Introducing Windows PowerShell
Introducing Powershell
Windows PowerShell is a commandline, which works object-oriented. It strongly looks like the command prompt one is already used to. The command prompt does exsist since the first Operating System of Microsoft (MS-DOS). PowerShell is its worthy successor. As already said, PowerShell works object-oriented, which means its commands do not only execute instructions, they can edit objects.
Objects, CMdlets and Pipelines
PowerShell works with objects. A cmdlet creates an object, which is passed onto the next cmdlet. For example, a Get command creates an object and lists it to the screen. This output is formatted internaly and displayed to the user. An object can be a procces, a service or an array of symbols. There are more than hunderd objects avaiable in PowerShell.
First steps
Get-Alias give an overview to all MS-DOS commands and its PowerShell definitions. Cmdlets follow the same pattern: a verb at first, like Set or Get, second a noun.
Set: Data is changed or createdGet: Data is requestedFormat: Data is formatedOut: created an output from data
with the use of the tabulator-button all possible option are shown.
Parameters always start with a -
Get-Help %name%shows help for a certain commandUpdate-Helpupdates the “Help” directoryShow-Command %name%provides a graphical interface for all parametersget-command | group commandTypeshows the quantity of all cmdlets , functions and aliases
The operator | is called a pipeline. Whith th euse of it, commands can be combined and forwarded to the next cmdlet
sort: with the use of sort-object the output can be sorted. P.E.: Get-Command | Sort-Object -Property Source sorts the commands by its source. Parameters are -descending or -ascending.
Date and Time
There are several options do display time with Powershell wit the use of get-Date :
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get-Date -format d
25.09.2023
get-Date -format t
10:25
get-Date -format T
10:25:36
get-Date -format HH:mm:ss:ff
10:25:49:11
The f-Operator
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"Es ist {0:dddd}, der {0:d},{0:t}" -f (Get-Date)
Es ist Montag, der 25.09.2023,10:27
With the use of the f-operator a String is read to the following command.
with the use of - two times can be subtracted.
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PS C:\Users\Administrator> (get-date)-(get-date "1/1/2019 0:0:0")
Days : 1728
Hours : 10
Minutes : 46
Seconds : 36
Milliseconds : 213
Ticks : 1493379962135507
TotalDays : 1728,44903024943
TotalHours : 41482,7767259863
TotalMinutes : 2488966,60355918
TotalSeconds : 149337996,213551
TotalMilliseconds : 149337996213,551
It is possible to get the time from a different computer, but not with the use of Get-Date. Therefore Win32_Currenttime has to be used.
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Get-CimInstance Win32_Currenttime -computername Win2019-2
Drive-, Folder- and Datamanagement
Get-Drive
With the use of Get-Disk and Get-PsDrive you can get information about from the drives.
New-Item
New-Item creates new Data or Structure, with -type file or directory it can be further defined. ni is an alias for New-Item.
Copy-Item
with Copy-Item data can be copied.
Move-Item
With Move-Item data can be moved.
Remove-Item
With Remove-Item data can be removed.
Get-Location / Test-Location
With Get-Location the current file-path is shown.
With Test-Location the given file-path is tested.
Measure-Object
dir | Measure-Object -property length sum
With the use of the Commands the size and quantity can be read. The number of all Files in a Subfolder can be found out with:
(Get-ChildItem -path $Env:Systemroot -Recourse).Count
Editing Textfiles
Get-Content
Textfiles are read with Get-Content
-path defines the path to the file.
If only a certain line is to be read, arrays can be used:
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(Get-Content test.txt)[-2][0]
2-dimensional arrays are used. The First dimension defines the rows, the second the columns. The can be counted positive or negative: 1 is the first, -1 the last column.
Set-Content
A new file can be created with the use of Set-Content.
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PS C:\Powershell> set-Content newtest.txt
Cmdlet Set-Content an der Befehlspipelineposition 1
Geben Sie Werte für die folgenden Parameter an:
Value[0]: This is a new File.
Value[1]:
PS C:\Powershell> Get-Content newtest.txt
This is a new File.
Add-Content
With Add-Content new data can be added to a file.
