Julia 中，变量即是关联到某个值的名字。当你想存储一个值（比如数学计算中的某个中间变量）以备后用时，变量的作用就体现出来了。举个例子：
```
# Assign the value 10 to the variable x
julia> x = 10
10
# Doing math with x's value
julia> x + 1
11
# Reassign x's value
julia> x = 1 + 1
2
# You can assign values of other types, like strings of text
julia> x = "Hello World!"
"Hello World!"
```
Julia 提供了极其灵活的变量命名系统。变量名区分大小写。
```
julia> x = 1.0
1.0
julia> y = -3
-3
julia> Z = "My string"
"My string"
julia> customary_phrase = "Hello world!"
"Hello world!"
julia> UniversalDeclarationOfHumanRightsStart = "人人生而自由，在尊严和权力上一律平等。"
"人人生而自由，在尊严和权力上一律平等。"
```
也可以使用 Unicode 字符（UTF-8 编码）来命名：
```
julia> δ = 0.00001
1.0e-5
julia> 안녕하세요 = "Hello"
"Hello"
```
在 Julia REPL 和其它一些 Julia 的编辑环境中，支持 Unicode 数学符号 的输入。只需要键入对应的 LaTeX 语句，再按 tab 键即可完成输入。 比如，变量名 `δ` 可以通过 `\delta-tab` 来输入，又如 ``α̂₂` `` 可以由` ``\alpha-tab-\hat-tab-\_2-tab` 来完成。
Julia 甚至允许重新定义内置的常数和函数：
```
julia> pi
π = 3.1415926535897...
julia> pi = 3
Warning: imported binding for pi overwritten in module Main
3
julia> pi
3
julia> sqrt(100)
10.0
julia> sqrt = 4
Warning: imported binding for sqrt overwritten in module Main
4
```
很显然, 不鼓励这样的做法。
可用的变量名
Variable names must begin with a letter (A-Z or a-z), underscore, or a subset of Unicode code points greater than 00A0; in particular, [Unicode character categories](http://www.fileformat.info/info/unicode/category/index.htm) Lu/Ll/Lt/Lm/Lo/Nl (letters), Sc/So (currency and other symbols), and a few other letter-like characters (e.g. a subset of the Sm math symbols) are allowed. Subsequent characters may also include ! and digits (0-9 and other characters in categories Nd/No), as well as other Unicode code points: diacritics and other modifying marks (categories Mn/Mc/Me/Sk), some punctuation connectors (category Pc), primes, and a few other characters.
Operators like `+` are also valid identifiers, but are parsed specially. In some contexts, operators can be used just like variables; for example` (+)` refers to the addition function, and `(+) = f` will reassign it. Most of the Unicode infix operators (in category Sm), such as` ⊕,` are parsed as infix operators and are available for user-defined methods (e.g. you can use `const ⊗ = kron` to define` ⊗` as an infix Kronecker product).
内置的关键字不能当变量名：
```
julia> else = false
ERROR: syntax: unexpected "else"
julia> try = "No"
ERROR: syntax: unexpected "="
```
命名规范
尽管 Julia 对命名本身只有很少的限制, 但尽量遵循一定的命名规范吧：
* 变量名使用小写字母
* 单词间使用下划线 ('_') 分隔，但不鼓励
* 类型名首字母大写, 单词间使用驼峰式分隔.
* 函数名和宏名使用小写字母, 不使用下划线分隔单词.
*修改参数的函数结尾使用 ! . 这样的函数被称为 mutating functions 或 in-place functions
