#!/usr/bin/perl -l

#use strict;
use warnings;
use Digest::SHA1;

my $fname = $ARGV[0];
my $sha1;

open(IN, $fname) || die "can't open '$fname' for input: $!";
binmode IN;
$sha1 = Digest::SHA1->new;
$sha1->addfile(IN);
print $sha1->hexdigest;

open(IN, $fname) || die "can't open '$fname' for input: $!";
binmode IN;
$sha1 = Digest::SHA1->new;
$sha1->addfile(*IN);
print $sha1->hexdigest;

open(my $fhIN, $fname) || die "can't open '$fname' for input: $!";
binmode $fhIN;
$sha1 = Digest::SHA1->new;
$sha1->addfile($fhIN);
print $sha1->hexdigest;

system 'sha1sum', $fname;

##</code><code>##

$ ./840698.pl foo
e242ed3bffccdf271b7fbaf34ed72d089537b42f
e242ed3bffccdf271b7fbaf34ed72d089537b42f
e242ed3bffccdf271b7fbaf34ed72d089537b42f
e242ed3bffccdf271b7fbaf34ed72d089537b42f  foo