[GRASS-dev] [GRASS GIS] #2189: PyGRASS Module does not work on Windows

[GRASS GIS]

#2189: PyGRASS Module does not work on Windows
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  Reporter:  annakrat     |       Owner:  grass-dev@…              
      Type:  defect       |      Status:  closed                   
  Priority:  normal       |   Milestone:  7.0.0                    
 Component:  Python       |     Version:  svn-trunk                
Resolution:  fixed        |    Keywords:  pygrass                  
  Platform:  MSWindows 8  |         Cpu:  Unspecified              
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Comment(by glynn):

 Replying to [comment:2 annakrat]:

 > Python documentation warns against using this but we are using it anyway
 in script.py.

 The warning in the Python documentation is misleading. It's not that
 shell=True is a problem by itself. The problem is shell=True in
 combination with passing the command as a string rather than a list, where
 the string is dynamically generated.

 On Unix, passing the command as a string practically requires shell=True
 (passing a string with shell=False will treat the entire string as the
 path to an executable, which will be executed without arguments).

 As the documentation notes, this combination risks an injection attack. If
 a chunk of text which is supposed to be a single argument or part of an
 argument contains shell metcharacters (spaces, quotes, etc), it can end up
 supplying additional arguments or even additional commands to be executed.
 Avoiding the shell and passing the command as a list avoids this problem.

 On Windows, the fundamental execution primitive (!CreateProcess) takes a
 string rather than a list of strings. A list passed to subprocess.Popen()
 is always converted to a string by "inverting" the rules by which MSVCRT
 parses the string back to an argument list.

 There, the only difference between shell=False and shell=True is that the
 latter prepends "cmd.exe /c " to the resulting string (actually, if the
 COMSPEC environment variable is set, its value is used in place of
 "cmd.exe"). This is the same behaviour as MSVCRT's system() function. The
 end result is that shell=True allows you to execute scripts (including
 batch files), documents, etc, whereas shell=False only works for binary
 executables (execution of scripts is implemented by the shell, rather than
 by the kernel as is the case on Unix).

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2189#comment:6>
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