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TOPIC 5.0. LINUX SHELLS. SHELL SCRIPT. Shell is the interface between end user and the Linux system , similar to the commands in Windows Typical operations performed by shell scripts include file manipulation, program execution, text printing. EXAMPLE OF A SHELL SCRIPT.

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topic 5 0

TOPIC 5.0

LINUX

SHELLS

shell script
SHELL SCRIPT
  • Shell is the interface between end user and the Linux system, similar to the commands in Windows
  • Typical operations performed by shell scripts include
    • file manipulation,
    • program execution,
    • text printing.
example of a shell script
EXAMPLE OF A SHELL SCRIPT
  • Use text editor to generate the “first” file
    • #!/bin/sh
    • # first
    • # this file looks for the files containing POSIX
    • # and print it
    • for file in *
    • do
    • if grep –q POSIX $file
    • then
    • echo $file
    • fi
    • done
    • exit 0
  • % /bin/sh first
  • % chmod +x first
  • %./first
importance of a shell script
IMPORTANCE OF A SHELL SCRIPT
  • easy program or file selection,
  • quick start, and interactive debugging.
  • A shell script can be used to provide a sequencing and decision-making linkage around existing programs
  • Non-expert users can use scripting to tailor the behaviour of programs.
various of linux shells
VARIOUS OF LINUX SHELLS
  • Bourne shell (sh commands)
  • C shell (csh commands)
  • Bourne-Again shell (bash commands)
  • Korn shells (kshcommands)
  • Almquist shells (ash commands)
bourne shell sh commands
BOURNE SHELL (sh commands)
  • The Bourne shell, or sh, was the default Unix shell of Unix Version 7,
  • It replaced the Thompson shell, but the executable file had the same name, sh.
  • It was developed by Stephen Bourne, and released in 1977 in the Version 7 Unix.
  • It remains a popular default shell for Unix accounts.
  • The binary program of the Bourne shell or a compatible program is located at /bin/shon most Unix systems
  • Its command interpreter contained all the features that are commonly considered to produce structured programs.
  • Although it is used as an interactive command interpreter, it was always intended as a scripting language.
c shell csh commands
C SHELL (csh commands)
  • The C shell is a Unix shell that was created by Bill Joy in the late 1970s.
  • It has been distributed widely in 1978.
  • The C shell is a command processor that\'s typically run in a text window, allowing the user to type commands which cause actions.
  • The C shell can also read commands from a file, called a script.
  • C shell has an interactive features and overall style.
  • Its new features made it easier and faster to use.
  • And the overall style of the language looked more like C and was seen as more readable.
bourne again shell bash commands
BOURNE-AGAIN SHELL (bash commands)
  • Bash is the shell, or command language interpreter, that will appear in the GNU operating system.
  • Bash is an sh-compatible shell that incorporates useful features from the Korn shell (ksh) and C shell (csh).
  • It offers functional improvements over sh for both programming and interactive use.
  • In addition, most sh scripts can be run by Bash without modification.
  • The manual is available online at www.gnu.org/software/bash/manual/.
  • BASH can be downloaded at http://ftp.gnu.org/gnu/bash/
korn shell ksh commands
KORN SHELL (ksh commands)
  • The Korn shell (ksh) is a UNIX shell which was developed by David Korn in the early 1980s.
  • It is backwards-compatible with the Bourne shell but includes many features of the C shell as well, such as a command history
  • The main advantage of ksh over the traditional Unix shell is in its use as a programming language.
  • Several features were gradually added, while maintaining strong backwards compatibility with the Bourne shell.
almquist shell ash commands
ALMQUIST SHELL (ash commands)
  • The Almquist shell (also known as A Shell, ash) was originally developed by Kenneth Almquist‘s
  • it is a fast, small, POSIX-compatible Unix shell designed to replace the Bourne shell in later BSD distributions.
  • Originally it did not feature line editingor command history mechanisms - should be moved into the terminal driver;
  • ash are installed as the default shell (/bin/sh) on FreeBSD, NetBSD, DragonFly BSD and Minix.
  • Debian\'s version of ash is known as DebianAlmquist Shell (dash).
methods to get shell interface
METHODS TO GET SHELL INTERFACE
  • Shell Prompts
    • It looks like an MS-DOS screen.
      • Users type commands at a shell prompt,
      • the shell interprets these commands,
      • and then the shell tells the OS what to do.
    • Linux functions can be completed faster from the shell prompt than from a GUI.
methods to get shell interface1
METHODS TO GET SHELL INTERFACE
  • Terminal Windows
    • synonymous with a command line shell or text terminal, the term terminal covers all remote terminals, including graphical interfaces.
    • A terminal emulator inside a GUI is often called as terminal window.
    • A terminal window allows the user access to Command Line Interfaces (CLI) and Text User Interface applications.
    • On Unix-like OS, it is common to have one or more terminal windows connected to the local machine.
methods to get shell interface2
METHODS TO GET SHELL INTERFACE
  • Virtual Terminal
    • In open systems, a virtual terminal (VT) is an application service that:
      • Allows host terminals on a multi-user network to interact with other hosts regardless of terminal type and characteristics,
      • Allows remote log-on by LAN managers for the purpose of management,
      • Allows users to access information from another host processor for transaction processing,
      • Serves as a backup facility.
    • ITU-T defines a virtual terminal protocol based on the OSI application layer protocols.
linux text editor
LINUX TEXT EDITOR
  • vi editor
    • Vi is often the default editor that pops up when we\'re ready to write an e-mail message or when we\'re posting a News message. 
    • Vi is complicated and seems difficult to learn at first. 
    • it is often the default for Unix and Linux systems. 
  • pico (Pine composer) editor
    • Pico is a simple text editor that provides straight-forward options and easy-to-use commands. 
    • it provides everything necessary to write long documents with minimal hassles. 
    • Pico is not very good when manipulating certain types of files such as making changes to .cgifiles
linux text editor1
LINUX TEXT EDITOR
  • emacs (Editor Macros) editor
    • Emacs falls somewhere between the straightforward Pico and the complicated Vi. 
    • Unlike Vi, we don\'t need to switch between modes to perform basic text editing functions. 
    • powerful commands themselves are difficult to remember. 
  • mcedit editor (Midnight Commander Editor)
    • mcedit is a link to mc, the main GNU Midnight Commander executable.
    • Executing GNU Midnight Commander under this name requests staring the internal editor and opening the file specified on the command line.
    • The editor is based on the terminal version of cooledit (standalone editor for X Window System).
linux text editor2
LINUX TEXT EDITOR
  • joe (Joe’s Own Editor)
    • JOE is a full featured terminal-based screen editor
    • It is distributed under the GNU General Public License (GPL).
    • JOE has been around since 1988
    • It is comes standard with many Linux distributions.
    • JOE is being maintained by its original author Joseph Allen
    • JOE is written in C and its only dependency is libc.
linux text editor3
LINUX TEXT EDITOR
  • Graphical text editors:

Nedit editor

    • already installed in Computer Systems
    • smaller and easier to use/customise than emacs
    • easy to get it to do syntax colouring for Java/HTML etc
    • suitable for Unix/Linux only (see below)
    • impossible to use via telnet/ssh
    • more difficult than emacs

Xedit editor

    • It is a text editor for the X Window System on Linux and UNIX
    • It is a visual text editor for the virtual machine operating system
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