I would prefer to use such a program like so: 
./monitor.pl -add -remove

[download]
but since that would surely involve an if-else of some kind, how about a usage such as this: 
./monitor.pl -action ADD -action REMOVE

[download]
instead? Especially since Getopt::Long will stuff all -action arguments into an array for you. If this is acceptable for you, then feel free to mangle the following skeleton. Since you wanted to use a regular expression, how about we bring Tie::Hash::Regex along for the ride. Hope you like Pod::Usage as well. ;) 

use strict;
use warnings;
use Pod::Usage;
use Getopt::Long;
use Tie::Hash::Regex;

our (%action,@action,$help);

# %action is a look-up hash whose values are (mostly) sub refs
tie %action, 'Tie::Hash::Regex';
%action = (
   ADD    => \&monitor_add,
   REMOVE => \&monitor_remove,
   DELETE => \&monitor_delete,
   ALL    => sub {},            #hack: do-nothing anon sub
);

GetOptions(
   'action|a=s' => \@action,
   'help|h|?'   => \$help,
); 

$help  and pod2usage(-verbose=>2);
@action or pod2usage(-verbose=>1);

# validate the actions
$action{$_} or die "bad action: $_\n" for @action;

# if ALL was specified, assign all actions to @action
grep /ALL/, @action and @action = keys %action;

# this is where the subs are actually called
$action{$_}->() for @action;
   
sub monitor_add    { print "ADD thingy is being monitored\n" }
sub monitor_remove { print "REMOVE thingy is being monitored\n" }
sub monitor_delete { print "DELETE thingy is being monitored\n" }

__END__
=head1 NAME

monitor.pl - monitor ADD REMOVE and DELETE thingies

=head1 SYNOPSIS

monitor.pl -action ADD|REMOVE|DELETE

 Options:
   -action    -a       which action to perform
                       (ADD REMOVE DELETE ALL)
   -help      -h       detailed help

=head1 DESCRIPTION

B<This program> monitors thingies. Currently it monitors
ADD, REMOVE, and DELETE thingies. You may specify one of
the three, or any combination.

=head1 EXAMPLES

1 - monitor ADD things

monitor.pl -action ADD

2 - monitor ADD and REMOVE things

monitor.pl -action ADD -action REMOVE
monitor.pl -a ADD -a REMOVE

3 - monitor all things

monitor.pl -a ALL

[download]

Oh, buy the way ... i really tried to avoid any if's or unless's by replacing them with and's and or's. I don't normally do that, as it's not always apparent what's really going on, but i thought you might enjoy Another Way To Do It. ;)

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

In reply to Re: build regular expression from scalar? by jeffa
in thread build regular expression from scalar? by shapi003

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