music

# arithmetic substitution

## summary

This subchapter looks at arithmetic substitutions in UNIX (and Linux).

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Teach Yourself UNIX/Linux System Administration and Shell Programming

## free computer programming text book project

If you like the idea of this project,

# arithmetic substitution

This subchapter looks at arithmetic substitutions in UNIX (and Linux).

### arithmetic substitution

You can use arithmetic substitution for quick integer artihmetic.

Place an integer arithmetic expression inside double parenthesis and place a dollar mark before the parenthesized expression (wow, that’s a lot of words), \$(( expression )).

\$(( 5 + 3 ))

You may use integer constants or integer variables:

\$(( 5 + \$z ))

You may post-increment, post-decrement, pre-increment, or pre-decrement variables:

\$(( --x + z++ ))

You may use negative integers:

\$(( -1 * -2 ))

You may use logical (!) and bitwise (~) negation:

\$(( !1 * ~2 ))

The order of precedence (and complete list of possible operations):

operatormeaning
VAR++ VAR--variable post-increment and pre-increment
++VAR --VARvariable pre-increment and pre-decrement
- +unary minus and plus
! ~logical negation and bitwise negation
**exponentiation
* / %multiplication, division, and modulo
<< >>left bitwise shift and right bitwise shift
<= >= < >comparison operators
== !=equality and inequality
&bitwise AND
^bitwise exclusive OR
|bitwise OR
&&logical AND
||logical OR
expression ? expression : expressionC-style conditional evaluation
= *= /= %= += -= <<= >>= &= ^= !=assignments
,separator between expressions

Applying the precedence rules:

\$(( ((3 + 5*2) -8) /2 ))

The result for the above expression is 2. It is not 2.5 because this is integer arithmetic. It is not 4 because the multiplcation has a higher precedence than addition.

You can have a raw expression, which is useful if it includes an assignment operator:

\$ n=1
\$ echo \$n
1
\$ (( n += 3 ))
\$ echo \$n
4
\$

phone number:
message:

# free music player coding example

Coding example: I am making heavily documented and explained open source code for a method to play music for free — almost any song, no subscription fees, no download costs, no advertisements, all completely legal. This is done by building a front-end to YouTube (which checks the copyright permissions for you).

View music player in action: www.musicinpublic.com/.

Create your own copy from the original source code/ (presented for learning programming).

## view text bookHTML file

Because I no longer have the computer and software to make PDFs, the book is available as an HTML file, which you can convert into a PDF.

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## free book on UNIX/Linux System Administration

Teach Yourself UNIX/Linux System Administration and Shell Programming

## free computer programming text book project

Building a free downloadable text book on computer programming for university, college, community college, and high school classes in computer programming.

If you like the idea of this project,

send donations to:
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