select-string not taking variable in powershell

Question

I have stored a MAC address as a string in a variable:

$macaddress= "1234567"

I'm trying to store the output from a command in another variable:

 $testing = { arp -a; | select-string  $macaddress }
 Write-Host $testing

If the command is executed in PowerShell, I do not see the value of $macaddress. It displays as a '$macaddress' in the screen instead of its value "1234567".

Please help me set the value of $macaddress correctly.

Answer 1

The problem is not how you define variable $macaddress, but in how you try to capture command output.
Remove the enclosing { ... } and the ;:

$testing = arp -a | select-string $macaddress

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As for what you tried:

{ ... } creates a script block, which is a piece of source code (loosely speaking) for later execution (e.g., with operators . or &).

If you pass a script block to Write-Host - whose use you should generally avoid, by the way - it is converted to a string, and the string representation is the literal contents of the script block between { and } - that's why you saw $macaddress appear (unexpanded) in your output.

; terminates a command, and it is only necessary if you place multiple commands on a single line.
A pipeline is still considered a single command, even though it is composed of multiple sub-commands; do not attempt to use ; in a pipeline - you'll break it (and, in fact, even your script-block-creating command would break).