![]() ![]() Every Unix shell offers two key facilities. If it is a command which is particular to a specific shell, then it needs interpretation in the context of a specific shell by interpreting its semantics. In case we have a built-in command then it has a wellunderstood interpretation across all the shells. As an example, if a user wishes to use the editor tool vi, then we notice that it has its own states like edit and text mode, etc. In that case shell hands in the control to another environment. A tool may have its own operational environment. Note that a shell distinguishes between the commands and a request to use a tool. ![]() 13.1 Facilities Offered by Unix Shells In Figure 13.1, we show how a user interacts with any Unix shell. Come to think of it, a shell is essentially a process which is a command interpreter!! In this module we shall explore ways in which a shell supports enhancement in a user's productivity. A user needs this command interface to use an OS, and the login shell immediately provides that (as soon as user logs in). The login shell offers the first interface that the user interacts with either as a terminal console, or through a window interface which emulates a terminal. When a user logs in, he has a login shell. A user obtains OS services through an OS shell. Bhat Indian Institute of Science Bangalore Operating Systems/Shell Scripts in UNIX Lecture Notes Module 13: Shell Scripts in UNIX A Shell, as we remarked in module-1, offers a user an interface with the OS kernel. ![]()
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