enc-converter cp1252 < file.txt > file_utf8.txt
#or
   some-process | enc-converter shiftjis | some-utf8-process
#or a mix:
   some-process | enc-converter koi8-r > file_utf8.txt
   enc-converter iso-8859-1 < file.txt | utf8-process

##</code><code>##

#!/usr/bin/perl

use strict;

( @ARGV == 1 and $ARGV[0] =~ /^\w[-\w]+$/ and ! -t )
    or die "Usage: $0 inp-enc < file.inp-enc > file.utf8\n";

my $inp_enc = sprintf( ":encoding(%s)", shift );
binmode STDIN, $inp_enc;
binmode STDOUT, ":utf8";

print while (<>);

##</code><code>##

perl -MEncode -le 'print for(Encode->encodings(":all"))'

##</code><code>##

perl -CO -pe 'BEGIN{binmode STDIN,":encoding(cp936)"}' < file.txt > file.utf8