Powershell: Select-Object with additional calculated difference value
- by David.Chu.ca
Let me explain my question. I have a daily report about one PC's free space as in text file (sp.txt) like:
DateTime FreeSpace(MB)
----- -------------
03/01/2010 100.43
DateTime FreeSpace(MB)
----- -------------
03/02/2010 98.31
....
Then I need to use this file as input to generate a report with difference of free space between dates:
DateTime FreeSpace(MB) Change
----- ------------- ------
03/01/2010 100.43
03/02/2010 98.31 2.12
....
Here are some codes I have to get above result without the additional "Change" calculation:
Get-Content "C:\report\sp.txt" `
| where {$_.trim().length -gt 0 -and -not ($_ -like "Date*") -and -not ($_ -like "---*")} `
| Select-Object @{Name='DateTime'; expression={[DateTime]::Parse($_.SubString(0, 10).Trim())}}, `
@{Name='FreeSpace(MB)'; expression={$_.SubString(12, 12).Trim()}}, `
| Sort-Object DateTime `
| Select-Object DateTime, 'FreeSpace(MB)' |ft -AutoSize # how to add additional column Change to this Select-Object?
My understanding is that Select-Object will return a collection of objects. Here I create this collection from an input text file(parse each line into parts: datetime and freespace(MB)).
In order to calculate the difference between dates, I guess that I need to add additional calculated value to the result of the last Select-Object, or pipe the result to another Select-Object with the calculation as additional property or column. In order to do it, I need to get the previous row's FreeSpace value. Not sure if it is possible and how?
