shell programing

8/7/2019 shell programing

1/26

Software Development 1:7005INT

Lecture 12


2/26

Announcements

Next weeks lecture topics (week 13): Revision

Discussion of the final exam

Course evaluation

Attendance essential!


3/26

Shell programming/scripts

What is a shell?

A shell is a program that allows system users tocommunicate with the operating system

The shell accepts commands from the system-users and passes them to the system for execution

In UNIX, three shells are available:

Bourne shell

Korn Shell

C Shell


4/26

UNIX Shells

The Bourne Shell was the first popularUNIX Shell

It is called the Bourne Shell because it was

written by Stephen Bourne

The Bourne Shell was written in the C

programming language and the executablefile (sh) is stored in the directory bin ( /bin/ )


5/26

UNIX Shells (cont.)

The C Shell was the second most popular UNIXShell after the Bourne Shell

It is called the C Shell because control structures

for the C Shell are very similar to the C language The Korn Shell is a mixture of the Bourne and C

Shells

It is called the Korn Shell because it was written

by David Korn


6/26

Shell Programming

What is shell programming? Shell programming is programming that

contains shell commands

A shell program is called a Shell Script

Shell programs or Scripts do not need acompiler because they contain shellcommands and can be executed from thecommand prompt


7/26

Example: A simple C Shell Script

File name: list.csh

#!/bin/csh

finger

ls -a | more

In the above script, the first line signals that thefile list.csh contains a C Shell Script (csh)

To execute the above script we must change thepermissions of the file list.csh using thechmod command as follows:

{/home1/staff/mblum} > chmod 700 list.csh

Run the script as follows:

{/home1/staff/mblum} > ./list.csh


8/26


9/26

Example: Assigning/Recallinginteger variable values

#!/bin/csh@ myage = 20

@ age1 = 10

@ age2 = 20

@ age = $age1 + $age2 + $myage

echo $age

The output of the above script will be 50


10/26

List Variables

The C shell allows users to create and access listvariables

Some examples are given below:

set programmingLanguages= (Pascal C LISP Java Ada) will create a list programmingLanguages with five

elements: Pascal, C, LISP, Java, Ada

echo $programmingLanguages will display Pascal C LISP Java Ada on the screen


11/26

List Variables (cont.)

set colors=(red blue green) will create a list colors with three elements red,

blue and green

echo $colors[2] will display blue on the screen

set colors=($colors yellow) will add yellow to the list colors


12/26

Example: Create and display a list

#!/bin/csh# create a list variable subjects

set subjects=(history, physics)

# add math to the list variable subjects

set subjects=($subjects math)

# display third element of the listecho $subjects[3]


13/26

Input/Output Commands

The echo command displays information on thescreen

For example:

echo I am here will display "I am here" on the screen

The $< command reads data from the keyboard

Example:

set myname = $

Documents

shell programing