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learnxinyminutes-docs/powershell.html.markdown
Andrew Ryan Davis 11db56b81c Making some minor fixes 
Adjusting some inconsistent names. 
Changing Remove-Array to Format-Array since Remove is not an approved Posh verb.
Adding Kevin Marquette's blog because it's awesome
Adding a simpler array reversal example
2020-08-20 12:30:32 -07:00

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---
category: tool
tool: powershell
contributors:
- ["Wouter Van Schandevijl", "https://github.com/laoujin"]
- ["Andrew Ryan Davis", "https://github.com/AndrewDavis1191"]
filename: LearnPowershell.ps1
---
PowerShell is the Windows scripting language and configuration management
framework from Microsoft built on the .NET Framework. Windows 7 and up ship
with PowerShell.
Nearly all examples below can be a part of a shell script or executed directly
in the shell.
A key difference with Bash is that it is mostly objects that you manipulate
rather than plain text. After years of evolving, it resembles Python a bit.
[Read more here.](https://docs.microsoft.com/powershell/scripting/overview)
Powershell as a Language:
```powershell
# Single line comments start with a number symbol.
<#
Multi-line comments
like so
#>
####################################################
## 1. Primitive Datatypes and Operators
####################################################
# Numbers
3 # => 3
# Math
1 + 1 # => 2
8 - 1 # => 7
10 * 2 # => 20
35 / 5 # => 7.0
# Single line comments start with a number symbol.
<#
Multi-line comments
like so
#>
####################################################
## 1. Primitive Datatypes and Operators
####################################################
# Numbers
3 # => 3
# Math
1 + 1 # => 2
8 - 1 # => 7
10 * 2 # => 20
35 / 5 # => 7.0
# Powershell uses banker's rounding
# Meaning [int]1.5 would round to 2 but so would [int]2.5
# division always returns a float. You must cast result to [int] to round
[int]5 / [int]3 # => 1.66666666666667
[int]-5 / [int]3 # => -1.66666666666667
5.0 / 3.0 # => 1.66666666666667
-5.0 / 3.0 # => -1.66666666666667
[int]$result = 5 / 3 # => 2
# Modulo operation
7 % 3 # => 1
# Exponentiation requires longform or the built-in [Math] class
[Math]::Pow(2,3) # => 8
# Enforce order of operations with parentheses
1 + 3 * 2 # => 7
(1 + 3) * 2 # => 8
# Boolean values are primitives (Note: the $)
$True # => True
$False # => False
# negate with !
!$True # => False
!$False # => True
# Boolean Operators
# Note "-and" and "-or" usage
$True -and $False # => False
$False -or $True # => True
# True and False are actually 1 and 0 but only support limited arithmetic
# However, casting the bool to int resolves this
$True + $True # => 2
$True * 8 # => '[System.Boolean] * [System.Int32]' is undefined
[int]$True * 8 # => 8
$False - 5 # => -5
# Comparison operators look at the numerical value of True and False
0 -eq $False # => True
1 -eq $True # => True
2 -eq $True # => False
-5 -ne $False # => True
# Using boolean logical operators on ints casts them to booleans for evaluation
# but their non-cast value is returned
# Don't mix up with bool(ints) and bitwise and/or (&,|)
[bool](0) # => False
[bool](4) # => True
[bool](-6) # => True
0 -and 2 # => 0
-5 -or 0 # => -5
# Equality is -eq (equals)
1 -eq 1 # => True
2 -eq 1 # => False
# Inequality is -ne (notequals)
1 -ne 1 # => False
2 -ne 1 # => True
# More comparisons
1 -lt 10 # => True
1 -gt 10 # => False
2 -le 2 # => True
2 -ge 2 # => True
# Seeing whether a value is in a range
1 -lt 2 -and 2 -lt 3 # => True
2 -lt 3 -and 3 -lt 2 # => False
# (-is vs. -eq) -is checks if two objects are the same type
# -eq checks if the objects have the same values.
[System.Collections.ArrayList]$a = @() # Point a at a new list
$a = (1,2,3,4)
$b = $a # => Point b at what a is pointing to
$b -is $a.getType() # => True, a and b equal same type
$b -eq $a # => True, a and b values are equal
[System.Collections.Hashtable]$b = @{} # => Point a at a new hash table
$b = @{'one' = 1
'two' = 2}
$b -is $a.GetType() # => False, a and b types not equal
# Strings are created with " or ' but " is required for string interpolation
"This is a string."
