Perl - Calling other script and showing output as it runs

Question

I am writing a Perl script that asks for some inputs and then eventually runs another script passing those inputs as arguments. That script I'm calling has print outputs that specify the % of how much processing is done as it goes through a foreach loop.

Currently I'm calling the other Perl script like this:

   print `perl /path/to/script.pl -x 0990;`

This works fine, but only prints any output when that called script finishes... so for example, when that script finishes, the output I get is:

   Status: 100% Completed
   Done!

When I want to be getting the output of every % number.

Any possible solutions for this?

Thanks!

vahid abdi · Accepted Answer · 2014-02-26 08:29:18Z

1

I hope this works for you:

#!/usr/bin/perl
use POSIX ":sys_wait_h";
use IPC::Open3;
use IO::Select;

# forces a flush to stdout
$| = 1;

# open a process for writing, reading, and error
my $pid = open3(0,\*READ,0,"perl /path/to/script.pl -x 0990");

# reading process output in non-blocking mode
my $sel = new IO::Select();
$sel->add(\*READ);

# read process output until process returns
do {
 foreach my $h ($sel->can_read)
 {
  my $buf = '';
  sysread(READ,$buf,4096);
  if($buf){print "response->$buf"}
 }
 $kid = waitpid(-1, WNOHANG);
} while $kid > -1;

EDITED:

This script is not working on Windows platform

edited Feb 26, 2014 at 8:29

answered Feb 26, 2014 at 5:47

vahid abdi

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7 Comments

jimtut Over a year ago

Doesn't work for me. I was working on a solution, but you posted yours first (and mine wasn't working!), so I tried yours. The DO loop runs for the exact length of time the child script run, but the FOREACH loop never gets entered.

vahid abdi Over a year ago

@jimtut Work's here. it might be because your process doesn't have any output so $sel->can_read block never executed.

jScott Over a year ago

Works on my end. However it does ONLY the print outputs INSIDE the foreach loop in the script that gets called. There are a couple print outputs in that script that did NOT get shown during the process... any idea why that would behave like that? Is that snippet just looking for outputs inside a foreach?

vahid abdi Over a year ago

Does your process prints to stderr?

jScott Over a year ago

Nvm - I added the $| = 1 line and that seemed to include EVERYTHING that has a print output. Seems good to go now! Would love to know how you came to this solution...

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