R - How to execute PowerShell cmds with system() or system2() - r

Question

I working in R (on a Windows OS) attempting to count the number of words in the text file without loading the file into memory. The idea is to get some stats on the file size, line count, word count, etc. A call to R's system() function that uses find for the line count is not hard to come by:
How do I do a "word count" command in Windows Command Prompt
lineCount <- system(paste0('find /c /v "" ', path), intern = T)
The command that I'm trying to work with for the word count is a PowerShell command: Measure-Object. I can get the following code to run without throwing an error but it returns an incorrect count.
print(system2("Measure-Object", args = c('count_words.txt', '-Word')))
[1] 127
The file, count_words.txt has on the order of millions of words. I also tested it on a .txt file with far fewer words.
"There are seven words in this file."
But the count again is returned as 127.
print(system2("Measure-Object", args = c('seven_words.txt', '-Word')))
[1] 127
Does system2() recognize PowerShell commands? What is the correct syntax for a call to the function when using Measure-Object? Why is it returning the same value regardless of actual word count?

Answer 1

The issues -- overview
So, you have two issues going on here:
You aren't telling system2() to use powershell
You aren't using the right powershell syntax
The solution
command <- "Get-Content C:/Users/User/Documents/test1.txt | Measure-Object -Word"
system2("powershell", args = command)
where you replace C:/Users/User/Documents/test2.txt with whatever the path to your file is. I created two .txt files, one with the text "There are seven words in this file." and the other with the text "But there are eight words in this file." I then ran the following in R:
command <- "Get-Content C:/Users/User/Documents/test1.txt | Measure-Object -Word"
system2("powershell", args = command)
Lines Words Characters Property
----- ----- ---------- --------
7
command <- "Get-Content C:/Users/User/Documents/test2.txt | Measure-Object -Word"
system2("powershell", args = command)
Lines Words Characters Property
----- ----- ---------- --------
8
More explanation
From help("system2"):
system2 invokes the OS command specified by command.
One main issue is that Measure-Object isn't a system command -- it's a PowerShell command. The system command for PowerShell is powershell, which is what you need to invoke.
Then, further, you didn't quite have the right PowerShell syntax. If you take a look at the docs, you'll see the PowerShell command you really want is
Get-Content C:/Users/User/Documents/count_words.txt | Measure-Object -Word
(check out example three on the linked documentation).