Powershell - Remove lines that begin with multiple strings

Question

I am hoping someone can help me. I have extracted certificates from a PFX and would like to remove all lines that start with a space, "Bag Attributes", "issuer" and "subject". My input file would look something like this:

Bag Attributes
    friendlyName: BLAH BLAH
    BLAH BLAH BLAH
subject=C = BLAH BLAH BLAH 
issuer=C = BLAH BLAH BLAH 
-----BEGIN CERTIFICATE-----
BLAH BLAH BLAH
BLAH BLAH BLAH 
-----END CERTIFICATE-----
Bag Attributes
    friendlyName: BLAH BLAH
    BLAH BLAH BLAH
subject=C = BLAH BLAH BLAH 
issuer=C = BLAH BLAH BLAH 
-----BEGIN CERTIFICATE-----
BLAH BLAH BLAH
BLAH BLAH BLAH 
-----END CERTIFICATE-----
Bag Attributes
    friendlyName: BLAH BLAH
    BLAH BLAH BLAH
subject=C = BLAH BLAH BLAH 
issuer=C = BLAH BLAH BLAH 
-----BEGIN CERTIFICATE-----
BLAH BLAH BLAH 
BLAH BLAH BLAH 
-----END CERTIFICATE-----

And the output should look like the following:

I have tried using the following which does remove lines beginning with spaces, however have not been able to successfully remove lines starting with "Bag Attrubutes","subject" and "issuer" with { $_ -notmatch "^ ","^subject","^issuer","^Bag Attributes" }

Get-Content "C:\ScriptRepository\Certs\CA-Chain.pem" | 
Where { $_ -notmatch "^ " } | 
Set-Content "C:\ScriptRepository\Certs\CA-chain2.pem"

Any help would be greatly appreciated.

This is a standard regex operation... You need to read the file via get-content (or one of the .net alterantives) and then check line by line the regex and if its fullfilled, remove the match. I personally prefer the .net regex operations, but the powershell regex operations should be fine too — Farbkreis
– Farbkreis, Commented Oct 22, 2021 at 9:55
Hi Farbkreis, thanks for the speedy response, I have been banging my head against the wall for a couple of days trying to get this to work, could you possibly provide an example. — Alexa Strange
– Alexa Strange, Commented Oct 22, 2021 at 10:02
BLAH BLAH BLAH is a bad representation of a certificate which per definition of your question shouldn't have spaces. So, the question is what DO you want to match ? (and not what you do not want to match). e.g. all valid certificate characters (excluding spaces) that start from the beginning to the end of the line: -Match '^[A-Z,a-z,0-9,=]+$' (or a specific length -Match '^[A-Z,a-z,0-9,=]{8,40}$' or -Match '^[A-Z,a-z,0-9,=]+\s*$' if you want to accept tailing spaces) — iRon
– iRon, Commented Oct 22, 2021 at 11:13
Hi Farbkreis , my first sentence in my question asks "remove all lines that start with a space, "Bag Attributes", "issuer" and "subject" that all that was required. — Alexa Strange
– Alexa Strange, Commented Oct 22, 2021 at 11:34

Theo · Accepted Answer · 2021-10-22 11:01:31Z

1

If you have that in a file, just use a switch with a very simple regex:

$result = switch -Regex -File 'X:\InputFile.pfx' {
    '^(Bag|subject|issuer|\s)'  { <# skip these lines #> }
    default { $_ }
}
$result | Set-Content -Path "C:\ScriptRepository\Certs\CA-chain2.pem"

Output:

Regex details:

^                 Assert position at the beginning of the string
(                 Match the regular expression below and capture its match into backreference number 1
                  Match either the regular expression below (attempting the next alternative only if this one fails)
      Bag         Match the characters “Bag” literally
   |              Or match regular expression number 2 below (attempting the next alternative only if this one fails)
      subject     Match the characters “subject” literally
   |              Or match regular expression number 3 below (attempting the next alternative only if this one fails)
      issuer      Match the characters “issuer” literally
   |              Or match regular expression number 4 below (the entire group fails if this one fails to match)
      \s          Match a single character that is a “whitespace character” (spaces, tabs, line breaks, etc.)
)

answered Oct 22, 2021 at 11:01

Theo

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1 Comment

Alexa Strange Over a year ago

Thanks Theo, I really appreciate your time for answering this for me, it has worked perfectly.

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