How are parenthesis around a powershell command different than without? - powershell

Question

I am using Get-NetIPAddress. ALL I want is the actual address without ANY formatting or tables or anything.
If I use
(Get-NetIPAddress).IPAddres
I get a list of addresses for all ports. I want only a single port so I tried to pipe it but gave nothing in return:
(Get-NetIPAddress).IPv4Address | Where-Object InterfaceAlias -eq "MyPortName"
But if I do this:
Get-NetIPAddress.IPv4Address | Where-Object InterfaceAlias -eq "MyPortName"
It says that this is an invalid command.
If I use this:
Get-NetIPAddress | Where-Object InterfaceAlias -eq "MyPortName" | Where-Object AddressFamily -eq IPv4 | Select-Object IPAddress
I get:
IPAddress
---------
10.45.22.100
So what is going on when I put parenthesis around Get-NetIPAddress and how can I get JUST the darn address number for a particular port?

Answer 1

By enclosing a command with () you create an order of precedence, so everything inside of () executes first and after that your other commands are evaluated.
also, there is no such construct as cmdlet.property
as for the second part, after you do (Get-NetIPAddress).IPv4Address you are probably getting another object, just compare output from:
Get-NetIPAddress | Get-Member
and
(Get-NetIPAddress).IPv4Address | Get-Member

Answer 2

Get-NetIpAddress is a cmdlet, PowerShell runs it. It outputs one or more objects, and by that I mean one many names and numbers and features all grouped together into one blob.
Get-NetIpAddress | Select-Object IPv4Address takes the object(s) and turns them into simpler, smaller objects with just one property, the IPv4Address.
That's what this is:
IPAddress
---------
10.45.22.100
it's a rendering of an object with one property.
Get-NetIpAddress | Select-Object -ExpandProperty IPv4Address takes the objects, takes just the IPv4Address, and throws away the grouping and leaves just the IPv4Address as a string.
That would output:
10.45.22.100
10.45.22.101
These have been expanded to strings, there's no column title. They've been unwrapped.
This is something you want to do a lot, but it's a lot of typing. $x = Get-NetIpAddress; $x.IPv4Address is a shortcut way of getting just the Ipv4Address unwrapped from the object and without anything else.
So you want to do
Get-NetIpAddress.IPv4Address but that falls over, because it looks like the name of a different cmdlet and PowerShell tries to run it and cannot. This is just a clash of syntax - it could be a name, it could be a property lookup, and powershell chooses differently. you need something (parens) to make the distinction.
(Get-NetIpAddress).IPv4Address makes it clear to the shell that there is a cmdlet, it runs that, then gets the result into the parentheses, then gets the property from them. That clears up the name clash. But at this point you have thrown away the InterfaceName, so pushing this output to the pipeline can't let you choose based on interface name.
Follow that through and you can see
If you do (Get-NetIPAddress).IPv4Address the output is strings and you have thrown away all the other data that came out of the cmdlet.
If you want to choose one string based on the interface name, you have to do that before you unwrap the IP and throw the interface name away.
So
Get-NetIpAddress |
Where-Object { pick the one I want } |
Select-Object -ExpandProperty 'the thing I want'

Answer 3

Brackets work in the same way as they do in mathematics, they set an order of precedence, so anything within brackets will execute first.
To get just the IP Address value from your final command, do this instead:
(Get-NetIPAddress | Where-Object InterfaceAlias -eq "MyPortName" | Where-Object AddressFamily -eq IPv4).IPAddress
This command:
(Get-NetIPAddress).IPv4Address
Returns the value of the IPv4Address property (probably as a string), which is why this command then doesn't work:
(Get-NetIPAddress).IPv4Address | Where-Object InterfaceAlias -eq "MyPortName"
As you are piping a string object that contains an IP Address into the Where-Object cmdlet and then are looking to filter on the InterfaceAlias property that does not exist in that object.
When you access a property via the . notation you get it's value. When you access a property via the Select-Object cmdlet you return an object (of the same type as the source object) that is filtered down to just containing that single property (unless you use the -ExpandProperty switch, which causes Select-Object to return the value of the defined property instead of an object in the same way as using . notation).
Long story short, do any filtering you need to do first, then access the property/properties you want as a result last.

Answer 4

Using this syntax you provided:
Get-NetIPAddress | Where-Object InterfaceAlias -eq "MyPortName" | Where-Object AddressFamily -eq IPv4 | Select-Object IPAddress
...getting just the IP address (without the object notation), can be done in two ways:
Get-NetIPAddress | Where-Object InterfaceAlias -eq "MyPortName" | Where-Object AddressFamily -eq IPv4 | Select-Object -Expand IPAddress
notice the "ExpandProperty" argument, abbreviated "Expand" on the above line ...or:
(Get-NetIPAddress | Where-Object InterfaceAlias -eq "MyPortName" | Where-Object AddressFamily -eq IPv4 | Select-Object IPAddress).IPAddress
...where we return the object and then reference the IPAddress property on the object.