Shell Scripting: -

Part – 1:

Q) Why we go for shell scripting ?

Ans – In Unix command prompt, we can run a single command at a time. To combine and run multiple command for performing certain tasks, shell script is evolved.

Q) What is shebang or Hash line or magic line or dang line ?

Ans – The 1^st line of the shell script is called hash line or shebang or magic line or dang line.

It is written as below.

For default shell,

#! /bin/sh

For K – Shell,

#! /bin/ksh

Q) Which command is used in shell script to print output in screen ?

Ans – echo command

Q) Print ‘Hello World’ in shell script ?

Ans –

#! /bin/sh

echo “Hello World”

Q) How to run a shell script ?

Ans – There are two ways to run a shell script. Such as –

1. 1^st Way –

$ vi script1.sh<Enter – Key>

#! /bin/sh

echo “Hello World”

Esc + :wq<Enter – Key>

$ chmod 755 script1.sh<Enter – Key>

$ ./script1.sh<Enter – Key>

Hello World

2. 2^nd Way –

#! /bin/sh

echo “Hello World”

Esc + :wq<Enter – Key>

$ sh script1.sh<Enter – Key>

For K – shell, $ ksh script1.ksh<Enter – Key>

Q) How to comment lines present in shell script ?

Ans – By inserting single ‘#’ or multiple ‘#’ in the beginning of the line make the line comment.

Example –

$ vi script2.ksh

#! /bin/ksh

###echo “Hello World” – Commented line

echo “Time Begins” – Uncommented line

###echo “Social Activity” – Commented line

ESC + :wq<Enter – Key>

$ ksh script2.ksh<Enter – Key>

Output – Time Begins

Q) What are variables in shell script ?

Ans – There are two types of shell script variable. Such as –

1. Scalar Variable – This Variable holds data of any data type. It stores only a single value at a time.

Example –

$ vi script3.ksh

#! /bin/ksh

i=5

echo “i value = $i”

i=4.5

echo “i value = $i”

i=’India’

echo “I value = $i”

i=’you are a good boy’

echo “i value = $i”

Esc + :wq<Enter – Key>

$ ksh script3.ksh<Enter – Key>

Output –

i value = 5

i value = 4.5

i value = India

i value = you are a good boy

2. Array – To store multiple values of different datatype in continuous memory location, we go for array.

Q) What are ways to read input from command line ?

Ans – There are two ways to read an input from command line. Such as –

1. 1^st Way –

$ vi script4.sh

#! /bin/sh

echo “Enter values of a and b: “

read a b

echo “Value of a = $a and Value of b = $b”

Esc + :wq<Enter – Key>

$ sh script4.sh<Enter – Key>

Output –

Enter values of a and b:

23 13

Value of a = 23 and Value of b = 13

2. 2^nd Way –

$ vi script5.sh

#! /bin/sh

echo “Value of a = $1”

echo “Value of b = $2”

echo “Value of c = $3”

Esc + :wq<Enter – Key>

$ sh script5.sh 43 23 67<Enter – Key>

Output –

Value of a = 43

Value of b = 23

Value of c = 67

Or

$ chmod 755 script5.sh<Enter – Key>

$./script5.sh 43 23 67<Enter – Key>

Output –

Value of a = 43

Value of b = 23

Value of c = 67

Q) What is the output of below script ?

#! /bin/sh

i=5

j=7

echo “Value of I = $i and j = $j”

echo ‘Value of I = $i and j = $j”

Ans –

Value of I = 5 and j = 7

Value of I = $i and j = $j

Q) Which variable is used in shell script to keep the value of the variable constant throughout the script?

Ans – readonly variable

Example –

#! /bin/sh

a=78

echo “Value of a = $a”

readonly a

a=56

echo “Value of a = $a”

Output –

Value of a = 78

Value of a = 78