This snippet shows how to define a callback using Term::ReadLine::Gnu which uppercases all "print" words :

     {
      my $old_line_buffer;
 
      $attribs->{event_hook} = sub {
 
        my $line_buffer = $attribs->{line_buffer};
          
        return if $line_buffer eq $old_line_buffer;
 
        $term->replace_line($line_buffer), $term->redisplay()
          if ($line_buffer =~s/print\W/\U$&/g);
 
      };
    }
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HTH!

UPDATE: Unfortunately readline doesn't support the interpretation of ANSI escape codes...