#!/usr/bin/perl -w
use strict;
use IPC::Open3;
use Symbol 'gensym';

my @queue = ("Line 1\nThis is the first line\n",
             "Line 2\nThis is the second line\n",
             "Line 3\nThis is the third line\n",
             );

single_thread(@queue);

sub single_thread {
    open my $oldout, ">&", \*STDOUT or die "Can't dup STDOUT: $!";
    
    for (@_) {
        local *STDOUT;
        open STDOUT, '>', \my $stdout or die "Can't redirect STDOUT: $!";

        test($_);

        print $oldout "STDOUT: $stdout\n" if defined $stdout;
        close STDOUT;
    }
}

sub test {
    my $line = shift;

    my $pid = open3(my $wtr, my $rdr, undef, 'cat', '-v');
    print $wtr $line;
    close $wtr;

    my $content=do{local $/;<$rdr>};

    local $\;
    print STDOUT $content;
    
    waitpid( $pid, 0 );
}
##</code><code>##

Line 1
This is the first line
Line 2
This is the second line
Line 3
This is the third line

##</code><code>##

sub test_mod {
    my $line = shift;

    my $content = `echo '$line'`;

    local $\;
    print STDOUT $content;
}
##</code><code>##

STDOUT: Line 1
This is the first line


STDOUT: Line 2
This is the second line


STDOUT: Line 3
This is the third line



##</code><code>##

sub single_thread {
    for my $line (@_) {
        my $pid = open3(my $wtr, my $rdr, undef, 'cat', '-v');
        print $wtr $line;
        close $wtr;

        my $content=do{local $/;<$rdr>};

        local $\;
        print "STDOUT: $content\n";
    }
}
##</code><code>##

STDOUT: Line 1
This is the first line

STDOUT: Line 2
This is the second line

STDOUT: Line 3
This is the third line