Append a new action at the end. Thecmd variable must be a validbourne shell command. Thekind variable consists of two letters.The first letter can be either of'-' (which means the commandreads its standard input),'f' (which means the commands readsa given file on the command line) or'.' (which means the commandsreads no input, and hence must be first.)
Similarly, the second letter can be either of'-' (which means the command writes to standard output),'f' (which means the command writes a file on the command line) or'.' (which meansthe command does not write anything, and hence must be last.)
