Develop Reference

Cannot perform subprocess.run inside a snap

In my snap (coded in python), I try to perform some sudo commands but it didn’t work. Here is an example of a command that didn’t work:
command = "sudo netmgr -i country_code set:" + countryCode
subprocess.run([command])
And when I run the snap in my device it won’t work and I got this error:
> Traceback (most recent call last): File
> “/snap/iotr-configuration/x17/bin/iotr-configuration”, line 11, in
> load_entry_point(‘iotr-configure==0.0.3’, ‘console_scripts’,
> ‘iotr-configuration’)() File
> “/snap/iotr-configuration/x17/lib/python3.5/site-packages/src/app.py”,
> line 53, in main configuration_program() File
> “/snap/iotr-configuration/x17/lib/python3.5/site-packages/src/app.py”,
> line 37, in configuration_program
> confNIC.set_nic_settings(“fd05:a40b:b47d:7340::4”, “1250”) File
> “/snap/iotr-configuration/x17/lib/python3.5/site-packages/src/configureNic.py”,
> line 16, in set_nic_settings subprocess.run([command]) File
> “/snap/iotr-configuration/x17/usr/lib/python3.5/subprocess.py”, line
> 693, in run with Popen(*popenargs, **kwargs) as process: File
> “/snap/iotr-configuration/x17/usr/lib/python3.5/subprocess.py”, line
> 947, in init restore_signals, start_new_session) File
> “/snap/iotr-configuration/x17/usr/lib/python3.5/subprocess.py”, line
> 1551, in _execute_child raise child_exception_type(errno_num, err_msg)
> FileNotFoundError: [Errno 2] No such file or directory: ‘sudo netmgr
> -i country_code set:1250’
This function exist because when I type it directly in the terminal, it works…
Can you help me on this issue ?

You're calling subprocess.run in the wrong way. You should either pass it a the command as a single string (like you're doing here) but then set shell=True, or break the command into several arguments, as in:
command = ["sudo", "netmgr", "-i", "country_code", "set:" + countryside]
subprocess.run(command)
See the FAQ part of the documentation:
args is required for all calls and should be a string, or a sequence of program arguments. Providing a sequence of arguments is generally preferred, as it allows the module to take care of any required escaping and quoting of arguments (e.g. to permit spaces in file names). If passing a single string, either shell must be True (see below) or else the string must simply name the program to be executed without specifying any arguments.

Subprocess in Python: File Name too long

I try to call a shellscript via the subprocess module in Python 2.6.
import subprocess
shellFile = open("linksNetCdf.txt", "r")
for row in shellFile:
subprocess.call([str(row)])
My filenames have a length ranging between 400 and 430 characters.
When calling the script I get the error:
File "/usr/lib64/python2.6/subprocess.py", line 444, in call
return Popen(*popenargs, **kwargs).wait()
File "/usr/lib64/python2.6/subprocess.py", line 595, in __init__
errread, errwrite)
File "/usr/lib64/python2.6/subprocess.py", line 1106, in _execute_child
raise child_exception
OSError: [Errno 36] File name too long
An example of the lines within linksNetCdf.txt is
./ShellScript 'Title' 'Sometehing else' 'InfoInfo' 'MoreInformation' inputfiile outputfile.txt 3 2
Any ideas how to still run the script?

subprocess.call can take the command to run in two ways - either a single string like you'd type into a shell, or a list of the executable name followed by the arguments.
You want the first, but were using the second
import subprocess
shellFile = open("linksNetCdf.txt", "r")
for row in shellFile:
subprocess.call(row, shell=True)
By converting your row into a list containing a single string, you're saying something like "Run the command named echo these were supposed to be arguments with no arguments"

You need to tell subprocess to execute the line as full command including arguments, not just one program.
This is done by passing shell=True to call
import subprocess
cmd = "ls " + "/tmp/ " * 30
subprocess.call(cmd, shell=True)

subprocess.check_output(): OSError file not found in Python

Executing following command and its variations always results in an error, which I just cannot figure out:
command = "/bin/dd if=/dev/sda8 count=100 skip=$(expr 19868431049 / 512)"
print subprocess.check_output([command])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/subprocess.py", line 566, in check_output
process = Popen(stdout=PIPE, *popenargs, **kwargs)
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
WHich file it is referring to ? other commands like ls,wc are running correctly though, the command is also running well on terminal but not python script.

