Question

I saw this Powershell statement in a recent Hanselminutes post –

cat test.txt | foreach-object {$null = $_ -match '<FancyPants>(?<x>.*)<.FancyPants>'; $matches.x} | sort | get-unique

I’m trying to learn Powershell at the moment and I think that I understand most of what is going on –

• The statement loops through each line of ‘test.txt’ and runs a regex against the current line
• All the results are collated and then sorted and duplicates removed

My understanding seems to fall down on this part of the statement –

$null = $_ -match '<FancyPants>(?<x>.*)<.FancyPants>'; $matches.x

• What is the ‘$null = ‘ part of the code doing, I suspect this is
  to handle a scenario when no match is returned but I’m not sure how
  it works?
• Is ‘$matches.x‘ returning the matches found?

Answer 1

Yes, the -match operator results in True or False; assigning to $null suppresses the output.

The (?<>) regex syntax creates a capture group. In this case it’s creating a capture group called x for any characters between <FancyPants> and <.FancyPants>. $matches contains the match info for the last match. Capture groups can be referenced by $matches.CaptureGroupName.

Here is an example you can use to see what is in the $Matches variable.

'123 Main','456 Broadway'| foreach{$_; $null = $_ -match '(?<MyMatch>\d+)'; ($Matches| ft *)}

In this example you would use $Matches.MyMatch to reference the match.