open (my $fh, '<', $input_file) or die "Can't read from '$input_file': $!";

while (<$fh>)
{
    my ($var1, $var2, $var3, $var4) = split (' ', $_);
    #Call to subroutine1 (by passing $var1, $var2, $var3, $var4) which calls subroutine2, which calls subroutine3.
}