while(read $handle, my $buffer, 57){
        $b64 .= encode_base64($buffer); # default trailer "\n"
}

use strict;

use File::Slurp qw(write_file read_file);
use MIME::Base64;
use Data::Dumper;

write_file( 'base64_test.txt', <<'END_TEXT' );
Beispielstext für Base64
aaaaaaaaaaaa
bbbbbbbbbbbb
cccccccccccc
END_TEXT

my $encoded = encode_base64( read_file('base64_test.txt') );
print Data::Dumper->Dump( [ $encoded, decode_base64($encoded) ], [ qw/encoded decoded/ ]  );