package X;

while(<DATA>){ print "X:".$_ }
#close(DATA);

sub check_data { return defined fileno(DATA) }

1;
__DATA__
1
2
3

##</code><code>##

package Y;

while(<DATA>){ print "Y:".$_ }
#close(DATA);

sub check_data { return defined fileno(DATA) }

1;
__DATA__
10
20
30
40
50
60

##</code><code>##

# main 
use lib '.';
use strict;
use warnings;
use X;
use Y;

warn "hehh";

print "X opened: ".X::check_data()
 ."\n"."Y opened: ".Y::check_data()
 ."\n";

##</code><code>##

X:1
X:2
X:3
Y:10
Y:20
Y:30
Y:40
Y:50
Y:60
hehh at x.pm line 7, <DATA> line 6.
Y opened: 1
Y opened: 1