Exit status on cmd executed via popen()

ruby-talk
1

Sometimes I write ruby scripts to filter the output of some
other command. So I write something like:

cmdout = IO.popen(somecmd, “r”)
cmdout.each_line {|aline|
# Do Stuff…
}
cmdout.close

Is there any way to find out what the exit status was from
the command given to popen? It would be nice to have some
method that I could use like:

if cmdout.popen_exit_status != 0
# Do Error-processing stuff
end

which could be done after reading all the lines, but before
the call to ‘close’.

Or do I need to do something more complicated than 'popen’
if I need to know the exit code from that command?

···

–
Garance Alistair Drosehn = gad@gilead.netel.rpi.edu
Senior Systems Programmer or gad@freebsd.org
Rensselaer Polytechnic Institute or drosih@rpi.edu

2

Try variable $?, it holds the status of the last executed command. Works
for commands executed with ‘system’, I think it is valid for popen as well.

Gennady.

Garance A Drosihn wrote:

···

Sometimes I write ruby scripts to filter the output of some
other command. So I write something like:

cmdout = IO.popen(somecmd, “r”)
cmdout.each_line {|aline|
# Do Stuff…
}
cmdout.close

Is there any way to find out what the exit status was from
the command given to popen? It would be nice to have some
method that I could use like:

if cmdout.popen_exit_status != 0
# Do Error-processing stuff
end

which could be done after reading all the lines, but before
the call to ‘close’.

Or do I need to do something more complicated than ‘popen’
if I need to know the exit code from that command?

3

Interesting. In the code sequence of:

cmdout = IO.popen(somecmd, “r”)
cmdout.each_line {|aline|
# Do Stuff…
}
cmdout.close

I had tried checking $? just before cmdout.close, and it had a
value of nil. However, checking it immediately after the
close, it does seem to have $? set to the desired value. As
long as I can depend on this, it will do the job very nicely.
Thanks!

···

At 7:27 AM +0900 11/25/03, Gennady wrote:

Try variable $?, it holds the status of the last executed
command. Works for commands executed with ‘system’, I think
it is valid for popen as well.

–
Garance Alistair Drosehn = gad@gilead.netel.rpi.edu
Senior Systems Programmer or gad@freebsd.org
Rensselaer Polytechnic Institute or drosih@rpi.edu

4

Garance A Drosihn wrote:

Try variable $?, it holds the status of the last executed
command. Works for commands executed with ‘system’, I think
it is valid for popen as well.

Interesting. In the code sequence of:

cmdout = IO.popen(somecmd, “r”)
cmdout.each_line {|aline|
# Do Stuff…
}
cmdout.close

I had tried checking $? just before cmdout.close, and it had a
value of nil. However, checking it immediately after the
close, it does seem to have $? set to the desired value. As
long as I can depend on this, it will do the job very nicely.
Thanks!

I have implemented a method available through Kernel.launch. It allows
you to execute several commands connecting all of them in a pipeline. I
makes available each command’s return status together with stderr
messages. The last command’s stdout is also available. I haven’t
released it, however if you are interested you can get it at

http://homepage.mac.com/bystr/Development/Ruby/launch.rb

It has a set of unit tests attached, so it should be easy to figure out
the usage. I am not sure if it works on Windows as it uses fork() and
Process.waitpid2()

I mentioned it on ruby-talk before, you may find some description there:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/72318

Gennady.

···

At 7:27 AM +0900 11/25/03, Gennady wrote: