Delete lines based on time stamp in text file PowerShell - powershell

Question

Novice at PS here, but I have a log file where each entry is written on a separate line with this date format: 2013-04-29 08:55:09,261
I am trying to use PowerShell to delete all lines older than 30 days. I have been trying to plug get-date -format "yyyy-MM-dd hh" output with some sort of greater than code, but at this point I’m just guessing. Also been trying forfiles with a batch file but would like to stick with PS if I can.
Any help would be much appreciated.

Answer 1

Assuming a file with the contents:
2013-04-29 08:55:09,261 line1
2013-01-29 08:55:09,261 line2
2013-03-31 08:55:09,261 line3
For me your dates are in the international standard date notation so you can just use :
$a = [datetime]"2013-04-29 08:55:09"
Then $a will be a date, so nothing to do with the culture.
You can just write the following to filter all lines from a date (here "2013-03-31")
get-content "C:\temp\date.txt" | where { [datetime]($_.split(','))[0] -ge "2013-03-31"}
I just split the line on the coma, take the first part and convert it to a date before compararing it.
For your 30 days (get-date).date give the date without hours and (get-date).date.adddays(-30) give the date 30 days before today.
get-content C:\temp\date.txt | where { [datetime]($_.split(','))[0] -ge (get-date).date.adddays(-30)}
You can pipe the result in a new file | set-content "C:\temp\newdate.txt"

Answer 2

Try this:
gc .\logfile.txt | %{if ([datetime][regex]::match($_, '^[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2},[0-9]{3}').Value -gt (Get-Date).AddDays(-30)) {$_}} > purgedlogfile.txt
Breakdown and explanation of the components:
.\logfile.txt is the path to the log file
^[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2},[0-9]{3} is a regular expression that matches your log file's timestamp format at the beginning of each line
[regex]::match($_, '^[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2},[0-9]{3}').Value returns the timestamp matched by the regular expression
Preceding it with the [datetime] typecast operator converts it to a DateTime object (in order to compare it to another DateTime)
(Get-Date) returns a DateTime object representing the current date and time, and .AddDays(-30) subtracts 30 days from it, to return a DateTime object representing 30 days ago
For each line in the logfile, the if block prints the line if the DateTime representing that line's timestamp is greater than the DateTime representing 30 days ago (i.e., the timestamp is more recent than 30 days), otherwise it ignores the line

Answer 3

Assuming a file with the contents:
2013-04-29 08:55:09,261 line1
2013-01-29 08:55:09,261 line2
2013-03-31 08:55:09,261 line3
You could get your desired output with:
$culture = [System.Globalization.CultureInfo]::InvariantCulture
$format = 'yyyy-MM-dd HH:mm:ss,fff'
Get-Content .\test.txt | ? { [datetime]::ParseExact(([string]$_).Substring(0,23), $format, $culture) -ge (Get-Date).AddDays(-30) }

Answer 4

Adi Inbar's answer is good, but if you'd prefer to avoid regular expressions, here's another way:
Get-Content e:\pathto\logfile.txt | Where-Object { ( (Get-Date) - (Get-Date $_.Substring(0,10)) ).Days -le 30} | Add-Content e:\pathto\NewLog.txt