This document discusses PowerShell functions including: - Defining functions with parameters and a function body - Calling functions and getting function details - Passing arguments by value and reference - Scope of functions inside and outside other functions - Using begin, process, and end blocks in advanced functions - Differences between functions and filters

1. Jason

2. function <name> (<parameter list>)
{
<function body>
}

3. function Say-Hello()
{
Write-Host "Hello World from a function in PowerShell."
}
> Say-Hello

4. function Say-Hello
{
Write-Host "Hello World from a function in PowerShell."
}
$helloFunction = Get-Command Say-Hello -type Function
$helloFunction.GetType().FullName
>System.Management.Automation.FunctionInfo

5.  $helloFunction | gm –type Property

6. $helloFunction.ScriptBlock
> Write-Host "Hello World from a function in PowerShell."
$helloFunction.ScriptBlock.GetType().FullName
> System.Management.Automation.ScriptBlock
& $helloFunction.ScriptBlock
>Hello World from a function in PowerShell.

7. $helloFunction. Definition
> Write-Host "Hello World from a function in PowerShell."
$helloFunction. Definition.GetType().FullName
> System.String
Invoke-Expression $helloFunction. Definition
>Hello World from a function in PowerShell.

8. function Write-Sum([int]$first =$(throw “first value required”) , [int]$second = “5”)
{
$sum = $first + $second
Write-Host "Sum:$sum"
}
Write-Sum 6 9

9. $name = “Jason"
function AssignValueToParam($name)
{
$name = “Hung"
Write-Host "inside function : $name"
}
AssignValueToParam $name
Write-Host "Outside function : $name"

10. function Write-Variable($name)
{
$v1 = Get-Variable $name -Scope 0 -ValueOnly
$v2 = Get-Variable $name -Scope 1 -ValueOnly
Write-Host "$v1 $v2"
}
$name = "Jason"
Write-Variable "name"

11. function Write-Variable([ref]$name)
{
$name.GetType().FullName
#System.Management.Automation.PSReference
$name.Value = "Hung"
}
$name = "Jason"
Write-Variable ([ref]$name)
$name

12. function Generate-NumberTo($max)
{
for($i=0; $i -lt $max; $i++)
{
$i
}
}
Generate-NumberTo 4

13. function Find-Object($target, $haystack)
{
foreach ($item in $haystack)
{
if($item -eq $target)
{
return $item
}
}
}
Find-Object 5 (2..19)

14. function OuterFunction()
{
function InnerFunction()
{
Write-Host "Printed by InnerFunction!"
}
InnerFunction
}
OuterFunction

15. function OuterFunction()
{
function Do-Something()
{
Write-Host "Original Do-Something function"
}
function InnerFunction()
{
function Do-Something()
{
Write-Host "Overriden Do-Something function"
}
Do-Something
}
InnerFunction
Do-Something
}
OuterFunction

16. function global:Do-Something()
{
Write-Host "Global Do-Something"
}
function InnerScope()
{
function local:Do-Something()
{
Write-Host "Local Do-Something"
}
local:Do-Something
global:Do-Something
}
InnerScope

17. function Get-FileSize
{
begin
{
$total = 0
}
process
{
Write-Host "processing: $($_.name)"
$total += $_.Length
}
end
{
return $total
}
}
dir *.txt | Get-FileSize

18. filter Even-Filter
{
if ($_ %2 -eq 0)
{
$_
}
}
function Even-Function
{
process
{
if ($_ % 2 -eq 0)
{
$_
}
}
}
Get-Command Even-Function -CommandType Function
Get-Command Even-Filter -CommandType Function
CommandType
----------Function
Filter
Name
---Even-Function
Even-Filter
Definition
---------process {...
...