Peamasii:

You mean something like this?

my %files = map { $_=>undef } ('part1.txt', 'part2.txt', 'part3.txt');
while ( my $fl=1 ) {
    for (keys %files) {
        my @t=stat $_;
        if ($t[9]>$files{$_}) {
            $files{$_}=$t[9];
            $fl=0;
        }
    }
    unless ($fl) {
        $fl = join(" ", "cat", keys %files);
        `$fl`;
    }
}
[download]

Untested, yadda, yadda.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Depending on platform and whether you want to poll for changes or be notified by event, you might want to look into File::Monitor, File::Monitor::Simple, Linux::Inotify2, Win32::ChangeNotify (and a couple of more referenced from there).

Thank you both for your answers, will look into doing it one of these ways.