Re^3: Capturing STDERR using IO::Handle

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]

It would be straightforward to then slurp in the contents of the saved-off files. Or did I misunderstand the question?

Comment on Re^3: Capturing STDERR using IO::Handle Download Code

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Re^4: Capturing STDERR using IO::Handle by xdg (Monsignor) on Nov 26, 2007 at 21:39 UTC
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.	[reply]
Re^4: Capturing STDERR using IO::Handle by ikegami (Patriarch) on Nov 26, 2007 at 18:19 UTC
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).	[reply] [d/l]
Re^5: Capturing STDERR using IO::Handle by educated_foo (Vicar) on Nov 26, 2007 at 21:00 UTC
Ah, right you are. But it's easy to screw yourself that way, since you're also blocking the child's STDIN and STDOUT.	[reply]
Re^6: Capturing STDERR using IO::Handle by ikegami (Patriarch) on Nov 26, 2007 at 23:05 UTC
No harder than your method, since you can pass open file handles to `open3` or `open`-style dup instructions. STDIN is moot. None of solutions pass anything to STDIN, since we weren't asked to pass anything to STDIN. You can close the child's STDIN if you want, or you can tie it to the parent's STDIN (by passing `'<&STDIN'`) if you want. Similarly, you can do anything you want with the child's STDOUT. You can tie it to the parent's STDOUT (`'>&STDOUT'`), you can close it, you can redirect it to `/dev/null`, etc.	[reply] [d/l] [select]