'This is also a string.'
# Strings can be added too! But try not to do this.
"Hello " + "world!" # => "Hello world!"
# A string can be treated like a list of characters
"Hello world!"[0] # => 'H'
# You can find the length of a string
("This is a string").Length # => 16
# You can also format using f-strings or formatted string literals
$name = "Steve"
$age = 22
"He said his name is $name." # => "He said his name is Steve"
“{0} said he is {1} years old.” -f $name, $age # => "Steve said he is 22 years old"
"$name's name is $($name.Length) characters long." # => "Steve's name is 5 characters long."
# $null is not an object
$null # => None
# $null, 0, and empty strings and arrays all evaluate to False.
# All other values are True
function test ($value) {
if ($value) {Write-Output 'True'}
else {Write-Output 'False'}
}
test ($null) # => False
test (0) # => False
test ("") # => False
test [] # => True
test ({}) # => True
test @() # => False
####################################################
## 2. Variables and Collections
####################################################
# Powershell uses the "Write-Output" function to print
Write-Output "I'm Powershell. Nice to meet you!" # => I'm Powershell. Nice to meet you!
# Simple way to get input data from console
$userInput = Read-Host "Enter some data: " # Returns the data as a string
# There are no declarations, only assignments.
# Convention is to use camelCase or PascalCase, whatever your team uses.
$someVariable = 5
$someVariable # => 5
# Accessing a previously unassigned variable does not throw exception.
# The value is $null by default
# Ternary Operators exist in Powershell 7 and up
0 ? 'yes' : 'no' # => no
# The default array object in Powershell is an immutable array
$defaultArray = "thing","thing2","thing3"
# you are unable to add or remove objects
$defaultArray.Add("thing4") # => Exception "Collection was of a fixed size."
# To have a mutable array, you will need to use the .NET ArrayList class
# ArrayLists store sequences
[System.Collections.ArrayList]$array = @()
# You can start with a prefilled ArrayList
[System.Collections.ArrayList]$otherArray = @(4, 5, 6)
# Add stuff to the end of a list with add (Note: it produces output, so append to $null)
$array.add(1) > $null # $array is now [1]
$array.add(2) > $null # $array is now [1, 2]
$array.add(4) > $null # $array is now [1, 2, 4]
$array.add(3) > $null # $array is now [1, 2, 4, 3]
# Remove from the end with index of count of objects-1 as arrays are indexed starting 0
$array.RemoveAt($array.Count-1) # => 3 and array is now [1, 2, 4]
# Let's put it back
$array.Add(3) > $null # array is now [1, 2, 4, 3] again.
# Access a list like you would any array
$array[0] # => 1
# Look at the last element
$array[-1] # => 3
# Looking out of bounds returns nothing
$array[4] # blank line returned
# You can look at ranges with slice syntax.
# The start index is included, the end index is not
# (It's a closed/open range for you mathy types.)
$array[1..3] # Return array from index 1 to 3 => [2, 4]
$array[2..-1] # Return array starting from index 2 => [4, 3]
$array[0..3] # Return array from beginning until index 3 => [1, 2, 4]
$array[0..2] # Return array selecting every second entry => [1, 4]
$array.Reverse() # mutates array to reverse order => [3, 4, 2, 1]
# Use any combination of these to make advanced slices
# Remove arbitrary elements from a array with "del"
$array.Remove($array[2]) # $array is now [1, 2, 3]
# Insert an element at a specific index
$array.Insert(1, 2) # $array is now [1, 2, 3] again
# Get the index of the first item found matching the argument
$array.IndexOf(2) # => 1
$array.IndexOf(6) # Returns -1 as "outside array"
# You can add arrays
# Note: values for $array and for $otherArray are not modified.
$array + $otherArray # => [1, 2, 3, 4, 5, 6]
# Concatenate arrays with "AddRange()"
$array.AddRange($otherArray) # Now $array is [1, 2, 3, 4, 5, 6]
