convert string to datetime in powershell 2.0

Question

I am trying to parse a file for only the most recent entries. Each entry in the log file starts with date in the format "m/d/yyyy h:mm:ss PM".

I write a script that accomplishes what I wanted but unfortunately this script runs on Powershell 5 but not Powershell 2

$regex = '\b([1-2][0-9]|[0-9])\/([1-3][0-9]|[0-9])\/(20[0-9][0-9]) ((1[0-2]|0?[1-9]):([0-5][0-9]):([0-5][0-9]) ([AaPp][Mm]))'

$lines = gci C:\temp\Gateway.log | select-string -pattern $regex |select linenumber, matches
$log=@()
foreach($line in $lines)
{
    [datetime]$logdate = ($line.matches).value
    $ln = $line.linenumber

    if ($logdate -gt '2017-06-29 12:00:00')
    {
        $log += $ln
    }
}

$log

When i try to run this script on the server with powershell 2, i get the following error.

Cannot convert null to type "System.DateTime".

I am having trouble converting the value found by the select-string into datetime. tried convert to string with tostring and also with out-string

  $dt = $line.matches
    $val = $dt|select Value
    $val1 = $val|Out-String
    $val2 = $val.tostring()
    [datetime]$val1
    [datetime]$val2

How can I get the value as datetime so I can do datemath on in it powershell 2?

Regardless of PowerShell version, simply casting the string to DateTime is poor form because it assumes the locale actually accepts date/time values of that specific format. Use something like [DateTime]::ParseExact($val1, "M/d/yyyy H:mm:ss tt", [CultureInfo]::InvariantCulture) instead. (I forget if there's a more PowerShellian way of doing that.) — Jeroen Mostert
– Jeroen Mostert, Commented Jul 4, 2017 at 21:56
Note also that your regex is overly complicated: there's really no need for you to care if someone tries to pass off 14/68/3016 1:62:63 PM as a valid date/time, just let the parser sort out that's invalid. Things like [0-9]+ are fine for simple delineation work. If the date/time happens to have a fixed size or a non-space delimiter it's even simpler. — Jeroen Mostert
– Jeroen Mostert, Commented Jul 4, 2017 at 22:03
@JeroenMostert the upper case H denotes a 24 hour format, change to lower case h — user6811411
– user6811411, Commented Jul 4, 2017 at 22:31
I think my issue is not so much the date conversion, but the convert to string. when i try to do $val.tostring() is returns null. the type of val is PSCustomObject. — Bob Klimes
– Bob Klimes, Commented Jul 5, 2017 at 13:46
@JeroenMostert yeah, i'm a novice at regex so this was first example I found that worked for me. But I will take your note in consideration, simpler the better. thx — Bob Klimes
– Bob Klimes, Commented Jul 5, 2017 at 13:56

user6811411 · Accepted Answer · 2017-07-04 22:42:32Z

1

To my experience the am/pm conversion doesn't work (also not with [CultureInfo]::InvariantCulture) if your current locale settings don't apply with it.

You need to specify a cultureinfo object which supports am/pm

$enUS = 'en-US' -as [Globalization.CultureInfo]
$val1 = (get-date).ToString("M/d/yyyy H:mm:ss tt", $enUS)
$val1
[DateTime]::ParseExact($val1, "M/d/yyyy H:mm:ss tt", $enUS)

answered Jul 4, 2017 at 22:42

user6811411

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2 Comments

Bob Klimes Over a year ago

I have to cast my matches date as an array because tostring() was not converting anything. $enUS = 'en-US' -as [Globalization.CultureInfo] $dt = $line.matches $val = @($dt|%{$_.Value}) $val = $val[0].ToString() [DateTime]::ParseExact($val, "M/d/yyyy H:mm:ss tt", $enUS)

user6811411 Over a year ago

Take care with the upper case H, according to these tables you need the lower case h for 12hour am/pm format.

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