Much of the code I looked for examples of accepting user options and suppplying defaults for those not specified seemed to go through extraordinary contortions, loops and stuff to do it. This is what I settled on.
sub myfunction {
    my %defs = ( optionA=>2e6, optionB=>'defA', optionC=>'defB' );
    my %user = ( %defs, @_ );
    my %opts; @opts{keys %defs} = delete @user{keys %defs};
    carp "Unknown options: '@{[ %user ]}' ignored." 
          if %user;
     # %opts user known user supplied options
     # defaults for unsupplied options
     # Warning issued about unknown options
     # do stuff.
}

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In reply to Accept user options with defaults and report unknowns. by BrowserUk

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