## get first argument
my $cmd = shift(@ARGV);
switch ($cmd) {case "start"   { start() }case "restart" { restart() }case "stop"    { stop() }else           { usage() }
}

my $PROCESS_FILE = "daemon.proc";
my $PROCESS_CONF = "daemon.conf";

if (-e $PROCESS_FILE) {print "fundamental services are running. Please stop them, then try again\n";exit 1;}my $fh;open ($fh, ">", $PROCESS_FILE) or die("unable to open $PROCESS_FILE");if (flock($fh,  LOCK_EX | LOCK_NB)) {## we have the lock, launch servicesmy $info = load();## form json formatmy $jsonText = $json->pretty->encode($info);print $fh $jsonText;print "services started\n";} else {## fail to get the lock, must be concurrencyprint "fail to get the lock of $PROCESS_FILE\n";exit 1;}

/var/lock   锁定文件.许多程序遵循在/var/lock 中产生一个锁定文件的约定，以支持他们正在使用某个特定的设备或文件.其他程序注意到这个锁定文件，将不试图使用这个设备或文件.  

sub load {## read cmds from config filemy $cmds = readFile();## collect process infomy $info = [];foreach my $cmd (@$cmds) {push(@$info, launch($cmd));}return $info;
}sub readFile {my $lines = [];open (my $fh, "<", $PROCESS_CONF) or die("unable to open $PROCESS_CONF");while (<$fh>) {chomp($_);if ($_ =~ m/^#/) {next;}## use regular expression to extract arguments,## especially those that are in Double quotation marksmy $fields = removeQuote($_=~/\s*(\".*?\"|\S+)\s*/g);push (@$lines, $fields);}return $lines;
}sub removeQuote {my @fields = @_;my $res = [];foreach my $field (@fields) {$field =~ s/\"//g;push(@$res, $field);}return $res;
}

sub launch {my $cmd = shift;my $child = fork();if ($child > 0) {## parent# sleep 1/4 second to ensure child is upselect(undef, undef, undef, 0.25);my $info = {};$info->{pid} = $child;$info->{cmd} = $cmd;return $info;} else {## child process## set as deamon processif (!setsid()) {print "unable to setsid()\n";exit 1;}## redirect STDERR and STDOUT to /dev/null,　　 ## we can also redirect them to ./logopen (STDOUT, ">/dev/null");open (STDERR, ">&STDOUT");eval {exec(@$cmd);};print "Faied to exec() cmd:".Dumper($cmd)." $@";exit 1;}
}

./count.pl

[{"cmd" : ["./count.pl"],"pid" : 4665}
]

sub stop {if (!-e $PROCESS_FILE) {print "no services are running\n";exit 1;}killProcess();
}sub killProcess {my $infoArray = Utils::SystemCalls->readJsonFile($PROCESS_FILE);foreach my $info (@$infoArray) {print "kill $info->{pid}\n";print `kill -15 $info->{pid}`; # send SIGTERM
  }print `rm $PROCESS_FILE`;
}