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when ( 'h' ) { ... }

if ( $k eq 'h' ) { ...; next }

use Getopt::Long qw( GetOptions );

...

@ARGV == 0
   or usage( "Too many arguments" );

use File::Basename qw( basename );

...
   say STDERR "Try '$prog --help' for more information.";
   exit( 1 );
}