Powershell notes

1. What is Powershell & cmdlets?
- 1.1. PowerShell scripts
- 1.2. What is a cmdlet?
2. Pipeline
3. Variables
4. If statement
5. Loops

1. What is Powershell & cmdlets?

Powershell (PS) is the Windows Scripting Language built using the .NET framework. PS is able to execute .NET functions directly from its shell. PS commands are called cmdlets - most of them is written in .NET. The output of cmdlets are objects. This approach makes PS shell modular - it's easy to apply some actions on the output objects or pass them to another cmdlet.

Format of cmdlet command: Verb-Noun. Common verbs:

Get
Start
Stop
Read
Write
New
Out
Invoke

All cmdlet verbs.

1.1. PowerShell scripts

Powershell ISE is the Powershell Text Editor most often used to write longer PowerShell scripts. Most common extension of PowerShell files is .ps1.

1.2. What is a cmdlet?

Cmdlets (pronounced: command-lets) are native PS commands, not stand-alone executables. Cmdlets are collected into PowerShell modules that can be loaded on demand. They can be written in any compiled .NET language or in the PS scripting language itself. Cmdlets return .NET objects.

NOTE: Cmdlets and their parameters are case-insensitive. However, Microsoft generally recommends entering a PowerShell cmdlet (or a parameter) with the first letter of each word capitalized.

2. Pipeline

To pass output from one cmdlet to another the pipline is used. Instead of passing text, PowerShell passes a .NET object to next cmdlet. Object contains methods and properties. Objects returned by the last command in a chain are printed out on the screen.

# Get members of command's output object
<command> | Get-Member -MemberType <Method | Property>
 
# Get only specific properties (show only selected fields)
<command> | Select-Object -Property <prop1>,<prop2> <modifier>
Modifiers:
    -first <x>                              # Get first :x objects
    -last <x>                               # Get last :x objects
    -unique                                 # Show unique objects
<command> | select <prop1>,<prop2>          # Alias
 
# Filter objects (get only these which match a specific value)
<command> | Where-Object <property-name> -<operator> <value>
Operators:
    -like                                   # String wildcard matching (*abc*)
    -contains                               # Property value contains
    -eq                                     # Property value equals
    -gt                                     # Property value is greater
<command> | where [...]                     # Alias
 
# Sort objects
<command> | Sort-Object
 
# Measure object (get number of objects, etc.)
<command> | Measure-Object

3. Variables

$var = Get-NetTCPConnection                 # Save returned object into var

4. If statement

if ($obj1 -<operator> $obj2) {
    # Do something
}

Full list of operators

NOTE: String comparisions are case-insensitive unless you use the explicit case-sensitive operator. To make a comparison operator case-sensitive, add a c after the - (-ceq is the case-sensitive version of -eq).

Most common:

-eq, -ne                                  # Equal / not equal
-gt, -ge                                  # Greater than / greater or equal
-lt, -le                                  # Less than / less or equal
-is, -isnot                               # Type comparision
-in, -notin                               # Value A in in a collection B
-like, -notlike                           # String wildcard matching
-match, -notmatch                         # String regex matching

5. Loops

# Iterate over set of objects
foreach ($item in $items) {
    echo $item
}