Because this is Perl, There Is More Than One Way To Do It. Here is an array-less solution given your statement about how the folders are named:

for ( my $i = 1; $i <= 4; $i++ ) {
    my $dir_name = sprintf 'abc_%03d', $i;
    chdir $dir_name or die "Unable to change to $dir_name: $!";
    ...
    chdir '..';
}

But in real life I would probably use File::Find like everyone else.