What are the ways to read contents of a file in Perl?

open (FH, "< io.txt") or die $!;
while(<FH>)
{
 print $_;
}
close(FH);

or

use Fcntl;

sysopen(FH, "io.txt", O_RDONLY) or die $!;
while(<FH>)
{
 print $_;
}
close(FH) || die "Couldn't close file properly.";

or

use IO::File;

my $FH = new IO::File("io.txt", "r") or die "could not open $filename : $!\n";
while ($line = $FH->getline())
{
   print $line;
}
$FH->close();