Re: Regex to match 20 chars of some digits followed by some spaces

[tachyon]

I can't see any good reason to use Parse::RecDescent to parse fixed width records. This would seem to be using a A-bomb to crack a walnut. Surely you would be better off to unpack the data into a structure and validate from there?

In addition to the examples above you can for fun autogenerate one that does the job you want - rather ugly but it does work.

for ( reverse 1..20 ) {
    $re .= sprintf "\\d{%d} {%d}|", $_, 20-$_;
}
chop $re;
$re = qr/^(?:$re)$/;
print $re, $/;

@tests = (
    '01234567890123456789', # OK
    '123                 ', # OK
    '123               ',   # NOK
    '123 123             ', # NOK
    '                    ', # NOK
    '123c                ', # NOK
);

for(@tests){
    print m/$re/ ? "'$_' #OK\n" : "'$_' #NOK\n"
}

__DATA__
(?-xism:^(?:\d{20} {0}|\d{19} {1}|\d{18} {2}|\d{17} {3}|\d{16} {4}|\d{
+15} {5}|\d{14} {6}|\d{13} {7}|\d{12} {8}|\d{11} {9}|\d{10} {10}|\d{9}
+ {11}|\d{8} {12}|\d{7} {13}|\d{6} {14}|\d{5} {15}|\d{4} {16}|\d{3} {1
+7}|\d{2} {18}|\d{1} {19})$)
'01234567890123456789' #OK
'123                 ' #OK
'123               ' #NOK
'123 123             ' #NOK
'                    ' #NOK
'123c                ' #NOK

[leriksen]

Not all the text I am parsing is fixed width, just this bit.

The rest is somewhat like this (deboned to protect client)

document : checkpoint address report(s?) doctrailer

report : report1 | report2 | report3 | ...

report1 : lt[100] report1_cost_centre(s?) lt[200]

report1_cost_centre : lt[300] report1_txn(s?) lt[400]

report1_txn : lt[500] lt[600] page_break(?) lt[700]

lt : "<LT$arg[0]>" lt_data

lt_data : /[^\\]*/ lt_end {$return = $item{__PATTERN1__}
...

but for 15 different reports, hundreds of lt records, lots of options, repeats and alternations.

[tachyon]

Ah that makes more sense. If you have to deal with fixed width records you may find this sub handy:

$str = 'first name       EOFlast name        EOFaddress field         
+     EOF';

my @rec_def = (
    [ 'first_name', 20 ],
    [ 'last_name',   20 ],
    [ 'address',    30 ],
);

sub parse_fixed_width {
    my ( $record, $rec_def ) = @_;
    my %struct;
    my $offset = 0;
    for my $rec(@$rec_def) {
        $struct{$rec->[0]} = substr $record, $offset, $rec->[1];
        $offset += $rec->[1];
    }
  return length($record) == $offset ? \%struct : '';
}

use Data::Dumper;
print Dumper parse_fixed_width( $str, \@rec_def );
__DATA__
$VAR1 = {
          'first_name' => 'first name       EOF',
          'address' => 'address field              EOF',
          'last_name' => 'last name        EOF'
        };