How do I pass a variable to os.popen?

[Paul David Mena]

This was exactly what I was looking for.  Thanks!

On Mon, Oct 31, 2011 at 4:48 PM, Chris Rebert <clp2 at rebertia.com> wrote:

> On Mon, Oct 31, 2011 at 1:16 PM, extraspecialbitter
> <pauldavidmena at gmail.com> wrote:
> > I'm trying to write a simple Python script to print out network
> > interfaces (as found in the "ifconfig -a" command) and their speed
> > ("ethtool <interface>").  The idea is to loop for each interface and
> > print out its speed.  os.popen seems to be the right solution for the
>
> os.popen() is somewhat deprecated. Use the subprocess module instead.
>
> > ifconfig command, but it doesn't seem to like me passing the interface
> > variable as an argument.  Code snippet is below:
> >
> > ============
> >
> > #!/usr/bin/python
> >
> > # Quick and dirty script to print out available interfaces and their
> > speed
> >
> > # Initializations
> >
> > output = " Interface: %s Speed: %s"
> >
> > import os, socket, types
> >
> > fp = os.popen("ifconfig -a")
> > dat=fp.read()
> > dat=dat.split('\n')
> > for line in dat:
> >    if line[10:20] == "Link encap":
> >       interface=line[:9]
> >    cmd = 'ethtool %interface'
>
> cmd will literally contain a percent-sign and the word "interface". If
> your shell happens to use % as a prefix to indicate a variable, note
> that Python variables are completely separate from and not accessible
> from the shell. So either ethtool will get the literal string
> "%interface" as its argument, or since there is no such shell
> variable, after expansion it will end up getting no arguments at all.
> Perhaps you meant:
> cmd = "ethtool %s" % interface
> Which could be more succinctly written:
> cmd = "ethtool " + interface
>
> >    print cmd
> >    gp = os.popen(cmd)
> >    fat=gp.read()
>
> The subprocess equivalent is:
> fat = subprocess.check_output(["ethtool", interface])
>
> >    fat=fat.split('\n')
> >
> > =============
> >
> > I'm printing out "cmd" in an attempt to debug, and "interface" seems
> > to be passed as a string and not a variable.  Obviously I'm a newbie,
> > and I'm hoping this is a simple syntax issue.  Thanks in advance!
>
> Cheers,
> Chris
> --
> http://rebertia.com
>



-- 
Paul David Mena
--------------------
pauldavidmena at gmail.com
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