use warnings;
use strict;

my @verzeichnis = (
    {
        vorname  => 'Peter',
        nachname => 'Bauer',
        alter    => 32,
    },
    {
        vorname  => 'Marie',
        nachname => 'Fink',
        alter    => 43,
    },
);

my $name = "Peter";

print join( " ", @{$_}{qw/vorname nachname alter/} ) . "\n" for @verzeichnis;

for my $person ( @verzeichnis ) {
    if ($person->{vorname} eq $name) {
        print "Peter gefunden\n";
        $person->{nachname} = "Bauer-Weider";
    }
}

print join( " ", @{$_}{qw/vorname nachname alter/} ) . "\n" for @verzeichnis;