How to print or access value of UDV (User defined variables)

 

To print or access UDV use following syntax

Syntax:
$variablename

Define variable vech and n as follows:
$ vech=Bus
$ n=10

To print contains of variable 'vech' type
$ echo $vech

It will print 'Bus',To print contains of variable 'n' type command as follows
$ echo $n

Caution: Do not try $ echo vech, as it will print vech instead its value 'Bus' and $ echo n, as it will print n instead its value '10', You must use $ followed by variable name.

Exercise
Q.1.How to Define variable x with value 10 and print it on screen.
Q.2.How to Define variable xn with value Rani and print it on screen
Q.3.How to print sum of two numbers, let's say 6 and 3?
Q.4.How to define two variable x=20, y=5 and then to print division of x and y (i.e. x/y)
Q.5.Modify above and store division of x and y to variable called z
Q.6.Point out error if any in following script
$ vi variscript # # # Script to test MY knowledge about variables! # myname=Vivek myos = TroubleOS myno=5 echo "My name is $myname" echo "My os is $myos" echo "My number is myno, can you see this number"

Answers : - 

Q.1.How to Define variable x with value 10 and print it on screen.
$ x=10
$ echo $x
Q.2.How to Define variable xn with value Rani and print it on screen
Ans.
$ xn=Rani
$ echo $xn

Q.3.How to print sum of two numbers, let's say 6 and 3
$ echo 6 + 3
This will print 6 + 3, not the sum 9, To do sum or math operations in shell use expr, syntax is as follows 
Syntax: expr   op1   operator   op2
Where, op1 and op2 are any Integer Number (Number without decimal point) and operator can be
+ Addition
- Subtraction
/ Division
% Modular, to find remainder For e.g. 20 / 3 = 6 , to find remainder 20 % 3 = 2, (Remember its integer calculation)
\* Multiplication
$ expr 6 + 3
Now It will print sum as 9 , But
$ expr 6+3
will not work because space is required between number and operator (See Shell Arithmetic)

Q.4.How to define two variable x=20, y=5 and then to print division of x and y (i.e. x/y)
Ans.
$x=20
$ y=5
$ expr x / y

Q.5.Modify above and store division of x and y to variable called z
Ans.
$ x=20
$ y=5
$ z=`expr x / y`
$ echo $z

Q.6.Point out error if any in following script
$ vi variscript # # # Script to test MY knolwdge about variables! # myname=Vivek myos = TroubleOS -----> ERROR 1 myno=5 echo "My name is $myname" echo "My os is $myos" echo "My number is myno, can you see this number" ----> ERROR 2

ERROR 1 is due to the space left between the equal to sign and the variable. This should not have spaces

ERROR 2 is due to the missing of $sign before the variable 'myno'

Following script should work now, after bug fix!
$ vi variscript # # # Script to test MY knolwdge about variables! # myname=Vivek myos=TroubleOS myno=5 echo "My name is $myname" echo "My os is $myos" echo "My number is $myno, can you see this number"