On Wednesday 03 May 2006 03:29 am, D. Bolliger wrote:
> tom arnall am Sonntag, 30. April 2006 22.57:
> [...]
>
> > OK, the above stuff is all good. And now I have another question. The
> > following code:
> >
> > #!/usr/bin/perl -w
> > use strict;
> > use Tie::Scalar;
> > use DB_File;
> >
> > my ($f,@f,%f);
> >
> > tie %f, "DB_File", "file.txt" ;
> > $f{'a'}='aaaa';
> > untie %f;
> > %f = ();
> > tie %f, "DB_File", "file.txt" ;
> > @f = %f;
> > print "
> > @f";
> >
> > tie $f,"Tie::StdScalar","scalar.txt","\$f";
> > $f = 'a';
> > untie $f;
> > $f = '';
> > tie $f,"Tie::StdScalar","scalar.txt","\$f";
> > print "
> > $f
> > ";
> >
> >
> > produces:
> >
> > a aaaa
> > scalar.txt
>
> Hello tom
>
> Since I'm not enough experienced with tie'ing, I can only provide a very
> basic
>
> and hopefully correct answer:
> > shouldn't the second line be 'a', i.e., shouldn't 'StdScalar' work along
> > the lines of the code handling the tied hash variable?
>
> When you look at the source of the Tie::StdScalar package, you can see that
> the TIESCALAR method just blesses a reference to the string 'scalar.txt' to
> the Tie::StdScalar class, FETCH gets the string, and STORE sets it.
> (further arguments, as "\$f" - the same as '$f' btw - above, are ignored).
>
> The class does not know that you want to treat 'scalar.txt' as a filename,
> and therefore no persistent storage is involved, and thus the change done
> by $f = 'a' is lost after untie'ing.
>
> > if this is not true,
> > is there a module that does work similarly to 'DB_File', i.e., one that
> > enables tie-ing a text file to a scalar?
>
> I don't know. Maybe you want to look at Tie::File to access the lines of a
> disk file via an array, search on search.cpan.org, or write your own
> subclass to get the desired behaviour (I can't see much sense in using
> Tie::StdScalar directly).
>
> Dani
I should have made clear my basic purpose in trying to use file-tied scalars.
I wanted to put a very large file (.5GB) into a scalar in a way that has the
system keeping most of the data on disk and putting in physical memory only
what I need at any given moment. The problem statement is s'thing like
$bigGulp = ` cat bigFile.txt`
in order to do multi-line regexing. My first try with the application froze
the rest of the system. I then configured linux with less virtual memory, and
got an 'out of memory' error. i then turned -- naively it seems now --
to 'tie' etc. But after finding an implementation module for a file-tied
scalar, I don't see now a solution via this route either, so I am resigned to
using s'thing along the lines of File::Stream.
(off topic for this list, but here it is anyhow: why can't you deal with this
type of problem using linux virtual memory?)
Hoping someone has some magic,
Tom Arnall
north spit, ca
--
thanks,
tom arnall
north spit, ca
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