Linux shells

When you login to a Linux system, you get a command shell.
Shells are listed in /etc/shells. Default Linux shell: bash
System commands, scripts and applications run in the shell - 
  they become child processes of the shell.
Shell variables are local to the shell.
A shell variable becomes an environment variable after 
 executing command 'export' on it:

    svar=VAR_1  #initialize shell variable
    export svar #becomes environment variable
    env | grep svar 
  Environment variables are inherited by the child shells and processes.

Commands executed in the shell should be either built-in shell
 commands, or addressed with the full path, or located in the 
 PATH env. variable.

    echo $PATH

Shell prompt is defined by PS1 env variable:

    echo $PS1 

[\u@\h \W]\$
\u - user name, \h - host name, \W - "bottom" of the cwd.





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