Shell ScriptingLinux shell programming

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Introduction • A shell is a program constructed of shell commands

( $shell,$path,Ls,pwd,mkdir..)• Shell is an environment for user interaction.But it is

not a part of kernel.• Shell is just like as BAT files in MS-DOS.• By default,Bash shell is default shell for Linux.

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Features of Shells• Shells are CASE SENSITIVE.• Shells allows interaction with kernel.• Shells allow one to create functions and pass

arguments to them.• Shells provide help for each and every command

using man or help.• Helps in automation of tasks and thus time saving

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Types of shells• Following types of shells are available in linux:

Some other types of shells available are KSH Korn shell,TCSH tenex/Tops C shell

Shell Name Developer Prompt

Description

Bash – Bourne again

Brian Fox &Chet Ramey

$ Bash is the replacement of sh shell.It provides many tools for editing and manipulating history.

CSH - C shell Bill Joy % C shell has its syntax much same as that of C language.

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Shell Scripting• A script is defined as just a plain text file or ASCII

file – with a set of linux / unix commands.– Flow of control– I\O facilities

• A shell script can be created using any

text editor like vim,emac,notepad++ etc.

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• Shell script allow use of variables.• Shell scripts are interpreted directly and are not

compiled as c\c++ codes.• Shells provide many features including loop

constructs,arrays,variables,branches and functions.• shells provide logic with other utilities like

pipelining,redirection etc.• Shells allow file and directory management features.

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Example of Shell scripting

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Structure of a script• #!/bin/bash –it defines that in which shell will be used

to run the script.• # comments –comments can be made by using #

symbol in a script.• Chmod +x script.sh – to tell the linux that file is

executable.• ./script.sh to execute the script.

To check current shell ,type following:

echo $SHELL.

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Advantages of shell scripting• Shell script is much quicker

than programming in any

other languages.

• To automate the frequently

performed tasks.

• Easy to use and understand.

Non-geeks can also modify

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Disadvantages of shell scripting

• Slow execution speed.

• Prone to costly errors.

• Compatability problems

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ReferencesShell Scripting for Unix/Linux: Shell scripting

advantages and disadvantages Bash Shell Script Function Examples Linux Shell Scripting Tutorial - A Beginner's

handbook LinuxHelp.net

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