my $string = slurp($file1) . slurp($file2);

sub slurp {
    my $file = shift;
    open $fh, <, $file or do {
        warn "Failed to open $file for input: $!\n";
        return '';
    }

    local $/ = undef;
    return <$fh>;
    # $fh goes out of scope, file closed automatically
}