Powershell#

Crash Course#

Basic terminology	Definition
Cmdlet	Commands built into shell written in .NET
Functions	Commands written in PowerShell language
Parameter	Argument to a Cmdlet/Function/Script
Alias	Shortcut for a Cmdlet or Function
Scripts	Text files with .ps1 extension
Applications	Existing windows programs

Basic Operators#


`=`,`+=`,`-=`,`*=`,`/=`,`%=`,`++`,`--`	assigns one or more values to variable
`-and`,`-or`,`-xor`,`-not`/`!`	logical operators
`-band`,`-bor`,`-bxor`,`-bnot`,`-shr`,`-shl`	bitwise operators
`-split`	splits a string (ex: `“abcdefghi” -split “de”`)
`-join`	joins multiple strings (ex: `“abc”,”def”,”ghi” -join “;”`)
`	`
`,`	comma operator (array constructor)
`@()`	array subexpression operator

Comparison Operators#


`-eq`,`-ieq`,`-ceq`	equal
`-ne`,`-ine`,`-cne`	not equal
`-gt`,`-igt`,`-cgt`	greater than
`-ge`,`-ige`,`-cge`	greater than or equal to
`-lt`,`-ilt`,`-clt`	less than
`-le`,`-ile`,`-cle`	less than or equal to
`-like`,`-ilike`,`-clike`	wildcard matching
`-notlike`,`-inotlike`,`-cnotlike`	negation of `-like`
`-match`,`-imatch`,`-cmatch`	regular expression match
`-notmatch`,`-inotmatch`,`-cnotmatch`	negation of `-match`
`-replace`, `-ireplace`, `-creplace`	replace matching elements (ex: `“abcde” -replace “bc”, “TEST”`)
`-contains`,`-icontains`,`-ccontains`	check if value in array (ex: `1,2,3,4,5 -contains 3`)
`-notcontains`,`-inotcontains`,`-cnotcontains`	negation of `-contains`
`-in`,`-notin`	syntactic reverse of `-contains/-notcontains` (ex: `3 -in 1,2,3,4,5`)

string comparisons: default case-insensitive
-c prefix: case sensitive variant e.g. -ceq
-i prefix: case-insensitive variant e.g. -ieq
$list -op $foo: shortcut for using operator as filter i.e. returns list items satisfying -op

[!important]
-contains, -in, -is, -replace: can't be used this way

PowerShell

$a = (1,2) -eq 3 
  := (1,2) | Where-Object { $_ -eq 2 }
$a.GetType().Name # result: Object[]
$a.Count          # result: 0

Type Operators#


`-is`,`-isnot`	test if object is an instance of a specified .NET type (ex: `42 –is [int]`)
`-as`	attempt type conversion to .NET type (ex: `$a = 42 –as [String]`)
`[]`	type cast (ex: `[datetime]$birthday = "1/10/66"`)
`()`	grouping expression operator

Flow Control#

PowerShell

if ($expr) {...} elseif ($expr) {...} else {...}
while ($expr) {...}
for ($i = 0; $i -lt 10; $i++) {...}
foreach ($file in Get-ChildItem 'C:\') { $file.name }
1..10 | ForEach-Object { $_ }

Special Operators#

($list).property/method: Member Access Enumeration i.e. shortcut for map on collection

PowerShell

(Get-Service -Name event*).DisplayName 
  := (Get-Service -Name event*).ForEach({ $_.DisplayName })
  := (Get-Service -Name event*) | ForEach-Object { $_.DisplayName }
# result: @('Windows Event Log', 'COM+ Event System', ...)

