Normally I'd just have the daemon print the command line it is called with to a specific file and have the script read that file.

If for some reason that doesn't work and you happen to be on Linux, you can get the exact command line a process was called with by examining the /proc/<process id>/cmdline file. So, for example, the below code will print out the command line:

#!/usr/bin/perl

use warnings;
use strict;

open (my $fh,"<","/proc/$$/cmdline") or die "Can't access proc file: $
+!";
my $line = (<$fh>);
close $fh or die "Can't close proc file: $!";

my @cmdline = split("\0",$line);

print join(" ",@cmdline)."\n";
[download]

use strict;
use warnings;

use Getopt::Long;
use Log::Dispatch::FileRotate;
use Log::Log4perl;

my $conf = q(
  log4perl.category.foo = DEBUG, FileRotateAppender
  log4perl.appender.FileRotateAppender           = Log::Dispatch::File
+Rotate
  log4perl.appender.FileRotateAppender.filename  = 667540.log
  log4perl.appender.FileRotateAppender.mode      = append
  log4perl.appender.FileRotateAppender.size      = 10000
  log4perl.appender.FileRotateAppender.max       = 5
  log4perl.appender.FileRotateAppender.layout    = PatternLayout
  log4perl.appender.FileRotateAppender.layout.ConversionPattern=[%P] %
+d %M %F:%L: %m%n
);
Log::Log4perl::init( \$conf );
my $log = Log::Log4perl::get_logger("foo");

my $man = undef;
my $woman = undef;

GetOptions(
  'man'   => \$man,
  'woman' => \$woman,
) or die(qq{Usage: $0 [--man] [--woman]});

# Set explicit to 0 or 1
$man   = ($man)   ? 1 : 0;
$woman = ($woman) ? 1 : 0;

$log->info(qq{man=$man}) if $log->is_info();
$log->info(qq{woman=$woman}) if $log->is_info();

# ------ main ------

# then do deamon stuff

__END__
$ perl  667540.pl
$ cat 667540.log
[3561] 2008/02/12 12:29:51 main:: 667540.pl:35: man=0
[3561] 2008/02/12 12:29:51 main:: 667540.pl:36: woman=0
$ perl  667540.pl --man
$ cat 667540.log
[3561] 2008/02/12 12:29:51 main:: 667540.pl:35: man=0
[3561] 2008/02/12 12:29:51 main:: 667540.pl:36: woman=0
[3574] 2008/02/12 12:30:00 main:: 667540.pl:35: man=1
[3574] 2008/02/12 12:30:00 main:: 667540.pl:36: woman=0
$ perl  667540.pl --man --woman
$ cat 667540.log
[3561] 2008/02/12 12:29:51 main:: 667540.pl:35: man=0
[3561] 2008/02/12 12:29:51 main:: 667540.pl:36: woman=0
[3574] 2008/02/12 12:30:00 main:: 667540.pl:35: man=1
[3574] 2008/02/12 12:30:00 main:: 667540.pl:36: woman=0
[3576] 2008/02/12 12:30:05 main:: 667540.pl:35: man=1
[3576] 2008/02/12 12:30:05 main:: 667540.pl:36: woman=1
[download]

One classic way of handling this problem is to have the daemon acquire a lock on a specific resource, and usually things are set up so that the lock is automatically released when the process exits. The challenge in your case is to come up with a command line -> resource mapping which will do what you want.

One simple idea is to map the command line to a file path. For instance, map "-a 1 -b 2 -c 3" to "/some/dir/locks/-a 1 -b 2 -c 3". Then use flock or File::lockf to obtain an exclusive lock on that file. You'll have to make sure that the path will work in all cases (e.g. be careful of special characters in your command line, path length, etc.) Another option is to use mysql's locking feature which allows you to identify a resource by an arbitrary string.

Some issues I'll think you'll run into:

• You might have to canonicalize your command line. E.g. is "-a 1 -b 2" the same as "-b 2 -a 1"?
• Is the instance identified by all the command line arguments? If not, you'll have to omit the ones that don't contribute to the identity of the daemon when mapping the command line to a resource.

In general when I've had to do this I've only needed a couple of different locks per daemon -- most of the time just one. If you tell us more about your application and its possible command line arguments, we can advise you on the what the best locking mechanism would be.

Thanks to all who have replied; I really appreciate your suggestions.