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a) Introduction to the Linux Shell

a) Introduction to the Linux Shell

27 Oct, 2020

The shell has been the major interface for the Unix/Linux operating system since it was first conceived. The shell allows interaction with the operating system through a text based interface. The shell provides the user with the following features:

  • An easy to use command line interface (CLI)

  • Combine existing tools to create new tools

  • Input/output redirection

  • Wildcard characters for filename abbreviation

  • Variables and options for environment customisation

  • Ability to write shell functions and programs

  • Command-line editing

  • Command history (quick access to previous commands)

  • Arithmetic

  • Command abreviations

The user starts the shell by logging into the computer with a userid and password

Logging in
****************************************************************************** *** THE UNIVERSITY OF YORK IT SERVICES *** *** *** *** THIS IS A PRIVATE COMPUTER *** *** UNAUTHORISED ACCESS STRICTLY PROHIBITED *** ****************************************************************************** login: user001 password: Last login: Mon Sep 8 14:12:44 2014 from gallifrey.york.ac.uk -bash-4.1$


The last line is a command prompt and it is the means by which the computer is telling you that it is ready to accept a command from you. If you do not see the prompt, the computer is probability still executing the last command you have typed. The user types commands which take the form:

command [ options ] [ arguments ]

Options to a command are usually proceeded by a '-' or '- -', this differentiates them from the arguments. The following example shows the echo command which prints the arguments and the ls command which take options arguments. The ls command display the users file. There will be more explanation of files and the ls command later.

Exmaple of command execution
-bash-4.1$ echo Hello World Hello World -bash-4.1$ ls bin Chemistry Desktop examples Experiments intel jobs logs tmp -bash-4.1$ ls -l total 296 drwxr-xr-x 2 abs4 csrv 4096 Jun 24 09:39 bin drwxr-xr-x 3 abs4 csrv 4096 Jun 6 09:23 Chemistry drwxr-sr-x 2 abs4 elecclust 4096 Mar 11 10:53 Desktop drwxr-xr-x 3 abs4 csrv 4096 Jun 30 12:21 examples drwxr-xr-x 5 abs4 csrv 4096 May 23 11:34 Experiments drwxr-xr-x 3 abs4 csrv 4096 Aug 14 12:26 intel drwxr-sr-x 3 abs4 elecclust 4096 Aug 15 12:49 jobs drwxr-xr-x 2 abs4 csrv 266240 Aug 15 13:48 logs drwxr-xr-x 3 abs4 csrv 4096 Aug 14 14:50 tmp -bash-4.1$

To logout of the shell type logout, exit or <CTRL>D

Logging out
-bash-4.1$ exit logout Connection to ecgberht closed.

 

The are a number of shells available to the user. In this tutorial we will be using BASH, the most widely used Linux shell.