Hi, Carl--
Using the input record separator for fixed length records does work,
just as the the fine manual says. However I left out one critical
character in the code I sent last night-- the magic happens when $/ is
assigned a _reference_ to an integer value, as below.
use strict;
{
local $/;
$/ = \4; # must be reference
open IN, "test.dbx" or die "bad open: $!\n";
binmode IN;
my $i = 0;
my $n = 0;
while(<IN>) {
$n = unpack("I", $_);
printf "%02d. %08X\n", $., $n;
$i++;
last if $i > 10;
}
close IN;
}
This behavior is documented in Wall, et al: _Programming perl, third
ed_, pg 666 (so I guess its sort of black magic). The above bit also
shows that $. does work in this mode.
--Will
Carl Jolley wrote on Thursday, February 21, 2002 1:35 PM
Subject: Re: pack
> On Thu, 21 Feb 2002, Will W wrote:
>
> > Sisyphus wrote on Wednesday, February 20, 2002 5:16 PM
> > Subject: Re: pack
> >
> >
> > > Thanks Will ..... now for a replacement for '$.' ?? :-))
> > > (Of course it's dead easy to craft one's own incremental counter.)
> > <snip>
> > > > > while (1) {
> > > > > sysread(READ, $ret, 4);
> > <snip>
> >
> > Everyone's fascination with sysread() got me to poking around in the
> > camel and cookbook a bit-- and I still can't see the advantage here
of
> > doing a low-level system call over using read(), which is generally
> > buffered for optimal efficiency on whatever system your using.
sysread()
> > makes a lot of sense on a port, but on a disk file I'm not seeing
the
> > why of it-- maybe someone will enlighten me.
> >
> > Anyway while poking around I ran yet another way to do the job which
> > really looks kind of interesting:
> >
> > [untested-- too much chianti on board to try it tonight]
> >
> > open IN, $somefile or die "gasp! $somefile! Uh! $!\n";
> > binmode IN;
> > { # closure for local
> > local $/;
> > $/ = 4; # see the camel
> > while (<IN>) { # Should work, but wait there's more
> > $n = unpack("I", $_); # may have mangled the syntax
> > $line = $.; # Yep, you get this too!
> > } # endwhile
> > } # end localizing closure
> >
> > Now its time for bed. Spent the day developing a single subroutine
I'm
> > calling recurse_the_kids because its so dang descriptive of my
feelings
> > about its convolutions. And I'm out of chianti anyway.
> >
>
> By doing a: $/ = 4; all you've done is to set the input record
seperator
> character to a character "4". That will mean that if your file
contained
> the characters 0123456789 that doing a <> on that file would result
> in two records being read. The first one would contain 01234 and the
> second (and last) one would contain 56789. By default, $/ is the
> new-line character. Changing it tells perl that a different character
> should be used to separate records. If you set $/ to undefined, then
> the first <> operation on the filehandle will read all the characters
> it contains. Setting $/ has no effect if you are using read() or
> sysread() to access the data since those function read a specified
> number of characters not a record.
>
>
> **** [EMAIL PROTECTED] <Carl Jolley>
> **** All opinions are my own and not necessarily those of my employer
****
> k
>
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