Update: waitpid added to serialize the kids in example code.

First, I suggest you enable strict and warnings. Multiprocess code has plenty of capacity to confuse about lexical scopes.

The order in which child processes execute is entirely up to the OS scheduler. It cannot even be said whether the parent or the child will run first. You are correct that print buffering is an issue in general, but your code is written so that the only printing is done in the parent.

Your program is actually exiting the parent and the loop is continuing in the child. Is that what you mean to do? That is one reason your prints are getting so out of order. Here's a version which does one print in the parent and the other in the child, with the original parent doing all the forking:

#!/usr/bin/perl -w
use strict;

my @LIST = 'A'..'E';
my $i=0;
$|++; # Unbuffered print on STDOUT
for (@LIST)
{
    my $pid;
    if ($pid = fork)  {
        # Parent, $pid is true, is certainly defined
    print "Mother says $_ is in position $i, with pid $pid\n";
        # waitpid serializes the kids
        waitpid $pid, 0;
    }
# $pid is 0 in the child
    elsif (defined $pid) {
    print "Child says That's what I said... $_ is in position ",
    "$i, with pid $$\n";
    exit 0;
    }
# $pid undefined -- error
    else {
    die "Error in forking at  $i: $!";
    }
    $i++;
}

=pod
That's what I said... A is in position 0, with pid 19041
A is in position 0, with pid 19041
B is in position 1, with pid 19042
That's what I said... B is in position 1, with pid 19042
That's what I said... C is in position 2, with pid 19043
C is in position 2, with pid 19043
D is in position 3, with pid 19044
E is in position 4, with pid 19045
That's what I said... D is in position 3, with pid 19044
That's what I said... E is in position 4, with pid 19045
=cut
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After Compline,
Zaxo

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