# Check for existence in a array with "in"
1 -in $array # => True
# Examine the length with "Count" (Note: Length method on arrayList = each items length)
$array.Count # => 6
# Tuples are like arrays but are immutable.
# To use Tuples in powershell, you must use the .NET tuple class
$tuple = [System.Tuple]::Create(1, 2, 3)
$tuple.Item(0) # => 1
$tuple.Item(0) = 3 # Raises a TypeError
# You can do some of the array methods on tuples, but they are limited
$tuple.Length # => 3
$tuple + (4, 5, 6) # => Exception
$tuple[0..2] # => $null
2 -in $tuple # => False
# Hashtables store mappings from keys to values, similar to Dictionaries
$emptyHash = @{}
# Here is a prefilled dictionary
$filledHash = @{"one"= 1
"two"= 2
"three"= 3}
# Look up values with []
$filledHash["one"] # => 1
# Get all keys as an iterable with ".Keys".
# items maintain the order at which they are inserted into the dictionary.
$filledHash.keys # => ["one", "two", "three"]
# Get all values as an iterable with ".Values".
$filledHash.values # => [1, 2, 3]
# Check for existence of keys or values in a hash with "-in"
"one" -in $filledHash.Keys # => True
1 -in $filledHash.Values # => False
# Looking up a non-existing key returns $null
$filledHash["four"] # $null
# Adding to a dictionary
$filledHash.Add("five",5) # $filledHash["five"] is set to 5
$filledHash.Add("five",6) # exception "Item with key "five" has already been added"
$filledHash["four"] = 4 # $filledHash["four"] is set to 4, run again and it does nothing
# Remove keys from a dictionary with del
$filledHash.Remove("one") # Removes the key "one" from filled dict
####################################################
## 3. Control Flow and Iterables
####################################################
# Let's just make a variable
$someVar = 5
# Here is an if statement.
# This prints "$someVar is smaller than 10"
if ($someVar -gt 10) {
Write-Output "$someVar is bigger than 10."
}
elseif ($someVar -lt 10) { # This elseif clause is optional.
Write-Output "$someVar is smaller than 10."
}
else { # This is optional too.
Write-Output "$someVar is indeed 10."
}
<#
Foreach loops iterate over arrays
prints:
dog is a mammal
cat is a mammal
mouse is a mammal
#>
foreach ($animal in ("dog", "cat", "mouse")) {
# You can use -f to interpolate formatted strings
"{0} is a mammal" -f $animal
}
<#
For loops iterate over arrays and you can specify indices
prints:
0 a
1 b
2 c
3 d
4 e
5 f
6 g
7 h
#>
$letters = ('a','b','c','d','e','f','g','h')
for($i=0; $i -le $letters.Count-1; $i++){
Write-Host $i, $letters[$i]
}
<#
While loops go until a condition is no longer met.
prints:
0
1
2
3
#>
$x = 0
while ($x -lt 4) {
Write-Output $x
$x += 1 # Shorthand for x = x + 1
}
# Switch statements are more powerful compared to most languages
$val = "20"
switch($val) {
{ $_ -eq 42 } { "The answer equals 42"; break }
'20' { "Exactly 20"; break }
{ $_ -like 's*' } { "Case insensitive"; break }
{ $_ -clike 's*'} { "clike, ceq, cne for case sensitive"; break }
{ $_ -notmatch '^.*$'} { "Regex matching. cnotmatch, cnotlike, ..."; break }
{ 'x' -contains 'x'} { "FALSE! -contains is for lists!"; break }
default { "Others" }
}
# Handle exceptions with a try/catch block
try {
# Use "throw" to raise an error
throw "This is an error"
}
catch {
Write-Output $Error.ExceptionMessage
}
finally {
Write-Output "We can clean up resources here"
}
# Writing to a file
$contents = @{"aa"= 12
"bb"= 21}
$contents | Export-CSV "$env:HOMEDRIVE\file.csv" # writes to a file
$contents = "test string here"
$contents | Out-File "$env:HOMEDRIVE\file.txt" # writes to another file
# Read file contents and convert to json
Get-Content "$env:HOMEDRIVE\file.csv" | ConvertTo-Json
####################################################
## 4. Functions
####################################################
# Use "function" to create new functions
# Keep the Verb-Noun naming convention for functions
function Add-Numbers {
$args[0] + $args[1]
}
Add-Numbers 1 2 # => 3
# Calling functions with parameters
function Add-ParamNumbers {
param( [int]$FirstNumber, [int]$SecondNumber )
$FirstNumber + $SecondNumber
}
Add-ParamNumbers -FirstNumber 1 -SecondNumber 2 # => 3
# Functions with named parameters, parameter attributes, parsable documentation
<#