[!note] Nuances
if property exists on collection, only the collection property is returned
PowerShell
(Get-Service).Count => 176
if error occurs during enumeration, method is invoked only on the items enumerated before error

more details around undefined members, $null values, errors, etc

$(): subexpression operator that evaluates inner expression with result treated as a variable i.e. expr form of block stmts
can contain statements e.g. i.e. expression operator

each statement's output appends to final scalar or array result

PowerShell

if($(code returning value) -eq "somevalue") { do_something }
$city="Copenhagen"
$strLength = "$($city.length)"
"The result of 2 + 3 = $(2+3)"
$(Get-WMIObject win32_Directory)

&: call/invocation operator to run command, script, or script block
can run commands stored in variables and represented by strings
does not parse or interpret command parameters
PowerShell
```
$c = "get-executionpolicy"
& $c
```
.: dot sourcing operator to run script in current scope
all script created functions/aliases/variables are added to the current scope
PowerShell
```
. c:/scripts/sample.ps1
. ./sample2.ps1
```
-f: format operator for string interpolation with format args e.g. padding, alignment, hex etc

PowerShell

1..10 | foreach { "{0:N2}" -f $_ }
Get-ChildItem c:\ | ForEach-Object {'File {0} Created {1}' -f $_.fullname,$_.creationtime}

..: range operator to produce number sequence

PowerShell

10..20
1..10 | foreach {$_ * 5}
-5..0.9 # a more readable version of the same thing.

Redirection Operators#

n	Output streams
`1`	`success` stream i.e. `stdout`
`2`	`error` stream i.e. `stderr`
`3`	`warning` stream
`4`	`verbose` stream
`5`	`debug` stream
`6`	`information` stream
`*`	`all` Streams


`n>`	send stream to file (default: `n=1`)
`n>>`	append stream to file (default: `n=1`)
`n>&1`	redirects stream to `success` stream (default: `n=1`)

[!note] limitations
can only redirect to success stream

PowerShell

Get-Process word* | Stop-Process
Do-Something 3>   warning.txt # Writes warning output to warning.txt
Do-Something 4>>  verbose.txt # Appends verbose.txt with the verbose output
Do-Something 5>&1             # Writes debug output to the output stream
Do-Something *>&1             # Redirects all streams to stdout
Do-Something *>   out.txt     # Redirects all streams to out.txt

Gotchas#

Common Parameters/Preference Variables not inherited across module scopes
Details

Cheatsheet#

Useful Commands#

Command
`Update-Help`	Downloads and installs newest help files
`Get-Help get-process`	Get help for command
`Get-Command`	Get all commands
`Get-Command -Module RGHS`	Get all commands in RGHS module
`Get-Command Get-p*`	Get all commands starting with get-p
`Get-Member`	Gets the properties and methods of objects
`Get-Module`	Gets all imported and importable modules
`Get-Process \\| Get-Member`	Get members of the object
`Get-Process \\| format-list -properties *`	Get-Process as list with all properties
`Ctrl`+`c`	Interrupt current command
`Left`/`Right`	Navigate editing cursor
`Ctrl`+`Left`/`Right`	Navigate a word at a time
`Home`/`End`	Move to start / end of line
`Up'/'Down`	Move up and down through history
`Insert`	Toggles between insert/overwrite mode
`F7`	Command history in a window
`Tab`/`Shift`+`Tab`	Command line completion

Scripting#

%: alias for foreach-object
$_: current item in foreach-object
Get-Member: object introspection
pretty print
object: Write-Host ($foo | Format-Table | Out-String)
array: Write-Host ($foo | Format-List | Out-String)
string interpolation
use $ in double quotes e.g. "blaaa $myvar" or "blaaaa$($myobjVar.name)"
no string expansion: '$blaaa'
invoke command/script
& foo @(arg0,arg2,...): call operator invokes expression in child scope that's discarded (e.g. any global variable changes not persisted)
. foo @(arg0,arg2,...): dot sourcing invokes expression in current scope (e.g. global changes are persisted)
common batch operations
get all items in a directory: Get-ChildItem *
get all subdirectories: Get-ChildItem -Attributes Directory -Recurse
get all files in directory: Get-ChildItem *.docx | % Name
enabling -WhatIf, -Confirm, etc
add [CmdletBinding(SupportsShouldProcess = $true)] to param block
inside function, wrap state change code with if ($PSCmdlet.ShouldProcess(target,operation)) {...}
dump variables in a scope e.g. scope captured by GetNewClosure()

