Here's the tiny test program to illustrate the problem: 
#!/usr/bin/perl
# teof2 20201104    NHA
# Test eof() for IPC over socketpair filehandle.

use diagnostics;
use strict 'subs';
use strict 'refs';
use Socket;
use IO::Handle;

my $child;      #filehandle to child process
my $parent;     #filehandle to parent process
my $pid;        #Process ID of child process

socketpair($child, $parent, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
                                                or die "socketpair: $!
+";
$child->autoflush(1);
$parent->autoflush(1);
if ($pid = fork()) {                    #parent
    close $parent  or die "close: $!\n";
    sleep 1;
    print STDOUT time%1000, ": polling child\n";
    if (eof($child)) {
        print STDOUT time%1000, ": no input from child yet\n";
    } else {
        my $line = <$child>;
        chomp $line;
        print STDOUT time%1000, ": received <$line>\n";
    }
} else {                                #child
    die "cannot fork: $!"  unless defined $pid;
    close $child or die "close: $!\n";
    print STDOUT time%1000, ": child started\n";
    sleep 5;
    print {$parent} time%1000, ": child printed\n";
    close $parent  or die "close: $!\n";
    exit;
}

[download]
Here's what I get when I run it: 
= ./teof2
325: child started
326: polling child
330: received <330: child printed>

[download]
The only way I can understand this is that eof() is blocking until input appears, and then returning false. Am I missing something here?

In reply to eof() blocking by azadian

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