[9fans] rc niggle, and proposed fix

[9fans] rc niggle, and proposed fix

[erik quanstrom]

ifs seems a holdover.  it's only ever used in `{} yet
it's a global inherited variable.  so it's easy to write
a script that assumes that ifs is set to the default.

a seemingly useful way to use ifs is as a local.  one
would think
	ifs=burble fu=`{bar}
would be sensible, but unfortunately this is doubly
wrong.  the assignments aren't local since there is
no command, just assignments.  this could be fixed by
	ifs=burble {fu=`{bar}}
but if bar is a script and isn't quite careful about
setting ifs before using it, bar will produce surprises.

it seems to me the easiest way to fix this is to introduce
a new form of `{} that allows the splitting characters
to be specified without fidding ifs, so
	fu=`burble {bar}
(fortunately rc didn't adopt byron's `word form.)
this has the advantage of not breaking anything while
still allowing one to write scripts more precisely.

the code is contrib quanstro/rchistory.  enjoy.

- erik

Re: [9fans] rc niggle, and proposed fix

[Charles Forsyth]

>ifs seems a holdover.  it's only ever used in `{} yet
>it's a global inherited variable.  so it's easy to write
>a script that assumes that ifs is set to the default.

i wonder if it's best left alone. it isn't detailed enough
to crack many plausible formats, for instance full csv.
if i needed one of those formats to feed into a `{} i'd add
a filter that converted to quoted & space-separated fields
that the default ifs would crack.

Re: [9fans] rc niggle, and proposed fix

[erik quanstrom]

On Wed Jun 22 12:00:07 EDT 2011, forsyth@terzarima.net wrote:
> >ifs seems a holdover.  it's only ever used in `{} yet
> >it's a global inherited variable.  so it's easy to write
> >a script that assumes that ifs is set to the default.
> 
> i wonder if it's best left alone. it isn't detailed enough
> to crack many plausible formats, for instance full csv.
> if i needed one of those formats to feed into a `{} i'd add
> a filter that converted to quoted & space-separated fields
> that the default ifs would crack.

yes.  rc splitting is limiting, and i'd love a better idea.
my argument isn't that this is great, but that it is better.
like the type system in c.  :-)

as a lame example, ...

the word splitting in `{} is good enough to handle many
formats, including splitting by naïve word and line.

at one point i rewrite iwhois to handle other
registrars than network solutions, and it was very handy
to have these functions

	fn split{
		ifs=. x=`{echo -n $*} echo $x
	}

	fn permute{
		while(! ~ $#* 0){
			echo $*|sed 's/ /./g'
			shift
		}
	}

to walk through whois databases for names like x.y.example.com.au
to find the registered name without having a database of which database
operates at which level.

- erik