I have a directory of data files I wanted to read line-by-line simply. You can loop through each file, open a filehandle, process the lines, close the filehandle, but that can be repetitive. Perl has a unique mechanism where it will iterate across all the files in the @ARGV array automatically. You can fake out the @ARGV array with your own list of files and then iterate accordingly:

local @ARGV = sort(glob("/tmp/data/*.txt"));

# Special ARGV filehandle reads all the files sequentially
while (my $line = readline(ARGV)) {
    print $line;
}