#!/usr/bin/perl
 use strict;
 use warnings;

 use FindBin;
 use POSIX qw( setsid );

 my $runDir  = "$FindBin::Bin";
 my $pidFile = "$FindBin::Bin/hup.pid";
 my $exeFile = $0;

 $SIG{HUP}      = \&doSigHup;
 $SIG{__DIE__}  = \&logDie;
 $SIG{__WARN__} = \&logWarn;

 # get process status
 if ( -e $pidFile ) {
     open( PIDFILE, $pidFile ) or die "[EMERG] $!\n";
     my $pid = <PIDFILE>;
     close PIDFILE;

     die "[EMERG] process is still running\n" if kill 0 => $pid;
     die "[EMERG] can't remove pid file\n"
       unless -w $pidFile && unlink $pidFile;
 }

 # go into daemon
 open( my $pidFH, ">", $pidFile ) or die "[EMERG] $!\n";
 my $parentPid = daemon();
 print $pidFH $parentPid;
 close $pidFH;

 hupMain();

 sub hupMain {

     while (1) {
         warn "Running hup main function.\n";
         sleep 3;
     }
 }


 sub logDie {

     my $errLog = "$FindBin::Bin/hup.err";
     my $time   = scalar localtime;
     open( my $errFH, ">>", $errLog );
     print $errFH $time, "  ", @_;
     close $errFH;
     die @_;
 }

 sub logWarn {

     my $errLog = "$FindBin::Bin/hup.err";
     my $time   = scalar localtime;
     open( my $errFH, ">>", $errLog );
     print $errFH $time, "  ", @_;
     close $errFH;
 }

 sub doSigHup {
     warn "[INFO] received SIGHUP,prepare to reload...\n";

     relaunch( $runDir, $pidFile, $exeFile );
     die "[EMERG] reload failed\n";
 }

 sub relaunch {
     my ( $rundir, $pidFile, $exeFile ) = @_;

     warn "[EMERG] rundir should not be undef"  and return unless $rundir;
     warn "[EMERG] pidfile should not be undef" and return unless $pidFile;
     warn "[EMERG] exefile should not be undef" and return unless $exeFile;

     chdir $rundir;
     unlink $pidFile;
     exec "$exeFile";
 }


 sub daemon {
     my $child = fork();
     die "[EMERG] can't fork\n" unless defined $child;
     exit 0 if $child;
     setsid();

     open( STDIN,  "</dev/null" );
     open( STDOUT, ">/dev/null" );
     open( STDERR, ">&STDOUT" );

     chdir $runDir;
     umask(022);
     $ENV{PATH} = '/bin:/usr/bin:/sbin:/usr/sbin';

     return $$;
 } ## end sub daemon

##</code><code>##

[monitor@august-dev tmp]$ ./hup.pl
[monitor@august-dev tmp]$ cat hup.pid
15393[monitor@august-dev tmp]$ kill -HUP 15393
[monitor@august-dev tmp]$ cat hup.pid
15395[monitor@august-dev tmp]$ kill -hup 15395
[monitor@august-dev tmp]$ cat hup.pid
15395[monitor@august-dev tmp]$ kill -hup 15395
[monitor@august-dev tmp]$ cat hup.pid
15395[monitor@august-dev tmp]$