I'm having some difficulty with forking and waiting for my processes to finish. At first I inserted a big 'sleep' after my wait, but after fiddling with the source I was able to duplicate my issue in a much smaller snippet of code. Bear with me: 
#! /usr/bin/perl -w -I.

use strict;

######################################################################
+##########
# DATA
######################################################################
+##########

# Standard Modules
use Data::Dumper;

my $pid      = '';                                                    
+       # For forking.

my $templog    = '';

my @smokearr = ( 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h');

# Run ls over and over.
#---------------------------------------------------------------------
+-
for ( my $index = 0 ; $smokearr[$index] ; $index++ ) {
        $templog  = "./$smokearr[$index].log";
        my $syscmd = "./smoke.sh > $templog 2>&1";
        fail("fatal: cannot fork: $!") unless defined( $pid = fork() )
+;

        # Run sort as a child and exit
        if ( !$pid ) {
                print STDERR "Running [$syscmd] ($$)\n";
                system($syscmd) == 0
                  or print STDERR "fatal: system  \"$syscmd\" failed: 
+$? See log $templog\n";
                exit 0;
        }
}

# Wait for the child processes to finish.
#----------------------------------------
wait;

# Check each log file for smoke.pl
#---------------------------------------------------------------------
+---
for ( my $index = 0 ; $smokearr[$index] ; $index++ ) {
        $templog  = "./$smokearr[$index].log";
        my $syscmd = "grep smoke.pl $templog";

        print STDERR "Running [$syscmd] ($$)\n";
        system($syscmd) == 0
          or print STDERR "fatal: system  \"$syscmd\" failed: $? See l
+og $templog\n";
}

exit 0;

[download]
The contents of smoke.sh: 
#!/bin/sh

cat smoke.txt |sort | uniq -c

[download]

As you can see, smoke.sh is trivial, but it has pipes.

The contents of smoke.txt is just a long text listing with smoke.pl being a line in there.

When I run my app, smoke.sh runs, wait gets the returned children but I get several failures in the log.

My theory is that smoke.sh returns before the piped grandchildren (I originally just had a cat without the pipes, but the error didn't occur). I also get the error if I put $syscmd = "cat smoke.txt |sort |uniq -c > $templog 2>&1"; directly.

So how can I get around this? I do a fork call 11 times writing to 11 log files and then I'm grepping those log files for a certain result and I get errors and this is presumably because the app I'm calling forks a writing thread.

$ uname -a
AIX nevd1 1 5 000DA5AF4C00 unknown unknown AIX
$ perl --version

This is perl, v5.6.0 built for aix

[download]

Any and all help is greatly appreciated.

In reply to Fork Wait and probably grandchildren by Discordanian

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