Re: ifs substitution, how should it work?

Re: ifs substitution, how should it work?

[Russ Cox]

Introducing contexts where singleton lists
and strings are not identical seems a very bad idea.
Then you have to explain that in general they
are but ifs isn't; and what if save ifs away
to another variable and then restore it?
What does "x=(abc); ifs=$x" do?

If you want basename, why not use basename or sed or awk?

Russ

Re: ifs substitution, how should it work?

[Tim Goodwin]

> i wanted
> x = asd
> and
> y = (asd)
> to mean that x and y where not identical.

No, no, no.  There is just one data type in rc: a list of strings.  You
might sometimes think you've got a string, but you haven't: you've got a
list with one element.

Now, when ifs is used, the list of strings that it holds is interpreted
as a set of characters.  I agree with you that the documentation should
be a bit clearer on this point: the man page doesn't seem to mention
anywhere what happens when ifs is a more-than-one element list.

Tim.

Re: ifs substitution, how should it work?

[Bengt Kleberg]

> From: "Russ Cox" <rsc@plan9.bell-labs.com>
> Introducing contexts where singleton lists
> and strings are not identical seems a very bad idea.

I agree about the context bit. ie, lists and strings should be (or not be) identical in all contexts.
it is just that I thought that they should not be identical.

i wanted
x = asd
and
y = (asd)
to mean that x and y where not identical.


Best Wishes, Bengt
===============================================================
Everything aforementioned should be regarded as totally private
opinions, and nothing else. bengt@softwell.se
``His great strength is that he is uncompromising. It would make
him physically ill to think of programming in C++.''

Re: ifs substitution, how should it work?

[Bengt Kleberg]

> From: Tim Goodwin <tjg@star.le.ac.uk>
> > ; x = ``(abc) {cmd...}
> > ; echo $x => 1a2b3 4c5

> If you want awk, you know where to find it.  :-)

Yes, but I had this little problem and suddenly realised that the mysterious 
``(abc) {cmd...}
actually might be used for something! I have never used it before.

> I don't think anything more complicated than single character field
> seperators belongs in a shell: particularly not rc.

OK. Would you consider making ``(abc)
a parse time error? only allow ifs=asd, or ifs=( a s d ), not ifs=(asd) too.
Or, as with the confusing

if ( {}  && {} ) {cmd...}
vs
if ( () && () ) {cmd...} 

document it.

> What's the actual problem you're trying to solve?

split a filename into directory, filename and suffix. the suffix should be allowed to have more than 1 character.
the idea is to make the previously emailed base_name function (made by Carlo Strozzi <carlos@linux.it>)
more like the os utility basename.


Best Wishes, Bengt
===============================================================
Everything aforementioned should be regarded as totally private
opinions, and nothing else. bengt@softwell.se
``His great strength is that he is uncompromising. It would make
him physically ill to think of programming in C++.''

Re: ifs substitution, how should it work?

[Tim Goodwin]

> ; x = ``(abc) {echo -n 1a2b3abc4c5}
> ; echo $x => 1a2b3 4c5

If you want awk, you know where to find it.  :-)

I don't think anything more complicated than single character field
seperators belongs in a shell: particularly not rc.

What's the actual problem you're trying to solve?

Tim.

Re: ifs substitution, how should it work?

[Bengt Kleberg]

> From: Byron Rakitzis <byron@rakitzis.com>
> So,
> 	ifs='abc'
> and
>	ifs=(a b c)
> should accomplish the same thing.
> Isn't that what you want?

No. I wanted ifs = (abc)
Ie, 
; x = ``(abc) {echo -n 1a2b3abc4c5}
; echo $x => 1a2b3 4c5

This is (IMHO) better, but I presume that there is too much code out there
that depends upon ifs='abc' beeing equal to ifs=(abc).
What if I volunteered to fix everybody elses code for them (provided that they send it to me :-)


Best Wishes, Bengt
===============================================================
Everything aforementioned should be regarded as totally private
opinions, and nothing else. bengt@softwell.se
``His great strength is that he is uncompromising. It would make
him physically ill to think of programming in C++.''

Re: ifs substitution, how should it work?

[Byron Rakitzis]

> From: Bengt Kleberg <bengt@softwell.se>
> Subject: Re: ifs substitution, how should it work?
>
> Re: ifs substitution, how should it work?
>
> > What would you expect
>
> >     ; ifs=(' ' '<tab>' '
> '
>
> > to do (where `<tab>' represents a literal tab)?
>
>
> I had but seen code with lists as ifs arguments, and therefore thought
> that rc was using lists.
> Ie, I would have written it as:
>
> ; ifs=(' ' '<tab>' '
> ')
>
> Would it create much trouble to change rc :-)

I am not sure what the problem is...

At the moment rc scans ifs as a list and as a sequence of characters.
i.e., the implementation is as follows:

[from glom.c:bqinput]

        memzero(isifs, sizeof isifs);
        for (isifs['\0'] = TRUE; ifs != NULL; ifs = ifs->n)
                for (s = ifs->w; *s != '\0'; s++)
                        isifs[*(unsigned char *)s] = TRUE;

So,

	ifs='abc'

and

	ifs=(a b c)

should accomplish the same thing.

Isn't that what you want?

Byron.

Re: ifs substitution, how should it work?

[Bengt Kleberg]

Re: ifs substitution, how should it work?

> What would you expect

>     ; ifs=(' ' '<tab>' '
'

> to do (where `<tab>' represents a literal tab)?


I had but seen code with lists as ifs arguments, and therefore thought
that rc was using lists.
Ie, I would have written it as:

; ifs=(' ' '<tab>' '
')

Would it create much trouble to change rc :-)


Best Wishes, Bengt
===============================================================
Everything aforementioned should be regarded as totally private
opinions, and nothing else. bengt@softwell.se
``His great strength is that he is uncompromising. It would make
him physically ill to think of programming in C++.''

Re: ifs substitution, how should it work?

[Tim Goodwin]

> (i have failed utterly to understand the simple rc syntax before, so
> presumably I only need a friendly explanation as to why they must be
> the same :-)

I bet you don't even need an explanation :-).  What would you expect

    ; ifs=' <tab>
    '

to do (where `<tab>' represents a literal tab)?

I don't know why Duff didn't make $ifs an rc list, but it remains
in rc as it was in Bourne: a string treated as a list of individual
characters.

Tim.

ifs substitution, how should it work?

[Bengt Kleberg]

Greetings,

I thought that these two expression would produce different output
; x = ``( a b c ) {echo -n 1a2b3abc4}
; echo $x
1 2 3 4

and then
x = ``( abc ) {echo -n 1a2b3abc4}
; echo $x
1 2 3 4

Obviously they do not, but since I was expecting
1a2b3 4
in the last case I wonder if this similarity is 'the real thing'?

(i have failed utterly to understand the simple rc syntax before, so presumably I only need
a friendly explanation as to why they must be the same :-)


Best Wishes, Bengt
===============================================================
Everything aforementioned should be regarded as totally private
opinions, and nothing else. bengt@softwell.se
``His great strength is that he is uncompromising. It would make
him physically ill to think of programming in C++.''