Simple configuration file editor for parameter = value config file.

Configure-RasPhoneDNSConfig.ps1

function Configure-RasPhoneDNSConfig {
    [CmdletBinding()] #we want to use verbose, so add cmdlet binding
    param ([string]$path = (Get-Location).path,
                    [string]$vpnConfigName = "rasphone.pbk",
                    [string]$configParam = "IpDnsFlags",
                    [string]$configValue = "1")
    #path defaults to current path or another path location.
    #vpnconfigname is the name of the file to configure, defaults to rasphone.pbk
    #configparam is the parameter we're updating. override it to look for another file name
    #configvalue is defaulting to 1
    #you could use validate parameters or even a more complex validation scheme that calls another function to validate against a library
    trap {
        Write-Error $Error[0]
        throw "Error encountered. Exiting."
        }
    #trap any other errors that are not explicit to the try statements

    Write-Verbose ("Searching path " + $path + " recursively for " + $VPNConfigName)
    
    #get the file starting at the path
    #if you give garbage path, trap out and then with no file list, not do anything. (basic error handlign here, always better to include more robust handling)
    #gci recursively from begining of path location.
    $fileList = $null #just make filelist variable null for sanitary sake
    $fileList = (Get-ChildItem -Recurse -path $path -Filter $VPNConfigName)
    Write-Verbose "Recursive search complete"
    
    #instead of .replace method, use a regex filter to catch various permuations of our configuration value.
    #This builds a regex string with the configuration parameter.
    #The configuration parameter in this regex expects an equal sign = as the value assignment operator.
    #The token flag does not impact the regex filter criteria. It is used in the replacement criteria only.
    #Below is a serial explaination of the regex string assembly.

    #open of regex string                                       -> [']
    #opening regex group                                        -> [(]
    #beginning of first token name identifier                   -> [?<]
    #first token name                                           -> [flag]
    #close token name                                           -> [>]
    #close of regex string (incomplete)                         -> [']
    #PS variable in middle of regex string building statement   -> [ + $configParam + ]
    #reopen of regex string (incomplete)                        -> [']
    #zero or more optional spaces after param name              -> [ *]
    #zero or more optional spaces after assignment character    -> [= *]
    #end of first token and beginning of second token           -> [)(]
    #beginning of second token name identifier                  -> [?<]
    #second token name                                          -> [value]
    #match any single word, this is the assigned value          -> [\w]
    #close the second token                                     -> [)]
    #close of regex string                                      -> [']


    Write-Verbose "Bulding regex match filter with flag and value tokens"
    $paramFilter = [regex]('(?<flag>' + $configParam + ' *= *)(?<value>\w)')

    #if filelist has values in it, do some work
    if ($fileList) {
        #for each file found in the gci
        ForEach ($item in $fileList) {
        #clear out config file for sanitary code
        $configFile = $null
            try {
                #try and get content of file (sometimes you can list a file but can't read a file)
                $configFile = Get-Content $item
                #if the contents of the file match the filter parameter in any way, process file
                #else, we found a file matching the name, but that file didn't contain the parameter we were looking for
                if ($configFile -match $paramFilter) {
                    Write-Verbose ($item.FullName + ": Updating configuration parameter: " + $configParam + " to value " + $configValue)
                    try {
                        #replace the regex string and attempt to save the file
                        $configFile -replace $paramFilter,('${flag}' + $configValue) | Set-Content -LiteralPath $item.FullName
                        Write-Verbose ($item.FullName + ": File updated successfully.")
                    }
                    catch {
                        #couldn't save the file for some reason.
                        Write-Error $Error[0]
                    }
                }
                else {
                    #file didn't have parameters, so nothing to do.
                    Write-Verbose ($item.FullName + ": Unable to locate parameters: " + $configParam + " for value update to " + $configValue)
                }
            }
            catch {
                #print the error out in the case we couldn't:
                #1) get the file contents
                #2) anything else
                Write-Error $Error[0]
            }
            finally {
                #finished inspecting files.
                Write-Verbose ("File inspection complete")
            }   
        }
    }
    else
    {
        #didn't find any files. no output to console unless verbosely named.
        Write-Verbose ("No configuration files found in path " + $path)
    }
    
}