IO#popen and exit status

C

Claudio Jeker

I'm a bit stuck with this porblem:
I need to write data to a process and then wait for the exit code of it to
see if it was successful or not.

Now I can IO.popen the process but there is no pclose instance method to
get the exitcode back. Additionally my workaround via Process.waitpid2 does
not work either. I think io.close does already all the cleanup.

e.g.

io = IO.popen(cmd, "w")
io.write(msg)
io.close
pid, status = Process.waitpid2(0)

Raises a "Errno::ECHILD: No child processes" exception.

How do other handle this situation? Do I need to take the hard road via
pipe, fork, exec or did I miss something obvious?
 
A

Andrew Johnson

On Tue, 21 Mar 2006 01:20:36 +0900, Claudio Jeker

[snip]
Now I can IO.popen the process but there is no pclose instance method to
get the exitcode back. Additionally my workaround via Process.waitpid2 does
not work either. I think io.close does already all the cleanup.

The $? variable will hold the exit status of the last child to terminate.

andrew
 
A

ara.t.howard

I'm a bit stuck with this porblem:
I need to write data to a process and then wait for the exit code of it to
see if it was successful or not.

Now I can IO.popen the process but there is no pclose instance method to
get the exitcode back. Additionally my workaround via Process.waitpid2 does
not work either. I think io.close does already all the cleanup.

e.g.

io = IO.popen(cmd, "w")
io.write(msg)
io.close
pid, status = Process.waitpid2(0)

Raises a "Errno::ECHILD: No child processes" exception.

How do other handle this situation? Do I need to take the hard road via
pipe, fork, exec or did I miss something obvious?


gem install open4

-a
 
S

Shea Martin

Andrew said:
On Tue, 21 Mar 2006 01:20:36 +0900, Claudio Jeker

[snip]
Now I can IO.popen the process but there is no pclose instance method to
get the exitcode back. Additionally my workaround via Process.waitpid2 does
not work either. I think io.close does already all the cleanup.

The $? variable will hold the exit status of the last child to terminate.

andrew
$? does not work with popen, or open3. I am not sure why one would want
to run a process, and monitor the output, yet not care what the exit
status is? One would think that this oversite will be fixed in future
releases.

~S
 
F

Farrel Lifson

Actually I just solved this a few threads below. You can just run
Process.wait after you've done with the IO.popen and it should update
$? with the correct values.

Andrew said:
On Tue, 21 Mar 2006 01:20:36 +0900, Claudio Jeker

[snip]
Now I can IO.popen the process but there is no pclose instance method = to
get the exitcode back. Additionally my workaround via Process.waitpid2= does
not work either. I think io.close does already all the cleanup.

The $? variable will hold the exit status of the last child to terminat= e.

andrew
$? does not work with popen, or open3. I am not sure why one would want
to run a process, and monitor the output, yet not care what the exit
status is? One would think that this oversite will be fixed in future
releases.

~S
 
S

Shea Martin

Shea said:
Andrew said:
On Tue, 21 Mar 2006 01:20:36 +0900, Claudio Jeker

[snip]
Now I can IO.popen the process but there is no pclose instance method to
get the exitcode back. Additionally my workaround via
Process.waitpid2 does
not work either. I think io.close does already all the cleanup.

The $? variable will hold the exit status of the last child to terminate.

andrew
$? does not work with popen, or open3. I am not sure why one would want
to run a process, and monitor the output, yet not care what the exit
status is? One would think that this oversite will be fixed in future
releases.

~S
ps - you can call Process.wait to update $?, but it is not reliable if
your program is multi threaded.
 
S

Shea Martin

$? does not work with popen, or open3. I am not sure why one would want
to run a process, and monitor the output, yet not care what the exit
status is? One would think that this oversite will be fixed in future
releases.

~S

Before I get flamed, know Process.waitpid can be used...
~S
 
T

Tanaka Akira

Claudio Jeker said:
I'm a bit stuck with this porblem:
I need to write data to a process and then wait for the exit code of it to
see if it was successful or not.

Now I can IO.popen the process but there is no pclose instance method to
get the exitcode back. Additionally my workaround via Process.waitpid2 does
not work either. I think io.close does already all the cleanup.

$? can be used after close.

I hope this documentation helps.

Index: io.c
===================================================================
RCS file: /src/ruby/io.c,v
retrieving revision 1.246.2.97
diff -u -p -r1.246.2.97 io.c
--- io.c 14 Feb 2006 02:23:33 -0000 1.246.2.97
+++ io.c 28 Mar 2006 01:47:15 -0000
@@ -2149,6 +2149,9 @@ rb_io_close(io)
* an <code>IOError</code> is raised if such an attempt is made. I/O
* streams are automatically closed when they are claimed by the
* garbage collector.
+ *
+ * If <em>ios</em> is opened by <code>IO.popen</code>,
+ * <code>close</code> sets <code>$?</code>.
*/

static VALUE
@@ -3062,7 +3065,9 @@ retry:
*
* If a block is given, Ruby will run the command as a child connected
* to Ruby with a pipe. Ruby's end of the pipe will be passed as a
- * parameter to the block. In this case <code>IO::popen</code> returns
+ * parameter to the block.
+ * At the end of block, Ruby close the pipe and sets <code>$?</code>.
+ * In this case <code>IO::popen</code> returns
* the value of the block.
*
* If a block is given with a <i>cmd_string</i> of ``<code>-</code>'',
@@ -3078,6 +3083,7 @@ retry:
* puts "Parent is #{Process.pid}"
* IO.popen ("date") { |f| puts f.gets }
* IO.popen("-") {|f| $stderr.puts "#{Process.pid} is here, f is #{f}"}
+ * p $?
*
* <em>produces:</em>
*
@@ -3086,6 +3092,7 @@ retry:
* Wed Apr 9 08:53:52 CDT 2003
* 26169 is here, f is
* 26166 is here, f is #<IO:0x401b3d44>
+ * #<Process::Status: pid=26166,exited(0)>
*/

static VALUE
 

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