PowerShell

$m = (Get-Command testFunc2).Module
& $m Get-Variable -Scope 0

dump function definition

[!warning] Function provider has no containers and is always rooted

PowerShell

Get-ChildItem -Path Function:              # Dump all the functions in the current session
(Get-Item -Path function:mkdir).Definition # Dump Function Definition
$function:mkdir                            # Alternate Syntax for above

create function closure

[!warning] appears to capture "only" local variables i.e. those from the caller's current scope

PowerShell

function New-Function {
  $x = $global:x
  $function:global:testFunc2 = {$x}.GetNewClosure()
}

invocation info
$PSScriptRoot, $PSCommandPath: info about the current script
$MyInvocation.PSScriptRoot, $MyInvocation.PSCommandPath: info about the invoker or calling script

$MyInvocation Properties

Property
`$MyInvocation.BoundParameters`	This member provides a dictionary of the parameters that were bound for this script or command.
`$MyInvocation.CommandOrigin`	This property tells you if you were being invoked inside the runspace or if it was an external request.
`$MyInvocation.DisplayScriptPosition`	The position for the invocation or error.
`$MyInvocation.ExpectingInput`	Is true if this command is expecting input...
`$MyInvocation.HistoryId`	History ID that represents the command. If unavailable, this will be -1.
`$MyInvocation.InvocationName`	Command name used to invoke this string - if invoked through an alias, then this would be the alias name.
`$MyInvocation.Line`	The text of the line that contained this cmdlet invocation.
`$MyInvocation.MyCommand`	Provide basic information about the command
`$MyInvocation.OffsetInLine`	Command's character offset in that line. If the command was executed directly through the host interfaces, this will be -1.
`$MyInvocation.PipelineLength`	How many elements are in the containing pipeline
`$MyInvocation.PipelinePosition`	which element this command was in the containing pipeline
`$MyInvocation.PositionMessage`	Formatted message indicating where the cmdlet appeared in the line
`$MyInvocation.PSCommandPath`	This property tells you the full path to the command from where you were being invoked
`$MyInvocation.PSScriptRoot`	This property tells you the directory from where you were being invoked
`$MyInvocation.ScriptLineNumber`	The line number in the executing script that contained this cmdlet.
`$MyInvocation.ScriptName`	The name of the script containing the cmdlet.
`$MyInvocation.UnboundArguments`	This member provides a list of the arguments that were not bound to any parameter

