main

docs/document/Powershell/docs/Language/Control Flow.md

@@ -31,11 +31,11 @@ gci `
 > [!TIP]
 > Stop using backticks! They're ugly! Use hashtable splatting instead.
 >```ps1
->$table = {
+>$table = @{
 >  Filter = '*.mp4';
 >  File = $true
 >}
->gci -file @table
+>gci @table
 >```
 
 ## Multi-Line Piping

docs/document/Powershell/docs/Language/Function.md

@@ -101,16 +101,6 @@ Foo -Foo foo -Bar bar
 Foo foo bar # it's the same # [!code highlight] 
 ```
 
-### Default Parameter
-
-```ps1
-function Foo {
-    param (
-        [string]$foo = "foo"
-    )
-}
-```
-
 ### Flags
 
 Defining flags that represents a toggle needs a special type called `switch`.
@@ -135,6 +125,32 @@ Manual assignment is also available:
 Foo -f:$false -b $true
 ```
 
+### Default Parameter
+
+- Explicitly typed parameters can have implicit default value.
+    - `switch` and `bool` is `$false` by default.
+    - `string` is `[string]::Empty` by default.
+    - Numeric types are zero value by default.
+- Parameters without type annotation are always typed as `object` which has the default value `$null`.
+- Can override default value by `=` in declaration.
+
+```ps1
+
+& { param([string]$name) $name -eq [string]::Empty } # True
+& { param($name) $name -eq $null } # True
+& { param([int]$age) $age -eq 0 } # True
+& { param([switch]$is) $is -eq $false } # True
+
+function Foo {
+    param (
+        [string]$foo = "foo"
+    )
+}
+```
+
+> [!NOTE]
+> For overriding default parameter outside the function, see [$PSDefaultParameterValues](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_parameters_default_values?view=powershell-7.4#long-description) 
+
 ### Required Parameter
 
 All parameters are optional by default. Use `[Parameter(Mandatory=$true)]` to mark it as required.
@@ -196,14 +212,49 @@ But things will explode when we're dealing with a pipeline input which might bri
 The pipeline mechanism is essentially based on the `Enumerator` so if we collect all items into a new collection as parameter value, it can be a huge performance issue.
 So named blocks are essentially to defined a shared process logic for each object in the pipeline input, and other logic like initializationa and finalization.
 
-> [!NOTE]
-> When no named block were specified, `end` block is used to represent the whole logic of a simple function.
+- `begin`: state initializationa for the pipeline iteration.
+- `process`: logic for each pipeline iteration.
+- `end`: final action for the completed pipeline iteration.
+- `clean`: a `finally` block to execute clean up no matter what happens.(PowerShell 7.3+)
 
 ```ps1
 function Foo {
     begin {}
     process {}
     end {}
+    clean {}
+}
+```
+
+> [!NOTE]
+> When no named block were specified, `end` block is used to represent the whole logic of a simple function.
+>```ps1
+>function Foo {
+>    end {
+>        echo hello
+>    }
+>}
+># equivalent to 
+>function Foo {
+>    echo hello
+>}
+>```
+
+## Filter Function
+
+Filter is a special kind of function that implicitly accepts pipeline to perform transformation(select) or filtering(where).
+Filter is useful when you need to reuse the same logic for unknown pipeline manipulations, reducing hard coding.
+
+```ps1
+filter Foo {
+    "$_" # can transform
+}
+
+# equivalent to
+function Foo {
+    process {
+        "$_"
+    }
 }
 ```
 

docs/document/Powershell/docs/Language/Invocation.md

@@ -9,11 +9,11 @@ Call operator `&` can be used for invoking one of the following:
 
 - Command without any option.
 - A `.ps1` script file
+- External executable
 - Script block
 
-**`&` is awared of the context of current session, it does not start a new process.**
-
-It's more like a system execution 
+> [!NOTE]
+> **`&` is awared of the context of current session, it does not start a new process when executing.**
 
 ```ps1
 & 'gps'

docs/document/Powershell/docs/Object Manipulation/Object Members.md

@@ -2,35 +2,35 @@
 
 ## Member Inspection
 
+### Inspect from Pipeline
+
+`Get-Member` can insepct objects from a pipeline input, which means by iterating them one by one.
+
 > [!TIP]
 > Use `gm` alias for `Get-Member`.
 
+**Only members from a unique type in that pipeline input enumeration will be collected as the result.**
+
 ```ps1
-ls | Get-Member
+(gci -file | select -first 1 | gm).Length # 53
+(gci -dir | select -first 1 | gm).Length # 47
+# assuming current directory has both directory and file
+(gci | gm).Length # 53 + 47 = 100
 ```
 
-When inspecting an array of objects, `gm` only returns members for distinct types.
+The whole array returned from `Get-Member` is `object[]`, each item inside is a `MemberDefinition`
 
 ```ps1
-@(123, '123') | gm | select -ExpandProperty TypeName -Unique
-# System.Int32
-# System.String
-
-(@('123', 123) | Get-Member).Length # 82
-(@('123', 123, 123) | Get-Member).Length # still 82
-
+(gci | gm) -is [object[]] # True
+(gci | gm | select -first 1) -is [MemberDefinition] # True
 ```
 
-`Get-Member` returns a `MemberDefinition[]` or a `MemberDefinition` with following properties.
+### Inspect from Object
+
+To treat a whole collection as the object to be inspected, do not pipe it, pass it to `-InputObject` instead.
 
-```cs
-class MemberDefinition
-{
-    public string Definition { get; } // expression or value or signature of the member
-    public System.Management.Automation.PSMemberTypes MemberType { get; } // type of member
-    public string Name { get; } // member name
-    public string TypeName { get; } // fullname of type or return type of the member
-}
+```ps1
+gm -InputObject (gci -file) # TypeName: System.Object[]
 ```
 
 ## Member Types

docs/document/Powershell/docs/Object Manipulation/Select.md

@@ -118,6 +118,26 @@ $partner['Status'] # Poisoned
 > [!NOTE]
 > `-ExpandProperty` can only take one property.
 
