#!/usr/bin/perl -T

use strict;
use Encode;

%ENV = (
    PATH => '/usr/bin'
);

open my $filehandle, "< :raw", "test.bin" or die $!;
my $word = readline $filehandle;

eval { $word = decode( "utf8", $word, Encode::FB_CROAK ) };

if ( $@ ) {
    warn "unusable input from test.bin\n";
}
else {
    my ($untainted) = $word =~ /^(\w+)$/;

    if ($untainted) {
    # It passed the regex, so it is "safe".
	system "echo $untainted";
    }
}