Dear Monks,

I have a script which dumps a table. When I pipe it to the same script, I use IO::Select and can_read() to check for input on STDOUT. My script works fine when I run it through the debugger, but sadly can_read() fails to detect anything when I don't. I tried writing a test script to see if I can reproduce the issue, but unfortunately the script works fine either way.

Interestingly, when I put a print statement (marked HERE) in my script, the can_read() seems to work.

Any ideas ? Thank you very much for your time !!! 

#!usr/bin/perl5.26.1
use strict;
use IO::Select;
use Text::ASCIITable;

$|=1;

my $t = Text::ASCIITable->new({ headingText => 'Basket' });
  
$t->setCols('Id','Name','Price');
$t->addRow(1,'Dummy product 1',24.4);
$t->addRow(2,'Dummy product 2',21.2);
$t->addRow(3,'Dummy product 3',12.3);
$t->addRowLine();
$t->addRow('','Total',57.9);

print STDOUT $t ."\n";


### print "checking pipe\n";  #<====  HERE
my $s = IO::Select->new();
$s->add(\*STDIN);

if ($s->can_read(.5)) {
     print STDOUT "reading from pipe data\n";
}

[download]
#
# TEST RUN
#
# perl test.pl
.------------------------------.
|            Basket            |
+----+-----------------+-------+
| Id | Name            | Price |
+----+-----------------+-------+
|  1 | Dummy product 1 |  24.4 |
|  2 | Dummy product 2 |  21.2 |
|  3 | Dummy product 3 |  12.3 |
+----+-----------------+-------+
|    | Total           |  57.9 |
'----+-----------------+-------'


# perl test.pl | perl test.pl
.------------------------------.
|            Basket            |
+----+-----------------+-------+
| Id | Name            | Price |
+----+-----------------+-------+
|  1 | Dummy product 1 |  24.4 |
|  2 | Dummy product 2 |  21.2 |
|  3 | Dummy product 3 |  12.3 |
+----+-----------------+-------+
|    | Total           |  57.9 |
'----+-----------------+-------'
reading from pipe data

[download]

In reply to IO::Select woes by Anonymous Monk

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