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How to tee STDERR on Windows

by freonpsandoz (Beadle)
on Jan 13, 2022 at 07:11 UTC ( #11140418=perlquestion: print w/replies, xml ) Need Help??

freonpsandoz has asked for the wisdom of the Perl Monks concerning the following question:

I'm looking for a way to tee STDERR so that all output to it also goes to a file. I'm using ActivePerl v5.20.2 for Windows. I tried code suggested in the topic It does tee STDERR, but not to the file I want. It creates a file named "GLOB(0xf7b278)" and the output goes to that file. It also creates the file I specified, but it's empty

use strict; use warnings; use open qw(:std :utf8); # Set the default encoding for STDIN, STDOUT +& STDERR to UTF-8 use IO::Tee (); my $logname = 'test-tee$.log'; open(my $logfile, ">:encoding(UTF-8)", $logname) or die qq(Can't open +"$logname for writing"\n); # Tee STDERR to log file. If running as Administrator, console window +may disappear quickly! open STDERR2, ">&=STDERR" or die "Failed to alias STDERR: $!"; *STDERR = IO::Tee->new(\*STDERR2, ">$logfile") or die "Failed to tee to aliased STDERR and '$logfile': $!"; print(STDERR "This is a test\n");

Any suggestions? Thanks in advance.

UPDATE: I found the problem. Line 9 should be:

*STDERR = IO::Tee->new(\*STDERR2, $logfile)

I thought I had tried that also, but apparently not!

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Re: How to tee STDERR on Windows
by Marshall (Canon) on Jan 13, 2022 at 08:15 UTC
    Interesting question. Windows supports redirection of STDERR and STDOUT, like >log 2>&1 will send both to a file. "tee" is available in the powershell. just typing "powershell" at the windows cmd prompt will start the powershell. But the problem is that there is no easy way to pipe STDERR into another program like tee. You can tee STDOUT and send STDERR to a file, but you want both on the screen and in the file.

    This is one heck of an ugly Win10 command line solution. But I tested this on my machine and it does work. I admit that I am still struggling to understand exactly why it works. I make no claims other than I did test this on Win10 home edition with an actual Perl program.

    Win10prompt>for /f "delims=" %L in ('perl 2^>^&1') do @echo %L & echo %L >> log

    I happened to have a short Perl program that I wrote for another post for testing. This appends both STDERR and STDOUT to log and of course the also both go to screen as requested.

    update: The only other info I have about this is: "The for command iterates over the output lines of the script. The carets escape the characters that follow them. The first echo goes to the screen and the second is appended to the file named "log"."

Re: How to tee STDERR on Windows
by LanX (Sage) on Jan 13, 2022 at 07:19 UTC

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