$ perl -MO=Deparse,-p,-q
# . . . your first example here
^D
unless (open(my $fh, '<f1.txt')) {
    do {
        print(STDERR "can't open <f1.txt, but nevermind, I'll try f2.txt\n");
        (open($fh, '<f2.txt') or die(q[still can't...]));
    };
}
print(<$fh>);