[Newbies] PipeableOSProcess shell interaction

[OpenSlate ChalkDust]

I tried to use your code but I don't have either class in my 4.3 or 4.4
images. Do they require adding something?


On Mon, Jun 17, 2013 at 1:38 PM, David T. Lewis <lewis at mail.msen.com> wrote:

> On Mon, Jun 17, 2013 at 10:16:05AM -1000, OpenSlate ChalkDust wrote:
> > On Wed, Jun 12, 2013 at 2:47 AM, David T. Lewis <lewis at mail.msen.com>
> wrote:
> >
> > > On Tue, Jun 11, 2013 at 10:34:47PM -0700, Sean P. DeNigris wrote:
> > > > When using PipeableOSProcess as a shell, how can I get feedback on
> the
> > > status
> > > > of the individual commands?
> > > [snip]
> > > PipeableOSProcess is designed to be part of CommandShell, so when you
> use
> > > it
> > > directly (rather than using a CommandShell), you need to take care of
> a few
> > > details. The important things are to set the output pipe for
> nonblocking
> > > reads
> > > (otherwise you will hang up your VM on a read), and to close pipes
> when you
> > > are done using them (otherwise you will "leak" file handles over time).
> > >
> > > Dave
> > >
> > >
> > Could the example you gave be implemented using CommandShell? In what
> > situations would I want to use PipeableOSProcess instead of CommandShell?
>
> Good question. CommandShell works at a higher level, and it manages the
> annoying details of closing pipe handles and making sure that you do
> not block the VM. In most cases, it is easier to use CommandShell rather
> than operating directly on the lower level PipeableOSProcess.
>
> For example (to build on the earlier example), if you want to run the
> Unix 'ls' command, and check its exit status to determine if a file was
> not found, it is not necessary to use the lower level PipeableOSProcess.
> You can do this instead:
>
>   CommandShell new
>     if: 'cd .. ; ls aFile'
>     then: ['the ls command succeeded']
>     else: ['the file was not found'] ==> 'the file was not found'
>
> Having said that, CommandShell is a simple simulation of a Unix shell,
> and it is not a complete replacement for something like bash. There
> are cases when you may need to use the features of a real Unix shell,
> so working directly with a PipeableOSProcess connected to /usr/bin/bash
> may be necessary in some cases.
>
> Dave
>
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-- 
Gary Dunn
Open Slate Project
http://openslate.org/
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