Capture specific text from output into a variable - powershell

Question

I'm trying to write a script that will detect what COM port a device is plugged into, then map it to a new port.
Here is the output from the "change port" command:
PS C:\> change port
COM11 = \Device\19H2KP0
COM2 = \Device\Serial1
COM5 = \Device\Serial2
KEYSPAN#*USA19HMAP#00_00#{4d36e978-e325-11ce-bfc1-08002be10318} = \Device\ComUs19H-00
KEYSPAN#*USA19HMAP#00_00#{86e0d1e0-8089-11d0-9ce4-08003e301f73} = \Device\ComUs19H-00
USA19HP0 = \Device\19H2KP0
I need to capture the COM number prior to "\Device\19H2KP0". So in this example output, I would capture COM11 into a variable.
Next I need to run the "change port" command with that variable. i.e.:
change port COM1=$CapturedText
Thank you in advance for any assistance!

Answer 1

Do you already know what the 19H2KP0 bit will be? If so, you could use a regular expression to detect the unique ID using a look-ahead.
Here's a fully working example, using your example text:
$Output = #"
COM11 = \Device\19H2KP0
COM2 = \Device\Serial1
COM5 = \Device\Serial2
KEYSPAN#*USA19HMAP#00_00#{4d36e978-e325-11ce-bfc1-08002be10318} = \Device\ComUs19H-00
KEYSPAN#*USA19HMAP#00_00#{86e0d1e0-8089-11d0-9ce4-08003e301f73} = \Device\ComUs19H-00
USA19HP0 = \Device\19H2KP0
"#
$Output -match "COM[0-9]{1,2}(?=.*$Id)";
Write-Host -Object ('COM port is: {0}' -f $matches[0]);
And now here is the example, using the in-line command:
$Id = '19H2KP0';
$Output = change port;
$Output -match "COM[0-9]{1,2}(?=.*$Id)";
Write-Host -Object ('COM port is: {0}' -f $matches[0]);
Result
COM port is: COM11

Answer 2

Longer, but perhaps more intuitive, you can also use chained -match and -replace operators with simpler regexes:
$CapturedText = (change port) -match 'COM.+19h2kp0' -replace '^(COM\d+).+','$1'
$CapturedText