use strict;
use warnings;

my $file = <<FILE;
1
2
3


FILE

open my $fIn, '<', \$file;
my $str = do {local $/; <$fIn>};
close $fIn;

print "1-->\n$str<--1\n";
$str =~ s/\n+\Z//;
print "2-->\n$str<--2\n";