Date: Mon, 10 Sep 2001 11:03:41 -0400 (EDT) From: Adrian Filipi-Martin <adrian@ubergeeks.com> To: Peter Pentchev <roam@ringlet.net> Cc: Ulf Zimmermann <ulf@Alameda.net>, <hackers@FreeBSD.ORG> Subject: Re: Question about what programs to use in /etc/rc* Message-ID: <20010910102943.N36056-100000@lorax.ubergeeks.com> In-Reply-To: <20010910110537.A2053@ringworld.oblivion.bg>
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On Mon, 10 Sep 2001, Peter Pentchev wrote:
> On Sun, Sep 09, 2001 at 06:06:01PM -0400, Adrian Filipi-Martin wrote:
> > On Sun, 9 Sep 2001, Ulf Zimmermann wrote:
> >
> > > These are some examples strings:
> > >
> > > "dhcp"
> > > "dhcp media 10baseTX"
> > > "media 10baseTX dhcp mediaopt half-duplex"
> > >
> > > The following code will get me inside a if condition:
> > >
> > > if [ `expr "${ifconfig_args}" : '.*[Dd][Hh][Cc][Pp].*'` -ne 0 ]; then
> > >
> > > ....
> > >
> > > fi
> >
> > You do everything you need within sh. Someone else pointed out
> > that case/esac is your friend here. It was not quite complete. Here's
> > more complete example that will let you pair up the options and their
> > arguments if they take them.
> >
> > ifconfig_args="media 10baseTX dhcp mediaopt half-duplex"
> > set -- ${ifconfig_args}
> > while [ $# -gt 0 ]; do
> > op=$1
> > case ${op} in
> > [Mm][Ee][Dd][Ii][Aa])
> > op_arg=$2
> > shift
> > echo "op=media op_arg=${op_arg}"
> > ;;
>
> I don't like this. This second-guessing of ifconfig(8)'s arguments
> is prone to error - consider the case of a new keyword added to
> ifconfig(8).. And blindly discarding unrecognized keyword would
> not really work either - a new keyword might take an argument,
> the shell script has no way of knowing that, so it would skip
> the keyword and try to look at its argument as another keyword;
> what if a keyword takes a string argument of, oh, say, 'dhcp'? :)
Sorry, but my example was meant to be more featureful than
necessary and let you strip it down, sinice you needs wern't completely
clear. If you just want to test for a substring, try this instead:
case "${ifconfig_args}" in
*[Dd][Hh][Cc][Pp]*)
echo "we are using dhcp..."
;;
esac
>
> A ${args#dhcp} might work better, but there is a problem with it -
The pattern after the # is a regular glob pattern. You can use
${args#[Dd][Hh][Cc][Pp]} to deal with case.
You probably really meant to say '${args##*[Dd][Hh][Cc][Pp]*}'
which will collapse to a null string if 'dhcp' is in the string, or the
string is empty to begin with. With only a single # and no *'s, you will
not modify the string unless it is exactly "dhcp".
Sill I don't recommend this approach, since you need to test the
string twice, once before and once after the expansion. The case/esac
idiom is pretty common as well.
Adrian
--
[ adrian@ubergeeks.com ]
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