did you read the docs?

Handling simple options is straightforward:

my $verbose = '';   # option variable with default value (false)
my $all = '';       # option variable with default value (false)

GetOptions ('verbose' => \$verbose, 'all' => \$all);
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The call to GetOptions() parses the command line arguments that are present in @ARGV and sets the option variable to the value 1 if the option did occur on the command line. Otherwise, the option variable is not touched. Setting the option value to true is often called enabling the option.