Your command is a list with one element. Imagine if you tried to run this at the shell:
/bin/'dd if='/dev/'sda8 count=100 skip=$(expr 19868431049 '/' 512)'
That's effectively what you're doing. There's almost certainly no directory named dd if= in your bin directory, and there's even more almost certainly no dev directory under that with an sd8 count=100 skip=$(expr 19868431049 directory with a program named 512 in it.
What you want is a list where each argument is its own element:
command = ['/bin/dd', 'if=/dev/sda8', 'count=100', 'skip=$(expr 19868431049 / 512)']
print subprocess.check_output(command) # notice no []
But that brings us to your second problem: $(expr 19868431049 / 512) isn't going to be parsed by Python or by dd; that's bash syntax. You can, of course, just do the same thing in Python instead of in bash:
command = ['/bin/dd', 'if=/dev/sda8', 'count=100',
'skip={}'.format(19868431049 // 512)]
print subprocess.check_output(command)
Or, if you really want to use bash for no good reason, pass a string, rather than a list, and use shell=True:
command = "/bin/dd if=/dev/sda8 count=100 skip=$(expr 19868431049 / 512)"
print subprocess.check_output(command, shell=True) # still no []
Although that still isn't going to work portably, because the default shell is /bin/sh, which may not know how to handle bashisms like $(…) (and expr, although I think POSIX requires that expr exist as a separate process…). So:
command = "/bin/dd if=/dev/sda8 count=100 skip=$(expr 19868431049 / 512)"
print subprocess.check_output(command, shell=True, executable='/bin/bash')

This worked for me using subprocess.popen
command = "echo $JAVA_HOME"
proc = subprocess.Popen(command,stdout=subprocess.PIPE,shell=True)

run a .exe file with additional parameters

I am using windows and struggeling to get this work...
I can execute this in cmd.exe:
"C:\Program Files (x86)\Test 123\Test.exe" "H:\Test Test\file.txt" -f "doStuff"
but when I try to do it in python:
subprocess.call([r'"C:\Program Files (x86)\Test 123\Test.exe" "H:\Test Test\file.txt" -f "doStuff"'])
I get this error:
Traceback (most recent call last):
File "testing12.py", line 20, in <module>
subprocess.call([r'"C:\Program Files (x86)\Test 123\Test\Test.exe" "H:\Test Test\Folder\file.txt" -f "doStuff"'])
File "c:\Python27\lib\subprocess.py", line 522, in call
return Popen(*popenargs, **kwargs).wait()
File "c:\Python27\lib\subprocess.py", line 709, in __init__
errread, errwrite)
File "c:\Python27\lib\subprocess.py", line 957, in _execute_child
startupinfo)
WindowsError: [Error 5] Access is denied
How can I execute it properly? Thanks.

If you're going to pass in an array, make it an actual array -- one argument per parameter, separated by commas. Otherwise you'll need to use shell=True, which has all the (generally undesirable) side effects of invoking a shell (and should just pass in your command string as a string, no array called for in that use case).
subprocess.call([
"C:\Program Files (x86)\Test 123\Test.exe",
"H:\Test Test\file.txt",
"-f", "doStuff"])
If you don't use commas between your strings, they're consolidated together.

NamedTemporaryFile cannot be acessed from command line

I have the following (simplified) code:
with NamedTemporaryFile() as f:
f.write(zip_data)
f.flush()
subprocess.call("/usr/bin/7z x %s" % f.name)
It dies with the following error:
Traceback (most recent call last):
File "decrypt_resource.py", line 70, in <module>
unpack(sys.argv[2])
File "decrypt_resource.py", line 28, in unpack
print(subprocess.check_output(cmd))
File "/usr/lib/python2.7/subprocess.py", line 568, in check_output
process = Popen(stdout=PIPE, *popenargs, **kwargs)
File "/usr/lib/python2.7/subprocess.py", line 711, in __init__
errread, errwrite)
File "/usr/lib/python2.7/subprocess.py", line 1308, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory
However, if I use NamedTemporaryFile(delete=False) and then print & execute the command, it works. What's wrong here?
My System is an ArchLinux with a 3.9.5-1-ARCH kernel.

You are using subprocess.call() incorrectly.
Pass in a list of arguments:
subprocess.call(["/usr/bin/7z", "x", f.name])
The argument is not handled by a shell and is not parsed out like a shell would do. This is a good thing as it prevents a security problem with untrusted command line arguments.
Your other options include using shlex.split() to do the whitespace splitting for you, or, as a last resort, telling subprocess to use a shell for your command with the shell=True flag. See the big warning on the subprocess documentation about enabling the shell.