Author Quigon
Recipients Quigon
Date 2007-11-29.20:16:55
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Message-id <1196367416.9.0.40290581495.issue1524@psf.upfronthosting.co.za>
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Content
Given a call to os.system() with a command string like this:

   os.system('"TheCommand" > "MyOutput"')  # fails

then the call fails with the following error message on the console:

   'TheCommand" > "MyOutput' is not recognized as an internal or 
external command, operable program or batch file.

Note that both the executable file name and the redirected output file 
name are quoted.

Apparently the command string is being parsed and the first quote is 
incorrectly being matched with the last quote. A more general statement 
of this bug might say that multiple quoted fields on a command line 
cause os.system() to fail. I have not done enough research to better 
characterize the problem.

By contrast, if only one of the file names is quoted then the call to 
os.system() succeeds. E.g., these calls succeed:

   os.system('TheCommand > "MyOutput"')  # succeeds
   os.system('"TheCommand" > MyOutput')  # succeeds

Of course this is a simplified example where it is not necessary to 
quote either file name. Real world examples include 2 file names with 
imbedded spaces. E.g.:

   os.system('"The Command" > "My Output"')  # fails

   'The' is not recognized as an internal or external command, operable 
program or batch file.

A further real-world example is a command line with full path 
specifications for both the executable file and the output file. Such 
path specifications may include imbedded spaces so both need to be 
quoted. However, quoting both causes os.system() to fail. E.g.:

   os.system(r'"C:\New Folder\TheCommand" > "C:\New Folder\MyOutput"')  
# fails

   'C:\New' is not recognized as an internal or external command, 
operable program or batch file.

The above described scenario is the situation in the attached script 
that includes logic for finding an executable file that may not be 
found on the system path but is co-located with the Python script file. 
Thus the script and its companion file(s) may be moved from machine to 
machine and will work correctly even if not in a directory that is 
included on the system path. The script fails because the command line 
that it constructs, with executable and output file specifications 
quoted, fails in os.system().

Here is output from running the attached script:

-----------------------------------------------

C:\New Folder>buggy.py
strCmdLine=["ListMetadata" > "20071129Metadata.txt"]
'ListMetadata" > "20071129Metadata.txt' is not recognized as an 
internal or external command,
operable program or batch file.
Could not find "ListMetadata" on path, looking in script directory
strCmdLine=["C:\New Folder\ListMetadata" > "20071129Metadata.txt"]
'C:\New' is not recognized as an internal or external command,
operable program or batch file.
Traceback (most recent call last):
  File "C:\New Folder\buggy.py", line 16, in <module>
    raise Exception("Could not locate command")
Exception: Could not locate command

-----------------------------------------------

Note that the command line that is constructed by the attached script 
runs just fine and produces the desired result if it is executed 
directly at a command line prompt. It is when executed via os.system() 
that the command line fails.

Testing environment:
   OS = Windows XP Professional
   Python = 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit 
(Intel)]
Files
File name Uploaded
buggy.py Quigon, 2007-11-29.20:16:55
History
Date User Action Args
2007-11-29 20:16:57Quigonsetspambayes_score: 0.00548248 -> 0.00548248
recipients: + Quigon
2007-11-29 20:16:56Quigonsetspambayes_score: 0.00548248 -> 0.00548248
messageid: <1196367416.9.0.40290581495.issue1524@psf.upfronthosting.co.za>
2007-11-29 20:16:56Quigonlinkissue1524 messages
2007-11-29 20:16:56Quigoncreate