PSScriptAnalyzer Linter#

[!info] Built-in Rules

Rule	Enabled	Config	Severity
PSAlignAssignmentStatement	No	Yes	Warning
PSAvoidAssignmentToAutomaticVariable	Yes		Warning
PSAvoidDefaultValueForMandatoryParameter	Yes		Warning
PSAvoidDefaultValueSwitchParameter	Yes		Warning
PSAvoidGlobalAliases	Yes		Warning
PSAvoidGlobalFunctions	Yes		Warning
PSAvoidGlobalVars	Yes		Warning
PSAvoidInvokingEmptyMembers	Yes		Warning
PSAvoidLongLines	No	Yes	Warning
PSAvoidMultipleTypeAttributes	Yes		Warning
PSAvoidNullOrEmptyHelpMessageAttribute	Yes		Warning
PSAvoidOverwritingBuiltInCmdlets	Yes	Yes	Warning
PSAvoidSemicolonsAsLineTerminators	No		Warning
PSAvoidShouldContinueWithoutForce	Yes		Warning
PSAvoidTrailingWhitespace	Yes		Warning
PSAvoidUsingBrokenHashAlgorithms	Yes		Warning
PSAvoidUsingCmdletAliases	Yes	Yes	Warning
PSAvoidUsingComputerNameHardcoded	Yes		Error
PSAvoidUsingConvertToSecureStringWithPlainText	Yes		Error
PSAvoidUsingDeprecatedManifestFields	Yes		Warning
PSAvoidUsingDoubleQuotesForConstantString	No	Yes	Warning
PSAvoidUsingEmptyCatchBlock	Yes		Warning
PSAvoidUsingInvokeExpression	Yes		Warning
PSAvoidUsingPlainTextForPassword	Yes		Warning
PSAvoidUsingPositionalParameters	Yes		Warning
PSAvoidUsingUsernameAndPasswordParams	Yes		Error
PSAvoidUsingWMICmdlet	Yes		Warning
PSAvoidUsingWriteHost	Yes		Warning
PSDSCDscExamplesPresent	Yes		Information
PSDSCDscTestsPresent	Yes		Information
PSDSCReturnCorrectTypesForDSCFunctions	Yes		Information
PSDSCStandardDSCFunctionsInResource	Yes		Error
PSDSCUseIdenticalMandatoryParametersForDSC	Yes		Error
PSDSCUseIdenticalParametersForDSC	Yes		Error
PSDSCUseVerboseMessageInDSCResource	Yes		Error
PSMisleadingBacktick	Yes		Warning
PSMissingModuleManifestField	Yes		Warning
PSPlaceCloseBrace	No	Yes	Warning
PSPlaceOpenBrace	No	Yes	Warning
PSPossibleIncorrectComparisonWithNull	Yes		Warning
PSPossibleIncorrectUsageOfAssignmentOperator	Yes		Warning
PSPossibleIncorrectUsageOfRedirectionOperator	Yes		Warning
PSProvideCommentHelp	Yes	Yes	Information
PSReservedCmdletChar	Yes		Error
PSReservedParams	Yes		Error
PSReviewUnusedParameter	Yes		Warning
PSShouldProcess	Yes		Warning
PSUseApprovedVerbs	Yes		Warning
PSUseBOMForUnicodeEncodedFile	Yes		Warning
PSUseCmdletCorrectly	Yes		Warning
PSUseCompatibleCmdlets	Yes	Yes	Warning
PSUseCompatibleCommands	No	Yes	Warning
PSUseCompatibleSyntax	No	Yes	Warning
PSUseCompatibleTypes	No	Yes	Warning
PSUseConsistentIndentation	No	Yes	Warning
PSUseConsistentWhitespace	No	Yes	Warning
PSUseCorrectCasing	No	Yes	Information
PSUseDeclaredVarsMoreThanAssignments	Yes		Warning
PSUseLiteralInitializerForHashtable	Yes		Warning
PSUseOutputTypeCorrectly	Yes		Information
PSUseProcessBlockForPipelineCommand	Yes		Warning
PSUsePSCredentialType	Yes		Warning
PSUseShouldProcessForStateChangingFunctions	Yes		Warning
PSUseSingularNouns	Yes		Warning
PSUseSupportsShouldProcess	Yes		Warning
PSUseToExportFieldsInManifest	Yes		Warning
PSUseUsingScopeModifierInNewRunspaces	Yes		Warning
PSUseUTF8EncodingForHelpFile	Yes		Warning

disable rule

PowerShell

[System.Diagnostics.CodeAnalysis.SuppressMessage('PSAvoidUsingWriteHost', '')]

[!note] can control scoping
scope to file, add to top of file and param() below attribute
PowerShell
[System.Diagnostics.CodeAnalysis.SuppressMessage('PSAvoidUsingWriteHost','')]
param()
namespace scope
PowerShell
[System.Diagnostics.CodeAnalysis.SuppressMessage('PSAvoidUsingWriteHost','',Scope='Namespace')]

list approved powershell verbs

PowerShell

Get-Verb | Sort-Object Verb

Resources#

PowerShell Cheatsheet
ss64 Powershell: concise reference
powershell.one: dives into more intermediate scripting topics like modules, scripting, etc
Everything You Wanted To Know About: series geared towards fast ramp up
Arrays
Hashtable
PsCustomObject
String Interpolation
PowerShell Best Practices and Style Guide