.SYNOPSIS
Setup a new website
.DESCRIPTION
Creates everything your new website needs for much win
.PARAMETER siteName
The name for the new website
.EXAMPLE
New-Website -Name FancySite -Po 5000
New-Website SiteWithDefaultPort
New-Website siteName 2000 # ERROR! Port argument could not be validated
('name1','name2') | New-Website -Verbose
#>
function New-Website() {
[CmdletBinding()]
param (
[Parameter(ValueFromPipeline=$true, Mandatory=$true)]
[Alias('name')]
[string]$siteName,
[ValidateSet(3000,5000,8000)]
[int]$port = 3000
)
BEGIN { Write-Verbose 'Creating new website(s)' }
PROCESS { Write-Output "name: $siteName, port: $port" }
END { Write-Verbose 'Website(s) created' }
}
####################################################
## 5. Modules
####################################################
# You can import modules and install modules
# The Install-Module is similar to pip or npm, pulls from Powershell Gallery
Install-Module dbaTools
Import-Module dbaTools
$query = "SELECT * FROM dbo.sometable"
$queryParams = @{
SqlInstance = 'testInstance'
Database = 'testDatabase'
Query = $query
}
Invoke-DbaQuery @queryParams
# You can get specific functions from a module
Import-Module -Function Invoke-DbaQuery
# Powershell modules are just ordinary Posh files. You
# can write your own, and import them. The name of the
# module is the same as the name of the file.
# You can find out which functions and attributes
# are defined in a module.
Get-Command -module dbaTools
Get-Help dbaTools -Full
####################################################
## 6. Classes
####################################################
# We use the "class" statement to create a class
class Instrument {
[string]$Type
[string]$Family
}
$instrument = [Instrument]::new()
$instrument.Type = "String Instrument"
$instrument.Family = "Plucked String"
$instrument
<# Output:
Type Family
---- ------
String Instrument Plucked String
#>
####################################################
## 6.1 Inheritance
####################################################
# Inheritance allows new child classes to be defined that inherit methods and
# variables from their parent class.
class Guitar : Instrument
{
[string]$Brand
[string]$SubType
[string]$ModelType
[string]$ModelNumber
}
$myGuitar = [Guitar]::new()
$myGuitar.Brand = "Taylor"
$myGuitar.SubType = "Acoustic"
$myGuitar.ModelType = "Presentation"
$myGuitar.ModelNumber = "PS14ce Blackwood"
$myGuitar.GetType()
<#
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True False Guitar Instrument
#>
####################################################
## 7. Advanced
####################################################
# The powershell pipeline allows us to do things like High-Order Functions
# Group Object is a handy command that does incredible things for us
# It works much like a GROUP BY in SQL would
<#
The following will get all the running processes
Group them by Name
And tell us how many instances of each process we have running
Tip: Chrome and svcHost are usually big numbers in this regard
#>
Get-Process | Foreach-Object ProcessName | Group-Object
<#
Asynchronous functions exist in the form of jobs
Typically a procedural language
Powershell can operate many non-blocking functions when invoked as Jobs
#>
# This function is commonly known to be non-optimized, and therefore slow
$installedApps = Get-CimInstance -ClassName Win32_Product
# If we had a script, it would hang at this func for a period of time
$scriptBlock = {Get-CimInstance -ClassName Win32_Product}
Start-Job -ScriptBlock $scriptBlock
# This will start a background job that runs the command
# You can then obtain the status of jobs and their returned results
$allJobs = Get-Job
$JobResponse = Get-Job | Receive-Job
# Math is built in to powershell and has many functions
$r=2
$pi=[math]::pi
$r2=[math]::pow( $r, 2 )
$Area = $pi*$r2
$Area
# To see all possibilities, check the members
[System.Math] | Get-Member -Static -MemberType All
<#
This is a silly one
You may one day be asked to create a func that could take $start and $end
and reverse anything in an array within the given range
based on an arbitrary array
Let's see one way to do that and introduce another data structure
