Re: Help with fixed columns

On Wed, 04 Feb 2004, [email protected] wrote:

> I'm not sure if the whitespace counts carried over accurately in the
> e-mail, so my answer is partly a guess.  Parse::RecDescent is likely
> overkill though since of a few regexes applied as follows would
> suffice:
> 
> ===========================
> while(<STDIN>) {
>      chomp;
>      if(/^(\d{2})/gc) {
>          my $size = $1;
>          my @fields = /(.{$size})/gc;
>          print join(';', @fields), "\n";
>      }
>}

While I agree that Parse::RecDescent is probably overkill for this
job, I think regular expressions are also an inefficient solution for
fixed-length fields.  unpack() is, I think, the best solution (I find
substr() a lot less elegant in this case).

perldoc -f unpack

perl -MData::Dumper -e'print Dumper(unpack("A2 A2 A1", "hello"))'
$VAR1 = 'he';
$VAR2 = 'll';
$VAR3 = 'o';

Bill McCormick can select the appropriate unpack template based on a
hash lookup, for instance.  There's no need to match a number if 0 is
an invalid ID, you can just get the numeric context of the data:

$data = "10 field1 field2"; # for example
$id = $data + 0; # numeric context of $data

%templates = ( 0 => undef, 10 => "A5 A8 A9" ); # for example

$entry = unpack($templates{$id}, $data)
 if exists $templates{$id} && defined $templates{$id};

Sorry for the off-topic post, I just thought this might be helpful...

Thanks
Ted