How to run a subprocess with Python wait for it to exit and get the full stdout as a string

Question

So I noticed subprocess call while it waits for the command to finish before proceeding with the python script  I have no way of getting the stdout  except with subprocess Popen  Are there any alternative function calls that would wait until it finishes   I also tried Popen wait    NOTE  I m trying to avoid os system call  result   subprocess Popen  commands                             self tmpfile path     stdout subprocess PIPE  stderr subprocess PIPE  out  err   result communicate   print out  HIHIHI    my output   HIHIHI   NOTE  I am trying to run wine with this

User · Answer

With Python 3 8 this workes for me  For instance to execute a python script within the venv       import subprocess     import sys     res   subprocess run                 sys executable               venv3 8 bin python                main py    --help                  stdout PIPE               text True      print res stdout

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If your process gives a huge stdout and no stderr  communicate   might be the wrong way to go due to memory restrictions   Instead   process   subprocess Popen cmd  shell True                             stdout subprocess PIPE                              stderr subprocess PIPE     wait for the process to terminate for line in process stdout  do something line  errcode   process returncode   might be the way to go   process stdout is a file-like object which you can treat as any other such object  mainly    you can read   from it you can readline   from it and you can iterate over it    The latter is what I do above in order to get its contents line by line

User · Answer

I d try something like      usr bin python from   future   import print function  import shlex from subprocess import Popen  PIPE  def shlep cmd          shlex split and popen             parsed cmd   shlex split cmd         if parsed cmd 0  not in approved commands            raise ValueError   Bad User   No output for you       proc   Popen parsed command  stdout PIPE  stderr PIPE      out  err   proc communicate       return  proc returncode  out  err        In other words let shlex split   do most of the work   I would NOT attempt to parse the shell s command line  find pipe operators and set up your own pipeline   If you re going to do that then you ll basically have to write a complete shell syntax parser and you ll end up doing an awful lot of plumbing   Of course this raises the question  why not just use Popen with the shell True  keyword  option   This will let you pass a string  no splitting nor parsing  to the shell and still gather up the results to handle as you wish   My example here won t process any pipelines  backticks  file descriptor redirection  etc that might be in the command  they ll all appear as literal arguments to the command   Thus it is still safer then running with shell True     I ve given a silly example of checking the command against some sort of  approved command  dictionary or set --- through it would make more sense to normalize that into an absolute path unless you intend to require that the arguments be normalized prior to passing the command string to this function

User · Answer

I am using the following construct  although you might want to avoid shell True   This gives you the output and error message for any command  and the error code as well   process   subprocess Popen cmd  shell True                             stdout subprocess PIPE                              stderr subprocess PIPE     wait for the process to terminate out  err   process communicate   errcode   process returncode

User · Answer

subprocess check output        calls the process  raises if its error code is nonzero  and otherwise returns its stdout  It s just a quick shorthand so you don t have to worry about PIPEs and things

[python] How to run a subprocess with Python, wait for it to exit and get the full stdout as a string?

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