--- 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 # 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)