Code in IPC::Open3 doc doesn't work

[ikegami]

Where

IPC::Open3

Description

The synopsis contains this code. It doesn't work. No output ends up in output.txt.

open my $outfile, '>>', 'output.txt' or die "open failed: $!";
my $pid = open3('<&STDIN', $outfile, undef,
                'some', 'cmd', 'and', 'args');

Passing a lexical variable containing a file handle to open3 has never worked. At least not on non-Windows systems. Never tried it on a Windows system which uses a very different implementation.

[ikegami]

Working version:

open local *OUTFILE, '>>', 'output.txt' or die "open failed: $!";
my $pid = open3('<&STDIN', '>&OUTFILE', undef, "printf", "foo\\n");

[ikegami]

Bug first reported on StackOverflow

[guest20]

'>&' . fileno $outfile

... should do the job without needing the bareword handle

[haarg]

These docs were changed in ef395fa. The previous version didn't include any examples of doing this.

[guest20]

I am always suspicious of "there's a bug in perl", "the other way is ugly" and "i'll do it myself" comments

At the first glance this comment is checking all the boxes:

    # simulate autovivification of filehandles because
    # it's too ugly to use @_ throughout to make perl do it for us
    # tchrist 5-Mar-00

[ikegami]

'>&' . fileno $outfile

... should do the job without needing the bareword handle

I don't know if the bug has been fixed, but that has not always been the case. It appears to work, but--IIRC--a close fails, which can cause issues--EOF never reached?--in some situations.

I allude to this problem in this post from 2012:

There is a way of passing lexical file handles (or rather its descriptor), but there's a bug concerning them, so I always use package variables with open3.

[ikegami]

I am always suspicious of "there's a bug in perl", "the other way is ugly" and "i'll do it myself" comments

As you should be. But rather than making such a comment, you should have tested it like I did.

$ perl -e'
   use strict;
   use warnings;
   use IPC::Open3 qw( open3 );
   open my $outfile, ">>", "output.txt" or die "open failed: $!";
   my $pid = open3( "<&STDIN", $outfile, undef, "printf", "foo\\n" );
   waitpid( $pid, 0 );
'

$ ls -l
total 0
-rw-rw---- 1 ikegami ikegami 0 Sep 18 09:23 output.txt

I've answered "hundreds" of questions about open3 on PerlMonks and StackOverflow, and I've even fixed a bug in the module.

The documentation doesn't reflect the behaviour of the module (past or present).

[guest20]

@ikegami Sorry I wasn't clear, I was talking about the comment I quoted (from IPC::Open3), not the reproducibility of your issue.

I did run the example you gave (from the docs) and it did the thing you said it would (leaving the file untouched) so I didn't have much to add on that topic (especially when I only tested it on BSD with 5.20.2 and your issue talked about windows too)