POWERSHELL
Dr. Sarah Gothard
CEG 233
Spring 2010
Reference Book Suggestion
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Windows PowerShell in Action by Bruce Payette (co-designer
of the PowerShell language) is available online at
http://proquest.safaribooksonline.com.ezproxy.libraries.wrig
ht.edu:2048/9781932394500
That same site has about 10 other PowerShell books
Posted examples from Windows PowerShell in Action:
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http://www.manning.com/payette/
To run a script for the first time, you must open PowerShell in
administrator mode (right click on the shortcut and choose “run as
Administrator) and type
“set-executionpolicy remotesigned”.
Unsigned scripts that were downloaded must be individually
unblocked in file properties from Windows Explorer.
PowerShell Introduction
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object based—everything in PowerShell is an object
built on MS .NET framework
can access any .NET object
 output is always a .NET object
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many common Linux commands work in PowerShell
full regex support
unless explicitly stated, nothing is case sensitive
PowerShell is technically strongly typed but performs
automatic type conversions as needed
scripts are not associated directly with the shell for
security
Handy starting commands

Help: man or Get-Help
 man
*
 man about_*
 man –detailed
 man -full
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Command list: gcm or Get-Command
Variable list: gv or Get-Variable
Drive information: gdr or Get-PSDrive
Run a cmd command: cmd /c target_command
Interface Operations
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To freeze the screen, highlight any text.
To copy text, highlight it and press enter.
To paste text, right click in the PowerShell window.
Use home and end to go to the beginning and the
end of a line, respectively.
Use up and down arrows to navigate command
history.
Use pg up to see the first command entered in a
session and pg dn to see the last.
Scripting and Command Line
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Any PowerShell cmdlet, control statement, operation,
etc., can be used both in a script and from the
command line.
If a typed command is clearly not finished,
PowerShell will begin a new console line after the
first. Once the code is complete, hit enter twice to
trigger completion.
To type something from the command line that
requires an extra line, put a backquote at the end
of the first line. Hit enter twice when you are done.
Scalar Variables
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$num = 1
$str = "Hi"
$flt = [Math]::Pi
$proc = (get-process)[0]
$date = Get-Date
Provided Variables (part 1)
Name
$_
Description
The current pipeline object; used in script blocks, filters, the process
clause of functions, where-object, foreach-object and switch
$^
contains the first token of the last line input into the shell
$$
contains the last token of last line input into the shell
$?
$Args
Contains the success/fail status of the last statement
Used in creating functions that require parameters
If an error occurred, the object is saved in the $error PowerShell
$Error
variable
$foreach Refers to the enumerator in a foreach loop.
$HOME
The user's home directory; set to %HOMEDRIVE%\%HOMEPATH%
$Host
Information about the currently executing host
$Input Input piped to a function or code block
Provided Variables (part 2)
Name
Description
$LastExitCode The exit code of the last native application to run
$Match
A hash table consisting of items found by the –match operator.
$MyInvocation Information about the currently script or command-line
$true
Boolean TRUE
$false
Boolean FALSE
$null
A null object
Output Field Separator, used when converting an array to a
$OFS
string. By default, this is set to the space character.
$profile
Path to a script file that will execute each time PS is opened.
The identifier for the shell. This value is used by the shell to
$ShellID
determine the ExecutionPolicy and what profiles are run at
startup.
$StackTrace
contains detailed stack trace information about the last error
Escape Sequences
Escape Sequence
`a
``
`b
`r
`$
`n
`0
`”
`’
`t
`
Description
Alert
Back quotation
Backspace
Carriage return
Dollar sign
Line feed
Null
Quotation mark
Single quotation mark
Tab
Continue to next line
Math and Time
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System.Math
 All
typical math operations
 Use with get-member -static
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System.DateTime
 Use
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with get-member -static
Get-Random
Timing a command:
 Measure-Command
{target command}
Collections
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Any variable can be treated like a collection of
one.
collections are zero based
Collections are automatically flattened when they
are sent down a pipe
To keep collections from being flattened, use a
comma before the collection. The unary comma
operator instructs PowerShell to wrap the object in
a new array that contains that single object. When
that array is flattened, we get our original array.
Collection Examples
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$nums = 1, 2, 3+7..20
$strs = “Hi”, “Mom”
$flts = [Math]::Pi, [Math]::E
$procs = Get-Process
$files = @(Get-ChildItem *.sys)
@
forces a collection
Empty Sets
Valid output can consist of an empty set
 $null is used to represent an empty set
 The foreach statement iterates over a
scalar once, even if that scalar happens
to be $null.
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Aliases
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Most PowerShell commands have a shorter alias.
Operations:
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List the current aliases: get-alias
Find aliases for a given command:
get-alias -def command
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Find command for a given alias: get-alias alias
Create an alias: set-alias name target
To load a set of aliases each time, put them in your profile
file, whose path is stored in the variable $PROFILE:
1.
2.
Create your profile file manually:
ni -path $profile -itemtype file -force
Open your file: notepad $profile
Files
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Get with Get-Item or Get-ChildItem
Call methods on files:
(Get-item books.txt).isReadOnly = $true
 (gi books.txt).set_isReadOnly($true)
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Create file: ni or New-Item
Remove file: rm or Remove-Item
Check if a file exists: Test-Path
Check if directory:
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Get-Item * | where {$_.PSISContainer}
Search
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File by name
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Get-Item -path path -filter pattern
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Get-Childitem -recurse -path path -filter pattern
File contents
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Select-String –path path –pattern pattern
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Get-Childitem -recurse * | select-string -pattern pattern
Service by name:
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Get-Service pattern
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Get-Service | Where-Object {$_.Status -eq "Stopped"}
Process by name
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Get-Process -Name pattern
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Get-Process | Sort-Object cpu | select-object -last 5
Variable by name: Get-Variable -Name pattern
Compare File Contents

