Skip to Main Content
bash Pocket Reference
book

bash Pocket Reference

by Arnold Robbins
May 2010
Beginner to intermediate content levelBeginner to intermediate
130 pages
3h 20m
English
O'Reilly Media, Inc.
Content preview from bash Pocket Reference

Arithmetic Expressions

The let command performs arithmetic. Bash is restricted to integer arithmetic. The shell provides a way to substitute arithmetic values (for use as command arguments or in variables); base conversion is also possible:

$(( expr ))

Use the value of the enclosed arithmetic expression.

B#n

Interpret integer n in numeric base B. For example, 8#100 specifies the octal equivalent of decimal 64.

Operators

The shell uses arithmetic operators from the C programming language, in decreasing order of precedence.

Operator

Description

++ --

Auto-increment and auto-decrement, both prefix and postfix

+ -

Unary plus and minus

! ~

Logical negation and binary inversion (one’s complement)

**

Exponentiation[a]

* / %

Multiplication, division, modulus (remainder)

+ -

Addition, subtraction

<< >>

Bitwise left shift, bitwise right shift

< <= > >=

Less than, less than or equal to, greater than, greater than or equal to

== !=

Equality, inequality (both evaluated left to right)

&

Bitwise AND

^

Bitwise exclusive OR

|

Bitwise OR

&&

Logical AND (short circuit)

||

Logical OR (short circuit)

?:

Inline conditional evaluation

= += -=

 

*= /= %=

 

<<= >>=

Assignment

&= ^= |=

 

,

Sequential expression evaluation

[a] The ** operator is right-associative. Prior to version 3.1, it was left-associative.

Examples

let "count=0" "i = i + 1"       Assign values to i and count
let "num % 2"                   Exit successfully if num is even
(( percent >= 0 && \
   percent <= 100 ))            Test the range of a value ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Bash Pocket Reference, 2nd Edition

Bash Pocket Reference, 2nd Edition

Arnold Robbins
bash Quick Reference

bash Quick Reference

Arnold Robbins
Mastering Bash

Mastering Bash

Giorgio Zarrelli

Publisher Resources

ISBN: 9781449388669Errata Page