#!/usr/bin/perl -CSDA

use utf8;
use strict;
use warnings;
use Carp;

my $whole_file = do {
        open my $f, "<", "mydata.txt" or croak "can't open mydata.txt: $!";
        local $/;
        my $x = <$f>; 
        $! and croak "can't read mydata.txt: $!";
        close $f or croak "can't close mydata.txt: $!";
        $x;
};      

print "data from file is: $whole_file\n";