Here is a version for ActivePerl:

#!perl -w
use Getopt::Std;
use POSIX;
use strict;

my %opt;
getopts("c", \%opt);
if ($opt{c}) {
  dochild();
} else {
  # MSWin version
   use Win32::Process;
   my $ProcessObj;
   Win32::Process::Create($ProcessObj,
      'C:\Perl\bin\wperl.exe',
      "perl $0 -c",
      0,
      NORMAL_PRIORITY_CLASS|DETACHED_PROCESS,
      ".")|| die ErrorReport();

}

sub bgerror {
  # Here I am just dying, but you may want to do something
  # else since this is a background process and the
  # errors are not going anywhere
  die $_[0];
}

sub dochild {
  my $tomorrow = 0;
  my $SCRIPTLOG;

  open APP, "cat testfile |" or bgerror("Cannot execute app.exe: $!\n"
+);
  while (<APP>) {
    if (time() >= $tomorrow) {
        my $now = time();
        $SCRIPTLOG = logname($now);
        $tomorrow = gettomorrow($now);
        open LOG, ">", $SCRIPTLOG 
      or bgerror("Cannot open $SCRIPTLOG: $!\n");
    select(LOG);
    $| = 1;
    }
    print $_;
  }
  bgerror("App.exe exited\n");
}

sub logname {
 my ($sec,$min,$hour,$mday,$mon,$year) = localtime($_[0]);
 sprintf "log%d%02d%02d", $year+1900, $mon+1, $mday;
}

sub gettomorrow {
 my ($sec,$min,$hour,$mday,$mon,$year) = localtime($_[0]);
 my $tomorrow = 25*60*60 + POSIX::mktime(0 ,0, 0, $mday, $mon, $year,0
+,0,-1);
     # 25 hours from midnight today (25 because of DST shift)
 ($sec,$min,$hour,$mday,$mon,$year) = localtime($tomorrow);
 return POSIX::mktime(0 ,0, 0, $mday, $mon, $year,0,0,-1);
}

sub ErrorReport{
    Win32::FormatMessage( Win32::GetLastError() ) . "\n";
}
[download]

and here is a version for Unix or for cygwin Perl (cygwin is Unix-like environment for Win32):

#!perl -w
use Getopt::Std;
use POSIX;
use strict;

# Unix/cygwin version
my $child = fork();
if (not defined($child)) {
  die "Fork unsuccessful: $!\n";
}
if ($child == 0) {
  dochild();
}


sub bgerror {
  # Here I am just dying, but you may want to do something
  # else since this is a background process and the
  # errors are not going anywhere
  die $_[0];
}

sub dochild {
  my $tomorrow = 0;
  my $SCRIPTLOG;

  open APP, "cat testfile |" or bgerror("Cannot execute app.exe: $!\n"
+);
  while (<APP>) {
    if (time() >= $tomorrow) {
        my $now = time();
        $SCRIPTLOG = logname($now);
        $tomorrow = gettomorrow($now);
        open LOG, ">", $SCRIPTLOG 
      or bgerror("Cannot open $SCRIPTLOG: $!\n");
    select(LOG);
    $| = 1;
    }
    print $_;
  }
  bgerror("App.exe exited\n");
}

sub logname {
 my ($sec,$min,$hour,$mday,$mon,$year) = localtime($_[0]);
 sprintf "log%d%02d%02d", $year+1900, $mon+1, $mday;
}

sub gettomorrow {
 my ($sec,$min,$hour,$mday,$mon,$year) = localtime($_[0]);
 my $tomorrow = 25*60*60 + POSIX::mktime(0 ,0, 0, $mday, $mon, $year,0
+,0,-1);
     # 25 hours from midnight today (25 because of DST shift)
 ($sec,$min,$hour,$mday,$mon,$year) = localtime($tomorrow);
 return POSIX::mktime(0 ,0, 0, $mday, $mon, $year,0,0,-1);
}
[download]

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