use strict;

my @all_files = </export/home/*_01day>;
   # angle brackets around a bareword path pattern  returns all matching file names

my %macs_found;

for my $path ( @all_files ) {
    my $file = $path . ":";
    $file =~ s{.*/}{:};  # now it's ":*_01day:"
    unless ( open( FILE, $path )) {
        warn "open failed on $path: $!\n";
        next;
    }
    while (<FILE>) {
        chomp;
        $macs_found{$_} .= $file unless $macs_found{$_} =~ /$file/;
    }
    close FILE;
}

# Now for each mac value, see how many files had it:

my $nfiles = scalar @all_files;
for my $mac ( sort keys %macs_found ) {
    if ( split( /::/, $macs_found{$mac} ) == $nfiles ) {
        print "$mac found in all $nfiles input files\n";
    }
}