Shell Commands

A simple shell command such as echo a b c consists of the command itself followed by arguments, separated by spaces.

More complex shell commands are composed of simple commands arranged together in a variety of ways: in a pipeline in which the output of one command becomes the input of a second, in a loop or conditional construct, or in some other grouping.

Simple Commands	The most common type of command.
Pipelines	Connecting the input and output of several commands.
Lists	How to execute commands sequentially.
Compound Commands	Shell commands for control flow.
Coprocesses	Two-way communication between commands.
GNU Parallel	Running commands in parallel.