PowerShell to match multiple lines with regex pattern - regex

Question

I write a Powershell script and regex to search two configs text files to find matches for Management Vlan. For example, each text file has two Management vlan configured as below:
Config1.txt
123 MGMT_123_VLAN
234 MGMT_VLAN_234
Config2.txt
890 MGMT_VLAN_890
125 MGMT_VLAN_USERS
Below is my script. It has several problems.
First, if I ran the script with the $Mgmt_vlan = Select-String -Path $File -Pattern $String -AllMatches then the screen output shows the expected four (4) Mgmt vlan, but in the CSV file output shows as follow
Filename Mgmt_vlan
Config1.txt System.Object[]
Config2.txt System.Object[]
I ran the script the output on the console screen shows exactly four (4) Management vlans that I expected, but in the CSV file it did not. It shows only these vlans
Second, if I ran the script with $Mgmt_vlan = Select-String -Path $File -Pattern $String | Select -First 1
Then the CSV shows as follows:
Filename Mgmt_vlan
Config1.txt 123 MGMT_123_VLAN
Config2.txt 890 MGMT_VLAN_890
The second method Select -First 1 appears to select only the first match in the file. I tried to change it to Select -First 2 and then CSV shows column Mgmt_Vlan as System.Object[].
The result output to the screen shows exactly four(4) Mgmt Vlans as expected.
$folder = "c:\config_folder"
$files = Get-childitem $folder\*.txt
Function find_management_vlan($Text)
{
$Vlan = #()
foreach($file in files) {
Mgmt_Vlan = Select-String -Path $File -Pattern $Text -AllMatches
if($Mgmt_Vlan) # if there is a match
{
$Vlan += New-Object -PSObject -Property #{'Filename' = $File; 'Mgmt_vlan' = $Mgmt_vlan}
$Vlan | Select 'Filename', 'Mgmt_vlan' | export-csv C:\documents\Mgmt_vlan.csv
$Mgmt_Vlan # test to see if it shows correct matches on screen and yes it did
}
else
{
$Vlan += New-Object -PSObject -Property #{'Filename' = $File; 'Mgmt_vlan' = "Mgmt Vlan Not Found"}
$Vlan | Select 'Filename', 'Mgmt_vlan' | Export-CSV C:\Documents\Mgmt_vlan.csv
}
}
}
find_management_vlan "^\d{1,3}\s.MGMT_"

Answer 1

Regex correction
First of all, there are a lot of mistakes in this code.
So this is probably not code that you actually used.
Secondly, that pattern will not match your strings, because if you use "^\d{1,3}\s.MGMT_" you will match 1-3 numbers, any whitespace character (equal to [\r\n\t\f\v ]), any character (except for line terminators) and MGMT_ chars and anything after that. So not really what you want. So in your case you can use for example this: ^\d{1,3}\sMGMT_ or with \s+ for more than one match.
Code Correction
Now back to your code... You create array $Vlan, that's ok.
After that, you tried to get all strings (in your case 2 strings from every file in your directory) and you create PSObject with two complex objects. One is FileInfo from System.IO and second one is an array of strings (String[]) from System. Inside the Export-Csv function .ToString() is called on every property of the object being processed. If you call .ToString() on an array (i.e. Mgmt_vlan) you will get "System.Object[]", as per default implementation. So you must have a collection of "flat" objects if you want to make a csv from it.
Second big mistake is creating a function with more than one responsibility. In your case your function is responsible for gathering data and after that for exporting data. That's a big no no. So repair your code and move that Export somewhere else. You can use for example something like this (i used get-content, because I like it more, but you can use whatever you want to get your string collection.
function Get-ManagementVlans($pattern, $files)
{
$Vlans = #()
foreach ($file in $files)
{
$matches = (Get-Content $file.FullName -Encoding UTF8).Where({$_ -imatch $pattern})
if ($matches)
{
$Vlans += $matches | % { New-Object -TypeName PSObject -Property #{'Filename' = $File; 'Mgmt_vlan' = $_.Trim()} }
}
else
{
$Vlans += New-Object -TypeName PSObject -Property #{'Filename' = $File; 'Mgmt_vlan' = "Mgmt Vlan Not Found"}
}
}
return $Vlans
}
function Export-ManagementVlans($path, $data)
{
#do something...
$data | Select Filename,Mgmt_vlan | Export-Csv "$path\Mgmt_vlan.csv" -Encoding UTF8 -NoTypeInformation
}
$folder = "C:\temp\soHelp"
$files = dir "$folder\*.txt"
$Vlans = Get-ManagementVlans -pattern "^\d{1,3}\sMGMT_" -files $files
$Vlans
Export-ManagementVlans -path $folder -data $Vlans```
Summary
But in my opinion in this case is overprogramming to create something like you did. You can easily do it in oneliner (but you didn't have information if the file doesn't include anything). The power of powershell is this:
$pattern = "^\d{1,3}\s+MGMT_"
$path = "C:\temp\soHelp\"
dir $path -Filter *.txt -File | Get-Content -Encoding UTF8 | ? {$_ -imatch $pattern} | select #{l="FileName";e={$_.PSChildName}},#{l="Mgmt_vlan";e={$_}} | Export-Csv -Path "$path\Report.csv" -Encoding UTF8 -NoTypeInformation
or with Select-String:
dir $path -Filter *.txt -File | Select-String -Pattern $pattern -AllMatches | select FileName,#{l="Mgmt_vlan";e={$_.Line}} | Export-Csv -Path "$path\Report.csv" -Encoding UTF8 -NoTypeInformation