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# This adds new text
add-content newtest.txt -value "NewText"
# A file can be added to another
add-content newtest.txt -value (get-content test.txt)
Clear-Content
Clears a File.
Searching Files
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#a file can be searched with this command:
Get-ChildItem -Path test.txt | Select-String "dazu"
#Output:
PS C:\Powershell> Get-ChildItem -Path test.txt | Select-String "dazu"
test.txt:2:Und hier die zweite Zeile dazu.
Replacing Content
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# replace , with ;
(Get-Content test.txt) -replace " ",";"
#Output:
PS C:\powershell> (Get-Content test.txt) -replace " ",";"
Dies;ist;eien;Testdate.
Und;hier;die;zweite;Zeile;dazu.
Danach;die;dritte.
Gefolgt;von;der;vierten.
Die;Fünfte;ist;die;Letzte.Nummer;6.
PS C:\powershell>
The Output happens only in the Terminal screen. It is nothing changed in the file.
Get-Item
Every Data and Folder has several attributes as name, length..
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PS C:\powershell> get-item test.txt
Verzeichnis: C:\powershell
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a---- 26.09.2023 16:28 141 test.txt
PS C:\powershell>
Some Values are read with Get-ItemProperty test.txt -name length
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PS C:\powershell> Get-ItemProperty test.txt -name length
length : 141
PSPath : Microsoft.PowerShell.Core\FileSystem::C:\powershell\test.txt
PSParentPath : Microsoft.PowerShell.Core\FileSystem::C:\powershell
PSChildName : test.txt
PSDrive : C
PSProvider : Microsoft.PowerShell.Core\FileSystem
Attributes
| Parameter | definition |
|---|---|
| d—– | Directory |
| -a—- | Archive (p.e. File) |
| –r— | ReadOnly |
| —h– | Hidden |
| —-s- | Systemfile |
| —–l | Link |
All letters have a destined place. Combinations are possible.
Get-ItemProperty
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PS C:\powershell> Get-ItemProperty test.txt -name mode
mode : -ar---
PSPath : Microsoft.PowerShell.Core\FileSystem::C:\powershell\test.txt
PSParentPath : Microsoft.PowerShell.Core\FileSystem::C:\powershell
PSChildName : test.txt
PSDrive : C
PSProvider : Microsoft.PowerShell.Core\FileSystem
The File show the attributes ar. It´s a File which is in ReadOnly.
Set-ItemProperty
Attributes can be changed with the use of Set-ItemProperty
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Set-ItemProperty test.txt -name attributes -value ([System.IO.FileAttributes]::Hidden -bxor [System.IO.FileAttributes]::Archive)
Changes the Attributs to hidden and archive.
In this example, the attributs are set as absolute, which means that already existing attributes are overwritten.
Making a lot of files
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1..500 | ForEach-Object {New-Item -ItemType File -Path ("Datei{0:000}.txt" -f $_)}
This command creates 500 empty textfiles with a schema.
Editing CSV- and logfiles
In Windows operating systems protocols are saved as logfiles. Those files are stored as text or as CSV-Files. Those are system independet and include readable data seperated by commas. Every CSV file starts with headings. A typical example is the dcpromo.csv. I contains information about the creation of a domain.
