#!/usr/bin/perl
use warnings;
use strict;

my $file = 'addressbook.ldif';

print "Eingabe Name : ";
my $regex = <>;

chomp( $regex );
$regex = qr/$regex/i;

open( my $fh, '<', $file ) or die $!;

while( <$fh> ) {
  print if /$regex/;
}