This is described in the POD: Configuring Getopt::Long. Use no_auto_abbrev: 
use warnings;
use strict;
use Getopt::Long qw(:config no_auto_abbrev);

my %opt;
GetOptions(\%opt, qw(readonly)) or die;

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In reply to Re: how to get the exact option string in Getopt::Long module by toolic
in thread how to get the exact option string in Getopt::Long module by chidori

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