use strict;
use warnings;
use Time:HiRes qw( gettimeofday );

open ( my $fh, "<", "./something.txt" || die "! open $!\n";
my $stime = gettimeofday;
while (<$fh>)
{ }
print gettimeofday - $stime, "\n";
close $fh;

open ( $fh, "<", ".something.txt" || die "! open $!\n";
$stime = gettimeofday;
while (<$fh>)
{
      # do something is your actual code!
}
print gettimeofday - $stime, "\n";
close $fh;