Is there a way to read the spawned process' STDERR? Gnuplot likes to write
most output to it. I've tried
readandwrite(`gnuplot 2>&1`)
but gnuplot interprets 2>&1 as a filename and fails.
This, however, works:
readandwrite(`gnuplot` .> "/tmp/gnuplot.err")
but I'd like to avoid having to create a file.
Thanks!
On Wed, Jun 17, 2015 at 1:05 PM, Kevin Squire <kevin.squ...@gmail.com>
wrote:
> `open(cmd, "w")` gives back a tuple. Try using
>
> f, p = open(`gnuplot`,"w")
> write(f, "plot sin(x)")
>
> There was a bit of discussion when this change was made (I couldn't find
> it with a quick search), about this returning a tuple--it's a little
> unintuitive, and could be `fixed` in a few different ways (easiest:
> returning a complex type that can be written to and read from), but it's
> probably been off most people's radar. If you're up for it, why don't you
> open an issue (if one doesn't exist).
>
> Anyway, for your particular application, you probably want `readandwrite`:
>
> help?> readandwrite
> search: readandwrite
>
> Base.readandwrite(command)
>
> Starts running a command asynchronously, and returns a tuple
> (stdout,stdin,process) of the output stream and input stream of the
> process, and the process object itself.
>
> Which *also* returns a tuple (but at least now you know).
>
> See also http://blog.leahhanson.us/running-shell-commands-from-julia.html,
> which has a full rundown of reading and writing from processes.
>
> Cheers!
> Kevin
>
> On Wed, Jun 17, 2015 at 9:03 AM, Miguel Bazdresch <eorli...@gmail.com>
> wrote:
>
>> Hello,
>>
>> Gaston.jl is a plotting package based on gnuplot. Gnuplot is command-line
>> tool, so I send commands to it via a pipe. I open the pipe (on Linux) with
>> a ccall to "popen", and write gnuplot commands to the pipe using a ccall to
>> fputs.
>>
>> This works fine, but I'm trying to see if Julia's native pipe and stream
>> functionality can make this process more Julian and, in the process, more
>> cross-platform. The documentation is encouraging:
>>
>> "You can use [a Cmd] object to connect the command to others via pipes,
>> run it, and read or write to it." and "Julia provides a rich interface to
>> deal with streaming I/O objects such as terminals, pipes and TCP sockets."
>> Unfortunately, I just can't figure out how to use Julia's functionality for
>> this purpose. This is what I've tried (I am on Julia 0.3.9):
>>
>> First, I tried using `open` with read and write:
>>
>> julia> f=open(`gnuplot`,"r+")
>> ERROR: ArgumentError("mode must be \"r\" or \"w\", not \"r+\"")
>>
>> So I tried with write only:
>>
>> julia> f=open(`gnuplot`,"w")
>> (Pipe(open, 0 bytes waiting),Process(`gnuplot`, ProcessRunning))
>>
>> So far, this looks good. I can see a gnuplot process running.
>>
>> Then I try to `write` to the pipe:
>>
>> julia> write(f,"plot sin(x)")
>> ERROR: `write` has no method matching write(::(Pipe,Process),
>> ::ASCIIString)
>>
>> OK, so let's try with `println`:
>>
>> julia> println(f,"plot sin(x)")
>> (Pipe(open, 0 bytes waiting),Process(`gnuplot`, ProcessRunning))plot
>> sin(x)
>>
>> and no plot is produced.
>>
>> I can't figure out how to read from the pipe, either:
>>
>> julia> readbytes(f)
>> ERROR: `readbytes` has no method matching readbytes(::(Pipe,Process))
>>
>> julia> readall(f)
>> ERROR: `readall` has no method matching readall(::(Pipe,Process))
>>
>> I'd appreciate any pointers. Thanks!
>>
>> -- mb
>>
>>
>
