Dear perlmonks---this is an indirect followup question to my need to write a safe mini interpreter. I want to figure out how module Safe works. the problem is that I want web user A to enter questions that web user B should answer. I need to avoid web user A doing mischief. This is easier to explain with an example: 

#!/usr/bin/perl -w
use strict;
use Safe;

my $secret="my-password-should-never-be-shown\n";

## the following are lines that a web user could try to pass to my pro
+gram
my $_ = <<HEREDOC;
sub round { return sprintf("%.\$_[1]f", \$_[0]); } ; my \$in=rand(); m
+y \$answer=(\$in+log(10)); print "what is \$in+log(10)?\\n"; round(\$
+answer,3)  ## this should evaluate just fine
print \$secret;                                          ## yikes, sho
+uld be an error
system("ls")                                             ## yikes, sho
+uld be an error
`ls`                                                     ## yikes, sho
+uld be an error
open(FIN, ">", "really-bad-to-write-to-fs")              ## yikes, sho
+uld be an error
HEREDOC

foreach (split(/\n/, $_)) {
  print "\n----------------\nExecuting '$_'\n\n";

  # this executes everything blindly and is a really bad idea
  my $result=eval($_);
  print "UNSAFE '$_'\n\t\t-> ".($result||"undef")."\n\n\n";

  # this does not do what I had hoped it to do
  # I want the first line be executed, and all other lines to be trapp
+ed.
  my $compartment= new Safe;
  $result= $compartment->reval("$_");

  print "SAFE '$_'\n\t\t-> ".($result||"undef")."\n\n\n";
}

[download]

Unfortunately, my reval does not execute anything. is there a set of ops that are what I should open up to allow exactly and only what I used in the first line?

Advice appreciated.

In reply to use of Safe module by iaw4

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