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I am trying to print out a line in a text file if it starts with any of the string in the array.

Here is a snippet of my code:

array = "test:", "test1:"
    if($currentline | Select-String $array) {
        Write-Output "Currentline: $currentline"
    }

My code is able to print lines in the text file if it has any of the strings in the array variable. But I only want to print lines if it starts with the string in array variable. 

Sample of text file:
abcd-test: 123123
test: 1232
shouldnotprint: 1232

Output: 
abcd-test: 123123
test: 1232

Expected output:
test: 1232

I have seen some questions asked on stackoverflow with the solution:

array = "test:", "test1:"
    if($currentline | Select-String -Pattern "^test:") {
        Write-Output "Currentline: $currentline"
    }

But in my case I am using an array variable instead of a string to select the content so I am stumped at this portion because it would not work. It will just now print anything.

Update: Thanks Theo for your answer! This is my code based on Theo's answer for reference

array = "test:", "test1:" 
$regex = '^({0})' -f (($array |ForEach-Object { [regex]::Escape($_) }) -join '|') 
Loop here:
   if($currentline -match $regex) {
       Write-Output "Currentline: $currentline"
   }
pikachu
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1 Answers1

2

Using the Regex -match operator should do what you want:

$array = "test:", "test1:"

# create a regex string from the array.
# make sure all the items in the array have their special characters escaped for Regex
$regex = '^({0})' -f (($array | ForEach-Object { [regex]::Escape($_) }) -join '|')
# $regex will now be '^(test:|test1:)'. The '^' anchors the strings to the beginning of the line

# read the file and let only lines through that match $regex
Get-Content -Path 'D:\Test\test.txt' | Where-Object { $_ -match $regex }

Or, if the file to read is really huge, use a switch -Regex -File method like:

switch -Regex -File 'D:\Test\test.txt' {
    $regex { $_ }
}
Theo
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  • Hi Theo, Thanks for your answer. Just to understand your code, it is attempting to loop through the array so that we could escape special characters and append a "|" to join each items together. This output will then be stored in $regex where we will use "Where-Object" to match the current line to the regex statement generated. May I know what does the "-f" option at line 3 mean? And is this "[regex]::Escape($_)" Powershell's equivalent of calling out a function (In this case Regex.Escape)? – pikachu May 11 '20 at 12:55
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    @pikachu `-f` is the string format operator. See [`Get-Help about_Operators`](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_operators?view=powershell-7#format-operator--f). And, yes, `[Regex]::Escape()` Is calling .Net's System.Text.RegularExpressions.Regex.Escape() function. Strictly, `[Regex]` is a class name, `::` is the static member operator,, and `Escape()` is the member function. You could call it as `[System.Text.RegularExpressions.Regex]::Escape()`. – Bacon Bits May 11 '20 at 13:16