extracting fields

extracting fields

[Dominic Mitchell]

I'm trying to extract stuff from a string in a similiar manner to cut(1)
and getting rather unstuck.  I'm sure that there's a simpler answer, but
I can't seem to find it.

I have the output of psql in an array:

    pg_tables=( "${(f)$( psql -At -c '\d' )}" )

Which gives an array of entries like these:

    % echo $pg_tables[0]
    public|book|table|dom

Now I'm interested in the table name which is the 2nd field.  But I
can't work out how.  I've been playing with things like this:

    % echo ${(@s:|:)pg_tables[2]}

But I can't figure out how to split the array and then subscript the
second word of that newly split array.  Any ideas on how I would do
this?

Thanks,
-Dom

Re: extracting fields

[Oliver Kiddle]

Dominic Mitchell wrote:
> I'm trying to extract stuff from a string in a similiar manner to cut(1)
> and getting rather unstuck.  I'm sure that there's a simpler answer, but
> I can't seem to find it.

> Now I'm interested in the table name which is the 2nd field.  But I
> can't work out how.  I've been playing with things like this:
> 
>     % echo ${(@s:|:)pg_tables[2]}

Zsh has no concept of two-dimensional arrays so you can't split every
element of an array and expect indexing tow work on each element like
that. You would have to have a for loop for each array element.

Alternatively, if it is is the second field you want, you can
probably do:

   ${${pg_tables#*|}%%|*}

Oliver

Re: extracting fields

[James Devenish]

In message <25039.1072086714@gmcs3.local>
on Mon, Dec 22, 2003 at 10:51:54AM +0100, Oliver Kiddle wrote:
> Dominic Mitchell wrote:
> Zsh has no concept of two-dimensional arrays so you can't split every
> element of an array and expect indexing tow work on each element like
> that. You would have to have a for loop for each array element.
> 
> Alternatively, if it is is the second field you want, you can
> probably do:
> 
>    ${${pg_tables#*|}%%|*}

Yes, I think he might simply have been overlooking the ${...${...}...}
construct. For example:

> Dominic Mitchell wrote:
> % echo $pg_tables[0]
> public|book|table|dom
[...]
> Now I'm interested in the table name which is the 2nd field.

Selecting "column c" of "record r" could be like this:
% integer r=1 c=2; echo ${${(s:|:)pg_tables[$r]}[$c]}

Re: extracting fields

[Dominic Mitchell]

On Mon, Dec 22, 2003 at 10:51:54AM +0100, Oliver Kiddle wrote:
> Dominic Mitchell wrote:
> > I'm trying to extract stuff from a string in a similiar manner to cut(1)
> > and getting rather unstuck.  I'm sure that there's a simpler answer, but
> > I can't seem to find it.
> 
> > Now I'm interested in the table name which is the 2nd field.  But I
> > can't work out how.  I've been playing with things like this:
> > 
> >     % echo ${(@s:|:)pg_tables[2]}
> 
> Zsh has no concept of two-dimensional arrays so you can't split every
> element of an array and expect indexing tow work on each element like
> that. You would have to have a for loop for each array element.

Aha, thank you.  I was thinking that I could do it in a for loop.

> Alternatively, if it is is the second field you want, you can
> probably do:
> 
>    ${${pg_tables#*|}%%|*}

That's perfect.  Thank you very much.  Funnily enough, I started going
down that line, until I realised I was interested in the second field,
not the first.  I got the %%|* bit, but didn't make the leap to
stripping the first field.

Many thanks,
-Dom