The right hand side of s/// does not execute code unless you use the "e" modifier.

Would you bet your money on that statement? I would not.

You are right, s/// usually does not execute code without the /e modifier. But Perl would not be Perl if you could not mess around with that. Note that even if you could mess with perl, you probably should not.

I'll abuse a trick invented by Andrew Pimlott, that I saw first in the "Perl hardware store" talks (1, 2, 3, 4) by Dominus:

#!/usr/bin/perl

use strict;
use warnings;

sub TIEHASH
{
    return bless {},$_[0];
}

sub FETCH
{
    return $_[1];
}

tie my %X,__PACKAGE__;

my $foo='look! no eval: 3735928559';
$foo=~s/(\d+)/$X{sprintf '0x%08X',$1}/;
print $foo;
[download]

>perl eval.pl
look! no eval: 0xDEADBEEF
>
[download]

But there is also a way without tie magic. Dereferencing an anonymous array reference:

#!/usr/bin/perl

use strict;
use warnings;

my $foo='look! no eval: 3735928559';
$foo=~s/(\d+)/${[sprintf '0x%08X',$1]}[0]/;
print $foo;
[download]

>perl eval2.pl
look! no eval: 0xDEADBEEF
>
[download]

Both tricks (ab)use the fact that s/// interpolates the replacement expression, unless you force it not to do so (using ' as the delimiter instead of /).

Alexander