powershell - Multiline regex to match config block

Question

I am having some issues trying to match a certain config block (multiple ones) from a file. Below is the block that I'm trying to extract from the config file:

ap71xx 00-01-23-45-67-89
 use profile PROFILE
 use rf-domain DOMAIN
 hostname ACCESSPOINT
 area inside
!

There are multiple ones just like this, each with a different MAC address. How do I match a config block across multiple lines?

Answer 1

The first problem you may run into is that in order to match across multiple lines, you need to process the file's contents as a single string rather than by individual line. For example, if you use Get-Content to read the contents of the file then by default it will give you an array of strings - one element for each line. To match across lines you want the file in a single string (and hope the file isn't too huge). You can do this like so:

$fileContent = [io.file]::ReadAllText("C:file.txt")

Or in PowerShell 3.0 you can use Get-Content with the -Raw parameter:

$fileContent = Get-Content c:file.txt -Raw

Then you need to specify a regex option to match across line terminators i.e.

• SingleLine mode (. matches any char including line feed), as well as
• Multiline mode (^ and $ match embedded line terminators), e.g.
• (?smi) - note the "i" is to ignore case

e.g.:

C:> $fileContent | Select-String '(?smi)([0-9a-f]{2}(-|s*$)){6}.*?!' -AllMatches |
        Foreach {$_.Matches} | Foreach {$_.Value}

00-01-23-45-67-89
 use profile PROFILE
 use rf-domain DOMAIN
 hostname ACCESSPOINT
 area inside
!
00-01-23-45-67-89
 use profile PROFILE
 use rf-domain DOMAIN
 hostname ACCESSPOINT
 area inside
!

Use the Select-String cmdlet to do the search because you can specify -AllMatches and it will output all matches whereas the -match operator stops after the first match. Makes sense because it is a Boolean operator that just needs to determine if there is a match.