Compose a single command line that displays the calendar of the last three months of 2010, one below the other. Do so by combining three separate cal commands. Now adjust your command such that
the complete command is executed in the background
the complete command is executed in the background and its resulting output is saved in a file
the separate subcommands are executed simultaneously and all their output is saved into the same file
Repeat the last command line a few times and check whether the content of the resulting file is the same after each iteration. Put all versions of the command into a file and make this file executable using the chmod command.