DEMO UNIX/Linux, for example, provides the user with a choice of different shells, which may either be configured to launch automatically at login, or which may be changed on the fly. each of these shells uses a different configuration file of initial settings and commands that are executed upon startup Different shells provide different functionality, in terms of certain commands that are implemented directly by the shell without launching any external programs. most provide at least a rudimentary command interpretation structure for use in shell script programming(loops, decision constructs, variables, etc.• UNIX/Linux, for example, provides the user with a choice of different shells, which may either be configured to launch automatically at login, or which may be changed on the fly. ( Each of these shells uses a different configuration file of initial settings and commands that are executed upon startup. ) • Different shells provide different functionality, in terms of certain commands that are implemented directly by the shell without launching any external programs. Most provide at least a rudimentary command interpretation structure for use in shell script programming ( loops, decision constructs, variables, etc. )