+### Calculated Property
+
+`Select-Object` can generate new NoteProperty to the `PSCustomObject` returned by specifying a HashTable with following shape:
+- `Name`(or `N`, `Lable`, `L`): the name of the new property.
+- `Expression`(`E`): the calculation logic for the new property represented as a script block.
+
+```ps1
+$person = @{
+    FirstName = 'John'
+    LastName = 'Smith'
+}
+
+# return a new PSCustomObject that has FirstName, LastName and FullName.
+$person | select *, @{ Name = 'FullName'; Expression = { "$($_.FirstName) $($_.LastName)" } }
+```
+
+> [!NOTE]
+> All selected properties from a HashTable will be regenerated as `NoteProperty`.
+> Those selected properties are essentially `Keys` of the HashTable, not real properties.
+
 ## Take a Count
 
 `Select-Object` can also take specific count of items from a collection, from start or end.

docs/document/Powershell/docs/Understanding Pipeline.md

@@ -1,4 +1,4 @@
-#
+# Understanding Pipeline
 
 Overview of pipeline in powershell:
 
@@ -9,6 +9,7 @@ Overview of pipeline in powershell:
 ## Pipeline Parameter Binding
 
 
+
 ## How Cmdlet Accept Pipeline Input
 
 There's two solution when a pipeline input comes in as a fallback:
@@ -29,10 +30,6 @@ spps -Name (gci -File | foreach Name)
 gci -File | spps
 ```
 
-
-> [!WARNING]
-> If multiple matches exist on ByPropertyName solution, powershell throws an error since these paramters might not be allowed to be used together.
-
 ByValue is always tried first, and then use ByPropertyName, or it finally throws.
 A parameter accepts pipeline input does not necessarily have both solutions, it can have at least one of them.
 
@@ -54,3 +51,99 @@ $table = @{ Name = 'foo'; Age = 18 }
 
 This is simply because these types are more likely to be treated as a whole object, even when dictionaries are `IEnumerable<KeyValuePair<,>>`.
 
+
+## Enumerate Pipeline Items
+
+You can use `$input` to refer to the enumerator passed to the function. This is another way to access pipeline input items but with more control.
+Another option is use `$_` to represent the current item in `process` block, this is way more limited but commonly used.
+
+- `$input` represents a enumerator for pipeline input in `process` block.
+- `$input` represents the whole collection for pipeline input in `end` block.
+- `$input` will be consumed after being used once in either `process` or `end`. Use `Reset` to get it back.
+- You can't use `$input` in both `process` and `end`.
+
+### Access Current Item
+
+`$input.Current` have to manually invoke `MoveNext` before you access `Current` in `process` block since it's not a `while` loop.
+
+```ps1
+function Test {
+    begin {
+        $input -is [System.Collections.IEnumerator] # True
+    }
+
+    process {
+        # $input.Current before MoveNext in each iteration is always $null
+        # How weird!
+        $input.Current -eq $null # True because we haven't start the enumeration!
+        $input.MoveNext() | Out-Null # [!code highlight] 
+        $input.Current -eq $null # False
+    }
+}
+
+1,2,3 | Test
+```
+
+> [!WARNING]
+> Before you read the following content, please keep in mind that `$input` behaves slightly different from general `IEnumerator` for `Reset`.
+
+`$input` itself is a wrapper of current item in `process` block, invoke `Reset` to get it back to current value.
+
+```ps1
+function Test {
+    process {
+
+    }
+}
+
+1,2,3 | Test
+```
+
+## Implicit Pipeline Input
+
+Function can accepts pipeline input without any specific parameter.
+Inside the `process` block, `$_` represents the current object from the pipeline input.
+
+```ps1
+function Test {
+    process {
+        $_ -is [System.IO.FileInfo] # True
+    }
+}
+
+gci -file | Test
+```
+
+> [!NOTE]
+> `$_` is only available in `process` block.
+
+## Explicit Pipeline Input
+
+If you write a custom function that have one or more parameters accept pipeline input, what is going on inside?
+
+- In `begin` block, there's no value assigned to each `ByPropertyName` parameter, they remain default.
+- In `process` block, each 
+
+```ps1
+function Foo {
+    param (
+        [Parameter(ValueFromPipelineByPropertyName)]
+        [string]$Name
+        [Parameter(ValueFromPipelineByPropertyName)]
+        [string]$Length
+    )
+
+    begin {
+        $Name -eq [string]::Empty # True
+        $Length -eq 0 # True
+    }
+
+    process {
+        $Name
+        $Length
+    }
+}
+
+gci -file | Foo
+```
+