such as -input) and arguments (such
as eggs.txt) that are separated by whitespace in the shell go in
separate list elements, while arguments that need quoting or backslash
escaping when used in the shell (such as filenames containing spaces) are single list elements.
Another useful tip you can get from the docs is to use shlex.split() to help you to properly split your command into a list.
Beware though that the use of special shell parameters (e.g. $USER) might not work well with subprocess.Popen() unless you would set the shell=True option, which you shouldn't do without reading the doc's Security Considerations.
Related
I m want to extract the scene change timestamp using the scene change detection from ffmpeg. I have to run it on a few hundreds of videos , so i wanted to use a python subprocess to loop over all the content of a folder.
My problem is that the command that i was using for getting these values on a single video involve piping the output to a file which seems to not be an option from inside a subprocess call.
this is my code :
p=subprocess.check_output(["ffmpeg", "-i", sourcedir+"/"+name+".mpg","-filter:v", "select='gt(scene,0.4)',showinfo\"","-f","null","-","2>","output"])
this one tell ffmpeg need an output
output = "./result/"+name
p=subprocess.check_output(["ffmpeg", "-i", sourcedir+"/"+name+".mpg","-filter:v", "select='gt(scene,0.4)',metadata=print:file=output","-an","-f","null","-"])
this one give me no error but doesn't create the file
this is the original command that i use directly with ffmpeg:
ffmpeg -i input.flv -filter:v "select='gt(scene,0.4)',showinfo" -f null - 2> ffout
I just need the ouput of this command to be written to a file, anyone see how i could make it work?
is there a better way then subprocess ? or just another way ? will it be easier in C?
You can redirect the stderr output directly from Python without any need for shell=True which can lead to shell injection.
It's as simple as:
with open(output_path, 'w') as f:
subprocess.check_call(cmd, stderr=f)
Things are easier in your case if you use the shell argument of the subprocess command and it should behave the same. When using the shell command, you can pass in a string as the command rather then a list of args.
cmd = "ffmpeg -i {0} -filter:v \"select='gt(scene,0.4)',showinfo\" -f {1} - 2> ffout".format(inputName, outputFile)
p=subprocess.check_output(cmd, shell=True)
If you want to pass arguments, you can easily format your string
I am trying to run the bash command pdfcrack in Python on a remote server. This is my code:
bashCommand = "pdfcrack -f pdf123.pdf > myoutput.txt"
import subprocess
process = subprocess.Popen(bashCommand.split(), stdout=subprocess.PIPE)
output, error = process.communicate()
I, however, get the following error message:
Non-option argument myoutput2.txt
Error: file > not found
Can anybody see my mistake?
The first argument to Popen is a list containing the command name and its arguments. > is not an argument to the command, though; it is shell syntax. You could simply pass the entire line to Popen and instruct it to use the shell to execute it:
process = subprocess.Popen(bashCommand, shell=True)
(Note that since you are redirecting the output of the command to a file, though, there is no reason to set its standard output to a pipe, because there will be nothing to read.)
A better solution, though, is to let Python handle the redirection.
process = subprocess.Popen(['pdfcrack', '-f', 'pdf123.pdf'], stdout=subprocess.PIPE)
with open('myoutput.txt', 'w') as fh:
for line in process.stdout:
fh.write(line)
# Do whatever else you want with line
Also, don't use str.split as a replacement for the shell's word splitting. A valid command line like pdfcrack -f "foo bar.pdf" would be split into the incorrect list ['pdfcrack', '-f', '"foo', 'bar.pdf"'], rather than the correct list ['pdfcrack', '-f', 'foo bar.pdf'].
> is interpreted by shell, but not valid otherwise.
So, that would work (don't split, use as-is):
process = subprocess.Popen(bashCommand, shell=True)
(and stdout=subprocess.PIPE isn't useful since all output is redirected to the output file)
But it could be better with native python for redirection to output file and passing arguments as list (handles quote protection if needed)
with open("myoutput.txt","w") as f:
process = subprocess.Popen(["pdfcrack","-f","pdf123.pdf"], stdout=subprocess.PIPE)
f.write(process.read())
process.wait()
Your mistake is > in command.
It doesn't treat this as redirection to file because normally bash does it and now you run it without using bash.
