[PowerShell]4. Variables(variable converting)

PowerShell does not distingush variable types. Rather PowerShell automatically declares the data type of variable when it is created. Data type is determined by data input.

 

Let's create variables by inputting data and figure out variable type with built-in PowerShell function, "GetType"

 

[Variable Data Type]

String

String variable is used when storing a mixture of characters, number and special characters

Declare a variable name with "$" sign then equal sign(=) then data enclosed in double quotes("")

PS C:\Users\jaehui.yoon> $temp = "Hello World"
$temp.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     String                                   System.Object

Integer

Integer variable is used when storing a number without decimal point

Declare a variable name with "$", equal sign(=) then number

PS C:\Users\jaehui.yoon> $temp = 1
$temp.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     Int32                                    System.ValueType

 

Double

Double variable is used when storing a number with decimal point

Declare a variable name with "$", equal sign(=) then number with decimal point

PS C:\Users\jaehui.yoon> $temp = 3.14
$temp.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     Double                                   System.ValueType

 

Boolean

Boolean variable is used when storing a state either true or false like a binary value.

Declare a variable name with "$", equal sign(=) then dollor sign($) the "true" or "false"

PS C:\Users\jaehui.yoon> $temp = $true
$temp.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     Boolean                                  System.ValueType

 

Array

Array variable is used when storing a series of values. It could be any type of values mentioned above.

Declare a variable name with "$", equal sign(=) then a series of numbers or/and strings with comma(,) as separator

PS C:\Users\jaehui.yoon> $temp = 1,2,3, "hi", "bye"
$temp.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     Object[]                                 System.Array

 

Hash table

Hash table is used when storing values with tag such as "name" = "jaehee yoon"

Hash table respresents a collection of key-value pairs. Data needs to be input enclosed in curly braces({})

PS C:\Users\jaehui.yoon> $temp = @{Name="J"; Age=5; City="Busan"}
$temp.GetType()
$temp

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     Hashtable                                System.Object                                                                                                                      

Key   : Name
Value : J
Name  : Name


Key   : Age
Value : 5
Name  : Age


Key   : City
Value : Busan
Name  : City

It is feasible to add/delete hash data after the hash table is created with the format below.

 

PS C:\Users\jaehui.yoon> $temp["GF"]="Honey"

PS C:\Users\jaehui.yoon> $temp

Name                           Value                                                                                                                                                          
----                           -----                                                                                                                                                          
GF                             Honey                                                                                                                                                          
Name                           J                                                                                                                                                              
Age                            5                                                                                                                                                              
City                           Busan

 

* Null

PowerShell supports creating variable without data. It can be done by explicitly input $null or without inputting data for a variable.

* When a variable created without data, data type cannot be determined so that GetType() function returns an error

PS C:\Users\jaehui.yoon> $temp = $null
$temp.GetType()
null 값 식에서 메서드를 호출할 수 없습니다.
위치 줄:2 문자:1
+ $temp.GetType()
+ ~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

 

[Variable Conversion]

There would be cases that a variable needs to be converted from one type to another. Three ways are availble for converting variables in PowerShell.

 

1. Cast operator

Cast operator[data type] can be placed after equal sign(=) then this can convert date type

PS C:\Users\jaehui.yoon> $temp = "42"
$temp.GetType()
$temp = [int]$temp
$temp.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     String                                   System.Object                                                                                                                      
True     True     Int32                                    System.ValueType

 

2. Parse method

"Parse" method can be used to convert a string to a type

PS C:\Users\jaehui.yoon> $temp = "42"
$temp.GetType()
$temp = [int]::parse($temp)
$temp.GetType()

IsPublic IsSerial Name                                     BaseType            
-------- -------- ----                                     --------            
True     True     String                                   System.Object       
True     True     Int32                                    System.ValueType

3. Conversion method

There are number of data converting method which can convert data type

PS C:\Users\jaehui.yoon> $temp = "42"
$temp.GetType()
$temp = [Convert]::ToInt32($temp)
$temp.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                                           
-------- -------- ----                                     --------                                                                                                                           
True     True     String                                   System.Object                                                                                                                      
True     True     Int32                                    System.ValueType