Essential UNIX and Linux for Oracle DBA

In UNIX/LINUX systems, any commands you issue to the OS are passed through a command interpreter layer around the kernel called the shell. The UNIX shell  has many variants but they are fundamentally the same, and you can easily migrate from one to another.
Here are the lists fof main UNIX/LINUX shell,

1. sh: The Bourne shell - it is the original UNIX shell.

2. csh: The C shell - it uses syntax similar to C programming language.

3. ksh: Korn shell -A superset of Bourne shell

4. bash:  Bourne again Shell - includes features of both sh and csh.

To find which shell you are using

[oracle@usha ~]$ which $SHELL

First line of any shell script identifies which UNIX/LINUX shell you are using to write your script.

There are some common shell variables.

HOME -> identifies a user's home directory

PATH -> specifies the directories in which the shell should look when it tries to execute any command.