We need to separate the problem into three parts:

1. The source of your data, and the encoding there
2. The Perl program and how the string is marked there
3. The output of your data, and the encoding there

In your first program, you have a source file that is plain ASCII. In the program, you hand Perl two octets that represent the UTF-8 encoding. So Perl thinks this string should have length 2, because it consists of two bytes and is a "Latin-1" string. When printing your data, you don't tell Perl that there should be anything special done, so Perl assumes you want Latin-1 as output format. Latin-1 means no modification to your string is made. Your console expects UTF-8 and the two bytes that Perl outputs happen to map to Eacute.

Here, adding a binmode STDOUT, ':encoding(UTF-8)'; should Perl tell that you want UTF-8 on output, and using my $string= decode('UTF-8', "\x{c3}\x{a9}"); to tell Perl that you want the string parts to be interpreted as UTF-8 should change the program to suit what you want.

In your second program, you have a source file that is UTF-8. In the program, you hand Perl two octets that represent the UTF-8 encoding, and tell Perl that the program source is UTF-8. So Perl thinks this string should have length 1, because it consists of two bytes and is an "UTF-8" string. When printing your data, you don't tell Perl that there should be anything special done, so Perl assumes you want Latin-1 as output format. So Perl converts your UTF-8 string to Latin-1 when printing it. Your console expects UTF-8 and the single byte that Perl outputs happens to be an invalid UTF-8 sequence.

Here, you only need to tell Perl that you want UTF-8 on output by using binmode on STDOUT.

The two modules you use expect Unicode input, but you hand them byte sequences. You want to use Encode::decode to decode them to real Unicode strings:

use Encode 'decode';
my $string= decode 'UTF-8', "\x{c3}\x{a9}";
...
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