#!perl
use strict;
use warnings;
use IPC::Open2;

eval {
my $pid = open2(\*OUT, \*IN, 'findstr hello');
};
if ($@ and $@ =~ /^open2:/) {
    die "$@:$!\n";
}

my $sometext = <<END;
Hello, World!
END
print IN $sometext;
close IN;

my @found = <OUT>;
print join " ", @found;
[download]

I've just played with this myself... and I think I can replicate your problem.  As I don't have findstr, I'm not entirely sure what it's doing, but I suppose it's some kind of 'grep', which reads lines from stdin, and writes lines to stdout if they match a given keyword.  So, I've used a little Perl program instead, which does the same.

The issue under Windows seems to be that the "close IN" in your script does not generate an end-of-file on stdin of the process spawned. So, the program keeps reading/writing... In other words - as it doesn't terminate yet - it doesn't close stdout either, which in turn means that your "@found = <OUT>" is waiting for more lines to come (i.e. it 'hangs').

The following test script demonstrates the issue:

#!/usr/bin/perl
use strict;
use warnings;
use IPC::Open2;

my $pid;
eval {
    $pid = open2(\*OUT, \*IN, qw(perl -ne), '$|=1; print if /hello/i')
+;
};
if ($@ and $@ =~ /^open2:/) {
    die "$@:$!\n";
}

my $sometext = <<END;
Hello, World!
END
print IN $sometext;
close IN;

# read/print line by line, so we see the output
while (<OUT>) {
    print ":: $_";
}
[download]

On Windows (tested with Perl 5.8.8 on XP), this prints ":: Hello, World!" and then hangs.  On Unix/Linux, it terminates after printing the line, as expected  (you can make it hang, too (like on Windows), by commenting out the line "close IN;").

Anyhow, I'm no Windows gal, so I'm afraid I can't help you any further...

BTW, an unrelated thing: in my original snippet, I had deliberately put the my $pid outside of the eval, because in case you'd need it later on, it would already have gone out of scope... — yes, you're not using it here, but just in case.

___

(PS: <PerlMonks-meta> I normally don't frontpage nodes where I'm the first/only one who has replied (feels like XP-whoring to me)... but in this case I did, in the hope that it'll get some more exposure, and that someone windows-savvy will know more... </PerlMonks-meta>)