Import-csv
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# The command import-csv import data to the console
PS C:\Powershell> Import-csv -path daten.csv
Name Datum Email IP-Adresse
---- ----- ----- ----------
Egon 3.1.1999 egon@mail.de 172.120.0.4
Uta 3.1.1999 uta@mail.de 168.130.1.1
Bernd 01.03.2019 156.120.0.3
Paul 04.08.2011 paul@mail.de 10.7.10.1
Marion 06.07.2001 marion@mail.de 172.140.0.1
Otto 04.12.2018 otto@mail.de 198.168.4,200
Anke 31.12.1980 200.100.6.2
PS C:\Powershell>
Sorting Data
Data can be sorted:
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#
# Import-CSV -Path daten.csv | Sort-Object -Property { Get-Date $_.Datum }
#
PS C:\Powershell> Import-CSV -Path daten.csv | Sort-Object -Property { Get-Date $_.Datum }
Name Datum Email IP-Adresse
---- ----- ----- ----------
Anke 31.12.1980 200.100.6.2
Egon 3.1.1999 egon@mail.de 172.120.0.4
Uta 3.1.1999 uta@mail.de 168.130.1.1
Marion 06.07.2001 marion@mail.de 172.140.0.1
Paul 04.08.2011 paul@mail.de 10.7.10.1
Otto 04.12.2018 otto@mail.de 198.168.4,200
Bernd 01.03.2019 156.120.0.3
Filtering Data
Filtering Data by Email - Show all entry where Email is not empty ($_.Email -ne “”)
- -ne = not equal
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PS C:\Powershell> Import-CSV -Path daten.csv | Where-Object { $_.Email -ne "" } | Sort-Object -Property { Get-Date $_.Datum }
Name Datum Email IP-Adresse
---- ----- ----- ----------
Uta 3.1.1999 uta@mail.de 168.130.1.1
Egon 3.1.1999 egon@mail.de 172.120.0.4
Marion 06.07.2001 marion@mail.de 172.140.0.1
Paul 04.08.2011 paul@mail.de 10.7.10.1
Otto 04.12.2018 otto@mail.de 198.168.4,200
The same can be done with the attribute -eq = equal:
PS C:\Powershell> Import-CSV -Path daten.csv | Where-Object { $_.Email -eq "" } | Sort-Object -Property { Get-Date $_.Datum }
Name Datum Email IP-Adresse
---- ----- ----- ----------
Anke 31.12.1980 200.100.6.2
Bernd 01.03.2019 156.120.0.3
More about the Topic
Searching CSVs underlies certain rules. The search is always for certain characteristics that are described in a regular expression. Regular expressions are character strings in which common letters, numbers as well as many special characters are used to describe patterns.
They differs from 5 categories:
- Character class - contains letters or numbers
- Quantifier - defines how often the character class has to repeat
- Anchor - defines start and end of an character class
- round brackets - groups elements
- Escape-Sign - ”" backslash
It Is handy to define create a Match-variable for searching.
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# Match-variable:
$DatumMuster = "\W[0-9]{2}\.[0-9]{2}\.[0-9]{4}\W"
# angular brackets contain the values that are allowed - [0-9] = any numbers
# curled brackets define the amount of values - {2} = 2 values; {4} = 4 values
# The start and end are define throug \W
PS C:\Powershell> $DatumMuster = "\W[0-9]{2}\.[0-9]{2}\.[0-9]{4}\W"
PS C:\Powershell> (Get-Content -Path daten.csv ) | Foreach-Object {if ($_ -Match $DatumMuster) {$_ }}
Bernd,"01.03.2019",,"156.120.0.3"
Paul,"04.08.2011",paul@mail.de,"10.7.10.1"
Marion,"06.07.2001",marion@mail.de,"172.140.0.1"
Otto,"04.12.2018",otto@mail.de,"198.168.4,200"
Anke,"31.12.1980",,"200.100.6.2"
this example show all data that follows “dd.mm.yyyy”. The Output does not contain the dates with single letters.
This can be changed:
$DatumMuster = "\W[0-9]{1,2}\.[0-9]{1,2}\.[1-9]{4}\W"
Introduction to Powershell Scripts
In Scripts, multiple commands can be stored and executed in a given order. Windows provides the PowerShell ISE, and development environment for powershell scripts.
Datatypes and variables
The following Datatypes are avaible in PowerShell:
| Datatype | Meaning |
|---|---|
| int | integer |
| int32 | integer (32 Bit) |
| int64+ | integer (64 Bit) |
| single | Number with decimal points |
| byte | Byte (8 Bit) |
| char | Character |
| DateTime | Date and Time |
| string | String of characters |
Powershell can automatically decide which datatype to use.
$value = 123 #will be stored as int
$value = "This is a String" #will be stored string
[int]$sum = 100 + 200 #forcably storing as int
Sequence
The easiest structure of a script is a sequence. Single commands are executed one after another.
