Python code to replace shell scripts

[Daven Nair]

Hi,

I would like to know if Python supports codes similar to shell scripts:

count=`ps -ef|grep "pattern"|w c -l`
for count in `echo $count`
do
done
fi

Can I export a variable say var from os.system("var= `ps -ef|grep pattern|wc
-l`")


thanks

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[Edvard Majakari]

Re: Python code to replace shell scripts

"Daven Nair" <nair_260@hotma il.com> writes:
[color=blue]
>
> I would like to know if Python supports codes similar to shell scripts:
>
> count=`ps -ef|grep "pattern"|w c -l`
> for count in `echo $count`
> do
> done
> fi[/color]

See 'pydoc commands'. You could probably do with

pattern = "<grep pattern>"
cmd_status, count = commands.getsta tusoutput("ps -ef|grep -c %s" % pattern)

for i in range(count):
# do something count times

Note: you don't need wc -l after grep, because grep has '-c' switch.

Note2: not tested, some typos etc may be present.

--
# Edvard Majakari Software Engineer
# PGP PUBLIC KEY available Soli Deo Gloria!

$_ = '45647661726420 4d616a616b61726 92c206120436872 69737469616e20' ; print
join('',map{chr hex}(split/(\w{2})/)),uc substr(crypt(60 281449,'es'),2, 4),"\n";

[Cameron Laird]

Re: Python code to replace shell scripts

In article <mailman.81.107 1167444.9307.py thon-list@python.org >,
Daven Nair <nair_260@hotma il.com> wrote:[color=blue]
>Hi,
>
>I would like to know if Python supports codes similar to shell scripts:
>
>count=`ps -ef|grep "pattern"|w c -l`
>for count in `echo $count`
> do
> done
>fi
>
>Can I export a variable say var from os.system("var= `ps -ef|grep pattern|wc
>-l`")[/color]

[William Park]

Re: Python code to replace shell scripts

Daven Nair <nair_260@hotma il.com> wrote:[color=blue]
> Hi,
>
> I would like to know if Python supports codes similar to shell scripts:
>
> count=`ps -ef|grep "pattern"|w c -l`
> for count in `echo $count`
> do
> done
> fi
>
> Can I export a variable say var from os.system("var= `ps -ef|grep pattern|wc
> -l`")[/color]

No. 'os.system()' will fork a subshell, and, as you know, subshell
cannot change parent's environment. Furthermore, your shell script is
not proper. It should go like
for count in `...`; do
...
done

In any case, although Python does something well, shell does most things
better. (It's okey... I've got my helmet on.)

--
William Park, Open Geometry Consulting, <opengeometry@y ahoo.ca>
Linux solution for data management and processing.

[Dennis Lee Bieber]

Re: Python code to replace shell scripts

Daven Nair fed this fish to the penguins on Thursday 11 December 2003
10:30 am:
[color=blue]
> I would like to know if Python supports codes similar to shell
> scripts:
>
> count=`ps -ef|grep "pattern"|w c -l`
> for count in `echo $count`[/color]

I suspect you would have to separate the `...` items, using something
like one of the popen() family, and capture the results, then process
those same results.

I'll speak blasphemy here (either that, or Tower of Babel polyglot <G>)

(o)REXX would be a bit more transparent (though I don't think IBM
makes it free to all -- you can get an "evaluation " copy for Linux). In
REXX, anything line that is not recognized as a REXX statement is
automatically passed to the current command processor (normally the
shell -- though the Amiga really took advantage of the ability to
change "command processor" making AREXX a scripting language for any
application that created an "AREXX port").

--[color=blue]
> =============== =============== =============== =============== == <
> wlfraed@ix.netc om.com | Wulfraed Dennis Lee Bieber KD6MOG <
> wulfraed@dm.net | Bestiaria Support Staff <
> =============== =============== =============== =============== == <
> Bestiaria Home Page: http://www.beastie.dm.net/ <
> Home Page: http://www.dm.net/~wulfraed/ <[/color]

[Alan Gauld]

Re: Python code to replace shell scripts

On 12 Dec 2003 01:58:23 GMT, William Park <opengeometry@y ahoo.ca>
wrote:
[color=blue][color=green]
> > count=`ps -ef|grep "pattern"|w c -l`
> > for count in `echo $count`
> > do
> > done
> > fi[/color][/color]

In this case you could change the style to a more slightly
more pythonic approach:

print len(os.popen('p s -ef|grep "pattern"').rea d().split())
[color=blue]
> In any case, although Python does something well, shell does most things
> better. (It's okey... I've got my helmet on.)[/color]

Shell is generally better at quickly gluing together existing
commands. But does so at a significant cost in machine resources
and often execution time. Python provides a different approach
that is generally better where the solution must be repeated
often or where no suitable set of commands already exists.

