Here is a script that saves, redirects, and restores STDOUT and STDERR using various methods:

        #!/usr/bin/perl
        open my $oldout, ">&STDOUT"     or die "Can't dup STDOUT: $!";
        open OLDERR,     ">&", \*STDERR or die "Can't dup STDERR: $!";
    
        open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!"
+;
        open STDERR, ">&STDOUT"     or die "Can't dup STDOUT: $!";
    
        select STDERR; $| = 1;      # make unbuffered
        select STDOUT; $| = 1;      # make unbuffered
    
        print STDOUT "stdout 1\n";  # this works for
        print STDERR "stderr 1\n";  # subprocesses too
    
        open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!";
        open STDERR, ">&OLDERR"    or die "Can't dup OLDERR: $!";
    
        print STDOUT "stdout 2\n";
        print STDERR "stderr 2\n";
[download]

Apart from the STDOUT typos above when redirecting STDERR, this approach is prone to dying if STDOUT or STDERR are already closed for some reason. Also, under wperl.exe on MSWin32, what you have may cause a segfault.

IO::CaptureOutput can deal with those kinds of edge cases for you.

Update: I misread the intent of the code example -- it's not a typo, it's merging STDERR and STDOUT intentionally.

-xdg

Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

Thanks. Yes, that would work. I didn't realize you were suggesting using temporary files. Seems like a lot of work that core function open3 (via IPC::Open3) already does for you (and it doesn't even require temporary files).

Ah, right you are. But it's easy to screw yourself that way, since you're also blocking the child's STDIN and STDOUT.