netdev - Re: iproute2 / question: returncode when query a match

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Date:	Fri, 26 Jun 2015 15:30:49 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Bastian Bittorf <bittorf@...ebottle.com>
Cc:	netdev@...r.kernel.org, Vadim Kochan <vadim4j@...il.com>
Subject: Re: iproute2 / question: returncode when query a match

On Fri, 26 Jun 2015 09:31:45 +0200
Bastian Bittorf <bittorf@...ebottle.com> wrote:

> * Vadim Kochan <vadim4j@...il.com> [15.06.2015 18:36]:
> > > root@box:~ ip route list exact '0.0.0.0/8'
> > > root@box:~ echo $?
> > > 0
> > > 
> > > i expected an RC of != 0 when there is no match.
> > > is this by design?
> > > 
> > > root@box:~ ip -V
> > > ip utility, iproute2-ss4.0.0-1-openwrt
> > 
> > I think that RC != 0 only in case error happened, but may be its good
> > idea to add such behaviour or add option to consider ret code
> > if there is no results ?
> 
> ofcourse this is only useful for scripting:
> 
> # ip route list exact '0.0.0.0/8' || do_some_action
> 
> instead of the now used construct:
> # [ -n "$( ip route list exact '0.0.0.0/8' )" ] || do_some_action
> 
> i'am sure there are other queries, where this also
> makes sense. there are 2 possible ways for implementing this IMHO:
> 
> introduce a commandlineswitch like --pedantic
> or just always throw an error 1 when there is no match like this:
> 
> root@box:~ echo foo | grep bar
> root@box:~ echo $?
> 1
> 
> more opinions about that?
> 
> bye, bastian

Exit codes for ip route are already used to handle errors.
See current man page.

If you want to handle both errors and no match, the scripting tricks
to look for empty output are better.

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