Powershell: Matching a line of text from one file and adding into another file - date

Question

I have a very large log file. It contains log data for multiple dates. Each line begins with a date (yyyy-dd-mm hh:mm:ss etc).
So, the log looks like this:
2016-02-17 10:15:24 some text that follows
2016-02-17 14:21:46 more text that follows
2016-02-19 11:54:11 other text that follows
2016-02-19 16:37:21 more text that follows
2016-02-19 19:52:17 other text that follows
2016-02-22 06:01:32 more text that follows
etc...
I am trying to write a PowerShell script that will:
Read each line of my file
Identify the date (first 10 characters)
Add this line to another file with the name targetfile-yyyy-mm-dd.log
My first attempt at this problem was to iterate through the whole range of dates in the file and parse the entire file from top to bottom for each date. This required multiple passes through the whole file (40GB of it!), which takes days.
My ideal solution would be to go through the file just one time, line by line, and copy each line into its appropriate target file based on the first ten characters in the line.
How would I do this to make it most efficient? Thank you for your thoughts!

Answer 1

Try this:
# Use StreamReader to read line by line the Log $file
$streamReader = New-Object System.IO.StreamReader -Arg "$file"
while($line = $streamReader.ReadLine()){
# Get the first 10 char to generate the $targetfile
$tagetfile = "target-file-$($line.Substring(0,10)).log"
# Add-Content of the $line value, skipping the first 20 char (Date)
$line.Substring(20) | Add-Content $tagetfile
}