use warnings;
use strict;

# iconv -f UTF-8 utf8.txt -t Latin9 -o latin9.txt
my ($ifile, $ienc) = ("utf8.txt",   "UTF-8");
my ($ofile, $oenc) = ("latin9.txt", "Latin9");
open my $ifh, "<:raw:encoding($ienc)", $ifile or die "$ifile: $!";
open my $ofh, ">:raw:encoding($oenc)", $ofile or die "$ofile: $!";
print $ofh do { local $/; <$ifh> };
close $ifh;
close $ofh;