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TOPIC 5.0

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

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  1. TOPIC 5.0 LINUX SHELLS

  2. 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.

  3. 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

  4. 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.

  5. VARIOUS OF LINUX SHELLS • Bourne shell (sh commands) • C shell (csh commands) • Bourne-Again shell (bash commands) • Korn shells (kshcommands) • Almquist shells (ash commands)

  6. 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.

  7. 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.

  8. 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/

  9. 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.

  10. 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).

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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).

  16. 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.

  17. 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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