#!/usr/bin/perl

use strict;
use warnings;

my $text = join '', (<DATA>);
my @match = $text =~ /^10.*\r?\n20.*\r?\n01.*$/mg;
s/\r?\n/---/g and print for @match;

__DATA__
01|1-123-878|Musterfrau
01|1-010-123|Muster
01|1-051-543|Mayer
20|2-123-452|Bauer
01|2-453-345|Huber
10|1-123-134|Max Mustermann
20|1-456-789|Peter Huber
01|1-457-123|Max Mayer

#!/usr/bin/perl

use strict;
use warnings;

my $memory = { lastcode => '', code => '', number => '', name => '' };

while(my $entry = <DATA>)
{
        chomp $entry;

        my ( $code, $number, $name ) = split /\|/, $entry;
        if ( $code eq '10' )
        {
                $memory = {
                        %$memory,
                        code => $code,
                        number => $number,
                        name => $name,
                };
        }
        else
        {
                if( $code eq '20' and $memory->{code} eq '10' )
                {                       
                        print join("|", map { $memory->{$_} } qw/code number name/) . " $entry\n"
                                unless cmp_memory( $number, $name);
                }
                elsif ( $code eq '01' and $memory->{code} eq '10' && $memory->{lastcode} eq '20' )
                {
                        print "$entry\n"
                                unless cmp_memory( $number, $name);
                }
        }
        $memory->{lastcode} = $code;
}

sub cmp_memory {
        my ( $number, $name ) = @_;
        return $number eq ( $memory->{number} || '' ) && $name eq ( $memory->{name} || '' );
}

__DATA__
01|1-123-878|Musterfrau
01|1-010-123|Muster
01|1-051-543|Mayer
20|2-123-452|Bauer
01|2-453-345|Huber
10|1-123-134|Max Mustermann
20|1-456-789|Peter Huber
01|1-457-123|Max Mayer

#!/usr/bin/perl
# vi:ts=4 sw=4 et:
use strict;
use warnings;

#http://board.perl-community.de/thread/12073/#MSG7

#> global variables
#> ----------------------------------------------------------------------------

my $last_num = undef;

#> main script
#> ----------------------------------------------------------------------------

while ( my $line = <DATA> ) {

    chomp $line;

    if ( $line =~ m{^\s*$} ) {

        print "--8<--\n";
        next;
    }

    my ( $code, $num, $name ) = split /\|/, $line;

    if ( defined $last_num ) {

        if ( $code ne '01' and $num ne $last_num ) {

            printf "%s|%s|%s\n", $code, $num, $name;
        }
    }

    $last_num = $num;

}

#> sub routines
#> ----------------------------------------------------------------------------

__DATA__
20|2-114-560|Mayer
01|2-114-560|Mayer

01|2-010-708|Huber
01|2-011-044|Bauer

10|2-147-169|Mayer
20|2-147-554|Bauer
01|2-147-695|Huber

10|2-147-169|Mayer
20|2-147-554|Bauer
30|2-148-554|Muster
01|2-147-695|Huber