Tuesday, August 30, 2011

Basics of Unix Commands

Unix is a command line based operating system. Unix commands can be combined to perform complex tasks.To perform these tasks repeatedly these commands can be placed in files called shell scripts and these shell scripts can be executed to provide the required output.

Unix users and processes:


Unix has two basic concepts : files have places and processes have life . All files are placed at some location and each process travels  in a life cycle from birth to death.


Each user in unix is identified by uniquely by an  identification number,name and group identification.A user is able to access  a unix system only after being given a login name and password by the system administrator. When a user tries to access a unix system it displays a  login  prompt where the users types in the login name and password. If the user is a valid user , a shell prompt($) appears on the screen where unix commands can be typed..


A user can end a unix session by pressing < ctrl+d >.  Ctrl+d kills a process.


Command Line is defined as the line on which the shell prompt occurs and a command with its arguments is  entered  and is considered complete only when the enter key is pressed.
The command may spill over multiple lines shown by a secondary prompt (>). The complete line is then fed to the shell as its input for interpretation and execution.


Unix is CASE SENSITIVE. All unix commands must be typed in LOWER CASE.


The next post would be concerning shell commands- the syntax and the  actual commands.


 

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