Unix shell

A Unix shell, also called terminal or console, is a program that accepts Unix commands from the keyboard and executes them. These commands can be installed programs, for example:
 ls to list files
 cp to copy files
 man to get more information on commands

The commands do not need to come from the keyboard. They will, generally speaking, come from stdin. A Unix shell is a command line interface made especially for the control of a Unix system. There are different Unix shells, most notably bash, sh, C Shell and zsh. Their syntax is similar, for example the following dialog to find out your CPU type would be possible with all of them:
 # cat /proc/cpuinfo | grep --max-count=1 "model name"
 model name      : Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz
Category:Unix