C:\>perldoc -q stderr
Found in C:\Perl\lib\pods\perlfaq8.pod
  How can I capture STDERR from an external command?
    There are three basic ways of running external commands:

            system $cmd;            # using system()
            $output = `$cmd`;               # using backticks (``)
            open (PIPE, "cmd |");   # using open()

    With "system()", both STDOUT and STDERR will go the same place as 
+the
    script's STDOUT and STDERR, unless the "system()" command redirect
+s
    them. Backticks and "open()" read only the STDOUT of your command.

    You can also use the "open3()" function from "IPC::Open3". Benjami
+n
    Goldberg provides some sample code:

    To capture a program's STDOUT, but discard its STDERR:

            use IPC::Open3;
            use File::Spec;
            use Symbol qw(gensym);
            open(NULL, ">", File::Spec->devnull);
            my $pid = open3(gensym, \*PH, ">&NULL", "cmd");
            while( <PH> ) { }
            waitpid($pid, 0);

    To capture a program's STDERR, but discard its STDOUT:

            use IPC::Open3;
            use File::Spec;
            use Symbol qw(gensym);
            open(NULL, ">", File::Spec->devnull);
            my $pid = open3(gensym, ">&NULL", \*PH, "cmd");
            while( <PH> ) { }
[download]

    pipe my $cin,  my $pin;
    pipe my $pout, my $cout;
    pipe my $perr, my $cerr;
    $pin->autoflush(1);
    $cout->autoflush(1);
    $cerr->autoflush(1);

    my $pid = fork();
    warn("Fork failed\n"),return unless defined $pid;
    if ($pid == 0) {
        # Child fork/TDE execute
        close $pin;
        open STDIN, "<&", $cin or die "Map fail (STDIN): $!, $?\n";
        exit 1 if fileno(STDIN) != 0;

        close $pout;
        close STDOUT;
        open STDOUT, ">&", $cout or die "Map fail (STDOUT): $!, $?\n";
        exit 1 if fileno(STDOUT) != 1;

        close $perr;
        close STDERR;
        open STDERR, ">&", $cerr or print("Map fail (STDERR): $!, $?\n
+"),exit 1;
        exit 1 if fileno(STDERR) != 2;

        exec $command;
    }

    # Parent fork/tester
    return 0 if eval {

        alarm $timeout;
        local $SIG{ALRM} = sub {
            kill 9, $pid;
            die "Calculation call failed to return with $timeout secon
+ds\n";
        };

        close $cin;
        close $cout;
        close $cerr;

        close $pin;
        local $/; # Slurp
        my $content = eof $pout ? '' : <$pout>;
        my $error = eof $perr ? '' : <$perr>;
        alarm 0;
        
        unless ($content =~ /\S/) {
            if ($error =~ /\S/) {
                $error =~ s/^/\t/mg;
                $error =~ s/\s*$/\n/;
                die "No result returned; STDERR=\n$error";
            } else {
                die "Case Aborted: No result, no error\n";
            }
        } elsif ($error =~ /\S/) {
            $error =~ s/^/\t/mg;
            warn "$executable output to STDERR for $case$command\n$err
+or";
        }
    }
[download]

I'm not sure this is what your looking for but Capture::Tiny seems to fit your requirements.

Hi,

Could you not just use 2> in the system arglist to redirect the stderr to a file? Or am I, as usual, missing something?

J.C.