[0]  # cat parameter_check.pl
use v5.10;
use warnings;
use strict 'subs';
use feature 'state';
use Getopt::Std;

getopts("b:cd:",\%options);

if( exists $options{'b'} ){
    if( $options{'b'} ){
        say "option b $options{'b'}";
    }else{
        say "b is zero length string or equvalent";
    }
}else{
   say 'key b does not exist';
}
say "option c:", $options{'c'};
say "option d: ", $options{'d'};

##</code><code>##

parameter_check.pl -b -ddd

##</code><code>##

parameter_check.pl -ddd -b

##</code><code>##

[0]  # perl parameter_check.pl -ddd  -c -b
b is zero length string or equivalent
option c:1
option d: dd


[0]  # perl parameter_check.pl -ddd   -b -c
option b: -c
Use of uninitialized value in say at parameter_check.pl line 18.
option c:
option d: dd

[0]  # perl parameter_check.pl -ddd -b -c
option b -c
Use of uninitialized value in say at parameter_check.pl line 18.
option c:
option d: dd

[0]  # perl parameter_check.pl -ddd  -c -b --
option b --
option c:1
option d: dd

[0]  # perl parameter_check.pl -c -b -ddd
option b -ddd
option c:1
Use of uninitialized value in say at parameter_check.pl line 19.
option d:

##</code><code>##

sub getopts ($;$) {
    my ($argumentative, $hash) = @_;
    my (@args,$first,$rest,$exit);
    my $errs = 0;
    local $_;
    local @EXPORT;

    @args = split( / */, $argumentative );
    while(@ARGV && ($_ = $ARGV[0]) =~ /^-(.)(.*)/s) {
	($first,$rest) = ($1,$2);
	if (/^--$/) {	# early exit if --
	    shift @ARGV;
	    last;
	}
	my $pos = index($argumentative,$first);
	if ($pos >= 0) {
	    if (defined($args[$pos+1]) and ($args[$pos+1] eq ':')) {
		shift(@ARGV);
		if ($rest eq '') {
		    ++$errs unless @ARGV;
		    $rest = shift(@ARGV);
		}
		if (ref $hash) {
		    $$hash{$first} = $rest;
		}
		else {
		    ${"opt_$first"} = $rest;
		    push( @EXPORT, "\$opt_$first" );
		}
	    }
	    else {
		if (ref $hash) {
		    $$hash{$first} = 1;
		}
		else {
		    ${"opt_$first"} = 1;
		    push( @EXPORT, "\$opt_$first" );
		}
		if ($rest eq '') {
		    shift(@ARGV);
		}
		else {
		    $ARGV[0] = "-$rest";
		}
	    }
	}
	else {
	    if ($first eq '-' and $rest eq 'help') {
		version_mess($argumentative, 'main');
		help_mess($argumentative, 'main');
		try_exit();
		shift(@ARGV);
		next;
	    } elsif ($first eq '-' and $rest eq 'version') {
		version_mess($argumentative, 'main');
		try_exit();
		shift(@ARGV);
		next;
	    }
	    warn "Unknown option: $first\n";
	    ++$errs;
	    if ($rest ne '') {
		$ARGV[0] = "-$rest";
	    }
	    else {
		shift(@ARGV);
	    }
	}