Re^2: Google has failed me! Using pack and substr for fixed width file output

Hi Roboticus,

It's good to know that there are other fixed width hackers out there :-)

I did use pack for a while and I did find it easier and faster to create a solution using it. But I had a problem explaining how to match up the fields with the pack format to the supporting teams. They couldn't seem to get their heads around it. So, for me, I got called less if I developed the solution using substr coz (I suppose) it was easier for the support bods to conceptualise the approach.

Thanks though, it's nice to know I'm <drum roll please> part of the <ahem> pack. Thank you very much, I'm here til Thursday - try the fish.

Cheers, Jake

Comment on Re^2: Google has failed me! Using pack and substr for fixed width file output

Replies are listed 'Best First'.
Re^3: Google has failed me! Using pack and substr for fixed width file output by AnomalousMonk (Archbishop) on Apr 09, 2014 at 09:13 UTC
There are all kinds of interesting games you can play with pack, and it should be easy to encapsulate your solution in a function (with lotsa validation) so that maintainers only see data. See below. Note that the `@` `pack` template specifier fills with nulls, so if you want space-filling, you need the `$packed =~ tr{\000}{ };` statement. Note also that `@` is absolute, so maybe play around and see, e.g., what happens if the `date` offset is set to 1 or 2. c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le "use constant ORDER => qw(date client_id info); ;; my %o_l = ( date => { qw(off 0 len 6 field 040814) }, client_id => { qw(off 6 len 8 field WayTooMuchClientID) }, info => { qw(off 20 len 7 field G1APD) }, ); ;; my $fields = join ' ', map qq{\@$o_l{$_}{off} A$o_l{$_}{len}}, map { exists $o_l{$_} or die qq{bad '$_'}; $_; } ORDER ; ;; my $packed = pack $fields, map $o_l{$_}{field}, ORDER; $packed =~ tr{\000}{ }; print 'packed len ', length $packed, qq{ '$packed'}; ;; my $total = 30; die 'truncation!' if length($packed) > $total; my $line = pack qq{A$total}, $packed; print 'total len ', length($line), qq{ '$line'}; ;; dd \$line; " packed len 27 '040814WayTooMu G1APD ' total len 30 '040814WayTooMu G1APD ' \"040814WayTooMu G1APD " [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^3: Google has failed me! Using pack and substr for fixed width file output
by AnomalousMonk (Archbishop) on Apr 09, 2014 at 09:13 UTC

There are all kinds of interesting games you can play with pack, and it should be easy to encapsulate your solution in a function (with lotsa validation) so that maintainers only see data. See below.

Note that the @ pack template specifier fills with nulls, so if you want space-filling, you need the
$packed =~ tr{\000}{ };
statement. Note also that @ is absolute, so maybe play around and see, e.g., what happens if the date offset is set to 1 or 2.

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"use constant ORDER => qw(date  client_id  info);
 ;;
 my %o_l = (
   date      => { qw(off  0  len 6  field 040814)             },
   client_id => { qw(off  6  len 8  field WayTooMuchClientID) },
   info      => { qw(off 20  len 7  field G1APD)              },
   );
 ;;
 my $fields =
   join '  ',
   map  qq{\@$o_l{$_}{off} A$o_l{$_}{len}},
   map  { exists $o_l{$_} or die qq{bad '$_'};  $_; }
   ORDER
   ;
 ;;
 my $packed = pack $fields, map $o_l{$_}{field}, ORDER;
 $packed =~ tr{\000}{ };
 print 'packed len ', length $packed, qq{ '$packed'};
 ;;
 my $total = 30;
 die 'truncation!' if length($packed) > $total;
 my $line = pack qq{A$total}, $packed;
 print 'total  len ', length($line), qq{ '$line'};
 ;;
 dd \$line;
"
packed len 27 '040814WayTooMu      G1APD  '
total  len 30 '040814WayTooMu      G1APD     '
\"040814WayTooMu      G1APD     "
[download]

[reply]
[d/l]
[select]