The first line writes "hello world" to the file "output", the second reads it back and writes it to standard output (normally the terminal). A "here" document is essentially a temporary, nameless file ...

filter A is a program that accepts input, transforms it, and outputs the transformed data. Filters are closely associated with several ideas basic to Unix: standard input, standard output, ...

In addition to the fairly common forms of input/output redirection the shell recognizes something called process substitution. Although not documented as a form of input/output redirection, its syntax ...

Industrial control systems can be categorized in two types: open-loop and closed-loop systems. The open-loop control system is a continuous control system that provides no feedback from its output.