I'm currently working on a wrapper script which needs to execute a script, and do the following:

• Append STDOUT and STDERR to two separate log files.
• Still echo STDOUT and STDERR to the terminal.
• Store STDOUT and STDERR in variables / temp files / whatever.
• Send a warning email if the script returns an error code, including the stored STDOUT and STDERR.

Previously, the script was written in shell, and accomplished the first two requirements thusly:

 ( ( perl foo.pl | tee -a output.log ) 3>&1 1>&2 2>&3 3>&- | tee -a er
+ror.log ) 3>&1 1>&2 2>&3 3>&-
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However, capturing the return code of the script as well, even if it is possible, is beyond my script-fu.
Given that, and the fact that writing a wrapper to a Perl script in shell strikes me as inherently nasty, I set about recoding it in Perl.

The obvious solution seemed to be to redirect STDERR and STDOUT, and then set @ARGV and 'do' the script.
I could use IO::Tee to tee between STDOUT or STDERR, an IO::File object for the logfile, and an IO::String object for the variable store (to potentially be used in an email); and to assign the whole lot back to the relevant glob.
i.e. something like:

my ($output_cache, $error_cache);
*STDOUT = multiplex( \*STDOUT, $output_cache, "$log_dir/output.$0" );
*STDERR = multiplex( \*STDERR, $error_cache, "$log_dir/errors.$0" );

do $script or die "Could not open '$script': $!"
exit;

sub multiplex {
  my ($handle, $cache, $log) = @_;
  my $cache_handle = IO::String->new( \$cache );
  my $log_handle = IO::File->new( $log, 'w' ) or die "Could not open l
+og file '$log': $!";
  my $tee = IO::Tee->new( $handle, $cache_handle, $log_handle );
  return $tee;
}
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However, this particular approach generates errors of the ilk 'print() on unopened filehandle STDOUT'.
I assume that assigning to globs only works with IO::File objects because they're blessed globrefs internally (though IO::Tee also uses Symbol::gensym in it's constructor, so perhaps I am wrong).

Another obvious approach is using 'select', which works fine for STDOUT, but not for STDERR.

So, my question boils down to two things:

• Can you see anything obviously wrong in my implementation?

  Is there a trick to assigning to STDERR I've missed?

• Can you see anything obviously wrong in my design?

  Is it the right way to do things, or even a sensible way? Should I be running the script as a subprocess and filtering the output, rather than altering its output handles? How would you tackle this problem yourself?

Bear in mind that the script I'm wrapping ships with a proprietary software distribution, which we upgrade semi-regularly; so I want to avoid treating it as anything other than a black box, despite the fact that I can see the source.