Branching
The simplest formof branching are if-conditions. an if-conditions proves whether a condition is true or false.
if-else
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$tp "C:\Powershell"
if (Test-Path $testpfad)
# if this condition is true
{Write-Host "The directory $tp exists"}
else
#if the condition is not true, else is executed
{Write-Host "The directory $tp does not exist"}
if-else with multiple else-if
It is possible to make an if condition with multiple alternatives:
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if ($condition = true)
{instruction 1}
else if ($condition2 = true)
{intruction 2}
else
{instruction 3}
switch instructions
Using a switch instruction, multiple conditions are displayed. a switch is recommended if more than 3 conditions are possible.
example 1
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$n = read-host "school note = ?"
switch ($n) {
"A" {
$comment = "excellent work!"
}
"B" {
$comment = "good work!"
}
"C" {
$comment = "___ work!"
}
"D" {
$comment = "just enough."
}
"E" {
$comment = "deficiency work!"
}
"F" {
$comment = "not enough."
}
default {
$comment ="no input"
}
}
example 2
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switch ((Get-Date).Hour) {
{$_ -ge 6 -and $_ -lt 12}} {$text = "Good Morning!"}
{...}
}
Write-Host "$text - The time is $(get-date -format HH:mm)"
Conditions
| expression | example | meaning | short |
|---|---|---|---|
| z1 -gt z2 | [6 -gt 5] | returns true if z1 > z2 | greater than |
| z1 -lt z2 | [5 -gt 6] | returns true if z1 < z2 | less than |
| z1 -ne z2 | [5 -gt 6] | returns true if z1 =/= z2 | not equal |
| z1 -le z2 | [5 -gt 5] | returns true if z1 <= z2 | less or equal |
| z1 -ge z2 | [5 -gt 5] | returns true if z1 >= z2 | greater or equal |
| z1 -eq z2 | [5 -gt 5] | returns true if z1 == z2 | equal |
Repetitions - loops
Commands are in dependency to a certain condition executed several times. A simple loop repeats a command until the the condition is no longer met. It might be that a while loop is never executed if the condition is not met.
while-loop
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$number = read-host "Enter Number:"
# The while-loop is repeated as long as the entered number is less or equal than 5.
while ($number -le 5) {
write-host $number
$number = read-host "Enter Number:"
}
# If a number greater than 5 is entered, the while loop ends.
write-host "The number is greater thatn 5.."
do-loop
A do-loop is at least executed 1 time. At the end of the loop-block a while or untilchecks a condition.
do-while
If the condition is met, the loop while be executed again.
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$n = 1
do {
"Loop nr. $n"
$n++
}
while ($n -lt 7)
do-until
If the condition is met, the loop ends.
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$n = 1
do {
"Loop nr. $n"
$n++
}
while ($n -ge 7)
The two loops do the same, only the condition differs.
for-loop
In a for loop the amount of repetitions is defined in the start.
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for ($n=1; $n -le 6; $n++) {
"loop nr. $n"
}
foreach-loop
In a foreach loop the amount of repetitions is defined in a array.
Example 1:
For each city in the citylist, the city is written to the output.
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$citylist = "Pisa", "Venedig", "Florenz"
foreach ($city in $citylist) {
write-host $city
}
Example 2:
All numbers from 1 to 50 are added to each other.
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$sum=[int]0;
foreach ($n in @(1..50)) {
$sum += $n
}
write-host $sum
Its noteable how the array is written. only the first and last number are declared and seperated by two dots. Such a area is defined with an @-sign.
Break-Command
Loops continue running until the condition is no longer met. It is possible to break the loop before that happens. the break operator stops a running loop.
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$sum=[int]0;
foreach ($n in @(1..50)) {
$sum +=$n
if ($sum -gt 100) { break }
}
write-host $sum
This loop stops when the $sum reaches 100.
Continue-command
With the continue command a loop is exited and started at the beginning.
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$n = 0
while ($n -lt 10) {
$n++
if ($n -eq 6) {continue}
Write-Host $n
}
This means that in this example, all nubers are written to the output except of number 6.
Debugging
Debugging is the step-by-step execution of a programme. For this purpose, you can have the programme stop at a certain point or execute each step individually. This is usefull for testing scripts, p.e. if a loop is exited to the wrong condition.