#>
$targetArray = 'a','b','c','d','e','f','g','h','i','j','k','l','m','n'
function Format-Range ($start, $end) {
[System.Collections.ArrayList]$firstSectionArray = @()
[System.Collections.ArrayList]$secondSectionArray = @()
[System.Collections.Stack]$stack = @()
for ($index = 0; $index -lt $targetArray.Count; $index++) {
if ($index -lt $start) {
$firstSectionArray.Add($targetArray[$index]) > $null
}
elseif ($index -ge $start -and $index -le $end) {
$stack.Push($targetArray[$index])
}
elseif ($index -gt $end) {
$secondSectionArray.Add($targetArray[$index]) > $null
}
}
$returnArray = $firstSectionArray + $stack.ToArray() + $secondSectionArray
Write-Output $returnArray
}
# The previous method works, but it uses extra memory by allocating new arrays
# It's also kind of lengthy
# Let's see how we can do this without allocating a new array
# This is slightly faster as well
function Format-Range ($start, $end) {
while ($start -lt $end)
{
$temp = $targetArray[$start]
$targetArray[$start] = $targetArray[$end]
$targetArray[$end] = $temp
$start++
$end--
}
return $targetArray
}
```
Powershell as a Tool:
Getting Help:
```Powershell
# Find commands
Get-Command about_* # alias: gcm
Get-Command -Verb Add
Get-Alias ps
Get-Alias -Definition Get-Process
Get-Help ps | less # alias: help
ps | Get-Member # alias: gm
Show-Command Get-EventLog # Display GUI to fill in the parameters
Update-Help # Run as admin
```
If you are uncertain about your environment:
```Powershell
Get-ExecutionPolicy -List
Set-ExecutionPolicy AllSigned
# Execution policies include:
# - Restricted: Scripts won't run.
# - RemoteSigned: Downloaded scripts run only if signed by a trusted publisher.
# - AllSigned: Scripts need to be signed by a trusted publisher.
# - Unrestricted: Run all scripts.
help about_Execution_Policies # for more info
# Current PowerShell version:
$PSVersionTable
```
```Powershell
# Remoting into computers is easy
Enter-PSSession -ComputerName RemoteComputer
# Once remoted in, you can run commands as if you're local
RemoteComputer\PS> Get-Process powershell
<#
Handles NPM(K) PM(K) WS(K) CPU(s) Id SI ProcessName
------- ------ ----- ----- ------ -- -- -----------
1096 44 156324 179068 29.92 11772 1 powershell
545 25 49512 49852 25348 0 powershell
#>
RemoteComputer\PS> Exit-PSSession
<#
Powershell is an incredible tool for Windows management and Automation
Let's take the following scenario
You have 10 servers
You need to check whether a service is running on all of them
You can RDP and log in, or PSSession to all of them, but why?
Check out the following
#>
$serverList = @(
'server1',
'server2',
'server3',
'server4',
'server5',
'server6',
'server7',
'server8',
'server9',
'server10'
)
[scriptblock]$Script = {
Get-Service -DisplayName 'Task Scheduler'
}
foreach ($server in $serverList) {
$CmdSplat = @{
ComputerName = $Server
JobName = 'checkService'
ScriptBlock = $Script
AsJob = $true
ErrorAction = 'SilentlyContinue'
}
Invoke-Command @CmdSplat | Out-Null
}
<#
Here we've invoked jobs across many servers
We can now Receive-Job and see if they're all running
Now scale this up 100x as many servers :)
#>
```
Interesting Projects
* [Channel9](https://channel9.msdn.com/Search?term=powershell%20pipeline#ch9Search&lang-en=en) PowerShell tutorials
* [KevinMarquette's Powershell Blog](https://powershellexplained.com/) Really excellent blog that goes into great detail on Powershell
* [PSGet](https://github.com/psget/psget) NuGet for PowerShell
* [PSReadLine](https://github.com/lzybkr/PSReadLine/) A bash inspired readline implementation for PowerShell (So good that it now ships with Windows10 by default!)
* [Posh-Git](https://github.com/dahlbyk/posh-git/) Fancy Git Prompt (Recommended!)
* [Oh-My-Posh](https://github.com/JanDeDobbeleer/oh-my-posh) Shell customization similar to the popular Oh-My-Zsh on Mac
* [PSake](https://github.com/psake/psake) Build automation tool
* [Pester](https://github.com/pester/Pester) BDD Testing Framework
* [Jump-Location](https://github.com/tkellogg/Jump-Location) Powershell `cd` that reads your mind
* [PowerShell Community Extensions](https://github.com/Pscx/Pscx)
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