Try with shell=True if you whan to use bash. And then you don't have to split command into list.
subprocess.Popen("pdfcrack -f pdf123.pdf > myoutput.txt", shell=True)
I am able to run this properly using os.system. It is writing pcap file into text.
os.system("tshark -z 'proto,colinfo,tcp.srcport,tcp.srcport' -r filename.pcap > testfile")
But when I tried to give input file from termimal, I got following error:
tshark: -z invalid argument
host = raw_input("Enter file name: ")
test = subprocess.Popen(["tshark","-z","'proto,colinfo,tcp.srcport,tcp.srcport'","-r",host,">","testfile"], stdout=subprocess.PIPE)
output = test.communicate()[0]
Can anybody please figure out where I am making mistake?
To emulate the os.system command, use the shell=True parameter to subprocess.Popen and provide the same command string (not an array of strings):
subprocess.Popen("tshark -z 'proto,colinfo,tcp.srcport,tcp.srcport' -r "
+ host + "> testfile", stdout=subprocess.PIPE, shell=True)
You need a shell to interpret your command line as you are using output redirection to a file ("> testfile").
In your example, you are passing each element of the string list to the execve() system call and hence as parameters to the tshark command (which gets 'proto,colinfo,tcp.srcport,tcp.srcport' as the argument to the -z option instead of proto,colinfo,tcp.srcport,tcp.srcport and which won't know what to do with the > and testfile arguments).
As wnnmaw points out in his comment, using os.system or subprocess.Popen with shell=True with command lines built from user input (the host variable in your case) allows a user to pass arbitrary data to the shell. This can be used to execute (potentially nasty) commands on your system.
For instance, setting host in your example to ; /bin/rm -rf / would delete every file on a UNIX system (assuming the user running the process had enough privilege).
It is therefore very important to validate an user input before adding it to the command string.
I'm trying to send a command through a socket from client to server to execute a command on the server and send the output back to me. Everything works fine if the command is one word with no options. However if I use an option such as netstat -an or dir c:\ then the command isn't recognized and from the output it looks like quotes are put around the command before being executed ('"netstat -an"' is not recognized as an internal or external command). I know they aren't saved in the variable this way because I printed it before being executed to error check. Please help. Here is what my code looks like:
commout = subprocess.Popen([data], stdout=subprocess.PIPE, shell=True)
(out, err) = commout.communicate()
Try make data an array of arguments (the first being the actual command).
For example:
commout = subprocess.Popen(['netstat', '-an'], stdout=subprocess.PIPE, shell=True)
The first element is a string representing the actual command (netstat), the next element is a string representing the first argument (-an).
To clarify, Popen(['echo', 'a', 'b'] is equivalent to echo a b on the command line, whereas Popen(['echo', 'a b'] would be equivalent to echo "a b" instead (ie. a single argument with a space between a and b.
If you pass a list, each item in it will be quoted separately. In this case, just pass a string:
subprocess.Popen(data, stdout=subprocess.PIPE, shell=True)
I'm trying to write an svn pre-commit hook in python. Part of this involves checking the diff file to see if there are any actual file changes (as opposed to just property changes).
I have a working grep command which I can execute fine on the shell
grep "^\(Added: \|Modified: \|Deleted: \)" diff filename | grep -v 'svn:'
However when I put it through subprocess.POpen it escapes all my backslashes, which knackers the regexp.
Executing command: ['grep', '"^\\Added: \\|Modified: \\|Deleted: \\)", ...]
How do I avoid this?
NB: I'm aware that I can pipe results between subprocesses and I can do the two greps that way. I need help getting the first one working first though :/
NB2: I also tried using filterdiff --clean instead and couldn't get it to work. Searching for Added, Modified or Deleted lines, removing those with 'svn:' in and checking I had some results seemed to work though.
Python code:
command = ['grep', '"^\(Added: \|Modified: \|Deleted: \)"', filename]
sys.stdout.write('Executing command: %s\n' % (command))
p = subprocess.Popen(command,
stdin = subprocess.PIPE
stdout = subprocess.PIPE
stderr = subprocess.STDOUT
shell = True)
data = p.stdout.read()
if len(data) == 0:
sys.stdout.write("Diff does not contain any file modifications./n")
exit(0)
You need to consider what you want grep to see in its command line arguments.
The first argument needs to be the literal string "^\(Added: \|Modified: \|Deleted: \)", so that means that it shouldn't include the double quotes but should include the backslashes.
The way to express this kind of string is to use Python raw strings:
command = ['grep', r'^\(Added: \|Modified: \|Deleted: \)', filename]
A good way to check what you're actually running is to replace grep by echo so you can at least see what you're passing to the command.