Add stdout = TRUE to R's system2 command and receive warning. Why?

Question

I require the number of Firefox processes running on Linux (Ubuntu) be stored in a variable in an R script. By itself the system2 command I use seems to work. However, when I add stdout = TRUE to capture the info in a character vector I get a warning. Why the warning?

system2(command = "ps", args = "aux | grep [f]irefox -c")
# 0

system2(command = "ps", args = "aux | grep [f]irefox -c", stdout = TRUE)

Warning message:
In system2(command = "ps", args = "aux | grep [f]irefox -c", stdout = TRUE) :
  running command ''ps' aux | grep [f]irefox -c' had status 1

kangaroo_cliff · Accepted Answer · 2020-11-17T06:06:53.910

1

Use ef instead of aux as the argument to ps. aux for BSD and ef and variants for standard syntex, as per man ps.

system2('ps', '-ef | grep [f]irefox -c', stdout = TRUE)
[1] "12"

edited Nov 17 '20 at 06:06

answered Nov 17 '20 at 03:35

kangaroo_cliff

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How do I capture the output in a character vector? If I say x <- system2... the value of x is one while the statement returns zero (at least on my machine at this time). – ixodid Nov 17 '20 at 03:38
I changed the answer. – kangaroo_cliff Nov 17 '20 at 06:08
I still get the same warning as my original question. – ixodid Nov 17 '20 at 16:41
That is surprising. I wander how our systems might differ. – kangaroo_cliff Nov 17 '20 at 22:05

Add stdout = TRUE to R's system2 command and receive warning. Why?

1 Answers1