There are two ways we can have the shell evaluate an expression. Either using $((expression)) syntax or the expr command.

The former does not require proper spacing, while the latter does.

$ echo $((2+3))
5
$ expr 2 + 3
5

Arithmetic expasion only supports integer values and no decimals.

$ expr 2.3 + 2
expr: not a decimal number: '2.3'

Operators

Here are a list of arithmetic operators.

++ --

Increment, Decrement

+ -

Unary plus and minus

* / %

Multiplication, division and remainder

== !=

Equal and not equal

! && ||

Logical negation, AND, and OR

<< >>

Bit-shift left and right

~ & ^ |

Bitwise negation, AND, exclusive OR, and OR

\= += -= *= /= %=

Assignment operators

&= ^- <<= >>= |=

Bitwise assignment operators

Arithmetic test

It's important to avoid using the = symbol when comparing numerals. The = looks for string equality, not numeric equality. Thus, when working with arithmetic equations, be sure to use -eq instead.

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Linux for Beginners doesn't make any assumptions about your background or knowledge of Linux. You need no prior knowledge to benefit from this book. You will be guided step by step using a logical and systematic approach. As new concepts, commands, or jargon are encountered they are explained in plain language, making it easy for anyone to understand.