[me@host scratch]$ perl -wle 'open STDERRIN,"<&STDERR" or die $!;  my 
+$line = <STDERRIN>;  print "YAY!!! $line";'
sadf
YAY!!! sadf

[me@host scratch]$
[download]

[me@host scratch]$ perl -v

This is perl, version 5.005_03 built for i386-linux
...
[download]

Seems to be version dependent:

#!/usr/bin/perl

use strict;
use warnings;
no warnings qw /syntax/;

my $program = 'open STDERRIN, "<&STDERR" or die $!;
               my $line = <STDERRIN>;  print "YAY!!! $line";';

foreach my $version (qw /5.005 5.6.0 5.6.1 5.8.0 5.8.1/) {
    print "Version $version\n";
    system "/opt/perl/$version/bin/perl -we '$program'"; 
}
 
__END__
Version 5.005
foo
YAY!!! foo
Version 5.6.0
bar
YAY!!! bar
Version 5.6.1
Filehandle STDERRIN opened only for output at -e line 2.
baz
YAY!!! baz
Version 5.8.0
Filehandle STDERRIN opened only for output at -e line 2.
Use of uninitialized value in concatenation (.) or string at -e line 2
+.
YAY!!! Version 5.8.1
Filehandle STDERRIN opened only for output at -e line 2.
Use of uninitialized value in concatenation (.) or string at -e line 2
+.
YAY!!!
[download]

It runs on 5.005, 5.6.0 and 5.6.1, although it gives a warning under 5.6.1. It won't read from STDERRIN in 5.8.0 or 5.8.1.

Abigail

Cool. Well, the better way is to try to open /dev/tty, anyway (which I referenced in the original post, too). I was just going off of "use STDERR as a reference to the controlling terminal" notion that is used in many tools... like vim, for example, when you pipe the file to edit in off of STDIN.

[me@host scratch]$ ptyexec man vim | grep stdin
       -           The file to edit is read from stdin.  Commands are 
+read from stderr, which should be a tty.
[me@host scratch]$
[download]


------------
:Wq
Not an editor command: Wq