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  Oracle Tips by Burleson

Evaluating expressions

Shells can evaluate complex expressions and allow you to perform math functions. The following examples demonstrate some simplistic math.

$ expr 6 + 3


$ expr 6 + 3 + 8


$ expr 8 - 2


$ expr 12 / 3


$ expr 15 \* 3


$ expr 20 % 3


$ echo `expr 15 + 3`


In the examples above:

The multiplication example uses an escape character before the * so that the * is not interpreted as a wildcard symbol.

20 % 3 is read as 20 mod 3 and yields the remainder when 20 is divided by 3.

The last example uses the backward quote sign (`) to enclose the command. The command within the backward quotes is executed and the result echoed to the screen.

Since we mentioned the use of the backward quote (backtick), this is probably a good time to explain the rules regarding the use of quotes:

Double quote () variables are expanded when enclosed in double quotes

Single quote () variables within single quotes are not expanded

Backward quote (`) enclose commands

The use of single versus double quotes

$ myname='Terry Clark'

$ echo 'My name is $myname'

My name is $myname

$ echo "My name is $myname"

My name is Terry Clark


The above book excerpt is from:

Easy Linux Commands
Working Examples of Linux Command Syntax

ISBN: 0-9759135-0-6   

Terry Clark 

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