diff -referenceobject $(get-content
reference file) -differenceobject $(getcontent compare file)
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diff -referenceobject $(get-content
reference file) -differenceobject $(getcontent compare file) –includeequal
Midline cmdlets
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Midline cmdlets are cmdlets that normally operate on
operands that are piped to them.
Examples:

where-object:

get-service | Where-Object {$_.Status –eq
“Stopped”}
more
 foreach
 Sort-Object
 Select-String
 Get-Member
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Comparison Operators
Operation
Equal to
Less than
Greater than
Greater than or equal to
Less than or equal to
Not equal to
Not
And
Or
Operator
-eq
-lt
-gt
-ge
-le
-ne
-not, !
-and
-or
Text Comparison Operators
Operation
Like
Not like
Match
Not Match
Replace
Equal
Not equal
Case-sensitive equal
Case-sensitive not equal
Operator
-like
-notlike
-match
-notmatch
-replace
-eq
-ne
-ceq
-cne
Branch Statements
if (condition) {code block}
elseif (condition) {code block}
else {code block}
switch (expression)
{
(test) {code block}
value {code block}
default {code block}
}
Loops
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do { code block } while (condition)
while (condition) { code block }
do { code block } until (condition)
for (init; condition; increment) { code block }
foreach ($var in $array) { code block }
break
continue
Functions
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Creation
function name
{
param($param1, $param2)
operations
}
Invocation
function_name arg1 arg2
Function returns
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A return statement essentially ends the method.
Any function output that wasn’t captured is
returned.
To keep from returning more than you intend,
throw away unwanted output:
 [void]$string.append ($i)
 mkdir folder 2> $null
Output from an echo is considered a return
value. If you want it to output to the screen
instead, use Write-Host.
Parsing Modes
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Strings do not need quotes unless they have spaces
& in front forces a string to be executed
A dot in front executes a script
Expression: ()
Subexpression (possibility of multiple semicolonseparated statements): $()
Array Subexpression: @()
Create Windows Shortcut
1.
2.
3.
4.
$wsh = New-Object -ComObject
WScript.Shell
$link = $wsh.CreateShortcut(“absolute
path to shortcut\shortcut name.lnk”)
$link.TargetPath = “absolute path of file”
$link.Save()
Advanced Topics (see reference book)
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Output text colors
Errors and exceptions
Built-in debugging
GUI scripts (several examples in reference book)
Windows system administration: WMI
Security
Provided Windows PowerShell ISE