Powershell

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Reference

Files

Powershell scripts have a .ps1 extension.

Syntax

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# Documentation, information
Update-Help              # Update help system - to run as Administrator
help Test-Path           # Get help on a command, on an alias...
help Test-Path -full     # ... and on all options
help Test-Path -examples # ... see examples. VERY USEFUL. Eg. help save-help examples

Get-Command about_*      # DOES NOT WORK
Get-Command -Verb Add

Get-Alias ps                      # 'Get-Process'
Get-Alias -Definition Get-Process # 'ps'
gal | findstr Get-Process         # Unix style

ps | Get-Member

# Options can be abbreviated
Get-Alias -Definition Get-Process
gal -def Get-Process

# Single line comments start with a number symbol.

<#
  Multi-line comments
  like so
#>

# Frequent aliases (sorted by definition)
#   %       -> ForEach-Object
#   foreach -> ForEach-Object
#   alias   ->  Get-Alias
#   gal     ->  Get-Alias
#   dir     ->  Get-ChildItem
#   ls      ->  Get-ChildItem
#   gci     ->  Get-ChildItem
#   gcm     ->  Get-Command
#   cat     ->  Get-Content
#   type    ->  Get-Content
#   help    ->  Get-Help
#   gm      ->  Get-Member
#   ps      ->  Get-Process
#   man     ->  help
#   ni      ->  New-Item
#   md      ->  New-Item
#   mkdir   ->  New-Item
#   del     ->  Remove-Item
#   erase   ->  Remove-Item
#   rd      ->  Remove-Item
#   ri      ->  Remove-Item
#   rm      ->  Remove-Item
#   rmdir   ->  Remove-Item
#   where   ->  Where-Object
#   echo    ->  Write-Output
#   write   ->  Write-Output

Primitive types / operators

# Numbers
3
1 + 1                  # 2
2 - 1                  # 1
10 * 2                 # 20
10 / 2                 # 5
10 / 3                 # 3.3333333
[int](10 / 3)          # 3
[int]1.5 -eq [int]2.5  # True !
10 % 3                 # 1
[Math]::Pow(2,3)       # 8

# Boolean
$True                  # True
$False                 # False
-not $True             # False
$True  -and $True
$False -or  $False
0 -eq $False           # True
2 -ne $True            # True
[bool](0)              # False

# Bitwise
0 -band 2              # 0
-5 -bor 0              # -5

# Comparison
1 -eq 1
1 -ne 0
0 -lt 1
1 -le 1
1 -gt 0
1 -ge 1

Strings / arrays / dictionaries / ...

# Strings
$hello = "Hello"
$world = "World"
'Hello, World!'                        # No interpolation
"Hello, $world!"                       # 'Hello, World!'
"Hello, World!".Length                 # Length
"{0}, {1}!" -f $hello, $world          # f-string
"$world is $($world.length) char long"
'Hello, World!'[0]                     # 'H'
'Hello, World!'[0..5]                  # 'H', 'e', 'l', 'l', 'o'
'Hello, World!'.Substring(0,5          # 'Hello'
'Hello, ' + 'World!'                   # 'Hello, World!'
'First line`nSecond line'              # Escape with backtick
"foo" | gm                             # Get all methods / properties

# Arrays
# TBC

# Dictionaries
# TBC

Control flow

# if-then-else
if ($someVar -gt 10) {                      # Testing variable
   Write-Output "..."
}
elseif (-not $(Test-Path "somefile.txt")) { # Testing cmd result
   Write-Output "..."
}
else {
   Write-Output "..."
}

# foreach
foreach ($animal in ("dog", "cat", "mouse")) {
    # You can use -f to interpolate formatted strings
    "{0} is a mammal" -f $animal
}

# for
$letters = ('a','b','c','d','e','f','g','h')
for($i=0; $i -le $letters.Count-1; $i++){
    Write-Host $i, $letters[$i]
}

# while
$x = 0
while ($x -lt 4) {
    Write-Output $x
    $x += 1  # Shorthand for x = x + 1
}

# switch
$val = "20"
switch($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 }
  default                 { "Others" }
}

