Python as a scripting language. Alternative to bash script?

[Michael Torrie]

On 06/28/2010 05:48 AM, Dave Pawson wrote:
> Main queries are: Ease of calling out to bash to use something like
> imageMagick or Java? Ease of grabbing return parameters? E.g. convert
> can return both height and width of an image. Can this be returned to
> the Python program? Can Python access the exit status of a program?

Sure.  I've created a module called runcmd that does 90% of what I want
(easy access to stdout, stderr, error code).  I've attached it to this
e-mail.  Feel free to use it; this post puts my code into the public domain.

> I'd prefer the advantages of using Python, just wondering if I got so
> far with the port then found it wouldn't do something?

Python really isn't a shell scripting language.  So there are things
that Bash does much better, such as spawning processes and piping them
together.  I've tried over the years to create a pythonic library that
would let me do that, but haven't found a good syntax that I like.

It turns out, though, that much of what I use piping for in Bash is to
run external processes to do things that I could use python modules for.
 For example, I typically pipe stuff to cut a lot to get certain fields.
For example:

ps ax | cut -c1-5

In python I could simply take the output of "ps ax" and use python's
own, superior, cutting routines (using my module):

(err, stdout, stderr) = runcmd.run( [ 'ps', 'ax' ] )
for x in stdout.split('\n'):
    print x.strip().split()[0]

Sure it's a couple more lines in this case, but in other cases, python's
abilities make it simpler than bash.  A great document on how you can
exploit python's abilities (particularly generators) to replace bash
pipelines is here:  http://www.dabeaz.com/generators/




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