Hi all:

I am learning PERL in a "head-first" manner. I am absolutely a newbie in this language:

I am trying to have a debug_mode switch from CLI which can be used to control how my script works, by switching certain subroutines "on and off".

And below is what I've got so far:

#!/usr/bin/perl -s -w

# purpose : make subroutine execution optional,
# which is depending on a CLI switch flag

use strict;
use warnings;

use constant DEBUG_VERBOSE             => "v";
use constant DEBUG_SUPPRESS_ERROR_MSGS   => "s";
use constant DEBUG_IGNORE_VALIDATION     => "i";
use constant DEBUG_SETPPING_COMPUTATION  => "c";

our ($debug_mode);

mainMethod();

sub mainMethod # ()
{
    if(!$debug_mode)
    {
        print "debug_mode is OFF\n";
    }
    elsif($debug_mode)
    {
        print "debug_mode is ON\n";
    }
    else
    {
        print "OMG!\n";
        exit -1;
    }

    checkArgv();
    printErrorMsg("Error_Code_123", "Parsing Error at...");
    verbose();
}

sub checkArgv #()
{
    print ("Number of ARGV : ".(1 + $#ARGV)."\n");
}

sub printErrorMsg # ($error_code, $error_msg, ..)
{
    if(defined($debug_mode) && !($debug_mode =~ DEBUG_SUPPRESS_ERROR_MSGS))
    {
        print "You can only see me if -debug_mode is NOT set".
          " to DEBUG_SUPPRESS_ERROR_MSGS\n";
        die("terminated prematurely...\n") and exit -1;
    }
}

sub verbose # ()
{
    if(defined($debug_mode) && ($debug_mode =~ DEBUG_VERBOSE))
    {
        print "Blah blah blah...\n";
    }
}

So far as I can tell, at least it works...:

1. the -debug_mode switch doesn't interfere with normal ARGV
2. the following commandlines work:
   • ./optional.pl
   • ./optional.pl -debug_mode
   • ./optional.pl -debug_mode=v
   • ./optional.pl -debug_mode=s

However, I am puzzled when multiple debug_modes are "mixed", such as:

1. ./optional.pl -debug_mode=sv
2. ./optional.pl -debug_mode=vs

I don't understand why the above lines of code "magically works".

I see both of the "DEBUG_VERBOS" and "DEBUG_SUPPRESS_ERROR_MSGS" apply to the script, which is fine in this case.

However, if there are some "conflicting" debug modes, I am not sure how to set the "precedence of debue_modes"?

Also, I am not certain if my approach is good enough to Perlists and I hope I am getting my feet in the right direction.

One biggest problem is that I now put if statements inside most of my subroutines for controlling their behavior under different modes. Is this okay? Is there a more elegant way?

I know there must be a debug module from CPAN or elsewhere, but I wanna a real minimal solution that doesn't depend on any other module than the "default"

And I cannot have any control on the environment where this script will be executed...

Many thanks to the suggestions in advance.