Alan G.
Author of the Learn to Program website

http://www.freenetpages.co.uk/hp/alan.gauld

[Cameron Laird]

Re: Python code to replace shell scripts

In article <va5oa1-c93.ln1@beastie .ix.netcom.com> ,
Dennis Lee Bieber <wlfraed@ix.net com.com> wrote:

[William Park]

Re: Python code to replace shell scripts

Alan Gauld <alan.gauld@bti nternet.com> wrote:[color=blue]
> On 12 Dec 2003 01:58:23 GMT, William Park <opengeometry@y ahoo.ca>
> wrote:[color=green]
> > In any case, although Python does something well, shell does most
> > things better. (It's okey... I've got my helmet on.)[/color]
>
> Shell is generally better at quickly gluing together existing
> commands. But does so at a significant cost in machine resources and
> often execution time. Python provides a different approach that is
> generally better where the solution must be repeated often or where no
> suitable set of commands already exists.[/color]

That is true, until you learn and program in shell.

--
William Park, Open Geometry Consulting, <opengeometry@y ahoo.ca>
Linux solution for data management and processing.

[Serge Orlov]

Re: Python code to replace shell scripts


"William Park" <opengeometry@y ahoo.ca> wrote in message news:brd7nv$264 kc$2@ID-99293.news.uni-berlin.de...[color=blue]
> Alan Gauld <alan.gauld@bti nternet.com> wrote:[color=green]
> > On 12 Dec 2003 01:58:23 GMT, William Park <opengeometry@y ahoo.ca>
> > wrote:[color=darkred]
> > > In any case, although Python does something well, shell does most
> > > things better. (It's okey... I've got my helmet on.)[/color]
> >
> > Shell is generally better at quickly gluing together existing
> > commands. But does so at a significant cost in machine resources and
> > often execution time. Python provides a different approach that is
> > generally better where the solution must be repeated often or where no
> > suitable set of commands already exists.[/color]
>
> That is true, until you learn and program in shell.[/color]

And that will be true again once you have handy module for gluing
together cli applications. Since Python is not popular among
system administrators, nobody was bothered to do it (yet?)

[Alan Gauld]

Re: Python code to replace shell scripts

On 12 Dec 2003 20:17:04 GMT, William Park <opengeometry@y ahoo.ca>
wrote:[color=blue][color=green]
> > often execution time. Python provides a different approach that is
> > generally better where the solution must be repeated often or where no
> > suitable set of commands already exists.[/color]
>
> That is true, until you learn and program in shell.[/color]

Well I've been programming Bourne and Korn shells for about 15
years now. But I still pick python for anything that needs a GUI
or has to run as a daemon or does heavy network calls. I'd also
use Python if I had to write a Web Browser or Word Processor or
Programming/Test environment.

In fact anything that needs more than a few hundred lines of
code. Shell is great for what its good at but orders of magnitude
slower and more resource hungry than Python for complex tasks.
Just think about how many processes get launched, the inefficient
text parsing, the nested shells etc. And as for data structure
support!

For sys admin type tasks, Shell is great, for applications its a
forced fit.

Alan g
Author of the Learn to Program website

http://www.freenetpages.co.uk/hp/alan.gauld

[Patrick TJ McPhee]

Re: Python code to replace shell scripts

[note follow-ups set to comp.lang.rexx]

In article <vtjp3e2bcihka4 @corp.supernews .com>,
Cameron Laird <claird@phaseit .net> wrote:

% There *are* open-source REXXs (even a mod_rexx!) which are
% alternatives to IBM's. Normally, at this point, I'd provide
% references to a couple;

Start with http://www.rexxla.org and look at the links page. I think
every implementation is referred to either there or at Cowlishaw's
rexx page.
--

Patrick TJ McPhee
East York Canada
ptjm@interlog.c om