Powershell: search backwards from end of file - powershell

Question

My script reads a log file once a minute and selects (and acts upon) the lines where the timestamp begins with the previous minute.
This is easy (the regex is simply "^$timestamp"), but when the log gets big it can take a while.
My thinking is the lines I want will always be near the bottom of the file, so I'd be searching far fewer lines if I started at the bottom and searched upwards, stopping when I get to the minute prior to the one I'm interested in.
My question is, how can I search from the bottom of the file instead of the top? Can I even say "read line $length", or even "read line n" (if so I could do a sort of binary search thing to find the length of the file and work backwards from there)?
Last question: would this even be faster (I'd still like to know how to do it even if it wouldn't be faster)?
Ideally, I'd like to do this all in my own code without installing anything extra.
Thanks

Answer 1

get-content bigfile.txt -tail 10
This words on huge files nearly instantly without any big memory usage.
I did it with a 22 GB text file in my testing.
Doing something like "get-context bigfile.txt | select -Last 10" works but it seems to have to load all of the lines (or objects in powershell) then does the select.

Answer 2

May I suggest just changing the regex to equal Get-Date + whatever time period you want?
For example (and this is without your log so i apologize)
$a = Get-Date
$hr = $a.Hour
$min = $a.Minute
Then work off those values to build out the regex to select the times you want. And if you don't already use it this website is awesome for building regex's quickly and easily http://gskinner.com/RegExr/ .
Got another fix, I think you will like this..
$a = get-content .\biglog.text
Use the length to slice the array from back to front change write host to select-string and your regex or whatever you want to do in reverse..
foreach($x in $a.length..0){ write-host $a[$x] }
Another option after the get-content cmdlet again, this option just reverse orders the array then you are reading $a from bottom to top
[array]::Reverse($a)
dc

Answer 3

If you only want the last bit of the file, depending on the format, you can just do this:
Get-Content C:\Windows\WindowsUpdate.log | Select -last 10
This will return the last 10 lines found in the file.