"codice_1" produces a process, the output (stdout) of which is piped to the input (stdin) of the process for "grep key"; and likewise for the process for "less". Each process takes input from the previous process and produces output for the next process via "standard streams". Each " codice_2 " tells the shell to connect the standard output of the command on the left to the standard input of the command on the right by an inter-process communication mechanism called an (anonymous) pipe, implemented in the operating system. Pipes are unidirectional; data flows through the pipeline from left to right.