# try-catch-finally
try {
    throw "This is an error"   # Use "throw" to raise an error
}
catch {
    Write-Output $Error.ExceptionMessage
}
finally {
    Write-Output "We can clean up resources here"
}

IO

# read / write
Write-Output "Hello, World!"            # alias: echo, write
"Hello, World!"                         # ... same!
Write-Host "Hello, World!"              # Direct to console!
$foo = $(Write-Host "Hello, World!")    # !!! LIKELY BAD !!!
$foo = $(Write-Output "Hello, World!")  # Good
$foo = Write-Output "Hello, World!"     # Better
$foo = "Hello, World!"                  # ... same ;-)
$foo = Read-Host "Enter foo"
$bar = Read-Host ("Enter {0}" -f $foo)

# Write to file
$contents = "Hello"
$contents | Out-File "$env:HOMEDRIVE\file.txt"

# Read from a file
$contents = Get-Content "file.txt"

New-Item c:\foo         # Create directory
New-Item -Path c:\foo -ItemType Directory # Same
Remove-Item c:\foo      # Remove directory
Test-Path c:\foo        # 'True'
Copy-Item -Path c:\foo -Destionation c:\bar

# Grep-like
gal | findstr Get-Process
gal | where {$_.Definition -eq 'Get-Help'}
dir Alias: | where {$_.Definition -eq 'Get-Help'}

# Iterating on every files in $Path
ls $Path | foreach {$_.Name}  
ls $Path | % {$_.Name}          # same
# ... size filter
ls $Path | where {$_.Length -ge 2*1024} | % {$_.Name} 
# ... same, using get-item
get-item $Path\* | where {$_.Length -ge 2*1024} | % {$_.Name} 

Get-Item $Path            # Get a file object
(Get-Item $Path).Parent   # Get parent directory
(Get-Item $Path).Parent.FullName   # ... get path only
(Get-Item $Path).Directory.Parent  # ... if file
# ... These assumes $Path exists. If not, use Split-Path

Functions

# Functions: keep 'Verb-Noun' convention!

function Add-Numbers {   # No explicit args
 $args[0] + $args[1]
}

Add-Numbers 1 2          # 3

function Add-Numbers($first,$second) { # Explicit args
 $first + $second
}
function Add-Numbers {   # Explicit args with type
 param( [int]$first, [int]$second )
 $first + $second
}

Add-Numbers 1 2          # 3
Add-Numbers -first 1 -second 2 # 3

$res = Add-Numbers 1 2
$res = $(Add-Numbers 1 2)

Exec

dotnet.exe                             # Start an exe
&"c:\program files\dotnet\dotnet.exe"  # With space, use call operator '&' ...
."c:\program files\dotnet\dotnet.exe"  # ... or '.'
&"c:\program files\dotnet\dotnet.exe" --help # option outside the quotes

# We can run scriptblocks with '&' (in own scope)
$i = 2
$scriptBlock = { $i=5; Write-Output $i }
& $scriptBlock                         # 5
$i                                     # 2

# ... but '.' run in current scope
& $scriptBlock                         # 5
$i                                     # 5

# Testing command success with $? or checking for $null
$res = ...  # Some command exec
if ($? -and $res -ne $null) {
    Write-Host "Command succeeded"
}
else {
    Write-Host "Command failed"
}

Miscellaneous

# Script environment
$MyInvocation.MyCommand
# CommandType     Name      Version  Source
# -----------     ----      -------  ------
# ExternalScript  test.ps1           C:\tmp\test.ps1
$MyInvocation.MyCommand.Definition    # C:\tmp\test.ps1

# Namespaces
ls "HKLM:\Software\Microsoft\PowerShell\1\ShellIds"  # HKLM for registry
"$env:PATH"                                          # Env variables

Tips

Measure execution time of a command

Measure-Command { dir }
Measure-Command { dir | Out-default}   # To get output
Measure-Command { choco list }

Update help on offline computers

From MS devblogs:

<source lang="powershell">

1. On online computer

New-Item c:\tmp\help Save-Help -DestinationPath c:\tmp\help -Module * -Force

1. On offline computer
2. ... transfer files to c:\tmp\help
3. ... start powershell in admin (Win-X-A)

Update-Help -SourcePath c:\tmp\help -Module * -Force </source