R devel - May 2015 - Reading exit code of pipe()

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)

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)
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

On Thu, May 14, 2015 at 1:27 AM, Kevin Ushey <kevinushey at gmail.com>
wrote:
[...]
> So maybe `cat` just doesn't set a status code, and so there's
nothing
> for R to forward back (ergo -- NULL)?
>
cat definitely sets the status. IMHO every command sets the exit status, by
definition, at least on Unix/Linux.

/tmp$ touch x
/tmp$ cat x
/tmp$ echo $?
0
/tmp$ cat y
cat: y: No such file or directory
/tmp$ echo $?
1

Gabor

[...]

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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)
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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