regex - powershell "ParseExact" with "3" argument(s): "String was not recognized as a valid DateTime

Question

When i'm trying to parse a line in a IIS log file and pulling the datetime on the line, I'm getting the following error

Exception calling "ParseExact" with "3" argument(s): "String was not recognized as a valid DateTime." At line:9 char:1

• $dateTime = [datetime]::ParseExact($dateTimeString, 'yyyy-MM-dd HH:mm ...

•   + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : FormatException
  

here is my powershell code:

$line = '2020-12-23 02:01:16.244 -06:00 [Information] 2020-12-23T08:01:16.2446161Z:     [Error] Oracle.ManagedDataAccess.Client.OracleException (0x80004005): Connection request timed out'
$dateTimeString = [regex]::Matches($line, 'dddd-dd-ddsdd:dd:dd')[0].Groups[1].Value
write-host "datetimestr:" $dateTimeString
$provider = New-Object System.Globalization.CultureInfo "en-US"
$dateTime = [datetime]::ParseExact($dateTimeString, 'yyyy-MM-dd HH:mm:ss', $provider)

write-host $dateTime
$dateTime -f 'MM/dd/yyyy HH:mm:ss' | write-host 

i guess i need some fresh eyes to see what i'm missing.

notes:

• i've tried copying and pasting the string in the $line var to validate there are no strange chars in the datetime
• i have tried adding .trim to the $line and that didn't help
• i've also narrowed the regex pattern to 'ddd-dd-dd' and parseexact() to ($dateTimeString, 'yyyy-MM-dd', $provider) and this doesn't help either.

Answer 1

You can use

$dateTimeString = [regex]::Match($line, 'd{4}-dd-ddsdd:dd:dd').Value

Your [regex]::Matches($line, 'dddd-dd-ddsdd:dd:dd')[0].Groups[1].Value code matches a datetime substring into Group 0. You are trying to get Group 1 value by using .Groups[1].Value, but there is no capturing group defined in the pattern.

Note there is no need using Matches that fetches all occurrences in the string since all you need is the first match, which can be done with a mere Match.

Also, repeating d four times in a regex is really redundant, you may use a {4} limiting quantifier.

If you want to only find a match at the start of the string, add ^ at the beginning: '^d{4}-dd-ddsdd:dd:dd'.