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'
```

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

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.

```
$ [ 1 = 1 ]; echo $?
0
$ [ 092 = 92 ]; echo $?
1
$ [ 092 -eq 92 ]; echo $?
0
```

Here is a list of more comparison tests we can use to compare two numbers. Be sure to *not* use canonical notations such as `>`

or `<`

!

- -eq
- Equal to
- -ne
- Not equal to
- -lt
- Less than
- -gt
- Greater than
- -le
- Less than or equal to
- -ge
- Greater than or equal to

```
$ [ 92 > 32 ]; echo $?
0 # Looks good...(but wrong)
$ [ 92 < 32 ]; echo $?
0 # Wrong
$ [ 92 -gt 32 ]; echo $?
0 # There we go!
```

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