I recently got asked if there was an easy way to find out the average time-taken for an IIS instance to complete a request.  This information is available in the IIS log files, you just need to parse it out.  Now there are many IIS log parsers available on the internet, but I thought “I wonder how easily I could do that in PowerShell”; it turns out very easily!

First thing is to define the path to you log file

$IISLogPath = "C:\Temp\sample.log" 

Next we need to find the headers that are available in this particular log file.  First load the file, pick the headers out (always on the 4th line) using ‘split’ to separate the headers delimitated by a white space, and then get rid of the “#Fields: “ prefix from the headers.

Note I’ve used  [System.IO.File]::ReadAllLines to load the file as it’s a lot faster than get-content, this makes a big difference if your iterating through a lot of files!

$IISLogFileRaw = [System.IO.File]::ReadAllLines($IISLogPath)
$headers = $IISLogFileRaw[3].split(" ")
$headers = $headers | where {$_ -ne "#Fields:"}

Now we need to actually import the file, which is nice and simple, as we’ve already got the headers we can just use import-csv to do the work for us, and then do a little bit of clean up removing any comment lines which start with a #.

$IISLogFileCSV = Import-Csv -Delimiter " " -Header $headers -Path $IISLogPath
$IISLogFileCSV = $IISLogFileCSV | where {$_.date -notlike "#*"}

Finally lets collect all the time-taken values into an array.  Note I have had a to do a little bit of hoop jumping to get the “-“ to not be interpreted by PowerShell.

$timeTaken = $IISLogFileCSV | foreach {$_.$("time-taken")}

So putting it all together and we get this:

$IISLogPath = "C:\Temp\sample.log" 
$IISLogFileRaw = [System.IO.File]::ReadAllLines($IISLogPath)
$headers = $IISLogFileRaw[3].split(" ")
$headers = $headers | where {$_ -ne "#Fields:"}
$IISLogFileCSV = Import-Csv -Delimiter " " -Header $headers -Path $IISLogPath
$IISLogFileCSV = $IISLogFileCSV | where {$_.date -notlike "#*"}
$timeTaken = $IISLogFileCSV | foreach {$_.$("time-taken")}

Once you’ve got the array of time-taken, you can ask questions like “what was the average and max time-taken”, but I’ll leave that bit up to you”!

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