powershell - Parse a log file's last modified date into a variable

Question

I am trying to set a variable to the number of days since a log file was modified. this way I can use that value as a flag for the next time a command runs.

example:

if the command ran yesterday, the value will be 1

if the command ran 5 days ago, the value will be 5

I'm seeing methods for similar issues such as:

OR %%f IN (%filename%) DO SET filedatetime=%%~tf

or

if (file.exists()) {
  Date lastModified = new Date(file.lastModified());
}

I just don't know batch scripting or powershell very well. I'm open to running this script in either. I think what I need to learn is:

1) extract the (tokens?) sub string of just the date from a date/time modified command

2) removing any colons or slashes

3) convert to an integer

4) repeat for today's date

Once I have two integers subtracting and setting a variable should be easy.

Any recommendations?

Answer 1

In PowerShell you can just subtract one date from another and get a timespan. So something as simple as:

$File = Get-Item C:PathToFile.txt
$DaysSinceMod = [datetime]::now - $File.LastWriteTime | Select -Expand Days

Then $DaysSinceMod would be how many days since the file was last modified. Or, using some shorthand, that can be reduced to:

$LastMod=(get-date)-(gi C:PathToFile.txt)|% Days