Can Getopt::Long GetOptions generate an error if the same option occurs multiple times?

Question

I have this getopt:

GetOptions(  GetOptions ("library=s" => \@libfiles);
    @libfiles = split(/,/,join(',',@libfiles));
     "help" => \$help,
     "input=s" => \$fileordir,
     "pretty-xml:4" => \$pretty
);

Is it possible for Getopt::Long::GetOptions to detect if the same option is provided on the command line multiple times? For example, I would like the following to generate an error:

perl script.pl --input=something --input=something

Thanks

Answer 1

I don't think there is direct way but you have two options:

• Use an array and check after processing the options

  #!/usr/bin/perl
  
  use warnings;
  use strict;
  
  use Getopt::Long;
  
  my @options;
  my $result = GetOptions ('option=i' => \@options);
  
  if ( @options > 1 ) {
     die 'Error: --option can be specified only once';
  }
  

• Use a subroutine and check if the option is already defined

  #!/usr/bin/perl
  
  use warnings;
  use strict;
  
  use Getopt::Long;
  
  my $option;
  my $result = GetOptions (
      'option=i' => sub {
          if ( defined $option) {
              die 'Error: --option can be specified only once';
          } else {
              $option = $_[1]; 
          }
      }
  );
  

  In this case you can use an exclamation mark ! at the beginning of the die and the error will be catched and reported as a usual Getopt error (see the documentation of Getopt::Long for the details)