Reading exit code of pipe()

The difference in the return value of close(pipeConnectionObject)
seems to depend on whether the pipe connection was opened via
the pipe() or open() functions (close() returns NULL)

   > con <- pipe("ls")
   > open(con, "r")
   > readLines(con, n=1)

   [1] "1032.R"

   > print(close(con))

   NULL

   > con <- pipe("ls", "r")
   > scan(con, n=1, what="")

  Read 1 item
  [1] "1032.R"

  > print(close(con))

  NULL
or via something like readLines() or scan() (close() returns status
integer).

  > con <- pipe("ls")
  > scan(con, n=1, what="")

  Read 1 item
  [1] "1032.R"

  > print(close(con))

  [1] 36096

  > sprintf("0x%x", .Last.value)

  [1] "0x8d00"






Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Wed, May 13, 2015 at 10:27 PM, Kevin Ushey <kevinushey at gmail.com>
wrote:

Hi Jeroen,

I think `pipe` might just be returning the status code of the
underlying command executed; for example, I get a status code of '0'
when I test a pipe on `ls`:

    conn <- pipe("ls")
    stream <- readLines(conn)
    print(close(conn))

Similarly, I get an error code if I try to `ls` a non-existent
directory (512 in my case), e.g.

    conn <- pipe("ls /no/path/here/sir")
    stream <- readLines(conn)
    print(close(conn))

So maybe `cat` just doesn't set a status code, and so there's nothing
for R to forward back (ergo -- NULL)?

Kevin

On Wed, May 13, 2015 at 5:24 PM, Jeroen Ooms <jeroen.ooms at stat.ucla.edu>
wrote:

Is there a way to get the status code of a pipe() command? The
documentation suggests that it might be returned by close, however
this does not seem to be the case.

  con <- pipe("cat /etc/passwd", "r")
  stream <- readLines(con, n = 10)
  err <- close(con)
  print(err)

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