Since use happens at compile-time, %hash is empty. That's not really a problem here, since keys %hash is treated as a literal string by qw//. Since you're not importing what you think you're importing, your eval fails. Since you're not checking $@, you don't know this.

I'd really rather write:

but if you really want to get your way to work, here's a start. I'm not sure if Env returns lvalue subs, though:

#!/usr/bin/perl -w

use strict;

my %hash;
BEGIN
{
    $hash{APP_DIR} = "/usr/vendor/app/version/";
    $hash{TMP_DIR} = "/usr/tmp/";
    $hash{PROJ_DIR} = "/usr/people/userid/app/";
    $hash{APP_LOCATION} = "/usr/vendor/app/version/bin/";
}

use Env (keys %hash);

foreach my $key (keys %hash) {
    eval("$key=\"$hash{$key}\"");
    print "Eval error '$@'\n" if $@;
    print "  $key=$hash{$key}\n";
}

system("printenv");
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