Linux Shell

Shell is an environment or a program for interacting with operating system. It is not a part of kernel, but uses the system kernel to execute programs.

-        A program that interprets commands.

-        Allows users to execute cmds by typing them manually at terminal, or automatically in programs called shell scripts.

-        A shell is not O. S. It is a way to interface with the O.S. And run commands.

Eg: sh, ksh, bash etc.

The bash:

-        bash stands for Bourne Again Shell.

-        Bash is a Unix shell written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell (sh). Bash is successor of 'sh'. So it has all of the features of original bourne shell , plus additionals that make it easier to program with and use from the command line.

-        Since it is free software, it has been adopted as the default shell on most of linux systems.

# file Globbing

#Tab key

history:

bash stores the history of commands that can be used to repeat if needed.

$history

-        displays the list of cmds history.

-        Arrow can be used to recall the commands.

-        Also;

!c         - to repeat the last command started with c.

!!          - to repeat the last command.

!n         - to repeat the command by its number.

Shell variables:

in linux shell there are two types of variables:

-       system variables:         created by linux developers(inbuilt)

                                         defined in upper case.

-      User Defined variables:           created by users.

 Defined in lower case.

Eg:       $echo $HOME

                 $echo $PATH

Getting help:

1)    $info <cmd>

eg $info ls

2)    $man <cmd>

eg: $man logout