Perl scripts & Open2

Posted on 2008-11-03
Medium Priority
Last Modified: 2012-06-27
I casually use open2 when I want to pipe to/from various programs. However, when I tried to read/write to one of my perl scripts, it failed to work and it is taking me too long to figure it out, so I am asking you guys. I am attaching a very simple example that I expect to work, but it does not. Running test1.pl does nothing, the script hangs at my $r=<READ>. What am I doing wrong?
use IPC::Open2;
my $pid=open2 (\*READ, \*WRITE, "./test2.pl");
binmode WRITE, ":utf8";
foreach (qw(one two three)) {
    print WRITE "$_\n";
    my $r=<READ>;
    print "+$r+\n"
while (<STDIN>) {
    print "*$_*\n";

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Question by:ecuador
  • 3
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Accepted Solution

ozo earned 2000 total points
ID: 22873021

while (<STDIN>) {
    print "*$_*\n";
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Expert Comment

ID: 22873062

Author Comment

ID: 22873534
Simple... thanks!
I wonder why this is not considered worth mentionig in the open2 man pages...
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Expert Comment

ID: 22873552
perldoc IPC::Open2
       This whole affair is quite dangerous, as you may block forever.  It
       assumes it's going to talk to something like bc, both writing to it and
       reading from it.  This is presumably safe because you "know" that
       commands like bc will read a line at a time and output a line at a
       time.  Programs like sort that read their entire input stream first,
       however, are quite apt to cause deadlock.


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