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

my @array = ("hallo", "du", "bist ja\n immer noch", "da");

print "'$_'\n" for @array;

my $i = $#array;
while ($i>=0) {
    my $count = $array[$i] =~ y/\n//;
    splice @array, $i, 1, split /\n/, $array[$i] if $count;
    --$i;
}

print "'$_'\n" for @array;