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.
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
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).
Try it this way:
$macAddress = "00-01-02-03-04"
arp -a | Select-String $macAddress
If you want to extract the IP address related to the MAC address, you can do this:
$macAddress = "00-01-02-03-04"
arp -a | Select-String ('\W*((?:[0-9]{1,3}\.){3}(?:[0-9]{1,3}))\W+(' +
$macAddress + ')') | ForEach-Object { $_.Matches[0].Groups[1].Value }
select-string ('('+$var+'regex'))