In Automated module install, I started to look at creating a simple script to untar some tarballs, and automatically install them. I have something that, at least before I started mangling it, was working on Linux. So I tried on Windows. Didn't get too far, I might mention. Perhaps someone here with a bit more Windows experience than I could shed some light.

Environment: ActiveState 5.8.0, WindowsXP, and lots of Cygwin tools. (I'm hoping we get this upgraded to 5.8.6 soon - so if that's the solution, I'll just apply that pressure.)

The command works fine if I run it at the command prompt, so it's not a lack of the proper tooling (gunzip and tar are both present).

=item do_pipe_command

Mostly-simply wrapper around open for piping from a command.
Since we generally want to capture stderr, too, we redirect stderr
to stdout in the command, so we get it all in a single filehandle.

=cut

sub do_pipe_command
{
    print 'Running: ', join(' ', @_[1..$#_]), $/;

    my $pid = open ($_[0], '-|');
    return $pid if $pid;

    # child - pipe the stderr to the stdout before exec'ing.
    open STDERR, '>&', \*STDOUT;
    my @cmd = @_[1..$#_];
    if ($^O =~ /MSWin/i)
    {
        @cmd = (qw(cmd.exe /c), join(' ',@cmd));
    }
    exec @cmd;
}

=item extract_tarball

Tries to untar the tarball.  Returns the directory name thusly
created.

=cut

sub extract_tarball
{
    my $tarball = shift;

    my $cmd = '';
    if ($tarball =~ /\.tar\.gz$/)
    {
        $cmd = "gunzip -c $tarball | ";
    }
    elsif ($tarball =~ /\.tar\.Z$/)
    {
        $cmd = "zcat $tarball | ";
    }
    elsif ($tarball =~ /\.tar$/)
    {
        $cmd = "cat $tarball | ";
    }
    else
    {
        die "Can't figure out how to untar $tarball";
    }

    $cmd .= 'tar -xvf -';
    print "Running $cmd\n";

    my $subdir;
    do_pipe_command my $tar, $cmd or die "Failed to run $cmd: $!";
    while (my $l = <$tar>)
    {
        print $l;
        next if $subdir;
        $subdir = $1 if $l =~ m:^(.*?)[/\\]:;
    }
    $subdir;
}
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The problem seems to be where I try to run the open. fork works fine that I can test, but this seems to go all wonky on me. The error message is:

Running gunzip -c Cache-Repository-0.01.tar.gz | tar -xvf -
Running: gunzip -c Cache-Repository-0.01.tar.gz | tar -xvf -
'-' is not recognized as an internal or external command,
operable program or batch file.
Use of uninitialized value in string eq at e:/perl5.8.0/lib/File/Spec/
+Unix.pm line
 77.
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Yet, as I said, if I run the given command at the command prompt manually, it works fine.

I just installed ActiveState 5.8.6 ... different uninitialized value error message, but same "not recognized" message.

As I'm writing this, I'm starting to wonder if opening '-|' is even going to work on Windows, or am I going to have to resort to some more trickery to get what I want? Namely, a way to get the directory that the untar command is doing. (I wish Archive::Tar and Compress::Zlib were part of the standard perl distribution!)

Update: After reading tye's recommendation, I noticed IPC::Open3 has documented that this is a problem, so I'm going to have to replace the open call with something else. Thanks!

Update: As a confirmation, the new do_pipe_command is:

sub do_pipe_command
{
    print 'Running: ', join(' ', @_[1..$#_]), $/;
    my @cmd = @_[1..$#_];

    my $wtr;
    require IPC::Open3;
    my $pid = IPC::Open3::open3($wtr, $_[0], undef, @cmd);
}
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It works perfectly. No need to launch cmd.exe (which may be because my @cmd is always a single string anyway, at least when I'm chaining subprocesses together in their own pipe). I do realise that this will leave a zombie process behind (at least on unix), but that should be automatically cleaned up when we exit, and this is a very short-lived process anyway. It runs on Linux in under 5 seconds currently, so a few zombies is pretty minor.