Wednesday, May 17, 2017

Unix sed, Python CsvKit under Windows Scripting Host (WSH); Problems and solutions


This is a just a short article that described problem and finding I encountered in one of my project and were wishing that what I found can be useful to someone following a similar path as me - A short side track: Nerds or people like me working and sharing knowledge, a lot of times, were overlooked as been anti-social and less of charity or volunteering to the society. I for one, would like to pass and dispatch the messages that we, the nerd and genuien hard worker, are to be proud of our contribution to the society and world for making the world a better place.

Back to the topic.

I were involved in a Windows automation project and were writing most of my code in VBA. However, with my knowledge about the Unix way of doing things, it makes totally sense for me wanting to run some tasks through some Unix utilities program. As we all know, Unix way basically means command lines. Fortunately, Windows did not fore go the access to command lines. For VBA, there are the general Shell() command. But that is not the only option for VBA. With Microsoft COM infrastructure, VBA programmer has access to wide variaty of objects. One of them is the Windows Scripting Host. By accessing to Windows Scripting Host, programmer can have better control of the DOS-shell/command-line environment.

While I was happily using the Windows Scripting Host to carry out my command line tasks, I notice that for most Windows/DOS based programs they all run great until I try to run some Unix utilities that ported over to the Windows/DOS world.

Before I go on, I would like to point out that I did not spend a lot of time try to figure out every single issues, so please bear with me for not able to provide all possible solution and explanation. 

One Unix utility I used is the sed command from the MinGW/msys. I was able to verify it functionality by running some test directly under the Windows/DOS command line after removing some conflicting search paths from the PATH environment variables - for example, in my system, I also have Qt and GNAT installed.

After verifying the sed under that Windows/DOS command line, I invoked it through the Windows Scripting Host via VBA. The command failed with a return code of 2, which, for sed, could just mean errors during execution or , for DOS, could mean file not found. By testing with non-existing command, we know the Windows Scripting Host do recognize the sed command. By testing with simple 'sed -help 2>file', I realize it may have something to do with the shall's interpretation/parsing of command line. This lead me to the thought of using the Cmd.exe /C to run the sed. By running 'Cmd.exe /C sed ...  ' under the Windows Scripting Host, everything worked out. The other command I run into the same problem is the Python CsvKit commands. Again, running with Cmd.exe solve the problem. At this point, I can't say I understand the problem. My hint is that it may have something to do with the redirection of the standard output since all my Unix and Python commands used the redirection.



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